Synthesis and conformational analysis of cAMP model
compounds
Citation for published version (APA):
Hermans, R. J. M. (1988). Synthesis and conformational analysis of cAMP model compounds. Technische
Universiteit Eindhoven. https://doi.org/10.6100/IR276952
DOI:
10.6100/IR276952
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Published: 01/01/1988
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SYNTHESIS AND CONFORMATIONAL ANALYSIS
OF cAMP MODEL.COMPOUNDS
PROEFSCHRIFT
TER VERKRIJGING VAN DE GRAAD VAN DOCTOR AAN DE
TECHNISCHE UNIVERSITEIT EINDHOVEN, OP GEZAG
VAN DE RECTOR MAGNIFICUS, PROF. DR. F.N. HOOGE, VOOR EEN COMMISSIE AANGEWEZEN DOOR HET COLLEGE VAN DEKANEN IN HET OPENBAAR TE VERDEDIGEN OP
DINSDAG 19 JANUARI 1988 TE 16.00 UUR DOOR
ROBERTUS JOZEF MATHIJS HERMANS
DIT PROEFSCHRIFf IS GOEDGEKEURD DOOR DE PROMOTOREN
PROF.DR. H.M. BUCK EN
SYNTHESIS AND CONFORMATIONAL ANALYSIS OF cAMP MODEL COMPOUNDS
CONTHNTS
Chapter 1
General introduetion
1.1 3' ,5'-Cyclic nucleotides and ce11 rnetabolism 1.2 Molecular rnechanisrns of cAMP-dependent enzyrnes 1.3 Scope of the thesis
References and Notes
chapter 2 9 9 12 13 14
Synthesis and conforrnational studies of a nurnber of saturated 17 bicyclic six-rnernbered ring phosphites
2.1 Introduetion
2.2 Results and Discussion 2.2.1 Synthesis 2.2.2 Characterization of diastereoroers 2.2.3 1 H NMR studies 2.3 Conclusions 2.4 Experirnental section References and Notes
Chapter 3
A 31P and 1H NMR study of the conforrnations of a series of diastereorneric 3-substituted trans-2.4-dioxa-3-oxo- and
trans-2.4-dioxa-3-thioxo-3-phosphabicyclo[4.3.0]nonanes as model cornpounds for cyclic nuc1eotides
3.1 Introduetion
3.2 Resu1ts and Discussion 3.2.1 Synthesis
3.2.2 Assignrnent of configuration at phosphorus 3.2.3 1
H NMR conforrnationa1 analysis 3.2.4 31P NMR rneasurernents
3.3 conclusions
3.4 Experirnental section References and Notes
18 19 19 21 21 26 26 32 34 35 36 36 39 39 45 47 47 55
Chapter 4
Influence of phosphorus-derivatization on the conformational 57 behaviour of model compounds for 3' ,5'-xylo-cAMP studled by
1
H NMR spectroscopy 4.1 Introduetion
4.2 Results and Discussion 4.2.1 Synthesis
4.2.2 Assignment of configuration at phosphorus 4.2.3 1H NMR conformational analysis
4.3 Experimental section References and Notes
Chapter 5 58 59 59 62 62 70 80
synthesis and conformational analysis of phosphorus-derivatized 83 no-base analogues of 3' ,5'-cyclic nucleotides
5.1 Introduetion 84
5.2 Results 85
5.2.1 Synthesis 85
5.2.2 Assignment of cis and trans configurations at 87 phosphorus
5.2.3 conformational analysis of the phosphate ring 5.2.4 conformation of the tetrahydrofuran ring 5.3 Discussion
5.4 Conclusions
5.5 Experimental section References and Notes
Chapter 6
concluding remarks 6.1 Introduetion
6.2 Dioxaphosphorinane ring conformations 6.3 Biologica! implications
References and Notes
summary 88 89 91 91 92 96 98 98 98 100 102 103
samenvatting 105
curriculum vitae 101
CHAPTER 1
GENERAL INTRODUCTION
1.1 3' ,5'-CYCLIC NUCLEOTIDES AND CELL METABOLISM
The knowledge of the existence of cyclic phosphates of purine and pyrimidine nucleosides is of fairly recent origin. The starting point of cyclic nucleotide research was the discovery of 3' ,5'-cyclic adeno-sine monophosphate (cAMP, Figure 1) by Sutherland and hls associates in the late fifties.1'2 Since then, this field of research has rapidly expanded to produce a wealth of knowledge about the mechanism and beha-viour of cAMP, and to a lesser degree of cGMP, in living cells. Nowa-days it is recognized that 3',5'-cyclic nucleotides, e.g. cAMPand cGMP, play a central role in the regulation of an exceptionally wide range of cellulàr processes in both eucaryotic3 and procaryotic4 cells. In eukariotes, cAMP serves as a second messenger to control processes such as glycogenolysis (vide infra), fatty acid synthesis5 and gene expression.6 In essentially all of these processes, the mechanism by which a cyclic nucleotide influences a biochemica! reaction is appa-rently the same: in the case of cAMP, adenylate cyclase catalyzes the formation of cAMP (second messenger) from adenosine triphosphate (ATP, Figure ll in response to an extracellular stimulus (first messenger). The cAMP then activatas a cAMP dependent protein kinase. The activated
(and often dissociated) form of protein kinase catalyzes the phospho-rylation of an enzyme, thereby altering its catalytic activity and pro-ducing the desired cellular respons. cAMP is removed from the system by lts hydrolysis to 5'-adenosine monophosphate (5'-AMP, Figure 1), which is catalyzed by a specific cyclic nucleotide phosphodiesterase. A well studled example of a biochemica! process controlled by cAMP is the breakdown of glycogen to blood glucose (glycogenolysis) in liver cells triggered by the hormone epinephrine (Figure 2). 7 Adenylate cyclase catalyzes the formation of cAMP from ATP upon binding of epinephrine
adenylate cyclase 0
j l
&NH20/"p'~W,o.
s· 0
~N7~-e:~t~
3 4 ,N~~N~2
9 3 2' I' CAMP HO~
phosphodiesterase NH20
{N~
-o)"'-o/'yo--,i N
-oH
HO OH 5'-AMP Figure 1. synthesis and degradation of cAMP.of cAMP to the regulatory subunits of the inactive protein kinase results in dissociation of this enzym into two active catalytic (ç)
8
subunits and a dimer of regulatory (R2) subunits. The catalytic sub-units activate phosphorylase kinase by phosphorylation. This enzyme activates in turn the inactive phosphohydrolase b. The result of this final activation is the breakdown of glycogen. During the degradation of this compound. it would be a waste of energy to continue its syn-thesis. Therefore. the enzyme glycogen synthetase, which catalyzes the synthesis of glycogen, is inactivated through phosphorylation by pro-tein kinase.
In procaryotes all known effects of cAMP are mediated by the cAMP receptor protein (CRP), also called catabolite gene activator protein (CAP).9 In B. colt. the cAMP receptor protein regulates the level of transcription of at least 20-25 genes.10 cAMP acts as an allosteric effector. In the absence of cAMP, CRP retains only a nonspecific DNA-binding affinity. In the presence of cAMP. the cAMP-CRP complex binds to specific DNA sites near the promoter of each gene that it regulates. This interaction results either in stimulation of transcription as in the case of the arabinose, lactose and maltose genes or in inhibition of transcription as in the case of the genesof CRP 1tself11 and ade-nylate cyclase12• In the galactose gene, which has two overlapping
promoters for RNA-polymerase, the complex is required for transcription from one operon but inhibits transcription from the other.
epinephrine epinephrine receptor ATP cAMP +PP; protein kinase
.
~I
inactive)L
protein kinase@
lactivel\
+ cAMP-@ATP + phosphorylase kinase - - - - 1 ... phosphorylase
kinase ( active
J
I
inactivelI
cell membrane + ADP ATP • phosphohydrolase bI
inactive) phosphohydrolase a + ADPI
glycogen + Pj -eelt membrane ( activel glucose giJose 1- phosphate 5 - phosphate -glucose + Pij
blood glucosel
1.2 MOLECULAR MECHANISMS OF cAMP-DEPENDENT ENZYMES
Since the discovery of cAMP, a huge number of analogues has been prepared in order to get information about the molecular mechanisms of the enzymes involved in cAMP-controlled processes e.g. cyclic nucleotide phosphodiesterases. cAMP-dependent protein kinases and the cAMP receptor protein and to find compounds which mimic or are antagonistic to the physiological action of cAMP. 10'13- 21
Investigations on cyclic phosphodiesterases have shown that hydro-lysis of cAMP proceeds in at least two steps: binding of cAMP to the enzyme and subsequent ring opening catalyzed by the enzyme.16 The structural requirements for both steps were found to depend on the exact souree of the enzyme. Using the SP and Rp isomees of adenosine 3' ,5'-cyclic monophosphorothioate {cAMPS), it was furthermore demon-strated that the hydrolysis of cAMP by bovine heart cyclic phospho-diesterase and yeast cyclic phosphophospho-diesterase both proceed with complete inversion of configuration at phosphorus.22'23 combining these results
with the results of quantumchemical calculations on trigonal bipyramidal model compounds for cAMP intermediates having an equatorial-axial alignment of the cyclic phosphate ring, a mechanism was proposed for the hydrolysis of cAMP by these enzymes.24-26
Binding studies on protein kinases have revealed that the regula-tory subunits contain two different binding sites which differ in kine-tic properties27 and specificity for certain derivatives.28- 32 The
interactions between cAMP and both binding sites were basically iden-tical: hydrogen bonds with the 2'-hydroxyl and 3' and 5' oxygen atoms but no hydrogen-bonding with the adenine moiety.17 The precise nature of the interaction with the exocyclic oxygen atoms on phosphorus, how-ever, could not be established, though a charge interaction seemed to be absent. The results of activation experiments showed that modifi-cations in the adenine and ribose moieties. including the endocyclic oxygen atoms of the cyclophosphate ring, did not affect the maximal activatien level, while alteratien of the two exocyclic oxygen atoms resulted in a reduced maximal activatien level and in one case, {Rp)-cAMPS, in total absence of activation. Since the SP isomee of the un-charged adenosine 3',5'-cyclic monophosphodimethylamidate {cAMPN{CH
3)2) activates the kinase effectively, an activation mechanism requiring a negatively charged oxygen atom could be rejected. However, these results
were compatible with a model, involving the formation of a covalent bond with phosphorus in both cAMP binding sites. 17'25'26
Screening of a number of systematically modified cAMP analogues for their ability to stimulate gene transcription revealed that the following atoms or rooieties on cAMP are involved in binding to the CRP and subsequent induction of the conformational change in this protein: the 2'-0H group, the 3' and 5' oxygen atoms, the negatively charged phosphate group and the N-1 and N-7 atoms of the adenine ring.19 How-ever, the precise mechanism of the activation of this protein is still unknown.
1.3 SCOPE OF THB THESIS
Studies on cAMP analogues have mainly been concentrated on the relation between their structure and biologica! activity. Rather few attempts have been made to correlate both factors to the conformational properties of these compounds. This is partly due to the limited
availability of studies dealing with the conformational aspects of cAMP analogues. The alm of this thesis is to determine the effects of varia-tions in the cyclic phosphate-ribose ring part on the conformational properties of the phosphorus containing ring in a number of cAMP model compounds.
Chapter 2 deals with the synthesis and conformational analysis of a set of tricoordinated analogues of cAMP. It is shown that the confor-mation of the dioxaphosphorinane ring primarily depends on the nature and orientation of the exocyclic substituant on phosphorus. The size and composition of the ring transannelated to the dioxaphosphorinane ring are found to have a relatively small influence on the conformation of the latter.
In chapter 3, a 31P and 1H NMR study of the conformation of the dioxaphosphorinane ring of a number of epimeric model phosphates for cAMP is presented. The cyclic phosphate ring is trans fused to a cyclo-pentane ring. It is shown that the conformation of the phosphate ring is determined by the nature and spatlal arrangement of the exocyclic substituents on the phosphorus atom. Furthermore, it is demonstrated that the chair-twist equilibrium available to the phosphate ring is solvent-sensitive. The results obtained for the epimeric
phosphoro-thioates are discussed in relation to the biologica! activity of the diastereomees of cAMPS.
In chapter 4. the conformation of the phosphate ring of a series of 3',5'-xylo-cAMP analogues is investigated. In these derivatives, the phosphate ring is cis fused to a cyclopentane ring. It is shown that the dioxaphosphorinane ring exists as an equilibrium between a chair and distorted-boat conformation. The mole fraction of the latter is found to vary with the composition of the phosphate group. The results on the phosphorothioates show a remarkable dependenee of the phosphate ring conformation on the exact (equatorial or axial) location of the negative charge.
chapter 5 describes the synthesis and conformational analysis of a number of no-base analogues of 3',5'-cyclic nucleotides. derivatized at phosphorus. The phosphate ring of these derivatives is found to exist as an equilibrium between a chair and twist conformer. The mole frac-tions of twist calculated for the various model compounds are compared with those estimated for corresponding model compounds derived from
thymidine and cyclopentane.
Finally, in chapter 6. the various dioxaphosphorinane ring confor-mations described in this thesis are rationalized in terms of steric and stereoelectronic factors. operative in these cAMP model compounds. Furthermore, the relevanee of the obtained results on the phospate ring conformations for the interaction of cAMP and lts analogues with enzymes
is briefly discussed.
REFERENCES AND NOTES
1 T.W. Rall. E.W. sutherland, J. Biol. Chem., 232, 1065 (1958).
2 E.W. sutherland. T.W. Rall. J. Biol. Chem., 232, 1077 (1958).
3 R.A. Steinberg. "Biochemica! Actionsof Hormones", Vol 11, pp 25-65, G. Litwak Ed., Academie Press. Orlando (1983}.
4 G. Zubay, D. Schwartz and J. seckwlth, Proc. Natl. Acad. Sci., u.s.A •• 66. 104 (1970).
5 E.G. Krebs, J.A. Beavo, Annu. Rev. Biochem., 48, 923 (1979). 6 M. Waterman, G.H. Murdoch, R.M. Evans, M.G. Rosenfeld, Science,
229, 267 (1985).
8 S.E. Builder, J.A. Beavo, E.G. Krebs, J. Biol. Chem .• 255, 2350 (1980).
9 B. de Crombrugghe, S. Busby, H. Buc, Science, 224. 831 (1984). 10 R.H. Ebright, S.F.J. Le Grice, J.P. Miller, J.S. Krakow, J. Mol.
Biol .• 182, 91 (1985) and references therein. 11 H. Aiba, Cell, 32, 141 (1983).
12 H. Aiba, J. Biol. Chem .• 260, 3063 (1985).
13 J.P. Miller, "Cyclic 3' ,5'-Nucleotides: Mechanisms of Action", pp 77-104, H. Cramer, J. Schultz, Eds., Wiley, London (1977). 14 J.P. Miller, "Advances in Cyclic Nucleotide Research", Vol 14, pp
335-344, J.E. Dumont, P. Greengard. G.A. Robison, Eds., Raven Press, New York (1981).
15 T.S. Yagura, J.P. Miller. Biochemistry, 20, 879 (1981).
16 P.J.M. van Haastert, P.A.M. Dijkgraaf, T.M. Konijn, E.G. Abbad, G. Petridis, B. Jastorff. Eur. J. Biochem .• 131. 659 (1983). 17 R.J.W. de Wit, D. Hekstra, B. Jastorff. W.J. Stee, J. Baraniak.
R. van Driel, P.J.M. van Haastert, Eur. J. Biochem .• 142. 255 (1984).
18 D. ~greid, R. Ekanger. R.H. Suva, J.P. Miller, P. Sturm. J.D. Corbin.
s.o.
D~skeland. Eur. J. Biochem .• 150. 219 (1985). 19 H.-G. Scholübbers, P.H. van Knippenberg, J. Baraniak, W.J. Stee,M. Morr, B. Jastorff. Eur. J. Biochem .• 138, 101 (1984). 20 P.J.M. van Haastert, R. van Driel, B. Jastorff. J. Baraniak,
W.J. Stee, R.J.W. de Wit, J. Biol. Chem .• 259, 10020 (1984). 21 C. Erneux. J. van Sande, B. Jastorff. J.E. Dumont, Biochem. J .•
234. 193 (1986).
22 J.A. Coderre,
s.
Mehdi, J.A. Gerlt, J. Am. Chem. Soc., 103, 1872 (1981).23 R.L. Jarvest, G. Lowe, J. Baraniak, W.J. Stee, Biochem. J., 203, 461 (1982).
24 P.J.J.M. van Ool, H.M. Buck, Reel. Trav. Chim. Pays-Bas, 100. 79 (1981).
25 P.J.J.M. van Ool, H.M. Buck, Eur. J. Biochem .• 121. 329 (1982). 26 P.J.J.M. van Ool, Ph.D. Thesis, Eindhoven University of
Technology (1983).
27 D. ~greid, S.O. ~skeland, FEBS Lett., 129, 282 (1981). 28 S.R. Rannels, J.D. Corbin, J. Biol. Chem .• 255, 7085 (1980). 29 S.R. Rannels. J.D. Corbin, J. Biol. Chem .• 256, 7871 (1981).
30 A.R. Ker1avage,
s.s.
Tay1or, J. Bio1. Chem., 257, 1749 (1982).31
s.o.
~ske1and, D. 9greid, R. Bkanger, P.A. Sturm, J.P. Mi11erR.H. Suva. Biochemistry, 22, 1094 (1983).
32 A.M. Robinson-Steiner, J.D. corbin, J. Bio1. Chem .• 258. 1032 (1983).
CHAPTER 2*
SYNTHESIS AND CONFORHATIONAL STUDIES OF A NUMBER OF SATURATED BICYCLIC SIX-MEMBERED RING PHOSPHITBS
ABSTRACT
A 1H NMR study of the conformation of the dioxaphosphorinane ring of a number of diastereomeric bicyclic saturated six-membered ring phosphites (3a,b-10a,b} has been perforrned. The dioxaphosphorinane ring of these phosphites is transannelated with a tetrahydrofuran, cyclopentane, tetrahydropyran or cyclohexane ring. The substituent on the phosphorus atorn is a rnethoxy or phenoxy group. It is shown that the cis isorners 3a-10a prefer a chair conformation of the dioxaphos-phorinane ring, independent of the substituent on the phosphorus atorn and of the nature of the transannelated ring. In contrast, for the trans isomers 3b-10b a twist rather than a chair conformation of the dioxaphosphorinane ring is preferred. The fraction of the twist confor-mer in the trans isorners is mainly determined by the substituent on phosphorus. The size and cornposition of the transannelated ring are relatively unirnportant in this respect. For both cis and trans isomers, the preferred geornetry is solvent-independent. The measured 3JPOCH couplings of the cis isomers 3a-10a are used to formulate an expres-sion for the dependenee of such couplings upon dihedral angles in bicyclic phosphites.
2. 1 INTRODUCTION
The conformatlans of monocyclic six-membered ring phosphites, 1,3,2-dioxaphosphorinanes, have been studled thoroughly.1'2 Little is known. however, about the conformational properties of saturated bicyclic six-membered ring phosphites. The only well investigated systems of this kind are the methyl and phenyl 3',5'-cyclic phosphites of thymidine, la,b-2a,b {Figure 1). 3
la: cis, X= OCH
3, Y= lone pair lb: trans, X= lone pair, Y= OCH
3 2a: cis. X= OPh, Y= lone pair 2b: trans, X= lone pair. Y= OPh T= Thymine
Figure 1. Compounds la.b and 2a,b.
It was demonstrated that the dioxaphosphorinane ring of the cis isomers la and 2a preferently adopts a chair conformation with the OR group axial. The thermodynamically less stable trans isomers lb and 2b. however. showed a preferenee for a twist conformation of the dioxaphos-phorinane ring in which the OR group accupies a pseudoaxial position. It was suggested that the strong stereoelectronic preferenee of the OR group for an axial or pseudoaxial position was responsible for the rather unusual twist conformation. A low chair-twist free energy diffe-rence, however, could nat be excluded. In order to establish whether these special conformational properties are only limited to the com-pounds la,b-2a,b which contain a dioxaphosphorinane ring transannelated with a deoxyribosering. a 1H NMR study of the conformation of the dioxaphosphorinane ring of the bicyclic phosphites 3a,b-10a,b {Figure 2) was undertaken.4 In these compounds the dioxaphosphorinane ring is transannelated with a tetrahydrofuran (3a,b-4a,b), cyclopentane (5a,b-6a,b), tetrahydropyran {ia,b-8a,b) and cyclohexane ring (9a,b-10a,b}, respectively. The observations made on these phosphites can be used to determine the effect of the size and composition of the transannelated ring on the preferentlal conformation of the phosphorus containing ring.
o=o
x,,o~
x ,ob x '"D
X...._ I
':P
0':P
y/~
0Y'
/~y-' 'o ----
y-'
'o----0---
0---3a,b Sa,b 7a,b 9a,b
4a,b 6a,b 8a,b lOa,b
3a, Sa, ?a, 9a: cis, X= OCH
3, Y= lone pair 3b, Sb, 7b, 9b: trans. x= lone pair, Y= OCH
3
4a, 6a, 8a, lOa: cis, x= OPh, Y= lone pair 4b, 6b, 8b, lOb: trans, X= lone pair. Y= OPh
Pigure 2. Model compounds 3a,b-10a,b.
2.2 R~SULTS AND DISCUSSION 2.2.1 synthesis
The isoroer 3b (less than 20% of 3a present as was established by
31
p NMR) was obtained by the reaction of methanol with the dimethyl-aminoderivative 12 (Scheme 1) at room temperature using lH-tetrazole as catalyst. Phosphite 3a was prepared by thermal isomerization of compound 3b. Reaction of methyl dichlorophosphinite with (1R,2S)-2-hydroxytetrahydrofuranmethanol 11 afforded a 40/60 mixture of the dia-stereoroers Ja and 3b. This ratio, however, varied considerably with the reaction. The percentage trans was mostly less than SO%. Phosphite 4b was synthesized from compound 12 by reaction with phenol at 70°C or at room temperature using lH-tetrazole as a catalyst. Thermal isomeriza-tion of 4b afforded 4a. Compound 4a cóuld also be obtained by the reaction of phenyl dichlorophosphinite with diol 11. Compound 11 was prepared from J,S-di-p-toluyl-2-deoxy-D-ribosylchloride. 7 Isoroer Sb was prepared from the corresponding chlorophosphonite 14 according to the method of Verkade et al. 8 Thermal isomerization of Sb gave com-pound Sa. Reaction of chlorophosphonite 14 with phenol afforded a mix-ture of 6a and 6b (approximately 70/30) suitable for NMR analysis. The starting diol 13 for the chlorophosphonite 14 was obtained in several steps from cyclopentanone as described by Penney and Belleau. 9 The com-pounds 7b-10b were obtained by reaction of the corresponding
chloro-l\) 0 lCH 3J2NrvP:O=a\ 0--- (CH l
")i'!>
2n<;!\...~~
12~
HO~
,o=G
Hi- or f:!.H2ln RO rvp, Z\ ROPC12 HO 0--- ICH I
~
~
2n 11, 13, 15. 17-~~~
~
0~
cis, trans Cl r v / 0=G
\ \ 0--- (CH I . 2 n0~
t RO-P, Z 0···IC~
I 2 n cis 14. 16. 18 ·SCheme I. 11, 12: Z= 0, n= 2; 13, 14: Z= CH 2, n= 2; 15, 16: Z= O, n= 3; 17, 18: Z= CH2, n= 3; R= CH3, Ph.phosphonites 16 and 18 with methanol (1b, 9b) and phenol (Sb, lOb). Isomerization of these compounds by addition of traces of trifluoro-acetic acid afforded the cis phosphites 1a-10a. The starting diol (1RS,2SR)-2-hydroxytetrahydropyranmethanol 15 for the chlorophospho-nite 16 was prepared from dihydropyran according to a method described by Bouchu and Dreux.1
°
Chlorophosphonite 18 was synthesized fromphos-phorus trichloride and (1RS,2SR)-2-hydroxycyclohexanemethanol 11. Com-pound 11 was prepared according to 1iterature procedures.11'12 The cis
isomers 3a-10a obtained by isomerization of the cortesponding trans isomees all contained less than 1% trans as shown by 31P NMR.
2.2.2 Characterization of diastereomees
Assignment of cis and trans geometries to the diastereomees 3a,b-10a,b was made by analogy to the compounds la,b-2a,b3 on the basis of the relative upfield 31P NMR shifts of the cis isomers compared to those of the trans.
2.2.3 1H NMR studies The 1
H NMR data of the dioxaphosphorinane part of the compounds 3a,b-10a,b in benzene-d
6 are listed in Tab1e I. The speetral parameters were obtained by iterative fitting of expansions of the H5a' HSb' H6
1 13
and H
1 patterns of the 300-MHz H NMR spectra using the PANIC program. For comparison, the values of la,b-2a,b in acetone-d~ and of 9a,b in tetra5 are also given.
The dioxaphosphorinane ring of the cis isomees 3a-10a dominantly populates the chair conformer 19 (Figure 3) on the basis of the
simi-J
larity of the JHP values for H5b (ranging from 10.3-11.1 Hz) and H5a (2.4-2.9 Hz) to those of la and 2a and other phosphites for which a chair conformation of the dioxaphosphorinane ring was established.1'3'5
3 3
The small J1,p couplings (1.6-2.5 Hz) and relatively large JSa,6 couplings (10.5-11.4 Hz) are in agreement with this assignment. From the data in Table I it can be concluded that the conformation of the phosphorus containing ring in 3a-10a is not altered by replacing the methoxy group on the phosphorus atom by the more electronegatlve
phe-3 3 3
noxy group. The somewhat larger J 5a,P' J 5b,P and Jl.P couplings of the phenyl phosphites compared to the methyl phosphite~ can be explai-ned by the dependenee of these couplings on the nature of the substi-tuent.14 The data in TableI also reveal that the flexibility of the
Table I. Selected 1H NMR speetral parameters for la,b-lOa,b at 300 MHZ and 300 K
ó(ppm) J(H:z)
compd Sa Sb 6 1 Sa,Sb Sa,P 5a.6 Sb,P 5b,6 1,6 l.P
1aa -9.1 2.4 10.8 10.6 4.3 9.5 1.8 2aa -9.2 2.6 10.1 10.8 4.4 9.1 -2 3ab 4.22 4.08 3.21 4.10 -9.1 2.4 10.6 10.5 4.4 9.0 1.6 4a b 4.36 4.15 3.25 4.23c -9.1 2.6 10.1 10.8 4.4 9.0 2.0c 5ab 4.04 3.19 d 3.96c -10.0 2.4 11.4 10.3 4.2 10.5c 1.9c 6ab 4.18 3.85 d 4.12c -10.0 2.8 11.4 10.6 4.2 10.5c 2.2c 1ab 4.16 3.81 3.24 4.20 -10.0 2.4 10.5 10.8 4.1 9.2 2.0 8ab 4.35 3.81 3.22 4.38c -10.0 2.1 10.6 11.1 4.1 9.3 2.2c 9ab 3.93 3.38 d 4.08c -10.5 2.6 11.4 10.S 4.2 10.0c 2.2c 9ae 3.94 3.49 -10.6 2.5 11.4 10.8 4.2 10ab 4.01 3.43
-
d 4.23c -10.6 2.9 11.4 10.9 4.1 10.2c 2.5c 1ba -9.6 1.1 9.1 3.0 6.2 9.5 1.1 2ba -9.1 9.2 9.8 1.4 6.6 9.1 1.1 3bb 3.88 4.34 3.95 3.55 -9.5 1.8 9.8 3.0 6.2 9.3 1.4 4bb 3.94 4.48 4.21 3.51c -9.6 9.3 9.1 1.4 6.5 9.5 1.1c 5bb 3.S9 4.16 d 3.52c -10.1 6.3 11.4 3.9 6.2 10.4c 1.6c 6bb 3.61 4.29 d 3.52c -10.0 1.6 11.6 1.5 6.6 10.6c 1.6c 1bb 3.11 4.11 3.63 d -10.4 6.9 9.2 6.6 5.9 9.0c-
d 8bb 3.18 4.34 4.01 3.S9c -10.3 9.2 9.1 2.0 6.9 9.8 1.9c 9bb 3.44 3.11-
d 3.52c -10.8 4.1 11.3 8.2 5.3-
d d 9a e 3.59 3.91 -10.1 4.6 11.2 8.3 5.5 10bb 3.39 3.92 d 3.54c -10.3 6.6 11.5 2.2 5.9 d 3.0c a b cFirst-order In acetone-d6 from ref 3. In benzene-d6• analysis. dcould not be determined. ein chloroform-dl from ref 5.
6.P <0.6 <0.6 <0.5 <0.5 d d <0.5 <O.S d d
--0.8 -1.0 -1.0 -1.0 d d d -0.9 d dchair 19 twist 20 cis: x= OCH
3 or OPh, Y= 1one pair trans: X= lone pair, Y= OCH
3 or OPh
Figure 3. chair-twist equilibrium of dioxaphosphorinane ring.
transannelated ring is unimportant with respect to the conformation of the dioxaphosphorinane ring in the cis isomers. Thus, the magnitude of the coupling constantsof 3a-methoxy-trans-2,4,1-trioxa-3-phospha-bicyclo[4.3.0]nonane 3a and its phenoxy analogue 4a, both having a transannelated tetrahydrofuran ring is almost similar to those of 3a-methoxy- and 3a-phenoxy-trans-2,4,1-trioxa-3-phosphabicyclo[4.4.0]decane la and Sa, respectively, possessing a tetrahydropyran ring. The same applies to Sa and 6a, containing a cyclopentane ring, and the phosphi-tes 9a and 10a, possessing a cyclohexane ring. Finally, comparison of the coupling patterns of the trioxa compounds 3a, 4a and la, Sa with those of the dioxa analogues 5a, 6a and 9a, lOa. respectively, indicate that the nature of the atom on position I in the transannelated ring is of little influence on the preferentlal geometry of the dioxaphos-phorinane ring. The differences in 3J5a,
6• 3 J 5b.6 and 3 J 1•6 between the trioxa and dioxa cis phosphites otiginate from the lower e1ectro-negativity of the carbon on position I in the dioxaphosphites. Aceoe-ding to the generalized Karplus re1ation for three bond 1H-1H
spin-~s.~6 3
spin coupling constants the values of 10.6 and 11.4 Hz of J
5a,6 for the trioxa and dioxa phosphites, respectively, both point to a dihedral angle
~ac
5
c
6
H
6
of 1S0°. The va1ues found for 3J5b,6 (4.2, 4.4 and 4.1 Hz) indicate that dihedral angle H
5bc5c6H6 is about 60° (65°, 64° and 62°, respectively). Both dihedra1 angles are consistent with conformation 19. With the dihedral angles P0
4c5H5a and P04c 5H5b of the cis isomers being equa1 to 60° and 1S0° in the chair
conforma-3 3
tion 19. the results obtained for the JSa,P and JSb,P couplings can be used to formulate a Karplus relation17 for the dihedral dependenee of 3JPOCH in these bicyclic phosphites. Hence. taking the average values for 3J
5 a. P (2.5 and 2.8 Hz for the methyl and phenyl cis phos-3
phites. respectively) and JSb,P (10.5 and 10.9 Hz. respectively) relation 1 is obtained with c= 0 for the methoxy compounds and c= 0.3 for the phenoxy compounds.
2
10.4 cos ~ 0.2 cos~ + c (l)
As can be seen in Figure 4. this relation gives nearly the same results as the Kainosho relation18 for the dihedral dependenee of 3JPOCH coup-lings in 2.7,8-trioxa-l-phosphabicyclo[3.2.l]octane 21. 10 H
o~"
NI
H ::c ::cP\~~H
~
I") I C"> 5 I lH 21 H 0 30 60 90 120 150 180 Dihedral angle ~ 3Figure 4. Plots of JPOCH vs. POCH dihedral angle relation 1 for phenoxy cis isomers (X)
Kainosho relation for phosphite 21 (0)17
From the data given in Table I it is clear that the dioxaphosphorinane ring of the trans isomers lb-lOb exists primarily in nonchair confor-mations. For lb and 2b a predominanee of the twist conformation 20
(Figure 3) was found. 3 Characteristic for the twist geometry is the combination of large couplings of H
is not possib1e in the chair conformer 19. Furthermore, the skewing of 3
the dioxaphosphorinane ring in 20 is such that coupling JSa,P is larger than 3J5b,P' The difference between both coup1ings is determi-ned by the extent of twisting of the dioxaphosphorihane ring (dihedral ang1e "sac
5
o
4p can be as large as 180°, reducing that for H5bc5o
4P to as low as 60°). The couplings of H1 to H6 and to phosphorus in 20 will be of the same order as in the chair 19 since the c6c1
o
2P side of the ring maintains the chairlike arrangement of 19. The somewhat reduced H5bc5c6H6 dihedral angle increases 3J
5b,6 in 20 as compared to 19. The couplings of 3b and 4b are equal to those of 1b and 2b, respectively, indicating that the thymine group on position 8 of the transannelated ring has no influence on the preferenee of the dioxaphosphorinane ring for a twist conformation. The decreased 3J5a,P and increased 3J5b,P values of 3b relative to 4b are caused by a greater popu1ation of the chair conformer 19. An exact quantification of the percentage of twist popu1ated by 3b and 4b is difficult to give, since the couplings in case of 100' twist are unknown. Assuming, however, 4b is 100% in the twist conformation and the couplings to "sa and H5b being equal for the chair conformers of 3a and 3b. a 80\ twist population for 3b is calculated. The cyclopentane derivative 6b exhibits coupling constants which also point toa major contribution of the twist conformer. The decreased 3J
5a,P coupling relative to 4b can be the result of a greater
population of the chair conformer 19 present in 6b. A lesser extent of twist of the dioxaphosphorinane ring in 6b, however, would also result in a smaller 3J
5a,P coupling. Substitution of the phenoxy group
in 6b by a methoxy group results in an increase of the fraction of conformer 19 as reflected in the decrease of 3J and increase of
3 5a,P
J 5b,P for Sb. The increase is comparable to the one observed going from 4b to 3b. compound Sb populates a twist conformer to a comparable extent as 4b as can be deduced from the coupling pattern. The couplings of lOb also indicate a dominant population of the twist conformer, although the percentage of chair conformer populated by lOb will be greater than for the other
from the smaller difference methyl phosphites 7b and 9b
trans phenyl phosphites as can
3 3
between the Jsa,P and JSb,P show quite different coupling compared with the other trans phosphites. Thus. 7b shows
3 3 3
J5a.P and
3
JSb,P couplings while the JSb,P coupling of twice the JSa,P coupling. These values can be explained
be concluded values. The patterns as nearly equal 9b is almost by assuming
a considerable amount of chair conformer 19 (50-10\ relative to their phenoxy analogues) present in these compounds. The speetral parameters for 3a,b-10a,b in the more polar solvent acetone-d
6 did not differ significantly from the results given in Table I. This shows that the prefeered conformations of these phosphites are solvent-independent which is in contrast with the results found for the fourcoordinated derivative of 10b.19
2.3 CONCLUSIONS
1H NMR analysis of the bicyclic phosphites 3a.b-10a,b shows that the cis isomees 3a-10a preferently populate the chair conformer 19, independent of the substituent on the phosphorus atom and of the nature of the transannelated ring. The dioxaphosphorinane ring of the trans
isomees 3b-10b shows a preferenee for a twist conformation. The frac-tion of twist conformer mainly depends on the electronegativity of the substituent on the phosphorus atom. The size of the transannelated ring and the nature of the atom on position 1 in this ring have only a minor influence on the preferentlal conformation of the dioxaphosphorinane ring. Furthermore, the prefeered conformation in both cis and trans phosphites is solvent-independent.
2.4 BXPBRIMENTAL SECTION
All solvents and materials were reagent grade and were used as received or purified as required. All reactions involving trivalent phosphorus compounds were routinely run under an atmosphere of dry nitrogen. 1H NMR spectra were run in the FT mode on a Beuker CXP-300 spectrometer at 300.1 MHz, 32K data base, 3000Hz
sw
and 5.41 s acqui-sition time. coupling constants were taken from expansions of the "sa' HSb' H6 and H1 patterns and iteratively analyzed with the PANICpro-gram.13 Chemica! shifts in partsper million for 1H are referenced to TMS. 31P spectra were run on a Bruker HX-90R spectrometer at 36.4 MHZ, using 85\ H3Po4 as external standard.
(1R,2S)-2-hydroxytetrahydrofuranmethanol (11). 56 g (140 mmol) of 3,5-di-p-toluyl-2-deoxy-D-ribosylchloride7 was added in portions in 2 h to a well-stirred suspension of 32 g of lithium aluminium hydride in 1400 mL of tetrahydrofuran with cooling in ice. The temperature varled between 10-l5°C. After the addition was completed, the mixture was refluxed for 3 days. The excess of lithium aluminium hydride was decomposed by careful addition of 120 mL of ethylacetata followed by 1500 mL of water. The precipitated roetal salts were removed by centri-fugation. The resulting solution was concentrated to approximately 500 mL and washed with 3 portions of 100 mL of chloroform. Percolation of
the strong basic solution through an Amberlite IR-120 (H+) column afforded a strong acidic effluent. This was rendered neutral by traat-ment with Amberlite IR-45. Evaporation of the water afforded 14.7 g of a yellow viscous syrup. Destillation of this syrup to remove dissolved ionexchange particles gave 11.2 g (95 mmol, 68\) of colourless 11, bp 104°C/0.03 mm: ~H NMR (acetonitrile-d
3) 5 1.6-2.4 (m, 2H, cH2). 3.2-4.3 (m, 8H, CH
20ff, CHOff, Cff20H, Qeff, CffOH, OCH2).
3-(Dimethylamino)-trans-2.4.7-trioxa-3-phosphabicyclo[4.3.0]no-nane (12). 3.06 g (25.9 mmol) of diol 11 and 0.05 equiv of lH-tetrazole were dissolved in 250 mL of dry dioxane. To this solution was added dropwise 4.23 g (25.9 mmol) of tris(dimethylamino)phosphine at room temperature. After the addition was completed, the mixture was stirred for 18 h at 70°C. The dioxane was evaporated and the resulting crude product was fractionated to give 1.0 g (5.2 mmol, 20\) of 12. bp 59-630C/0.35 mm; 3~P NMR (benzene-d 6)
5
145.1; ~H NMR (benzene-d6)S
1.6-1.9 (m, 2H, H 9a, H9b), 2.6 (d, 6H, N(CH3)2, J= 9 Hz), 3.5-4.4 (m, 6H• H5a' H5b' H6' Hl' H8a' H8b). 3~- and 3~-Methoxy-trans-2.4.7-trioxa-3-phosphabicyclo[4.3.0]nonanes (3a) and (3b). (a) From diol 11 and methyl dichlorophosphinite. A solution containing the diol 11 (10.40 g, 88 mmol) and triethylamine
(17.81 g, 176 mmol) in methylene chloride (130 mL) and a separate solution containing the methyl dichlorophosphinite (11.70 g, 88 mmol) in methylene chloride (150 mL) were added dropwise at equal rates to 225 mL of methylene chloride at -l0°C over a 2.5 h period. The mixture was stirred further at 0°C for 30 min and at 25°C for 2 h. The solvent was removed at 25°C/30 mm and the residue was triturated with dry ether
{150 mL) and fi1tered. The ether was evaporated. Destillation of the residue afforded 3.35 g {18.8 mmol, 21\) product with bp 53°C/0.7 mm which consistedof 40\ of 3a and 60\ of 3b as shown by 31P NMR. Pure 3a {>99\) could be obtained by theemal isomerization of this mixture of diastereomers.
{b) From 3-(dimethy1amino)-trans-2,4,7-trioxa-3-phosphabicyclo-[4.3.0]nonane 12 and methanol. A solution of 0.25 g (1.3 mmol) of 12, 0.042 g (1.3 mmol) of methanol and 4.5 mg (0.065 mmol) of lH-tetrazole in 50 mL of dry dioxane was stirred for 28 h at room temperature. Eva-poration of the dioxane and destillation afforded a1most pure 3b. Ja:
31 P NMR (benzene-d ó • 20 ó 1 6) 122.4 {llt. 121.5); H NMR (benzene-d6) Ó 1.5-1.7 (m, 2H, H 9a, H9b), 3.2 (d, 3H, OCH3, J= 12.2 Hz), 3.2-3.3 (m, lH, H 6), 3.4-3.5 (m, 2H. H8a' HBb), 4.0-4.1 (m, 2H, H1, H5b), 4.2-31 ó 1 4.3 (m, 1H, H
5a). Jb: P NMR (benzene-d6) 129.5; H NMR (benzene-d6) Ó 1.5-1.8 (m, 2H, H9a' H9b)' 3.2 (d, 3H, OCH3, J= 11.9 Hz), 3.4-3.6 (m, 3H. H8a' H8b' H1). 3.8-4.0 (m, 2H. H6, H5a>· 4.3-4.4 (m. 1H, H5b)'
JB- and 3a-Phenoxy-trans-2,4,7-trioxa-3-phosphabicyc1o[4.3.0]-nonanes (4a) and (4b). A solution of 0.25 g (1.3 mmol) of 12 and 0.123 g (1.3 mmo1) of pheno1 in 50 mL of dry dioxane was ref1uxed for 18 h at 70°C. Evaporation of the dioxane afforded 4b. Thermal isomerization
3 1 1
of 4b gave lts cis isomer 4a. 4a: P NMR (benzene-d6) ó 114.1: H NMR (benzene-d 6) ó 1.5-1.8 (m, 2H, H98, H9b), 3.2-3.3 (m, lH, H6), 3.4-3.5 (m, 2H, H8a' H8b>' 4.1-4.2 (m, lH, H5b>' 4.2-4.3 (m, 1H. H58). 6.7-7.3 31 1 (m, 5H, Ar H). 4b: P NMR (benzene-d6) ó 120.3; H NMR (benzene-d6) Ó 1.6-1.9 (m, 2H, H9a' H9b), 3.4-3.6 (m, 3H, H1 , H8a' H8b)' 3.9-4.0 (m, lH, H 5a), 4.2-4.3 (m, 1H, H6), 4.4-4.5 (m, 1H, H5b), 7.0-7.2 (m, 5H, Ar H).
(1RS,2SR)-2-hydroxycyc1opentanemethano1 (13). This compound was prepared in severa1 steps from cyc1opentanone as described by Penney and Bel1eau.9 Bp 97-100°C/1.0 mm (lit.9 bp 96-99°C/1 mm): 1H NMR (chloroform-d1) ó 0.8-2.2 (m, 7H, CH
2, CH), 3.2-4.2 (m, 5H, cH2QH. CHQH. Ctl20H, CtlOH). GC showed this compound to contain no cis dio1.
3-ch1oro-trans-2,4-dioxa-3-phosphabicyc1o[4.3.0]nonane (14). This compound was prepared from diol 13 and phosphorus trichloride as
des-cribed by Ramirez et al. 21 Yield 42\, bp 68-70°C/0.85 mm (lit.21 yield 31 21 53\, bp 49-50°C/0.4 mm); P NMR (benzene-d 6) ó 146.3 (lit. ó 145.4); 1 H NMR (benzene-d
6): ó 0.3-1.7 (m, 7H, H6 , H7a' H7b' H8a' H8b' H9a' H
9b), 3.6-3.8 (m, lH, H5b), 3.9-4.2 (m, 2H, H1• H5a)
3a-Methoxy-trans-2,4-dioxa-3-phosphabicyclo[4.3.0]nonane (5b). Phosphite 5b was prepared from compound 14 and methanol by the general method of Verkade et al. 8 Toa solution of the chlorophosphonite 14
(0.72 g, 4.0 mmol) in 10 mL of anhydrous ether maintained at 0°C was added dropwise with stirring a solution containing 0.9 equiv of metha-nol (0.116 g, 3.6 mmol) and 1 equiv of triethylamine (0.404 g, 4.0 mmol) in S mL of anhydrous ether. After removal of the triethylamine-Hel salt by fi1tration, the ether solution was evaporated and the resi-due distilled to give 0.41 g (2.34 mmol, 65\) of 5b, bp 57-58°C/0.8 mm (li t. :~o bp 54 o
c
I 0. 7 mm ; ) 31 P NMR ( benzene-d ) • ( i 20 • )6 o 130.8 1 t. o 130.4 :
1
H NMR (benzene-d6 ) ó 0.5-2.4 (m, 7H, H6 , H7a' H7b' H8a' H8b' H9a'
H
9b)' 3.4 (d, 3H, OCH3, J= 11.7 Hz), 3.5-3.6 (m, lH, H1), 3.6 (m, lH, H5a>• 4.1-4.2 (m. 1H, H5b).
36-Methoxy-trans-2,4-dioxa-3-phosphabicyclo[4.3.0]nonane (5a). This compound was obtained by thermal isomerization of its trans isoroer
31 1
Sb. P NMR (benzene-d
6) ó 125.0; H NMR (benzene-d6) ó 0.5-1.9 (m, 7H, H6 , H7a' H7b' H8a' H8b' Hga• H9b)' 3.3 (d, 3H, OCH3 , J= 12.1 Hz), 3.7-3.8 (m, lH, H5b)' 3.9-4.1 (m. 2H. H1• Hsa>·
36- and 3a-Phenoxy-trans-2,4-dioxa-3-phosphabicyclo[4.3.0]nonanes (6a) and (6b). A 70/30 mixture of 6a and 6b, suitable for NMR analysis, was obtained by the reaction of chlorophosphonite 14 with phenol accor-ding to the procedure that was described for the preparatien of Sb. Yield 57\, bp 93-99°C/O.S5 mm. Addition of traces of trifluoroacetic acid to this mixture afforded nearly pure (>99\) cis isoroer 6a. 6a:
31
P NMR (benzene-d
6) ó 117.0;
1H NMR (benzene-d
6) ó 0.5-1.9 (m, 7H, H6 , H7a' H7b' H8a' H8b' H9a' H9b), 3.8-3.9 (m, lH, HSb)' 4.1-4.2 (m, 2H, H
1, HS ), 7.0-7.2 (m, SH. Ar,H). 6b:
31
PNMR (benzene-d) ó 121.6;
1 a 6
H NMR (benzene-d6 ) ó O.S-2.8 (m, 7H, H6 , H7a' H7b' H8a' H8b' H9a' H9b), 3.S-3.6 (m, lH, H1), 3.6-3.7 (m, lH, HSa)' 4.2-4.3 (m, lH, H5b), 7.0-7.2 (m, 5H, Ar H).
(1RS,2SR)-2-Hydroxytetrahydropyranmethanol (15}. compound 15 was prepared in several steps from dihydropyran according to the procedure described by Bouchu and Dreux.10 overall yield 11\, bp 108-ll2°Cil.9
10 1
rnm (1it. bp 130-135°C/2.0 rnm); H NMR (chloroform-d
1) b 1.0-2.4 (m, 4H, CH
2), 2.8-4.2 (m, 7H, Ctl20H, CH2Qtl, OCH2, OCtl, CtlOH).
3-Chloro-trans-2,4,7-trioxa-3-phosphabicyclo[4.4.0]decane (16). This chlorophosphonite is prepared from diol 15 and phosphorus trichlo-ride by the metbod described for the preparation of compound 14. Yield 32%, bp 95°C/2.2 mm; 31P NMR (benzene-d
6) b 147.3: 1
H NMR (benzene-d 6)
b 0.9-1.7 (m, 4H, H9a' H9b, HlOa' HlOb}, 2.8-3.0 (m, 2H, H6 , H8 ),
3.4-3.5 (m, lH. H
8), 3.6-3.9 (m, lH, H5b)' 4.1-4.4 (m, 2H, H1, H5a>· 3a-Methoxy-trans-2,4,7-trioxa-3-phosphabicyclo[4.4.0]decane (7b). Phosphite 7b was prepared from ch1orophosphonite 16 and methanol accor-ding to the procedure described for the preparation of 5b. Yield 74\, bp 70-76°C/2.0 rnm; 31P NMR (benzene-d 6) b 131.3; 1 H NMR (benzene-d 6) b 1.0-1.9 (m, 4H, H9a' H9b' H10a' H10b), 2.9-3.0 (m, lH, H8 ), 3.3 (d, 3H, OCH 3, J= 11.2 Hz), 3.5-3.7 (m, 3H, H1, H6, H8), 3.7-3.8 (m, 1H, H5a)' 4.1-4.2 (m, 1H. H5b}. 3B-Methoxy-trans-2,4,7-trioxa-3-phosphabicyclo[4.4.0]decane (7a). Addition of traces of trif1uoroacetic acid to compound 7b afforded near1y pure (>99\) 7a. 31P NMR (benzene-d
6) b 125.8; 1 H NMR (benzene-d6) Ö 1.0-1.8 (m, 4H, H9a' H9b' H10a' H10b)' 2.9-3.0 (m, 1H, H8 ), 3.2 (d, 3H, OCH 3, J= 12.0 Hz), 3.2-3.3 (m, lH, H6}, 3.5-3.6 (m, lH, H8), 3.a-3.9 (m, lH, H 5b)' 4.1-4.2 (m, 2H, H1, H5a). 3a-Phenoxy-trans-2,4,7-trioxa~3-phosphabicyc1o[4.4.0]decane (Sb).
Reaction of the chlorophosphonite 16 with phenol according to the procedure described for the preparation of 5b furnished Sb, bp 113-1140C/0.5 rnm; 31P NMR (benzene-d
6) ö 122.2; 1
H NMR (benzene-d
6) ö 1.0-2.0 (m, 4H, Hga' Hgb' H10a' H10b)' 2.9-3.0 (m, lH, Ha), 3.4-3.6 (m, 1H, Ha), 3.5-3.7 (m, 1H. H1}, 3.7-3.9 (m, 1H, HSa)' 4.0~4.1 (m, 1H, H
6), 4.3-4.5 (m, 1H, HSb), 6.8-7.3 (m, 5H, Ar H).
3B-Phenoxy-trans-2,4,7-trioxa-3-phosphabicyclo[4.4.0]decane (Sa). Cis isomer Sa was prepared from compound Sb by isomerization caused by
traces of trif1uoroacetic acid. 3~P NMR (benzene-d
6) ó 117.6; 1
H NMR (benzene-d
6) ó 1.0-1.8 (m. 4H, Hga' Hgb' H10a' HlOb), 2.8-3.0 (m, lH, H
8), 3.2-3.3 (m, lH. H6), 3.5 (m, lH, H8), 3.8-4.0 <m. lH. H5b>. 4.3-4.5 (m, 2H, H
1, H5a), 6.7-7.2 (m, 5H, Ar H).
{1RS,2SR)-2-hydroxycyclohexanemethano1 {17). Diol 17 was prepared from cyclohexene and paraformaldehyde according to literature proce-dures.11'12 1H NMR {chloroform-d
1l ó 0.7-2.3 (m, 9H, CH2• CH), 3.1-4.7 (m, 5H, CH
20H, CHOH, cH20H, CHOH).
3-Chloro-trans-2,4-dioxa-3-phosphabicyclo(4.4.0]decane {18). This compound was prepared from diol 17 and phosphorus trichloride by the metbod described for the preparation of 14. Bp. 92-94°C/2.2 mm {lit.22
31 22 1
bp 102°C/2.2 mm); P NMR {benzene-d
6) ó 152.4 (lit. ó 152.2); H NMR (benzene-d6 ) ó 0.5-1.8 (m. 9H, H6 • H7a' H7b' "sa' HBb' H9a' H9b'
HlOa' H10b)' 3.3-3.4 {m, lH, H5b)' 3.9-4.0 {m, lH, H5a), 4.1-4.3 (m, lH, H
1).
3a-Rethoxy-trans-2,4-dioxa-3-phosphabicyclo(4.4.0]decane (9b). The preparation of phosphite 9b was analogous to that of compound 5b. Yield 65\, bp 70-71°C/0.59 mm (lit.22 bp 100-103°C/3.3 mm); 31P NMR (benzene-d 6) ó 133.1 (lit. 22 ó 133.5): 1H NMR (benzene-d 6) ó 0.8-2.2 (m, 9"· H6' H7a' H7b' H8a' H8b' H9a' H9b' HlOa' HlOb)' 3 · 4 (d, 3"•
OCH3 , J= 10.9 Hz), 3.3-3.6 (m, 2H, Hlb' H
5a>• 3.7-3.8 (m. lH, H5b). 3B-Rethoxy-trans-2,4-dioxa-3-phosphabicyclo(4.4.0]decane (9a). Acidic isomerization of phosphite 9b afforded isomer 9a. 31 P NMR (ben-zene-d6) ó 130.3 (lit.22 ó 129.8); 1H NMR {benzene-d
6) ó 0.8-1.9 (m, gH, H6, H7a' H7b' H8a' H8b' H9a' H9b' HlOa' HlOb), 3 · 3 (d, 3H• OCH3' J= 12.0 Hz), 3.3-3.4 (m, lH, H5b). 3.9-4.0 (m, lH, H
5a>· 4.0-4.1 (m, lH, H
1).
3a-Phenoxy-trans-2.4-dioxa-3-phosphabicyclo(4.4.0]decane (lOb). Compound lOb was prepared according to the method described for the preparation of phosphite 5b. Yield 72\, bp 118-120°C/0.4 mm; 3 NMR
l (benzene-d
6) ó 124.3; H NMR (benzene-d6) ó 0.6-2.7 (m. 9H, H6, H7a, H7b' H8a' H8b' H9a' H9b' HlOa' HlOb), 3.3-3.4 (m, lH, H5a), 3.5-3.6
(m, lH, H
3P-Phenoxy-trans-2,4-d1oxa-3-phosphab1cyclo[4.4.0]decane (lOa). Cis isomer lOa was obtained by isomerization of compound lOb. 81P NMR
1
(benzene-d
6) 6 122.5: H NMR (benzene-d6) 6 0.8-1.8 (m, 9H, H6, H1a' H1b' H8a' H8b, H9a' H9b, H10a' HlOb), 3.4-3.5 (m, lH, H5b), 4.0-4.1
(m, 1H, H ), 4.2-4.3 (m, 1H, H
1), 1.0-1.2 (m, 5H, Ar H).
5a
1 B.E. Maryanoff. R.O. Hutchins. C.A. Maryanoff. Top. Stereochem., 11. 181 (1919).
2 E.E. Nifant'ev, s.F. sorokina, A.A. Borisenko, Zh. Obshch. Khim., 55. 1665 (1985).
3 K.A. Nelson, A.E. sopchik, W.G. Bentrude, J. Am. Chem. soc., 105, 1152 (1983).
4 Compounds 9a and 9b have already been investigated by NMR spec-troscopy by Haemers et al.5' 6 However, these studies dealt mainly
with the prefeered orientation of the substituent on the phosphorus a torn.
5 M. Haemers, R. Ottinger, J. Reisse, 0. Zimmermann. Tetrahedron Lett., 461 (1911).
6 M. Haemers, R. Ottinger,
o.
Zimmermann. J. Reisse, Tetrahedron. 29. 3539 (1913).1 M. Hoffer, Chem. Ber., 93, 2177 (1960).
8 J.A. Mosbo, J.G. verkade, J. Am. chem. soc •• 19, 3411 (1951). 9 C.L. Penney, B. Bel1eau, Can. J. Chem., 56, 2396 (1918). 10 0. Bouchu, J. Oreux, Phosphorus and su1fur, 13. 25 (1982). 11 A.T. B1omquist, J. Wo1insky, J. Am. Chem. soc., 79, 6025 (1951). 12 E.E. Smissman, R.A. Mode, J. Am. Chem. soc., 19, 3441 (1957). 13 PANIC program: copyright, Bruker speetrospin AG. switzer1and. 14 A significant change of the conformation of the dioxaphosphorinane
ring can be exc1uded on the basis of the unchanged J5a, 6 and J5b, 6
coup1ings.
15 C.A.G. Haasnoot, F.A.A.M. de Leeuw, c. A1tona, Tetrahedron. 36, 2783 (1980).
16 In this genera1ized equation the standard Karplus re1ation17 is extended with a correction term which accounts for the 1nf1uence
3
3 2 2
JHH= 13. 22cos 41 -0. 99cos41+I: { 0. 87-2. 46cos ( Ç i 41 + 19.91 t! x. i
I}
}t!x.i.41 is the proton-proton torsion ang1e, t!x.i is the difference in electronegativity between the substituent and hydrogen actording to the e1ectronegativity scale of Huggins. and Çi is a substituent or1entation parameter.
17 M. Karp1us, J. Chem. Phys •• 30. 11 (1959}.
18 M. Kainosho. A. Nakamura. Tetrahedron. 25. 4071 (1969}.
19 D.G. Gorenstein. R. Rowe11, J. Find1ay, J. Am. Chem. soc •• 102, 5077 (1980} .
20 P.J.J.M. van 001, H.M. Buck, Reel. Trav. Chim. Pays-Bas, 103, 119 (1984}.
21 F. Ramirez. J.F. Marecek, I. Ugi, P. Lemmen, D. Marquarding. Phos-phorus, 5. 73 (1975}.
22 K. Taira, W.L. Hoek, D.G. Gorenstein, J. Am. Chem. Soc., 106, 7831 (1984}.
CHAPTRR 3*
A 3 1 P AND 1 H NHR STUDY OF THB CONFORHATIONS OF A
SBRIBS OF DIASTBRBOMERIC 3-SUBSTITUTBD TRANS-2,4-DIOXA-3-QXQ- AND
TRANS-2,4-DIOXA-3-THIOXo-3-PHOSPHABICYCL0[4.3.0]NONANES AS HODBL COMPOUNDS FOR CYCLIC NUCLBOTIDES
ABSTRACT
A number of epimeric pairs of 3-X-trans-2,4-dioxa-3-Y-3-phospha-bicyclo[4.3.0]nonanes (1, X= OCH 3, Y= O; 2, X= OCH3, Y= S; 3, X= OPh, Y= O; 4, X= OPh, Y= S; 5, X= Cl, Y= 0; 6. X= Cl, Y=_s; 7, X= N(CH 3)2, Y= O; 8, X= N(CH 3)2, Y= S; 9, X= S , Y= 0; 10, X= 0 , Y= 0) has been prepared and their configuration and conformation studled by 31P and 1
H NMR. The cis isomers la-6a and the trans isomers 7b and 8b are shown to populate exclusively chair conformation 18. Their diastereoroers lb-6b, 7a and 8a, however, exist as an equilibrium between chair confor-mation 18 and twist conforconfor-mation 19. The mole fraction of twist is found to vary with the nature of the exocyclic substituents on the phosphorus atom, being maximal for the chloro compounds Sb and 6b. In addition, it is shown that the chair ::;~:;twist equilibrium is solvent-sensitive. The charged compounds 9a, 9b and 10 are in a chair confor-mation. The position of the negative1y charged sulfur atom has no in-fluence on the preferred conformation of the phosphorothioates 9a and 9b. The results for 9a and 9b are discussed in relation to the diffe-rence in biologica! activity of (SP)- and (RP)-cAMPS.
3. 1 INTRODUCTION
3',5'-cyclic nucleotides, e.g. cAMPand cGMP, play a central role in hoernone action and cell communication.1 Recently, it was shown that the biologica! activity of cyclic nucleotide analogues, derivatized at phosphorus, is governed by the configuration on the phosphorus atom (S p
oeR ). 2 Furthermore, it was established that the conformation of the
p
dioxaphosphorinane ring of comparable cyclic nucleotides is determined by the phosphorus configuration. 3 In this chapter, a detailed configu-rational and conformational analysis of a number of epimeric trans-2,4-dioxa-3-oxo- and trans-2.4-dioxa-3-thioxo-3-phosphabicyclo[4.3.0]-nonanes la,b-9a,b and 10 (Figure 1) is described.
x,
,0=0
v,
Io=o
,P
p.
\ .• \ Y' 0 ... .x·
o···
isomee a isomee bx
yx
y 1 OCH 3 0 6 cls
2 OCH 3s
1 N(CH3}2 0 3 OPh 0 8 N(CH 3)2s
4 OPhs
9s
0 5 Cl 0 10 0 0Figure 1. Model compounds la,b-9a,b and 10.
These compounds contain a dioxaphosphorinane ring trans fused to a cyclopentane ring and can be considered as simple model compounds for cyclic nucleotides. Other bicyclic model compounds in which the phos-phorus containing ring was transannelated with a six-membered tetra-hydropyran or cyclohexane ring have been already studied.4 '
5
I t seems however likely that conclusions drawn from model compounds possessing a five-membered ring adjacent to the dioxaphosphorinane ring are more directly applicable to cyclic nucleotides.
3.2 RESULTS AND DISCUSSION
3.2.1 synthesis
The cis compounds la and 3a (singly bonded substituent on phos-phorus cis to H
1) were prepared from the corresponding cis methyl and phenyl phosphites lla and 12a,6 respectively, by stereochemically
re-7 tentive No
21N2o4 oxidation (Scheme I). The trans diastereoroers lb and 3b were obtained in an analogous way from the trans phosphites llb and 12b. respectively. Since these phosphites were never completely free of their thermodynamically favoured cis isomers, the trans phos-phates lb and 3b were always obtained as mixtures with their cis epi-roers la and 3a. The phenyl phosphates 3a and 3b, however, could be separated by column chromatography. Reaction of the phosphites lla and 12a with elemental sulfur, which is known to proceed with
reten-a
tion of configuration at the phosphorus atom, yielded the cis thioxo-phosphorinanes 2a and 4a. respectively. The trans isoroers 2b and 4b were obtained by separation of the cis/trans mixtures which resulted from the reaction of sulfur with the mixture of lla and llb and of 12a and 12b (Scheme I). Stereospecific removal of the methyl group of the phosphates la,b and 2a,b by t-butylamine9 led almost quantitatively to the charged compounds 10 and 9b,a, respectively.
x,
,a~
NO/N2o4x,
,a~
ssx,,o~
.P p .P
a·:-· '
-·
\s';-· '
o--
y. 0--0--la: X= OCH
3 lla: X= OCH3, Y= lone pair 2a: X= OCH3 3a: X= OPh 12a: X= OPh, Y= lone pair 4a: X= OPh
0~0~
NO/N2o 4v,P~
sss~p~
~I .P p.P
.
\-·
\.
\x.
0--x.
0--x.
o--lb: x= OCH3 llb: x= OCH3, Y= lone pair 2b: X= OCH3 3b: x= OPh 12b: X= OPh, Y= lone pair 4b: X= OPh
The chlorophosphonates 5a and 5b were prepared in two steps from the thiophosphates 9a and 9b via the intermedlate sulfenylchlorides 13a and 13b according to a method described by Miehalski et al. 10 Both steps proceeded with predominant retention of configuration at phos-phorus. compound 5a was also obtalned as major product by the
oxida-11
tion of the cis chlorophosphonite 14 wlth
No
2tN
2
o
4 (Scheme II). \\ o\\Ct,P~~lb
9a o-.. ~Io~
.P - 5,. \ o--9b - .Po,·.·
'o-·
13a (;;;-;-.... 7b 5a 3 2Nlt 14: Y= lone pair ~p'o ...
0~
.·
\ CIS' 0--13b Scheme II.Independent confirmation of the configurational assignment of the chlorophosphonates 5a and 5b was obtained by their transformation into the methyl phosphates lb and la, respectively. In addition, nucleophi-lic substitution of the chlorine atoms in 5a and 5b by dimethylamine yielded the phosphoramidates 7b and ?a, respectively, with complete inversion of contiguration at phosphorus. Reaction of thiophosphoryl chloride 15 with (1RS.2SR)-2-hydroxycyclopentanemethanol (16)13 affor-ded a mixture of the thiophosphonates 6a and 6b (ratio 22/78 as judged
31
by P NMR), which could not be separated by column chromatography. Methanolysis of this mixture at
room
temperature yielded a mixture of2b and 2a (22/78)(Scheme III). On the basis of this result, 6a could be assigned the cis configuration and 6b the trans configuration. This assignment was confirmed by the formation of the phosphoramidates Sb and Sa (18/82) in the reaction of a mixture of 6a and 6b (19/Sl) with dimethylamine. Equilibration of the initial mixture of 6a and 6b with a catalytic amount of tetraethylammoniumchloride in acetone at room temperature resulted in the formation of a mixture containing 6a and 6b in the ratio 76/24.
CI~PPlJY2b
s -:..- \
o--HO~-<
6~a~
(V;;:--
8b SPCl\_j
(C2H5)4NC1 3 +HO'
15 16s~
,O)J
y
2a ,P , \ Cl' 0 .. 6b(~Sa
3 2·•rz Scheme I I I .Oxidation of a mixture of (dimethylamino)phosphonites 17a (20%, di-methylamino group cis) and 17b (80\, didi-methylamino group trans) fur-nished a mixture of phosphoramidates 7a and 7b (20/80). A mixture of 7a and 7b (23/77) was also obtained by the reaction of dimethylchloro-amine with a mixture of methyl phosphites lla and llb (40\ of lla) (Scheme IV). 3
17a: Y= lone pair
The speetral parameters of the phosphoramidates thus obtained were identical to those of the compounds obtained by the reaction of the chlorophosphonates 5a and 5b with dirnethylarnine. A mixture of the
isomerie thiophosphorarnidates Sa and Sb (20/SO) was obtained by the reaction of elernental sulfur with a mixture of 17a and 17b (20/SO) (Scherne V). Chrornatographic separation of this mixture yielded the single diastereoroers which were identical to the ones obtained by the reaction of the chloro compounds 6a and 6b with dimethylamine (Schernes
III and V). 6b 17b
_s_s___
s~ p~
,P
...
\ ICH 312N • o--6a Sb Schernev.
3.2.2 Assignrnent of confiquration at phosphorus
The assignrnent of the cis and trans configurations to the diaste-reomers la,b-9a,b was made on the basis of their stereospecific way of synthesis (vide supra). As was noted previously for other isomerie pairs of monocyclic and bicyclic l,3,2-dioxaphosphorinanes,4 '5' • the
31
P chemica! shifts of the cis isorners of 1-9 (Table III) are upfield of those for the trans isorners except for the chlorophosphonates 5a and 5b and the dirnethylamino cornpounds Sa and Sb.
3.2.3 1H NMR conforrnational analysis
The 1H NMR data of the dioxaphosphorinane part of the cornpounds la,b-Sa,b (in acetone-d
6) and of 9a.b and 10 (in
o
2o) are listed in Table I. The speetral parameters for H and H were obtained byite-5a 5b
rative fitting of expansions of the H and H patterns of the 300-MHz
5a 5b
1 J. 4
H NMR spectra using the PANIC program. The chemical shift and Jl.P coupling of H
1 are first-order approxirnations. For comparison, the rele-vant parameters of 2'-deoxy-3',5'-cyclic AMP (dcAMP) 15 arealso given.
Table I. Se1ected 1H NMR speetral parameters for la,b-9a,b and 10 at 300 MHz and 300 K and for dcAMPa
ó(ppm) J(Hz}
compd 5a 5b lb 5a,5b 5a,P 5a,6 5b,P 5b,6 LP b
1ac 4.20 4.46 4.32 -10.4 0.5 11.4 22.2 4.5 <0.6 2ac 4.26 4.42 4.32 -10.2 1.0 11.5 22.7 4.5 1.1 3ac 4.39 4.54 4.56 -10.3 0.5 11.5 22.9 4.6 <0.6 c 4a 4.49 4.56 4.59 -10.2 1.2 11.5 23.5 4.5 1.4 5a c 4.42 4.67 4.52 -10.6 1.5 11.5 27.6 4.5 2.2 6a c 4.47 4.66 4.52 -10.6 2.8 11.6 28.2 4.4 3.6 7ac 4.03 4.39 4.22 -10.0 7.1 11.4 13.5 5.3 0.8 c 4.16 Sa 4.37 4.30 -10.1 3.6 11.4 19.2 4.8 1.3 9a d 4.12 4.27 4.31 -10.3 2.5 11.4 24.4 4.5 3.0 10d 4.01 4.25 4.17 -10.5 1.3 11.4 21.2 4.6 0.8 lbc 4.27 4.51 4.43 -10.2 5.7 11.6 15.6 5.3 <0.6 2bc 4.29 4.46 4.44 -10.1 4.6 11.5 20.8 4.9 2.3 3bc 4.32 4.59 4.56 -10.2 10.2 11.7 10.2 5.9 <0.6 4bc 4.39 4.60 4.55 -10.3 7.3 11.6 17.2 5.3 1.8 5bc 4.49 4.79 4.57 -10.1 17.5 11.9 5.4 6.5 1.6 6bc 4.52 4.81 4.69 -10.2 18.5 11.8 6.5 6.6 1.6 7bc 4.18 4.33 4.30 -10.4 0.9 11.5 21.7 4.6 1.2 8bc 4.25 4.31 4.41 -10.4 2.0 11.5 24.7 4.5 2.6 9bd 4.14 4.27 4.24 -10.5 2.4 11.5 21.4 4.5 1.8 dcAMP a 1.10 1.27 1. 73 -9.7 2.2 10.7 20.6 4.6 2.0 a
from ref 15. bFirst-order In
o
2
o
with TMA as interna1 standardc d
ana1ysis. In acetone-d
Neutral phosphorinanes la,b-Sa,b. The dioxaphosphorinane ring of the compounds la-6a, ?b and Sb is readily assigned the chair confor-mation lS (Figure 2) on the basis of the similarity of its coupling constants to those for underivatized cyclic nucleotides, for instanee dcAMP, which unquestionably possess chair form phosphate rings.
lS
Figure 2. chair conformation lS.
Most diagnostic is the combination of a large JSb.P coupling constant (21.7-2S.2 Hz) with small J
5 a,P and J1 .P coupling constants (0.5-3.6 Hz). The variations in JSa,P and particularly JSb,P values for the compounds la-6a, ?b and Sb, result from the dependenee of these
coup-lings on the nature of the substituents on the phosphorus atom.16 A significant change in the conformation of the dioxaphosphorinane ring, resulting also in differences in the JSa,P and JSb,P couplings, can be excluded since J5a,6 and JSb, 6 are almost equal for the compounds la-6a, ?b and Sb. The population of a chair conformation by the cis isomers la-6a is consistent with the strong predilection of the electronegative methoxy (la, 2a), phenoxy (3a, 4a) and chloro (Sa, 6a) substituents for an axial position in 2-oxo- and 2-thioxo-1,3,2-dioxaphosphori-nanes.8'16 The relatively large size of the dimethylamino group and its consequent preferenee for an equatorlal position explains the chair conformation of ?b and Sb. The coupling constants of lb-6b, ?a and Sa are inconsistent with chair conformation IS. Due to the trans fusion of the dioxaphosphorinane ring with the cyclopentane ring, the only nonchair conformation energetically accessible to these isomers is the twist conformation 19 (Figure 3). In conformation 19, dihedral angle H5ac5o4P can be as large as 180° leading to a large JSa,P coupling
(~22Hz) and a smal! JSb,P coupling (~1 Hz). The JSa,6 coupling in 19 will remain relatively unchanged compared to that in the chair conformation 18. This leads to the combination of large couplings of
