Development and application of novel scaffolds in drug discovery
Boltjes, André
DOI:
10.33612/diss.98161351
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Publication date: 2019
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Boltjes, A. (2019). Development and application of novel scaffolds in drug discovery: the MCR approach. Rijksuniversiteit Groningen. https://doi.org/10.33612/diss.98161351
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Chapter 4
Ugi 4-CR Synthesis of γ- and
δ-Lactams providing new access to
diverse enzyme interactions, a PDB
analysis
André Boltjes, George P. Liao, Ting Zhao, Eberhardt Herdtweck, and Alexander Dömling
Abstract
A three step synthesis of N-unsubstituted tetrazolo γ- and δ-lactams involving a key Ugi-4CR is presented. The compounds, otherwise difficult to access, are conveniently synthesized in overall good yields by our route. PDB analysis of the N-unsubstituted γ- and δ-lactam fragment reveals a strongly tri-directional hydrogen bond donor acceptor interaction with the amino acids of the binding sites.
4
Introduction
The γ-and δ-lactam moiety is an often found fragment in bioactive compounds. Examples of compounds with a lactam fragment include the anti-Parkinson drug oxotremorin1 or the anti-rhinoviral and -enteroviral rupintrivir.2 Generally, the
lactam nitrogen can be either unsubstituted or substituted, which influences its hydrogen bonding profile in the receptor binding site. For example in the crystal structure of rupintrivir with the human rhinovirus 3C protease, the γ-lactam-N forms a short hydrogen bond to the Thr142 backbone carbonyl, whereas the δ-lac-tam-O forms two short contacts to side chain His161-NH and the Thr142-OH, re-spectively (Fig. 1).3 In our ongoing efforts in structure- and computational-based
design of bioactive compounds we were interested in a short and versatile synthe-sis of N-unsubstituted γ- and δ-lactams with potential multiple hydrogen bond interactions.4 Combining the lactam functionality with a 1,5 disubstituted
tetra-zolo peptidomimetic could enhance the affinity of this tetrazole analog which is a well-known cis-amide bond mimic, which provides new synthetic probes for a series of biological targets.5-9 Multicomponent reactions (MCR) were found
to be an excellent tool to rapidly access a large and versatile drug-like chemical space to address the corresponding biological space.5 A convenient and versatile
synthesis of N-substituted γ- and δ-lactams using convergent Ugi-type MCR’s was recently introduced by Marcos et al. and refined by others.10-12 However no
MCR-based synthesis of N-unsubstituted γ- and δ-lactams has been described up to date. Clearly many synthetic approaches towards N-unsubstituted γ- nd δ-lactams are described, however these contain limitations regarding variability d length of the synthetic routes.13
Figure 1.Trifurcated hydrogen bonding interactions (red dotted lines) of an
N-unsubsti-tuted γ-lactam (cyan sticks) with some protease amino acids in the example of rupintrivir (PDB ID 1CQQ).
Ammonia is one of the few amine components which does not regularly give convincing results in the Ugi MCRs.14-18 Therefore we recently introduced
trityl-amine as an ammonia surrogate in the Ugi tetrazole MCR.19 This reaction forms
the core of our design of a synthetic pathway towards N-unsubstituted γ- and δ-lactams (Scheme 1). The first step comprises the Ugi tetrazole MCR using tr-itylamine, followed by cleavage of the trityl group. The formed primary amine should easily undergo cyclisation to form the target γ- and δ-lactam compounds.
4
Scheme 1. Devised synthetic pathway to tetrazolo N-unsubstituted γ- and δ-lactams
Results and Discussion
The Ugi tetrazole synthesis was initially performed under Ugi azide conditions with tritylamine (1), azidotrimethylsilane (2), phenylethylisonitrile and various aldehyde esters to check scope and limitations.20 The aliphatic aldehydes 3a-b
were prepared according to previous described methods starting from the acid chloride (Scheme 2.).21 Cl O O O 2,6-Lutidine Pd/C 10% 3 atm H2 n O O O n 3a, n=2 3b, n=3
Scheme 2. The two aldehydes utilized in the Ugi tetrazole synthesis
Due to the steric hindrance of the trityl moiety, the Schiff-base condensation step of the Ugi reaction only proceeds smoothly under microwave irradiation.19
More-over, it was found that only aliphatic aldehydes such as 3a and 3b gave good yields varying between 40 and 80 %. The used number of aldehydes was bigger with even n=4 and a cyclopropyl moiety in the chain. The Ugi tetrazole reac-tion was also successful for these aldehydes, however, the subsequent cyclisareac-tion gave problems, not yielding the desired lactams. Aromatic aldehydes were inves-tigated and only in some reactions a moderate yield was observed.19 Aryl ester
aldehydes did not yield any product at all.
Product diversity by using four other isonitriles (4) (Table 1.) showed yields com-parable with phenylethylisocyanide. Deprotection conditions in order to cleave the trityl from the amine requires at least 2 equivalents of TFA. Full conversion into the amine is achieved within seconds monitored by TLC. Simple
purifica-tion was performed by pouring the reacpurifica-tion mixture directly onto a 5 cm silica gel filter wetted with heptane:EtOAc (1:1) removing the impurities by washing with 50 mL heptane:EtOAc. Then the product was eluted from the filter using 50 mL CH2Cl2:MeOH (1:1) to obtain the pure amine. Subsequent cyclisation gave difficulties. Generally Et3N or potassium carbonate is sufficient to cyclize compa-rable molecules, however it was found that the resulting TFA salt needed to be liberated using a strong base prior to cyclisation. The main disadvantage of using a strong base is that this results in saponification of the initial ester and thus pre-venting cyclisation at all. Sodium hydride was found to be a suitable base giving in most cases only a minor conversion to amino acids and reasonable to very good yields for the γ- and δ-lactams (Table 1).
We could grow four crystals of γ- (6b, 6e) and δ-lactams (6f, 6j) suitable for single crystal structure determination (Fig. 2). Interestingly the lactam amide group in all cases show intermolecular hydrogen bonding involving the amide NH and the carbonyl CO. Five-membered γ-lactam 6b shows an intermolecular hydro-gen bonding with a neighboring γ-lactam amide with a distance between the heavy atoms of 2.8 Å. Six-membered δ-lactam 6, however, exhibits a trifurcated hydrogen bonding network involving a neighboring δ-lactam and a co-crystal-lized water molecule. Thus the oxygen atom shows two hydrogen bonds along the lone pair electrons.
Table 1. Cyclization of the Ugi 4-CR to yield the isoindolone scaffold.
N N N N R4 NHTrityl COOMe n 5 N N N N R4 NH O n 6
entry R(4) n Ugi (%) a entry cyclisation(%) b
5a 2 73 6a 55
5b 2 50 6b 89
5c 2 75 6c 32
4
5e 2 40 6e 95 5f 3 78 6f 76 5g 3 62 6g 42 5h 3 43 6h 40 5i 3 68 6i 99 5j 3 41 6j 79 a TFA, CH 2Cl2, RT. 1 min. b NaH, THF, RT, 4h6b
6f
Figure 2. Intermolecular hydrogen bond network of exemplary γ- and δ-lactams in the
solid state. Molecule 6a shows a pair wise hydrogen bonding with a neighbour molecule, while 6f shows a bifurcated hydrogen bonding pattern including a neighbour molecule and a water molecule.
The γ- and δ-lactam moiety is present in many bioactive molecules and there-fore we also decided to analyze the moieties in the protein data bank (PDB).1
Structure search on γ-lactams yielded a total of 817 structures containing this moiety; δ-lactams resulted in 37 structure hits. After removing structures with ≥ 95% structure similarity, the results were reduced to 281 structures and 27 struc-tures respectively. Of those strucstruc-tures, only the N-unsubstituted lactam rings were included in the analysis. In addition, all lactam structures that were part of the protein and photosynthesis related structures were also excluded due to redundancy of the ligands. Although 37 and 11 structures, respectively for the γ- and δ-lactams, are not sufficient for a statistical analysis, it well provides the basis for a trend. Key findings include: 1) for the majority of structures, the lact-am lact-amide group undergoes a trifurcated hydrogen bond network involving the carbonyl oxygen twice and the amide NH once. 2) the γ-lactams interact with the histidine side chains most frequently through the carbonyl oxygen. Analysis
4
of the structures show that the histidines are, all but one, part of viral proteas-es. In addition, the amide-nitrogen polar interactions are also similar for these structures. 3) the δ-lactams possess more hydrogen bonding interaction possi-bilities as many amino acid residues are found in close proximity to the lactam moiety. In figure 3, ten random structures (3D23, 3EWJ, 3QZR, 3RHK, 3TNT, 3UR9, 3DPM, 1H0V, 3JUC and 3Q3Y) are aligned showing the amino acid resi-dues/molecules with which the γ-lactam moiety shows polar interactions.
Figure 3. Above: Alignment of several PDB structures showing the polar interactions for
10 γ-lactam containing ligands. The ligand γ-lactam moiety is shown as green sticks, the interacting receptor amino acids as colored lines and the hydrogen bonding as yellow dotted lines.
Conclusions
We have designed a fast and reliable synthetic route to 5- and 6-membered unsubstituted tetrazololactams using a key azido-Ugi reaction, followed by a deprotection and cyclisation step. Analysis of the scaffold in the protein data bank indicates that the lactam-NH can undergo multiple and strong H-bonds. Moreover the scaffold is underused in medicinal chemistry and thus provides multiple chances for drug design.
Experimental procedures and Spectral Data
All isonitriles were made in house by either performing the Hoffman or Ugi pro-cedure. Other reagents were purchased from Sigma Aldrich, ABCR, Acros and AK Scientific and were used without further purification. All microwave irradi-ation reactions were carried out in a Biotage Initiator™ Microwave Synthesizer. The Ugi tetrazoles were purified by flash chromatography, on a Teledyne ISCO Rf 200, using RediSep Rf Normal-phase Silica Flash Columns (Silica Gel 60 Å, 230 - 400 mesh) unless otherwise noted. Column chromatography was performed with MP Ecochrom Silica Gel 32–63, 60 Å. 1H (500 MHz) and 13C (125 MHz) NMR
spectra were recorded on a Bruker Avance DRX 500. Chemical shift values are reported as part per million (δ) relative to residual solvent peaks (CDCl3, 1H δ =
7.26, 13C δ = 77.16 or TMS 1H δ = 0.00 ppm). The coupling constants (J) are
report-ed in Hertz (Hz). Electrospray ionization mass spectra (ESI-MS) were recordreport-ed on a Waters Investigator Semi-prep 15 SFC-MS instrument.
Synthetic Procedures and characterization data for compounds
5a-j and 6a-j
Synthetic procedure 1
Aldehyde (1 mmol), tritylamine (1 mmol) were mixed in methanol (1 mL) and subjected to microwave irradiation for 15 minutes. Subsequently azidotrimeth-ylsilane (1 mmol) and isonitrile (1mmol) were added and the mixture was again subjected to microwave irradiation for 15 minutes at 100°C. The solvent was evaporated under reduced pressure and the residue was purified using flash chromatography to obtain the product.
Synthetic procedure 2
To a solution of Ugi tetrazole (0.5-1.0 mmol) in 3 mL was added TFA (150 µL, 2 mmol). After 1 minute the mixture was filtered through a silica bed washing with 50 mL Heptane:EtOAc 1:1 (v/v) to remove the trityl cation impurity. The amine was collected by washing the silica bed with 50 mL CH2Cl2:MeOH 1:1 (v/v). The mixture was concentrated under reduced pressure and redissolved in dry THF (3 mL). Sodium hydride (5 mmol) was washed with heptanes prior to addition. After 4 hours of stirring, EtOH was added to quench the reaction. The solvents were removed under reduced pressure, and the residue was purified by column chromatography using CH2Cl2:MeOH 20:1 (v/v) to afford the lactam.
4
Methyl 4-(1-(tert-butyl)-1H-tetrazol-5-yl)-4-(tritylamino)butanoate (5a)
Trt N H N NN
N O
O The product was obtained using procedure 1 starting from t-butyliso-cyanide and 3a as a white solid (73%): Rf 0.50 (EtOAc:Hept 1:1). 1H
NMR ( 500MHz, CDCl3): δ 7.40 (d, J = 7.5, 6H), 7.19 (t, J = 7.5, 6H), 7.13 (t, J = 7.2, 3H), 4.41 (t, J = 3.5 Hz, 1H), 3.63 (s, 3H), 2.80 – 2.67 (m, 1H), 2.49 – 2.34 (m, 1H), 2.28 – 2.22 (m, 1H), 1.87 – 1.80 (m, 1H), 1.42 (s, 9H) ppm. 13C NMR (125 MHz, CDCl 3) δ 173.67, 156.79, 145.62, 128.92, 127.89, 126.72, 71.71, 61.76, 51.76, 48.35, 32.29, 29.91, 28.34 ppm. Methyl 4-(1-(2,4,4-trimethylpentan-2-yl)-1H-tetrazol-5-yl)-4-(tritylamino)bu-tanoate (5b) Trt N H N NN N O
O The product was obtained using procedure starting from
t-octyliso-cyanide and 3a as a white solid (50%): Rf 0.50 (EtOAc:Hept 1:1). 1H
NMR (500 MHz, CDCl3) δ 7.39 (d, J = 7.5, 6H), 7.19 (t, J = 7.5, 6H), 7.14 (t, J = 7.2, 3H), 4.50 – 4.40 (m, 1H), 3.62 (s, 3H), 3.54 (d, J = 9.0, 1H), 2.74 – 2.60 (m, 1H), 2.35 – 2.25 (m, 1H), 2.20 – 2.13 (m, 1H), 1.90 – 1.83 (m, 1H), 1.73 (m, 2H), 1.52 (s, 3H), 1.43 (s, 3H), 0.81 (s, 9H) ppm. 13C NMR (125 MHz, CDCl3) δ 173.61, 156.98, 145.72, 128.99, 127.93, 126.76, 71.71, 66.13, 55.21, 51.69, 48.60, 32.18, 31.61, 31.11, 29.89, 28.45, 28.39 ppm. Methyl 4-(1-phenethyl-1H-tetrazol-5-yl)-4-(tritylamino)butanoate (5c) Trt N H N NN N O
O The product was obtained using procedure 1 starting from phene-thylisocyanide and 3a as a white solid (75%): Rf 0.31 (EtOAc:Hept 1:2). ). 1H NMR (500 MHz, CDCl 3) δ 7.35 (d, J = 7.5, 6H), 7.27 – 7.09 (m, 12H), 7.00 (d, J = 7.2, 2H), 4.02 – 3.84 (m, 2H), 3.81 – 3.71 (m, 1H), 3.64 (s, 3H), 3.15 – 2.96 (m, 3H), 2.56 – 2.40 (m, 1H), 2.18 – 2.02 (m, 1H), 1.93 – 1.87 (m, 1H), 1.43 – 1.37 (m, 1H) ppm. 13C NMR (125 MHz, CDCl 3) δ 173.33, 157.14, 145.15, 136.69, 128.96, 128.81, 128.62, 127.98, 127.32, 126.84, 71.59, 51.76, 48.56, 47.01, 35.43, 31.76, 29.01 ppm.
Methyl 4-(1-benzyl-1H-tetrazol-5-yl)-4-(tritylamino)butanoate (5d)
Trt N
H N NN
N O
O The product was obtained using procedure 1 starting from
benzyli-socyanide and 3a as a white solid (56%): Rf 0.50 (EtOAc:Hept 1:1). 1H
NMR (500 MHz, CDCl3) δ 7.32 (d, J = 8.1, 6H), 7.24 – 7.27 (m, 3H), 7.20 – 7.11 (m, 9H), 7.05 (d, J = 6.7, 2H), 5.21 (d, J = 15.3, 1H), 4.76 (d, J = 15.3, 1H), 4.14 – 4.10 (m, 1H), 3.58 (s, 3H), 3.00 (d, J = 9.2, 1H), 2.47 – 2.41 (m, 1H), 2.20 – 2.07 (m, 1H), 1.96 – 1.89 (m, 1H), 1.59 – 1.53 (m, 1H), 1.33 – 1.24 (m, 1H) ppm. 13C NMR (125 MHz, CDCl 3) δ 173.31, 157.08, 145.21, 133.28, 129.14, 128.92, 128.58, 128.03, 128.00, 126.83, 71.49, 51.73, 50.82, 47.06, 31.50, 28.86 ppm.
Methyl 4-(1-cyclohexyl-1H-tetrazol-5-yl)-4-(tritylamino)butanoate (5e)
O O N H N NN N Trt
The product was obtained using procedure 1 starting from cyclohex-ylisocyanide and 3a as a white solid (40%): Rf 0.50 (EtOAc:Hept 1:1).
1H NMR (500 MHz, CDCl 3) δ 7.40 (d, J = 8.1, 6H), 7.20 (t, J = 7.5, 6H), 7.15 (t, J = 6.8, 3H), 4.16 – 4.02 (m, 1H), 3.78 – 3.68 (m, 1H), 3.61 (s, 3H), 3.12 (d, J = 8.3, 1H), 2.68 – 2.49 (m, 1H), 2.34 – 2.13 (m, 2H), 1.96 – 1.76 (m, 4H), 1.76 – 1.57 (m, 4H), 1.37 – 1.18 (m, 3H) ppm. 13C NMR (125 MHz, CDCl3) δ 173.33, 156.11, 145.39, 128.74, 127.97, 126.85, 71.80, 57.45, 51.77, 47.09, 33.59, 32.02, 31.99, 28.88, 25.34, 25.29, 24.80 ppm. Methyl 5-(1-(tert-butyl)-1H-tetrazol-5-yl)-5-(tritylamino)pentanoate (5f) Trt N H N NN N O O
The product was obtained using procedure 1 starting from t-butyliso-cyanide and 3b as a white solid (78%): Rf 0.50 (EtOAc:Hept 1:1). 1H
NMR (500 MHz, CDCl3) δ 7.43 (d, J = 8.0, 6H), 7.20 (t, J = 7.5, 6H), 7.13 (t, J = 7.0, 3H), 4.34 – 4.25 (m, 1H), 3.62 (s, 3H), 3.40 (d, J = 9.3, 1H), 2.25 (t, J = 6.9, 2H), 1.94 – 1.70 (m, 2H), 1.64 – 1.48 (m, 2H), 1.41 (s, 9H) ppm. 13C NMR (125 MHz, CDCl 3) δ 173.47, 157.18, 145.78, 128.95, 127.91, 126.69, 71.75, 61.64, 51.57, 49.33, 37.13, 33.91, 30.02, 19.88 ppm.
4
Methyl 5-(1-(2,4,4-trimethylpentan-2-yl)-1H-tetrazol-5-yl)-5-(tritylamino)pen-tanoate (5g) Trt N H N NN N O OThe product was obtained using procedure 1 starting from t-octyliso-cyanide and 3b as a white solid (62%): Rf 0.50 (EtOAc:Hept 1:1). 1H
NMR (500 MHz, CDCl3) δ 7.43 (d, J = 7.5, 6H), 7.21 (t, J = 7.5, 6H), 7.14 (t, J = 7.2, 3H), 4.42 – 4.25 (m, 1H), 3.61 (s, 2H), 3.39 (d, J = 8.9, 1H), 2.29 – 2.08 (m, 2H), 1.82 – 1.65 (m, 4H), 1.64 – 1.53 (m, 1H), 1.52 – 1.41 (m, 7H), 0.81 (s, 9H) ppm. 13C NMR (125 MHz, CDCl 3) δ 173.42, 157.20, 145.87, 129.01, 127.94, 126.74, 71.72, 66.00, 55.22, 51.56, 49.55, 36.62, 33.89, 31.63, 31.14, 30.04, 28.53, 19.87 ppm. Methyl 5-(1-phenethyl-1H-tetrazol-5-yl)-5-(tritylamino)pentanoate (5h) Trt N H N NN N O O
The product was obtained using procedure 1 starting from phene-thylisocyanide and 3b as a white solid (43%): Rf 0.50 (EtOAc:Hept 1:1). 1H NMR (500 MHz, CDCl 3) δ 7.35 (d, J = 7.6, 6H), 7.29 – 7.21 (m, 3H), 7.19 (t, J = 7.4, 6H), 7.16 – 7.10 (m, 3H), 7.00 (d, J = 6.5, 2H), 4.04 – 3.92 (m, 1H), 3.85 – 3.69 (m, 2H), 3.65 (s, 3H), 3.13 – 2.99 (m, 2H), 2.93 (d, J = 8.3, 1H), 2.19 – 2.01 (m, 2H), 1.62 – 1.48 (m, 1H), 1.42 – 1.30 (m, 2H), 1.25 – 1.14 (m, 1H) ppm. 13C NMR (125 MHz, CDCl 3) δ 173.32, 157.38, 145.23, 136.82, 128.99, 128.82, 128.63, 127.99, 127.34, 126.83, 71.67, 51.61, 48.67, 48.01, 36.44, 35.46, 33.61, 20.31 ppm.
Methyl 5-(1-benzyl-1H-tetrazol-5-yl)-5-(tritylamino)pentanoate (5i)
Trt N H N NN N O O
The product was obtained using procedure 1 starting from benzyli-socyanide and 3b as a white solid (43%): Rf 0.50 (EtOAc:Hept 1:1). 1H
NMR (500 MHz, CDCl3) δ 7.36 (d, J = 7.4, 6H), 7.31 – 7.24 (m, 3H), 7.21 (t, J = 7.3, 6H), 7.19 – 7.13 (m, 3H), 7.01 (d, J = 5.5, 2H), 5.29 (d, J = 15.4, 1H), 4.68 (d, J = 15.4, 1H), 4.02 – 3.91 (m, 1H), 3.58 (s, 3H), 2.87 (d, J = 8.3, 1H), 1.96 (t, J = 6.9, 2H), 1.54 – 1.43 (m, 1H), 1.32 – 1.16 (m, 3H) ppm. 13C NMR (125 MHz, CDCl 3) δ 173.12, 157.33, 145.25, 133.59, 129.11, 128.85, 128.59, 128.01, 127.74, 126.85, 71.62, 51.49, 50.87, 48.02, 36.09, 33.58, 20.23 ppm.
Methyl 5-(1-cyclohexyl-1H-tetrazol-5-yl)-5-(tritylamino)pentanoate (5j) Trt N H N NN N O O
The product was obtained using procedure 1 starting from cyclohex-ylisocyanide and 3b as a white solid (43%): Rf 0.50 (EtOAc:Hept 1:1).
1H NMR (500 MHz, CDCl 3) δ 7.41 (d, J = 7.5, 6H), 7.21 (t, J = 7.5, 6H), 7.15 (t, J = 7.2, 3H), 4.07 – 3.95 (m, 1H), 3.89 – 3.75 (m, 1H), 3.60 (s, 3H), 2.90 (d, J = 7.3, 1H), 2.22 – 2.06 (m, 2H), 1.96 – 1.62 (m, 8H), 1.58 – 1.45 (m, 1H), 1.43 – 1.19 (m, 5H)ppm. 13C NMR (125 MHz, CDCl 3) δ 173.28, 156.28, 145.47, 128.75, 128.02, 126.87, 72.01, 57.61, 51.57, 48.12, 36.43, 33.58, 33.56, 32.27, 25.39, 24.90, 20.34 ppm. 5-(1-(tert-butyl)-1H-tetrazol-5-yl)pyrrolidin-2-one (6a) N NN N N H
O The product was obtained using procedure 2 starting from 5a as a
white solid (55%): 1H NMR (500 MHz, CDCl 3) δ 7.69 (s, 1H), 5.40 – 5.13 (m, 1H), 2.75 – 2.57 (m, 2H), 2.43 – 2.31 (m, 2H), 1.80 – 1.75 (m, 9H) ppm. 13C NMR (125 MHz, CDCl 3) δ 178.69, 155.80, 61.61, 49.12, 30.34, 29.32, 28.12 ppm. MS (ESI) (m/z) 210.1 [M+H]+. 5-(1-(2,4,4-trimethylpentan-2-yl)-1H-tetrazol-5-yl)pyrrolidin-2-one (6b) N NN N N H
O The product was obtained using procedure 2 starting from 5b as a
white solid (89%): 1H NMR (500 MHz, CDCl 3) δ 7.75 (s, 1H), 5.35 – 5.20 (m, 1H), 2.78 – 2.56 (m, 2H), 2.46 – 2.31 (m, 2H), 1.97 (q, J = 15.3, 2H), 1.86 (d, J = 3.4, 6H), 0.79 (s, 9H) ppm. 13C NMR (125 MHz, CDCl 3) δ 178.67, 156.33, 64.96, 54.34, 49.28, 31.84, 30.78, 30.53, 29.38, 28.20 ppm. MS (ESI) (m/z) 266.1 [M+H]+. 5-(1-phenethyl-1H-tetrazol-5-yl)pyrrolidin-2-one (6c) N NN N N H
O The product was obtained using procedure 2 starting from 5c as a
white solid (32%): 1H NMR (500 MHz, CDCl 3) δ 7.28 (d, J = 4.2, 3H), 7.06 – 6.91 (m, 2H), 6.82 (s, 1H), 4.71 – 4.46 (m, 2H), 4.44 – 4.25 (m, 1H), 3.37 – 3.11 (m, 2H), 2.54 – 2.37 (m, 1H), 2.33 – 2.08 (m, 2H), 2.08 – 1.87 (m, 1H) ppm. 13C NMR (125 MHz, CDCl 3) δ 178.26, 155.80, 136.55, 129.32, 128.95, 127.76, 49.33, 47.19, 36.35, 29.26, 26.50 ppm. MS (ESI) (m/z) 258.1 [M+H]+.
4
5-(1-benzyl-1H-tetrazol-5-yl)pyrrolidin-2-one (6d) N NN N N HO The product was obtained using procedure 2 starting from 5d as a
white solid (72%): 1H NMR (500 MHz, CDCl 3) δ 7.83 (s, 1H), 7.37 (d, J = 6.3, 3H), 7.28 – 7.17 (m, 2H), 5.67 (dd, J = 47.8, 15.6, 2H), 5.02 – 4.88 (m, 1H), 2.44 – 2.33 (m, 1H), 2.33 – 2.18 (m, 2H), 2.05 – 1.90 (m, 1H) ppm. 13C NMR (126 MHz, CDCl 3) δ 178.70, 155.53, 133.33, 129.40, 129.17, 127.73, 51.31, 47.89, 29.24, 26.30 ppm. MS (ESI) (m/z) 244.1 [M+H]+. 5-(1-cyclohexyl-1H-tetrazol-5-yl)pyrrolidin-2-one (6e) N NN N N H
O The product was obtained using procedure 2 starting from 5e as a white solid (95%): 1H NMR (500 MHz, CDCl 3) δ 7.84 (d, J = 26.2, 1H), 5.18 – 4.93 (m, 1H), 4.37 – 4.14 (m, 1H), 2.74 – 2.55 (m, 2H), 2.53 – 2.33 (m, 2H), 2.13 – 1.91 (m, 6H), 1.78 (d, J = 12.7, 1H), 1.53 – 1.40 (m, 3H), 1.39 – 1.26 (m, 1H) ppm. 13C NMR (126 MHz, CDCl 3) δ 178.73, 154.46, 58.17, 47.72, 33.45, 32.73, 29.48, 26.81, 25.19, 25.11, 24.75 ppm. MS (ESI) (m/z) 236.0 [M+H]+. 6-(1-(tert-butyl)-1H-tetrazol-5-yl)piperidin-2-one (6f) N NN N N H O
The product was obtained using procedure 2 starting from 5f as a white solid (76%): 1H NMR (500 MHz, CDCl 3) δ 7.48 (s, 1H), 5.22 – 5.09 (m, 1H), 2.46 – 2.37 (m, 1H), 2.36 – 2.27 (m, 1H), 2.20 – 2.08 (m, 2H), 2.07 – 1.98 (m, 1H), 1.77 (s, 10H) ppm. 13C NMR (126 MHz, CDCl 3) δ 172.08, 155.39, 61.63, 47.93, 30.90, 30.21, 28.03, 18.59 ppm. MS (ESI) (m/z) 224.1 [M+H]+. 6-(1-(2,4,4-trimethylpentan-2-yl)-1H-tetrazol-5-yl)piperidin-2-one (6g) N NN N N H O
The product was obtained using procedure 2 starting from 5g as a white solid (42%): 1H NMR (500 MHz, CDCl 3) δ 6.58 (d, J = 25.2, 1H), 5.15 (t, J = 6.1, 1H), 2.59 – 2.39 (m, 2H), 2.28 – 2.10 (m, 3H), 1.94 (q, J = 15.3, 2H), 1.86 (d, J = 12.9, 7H), 1.83 – 1.71 (m, 1H), 0.79 (s, 9H) ppm. 13C NMR (126 MHz, CDCl 3) δ 171.79, 155.62, 65.21, 54.45, 48.58, 31.86, 31.07, 30.83, 30.71, 30.65, 28.35, 19.01 ppm. MS (ESI) (m/z) 280.2 [M+H]+.
6-(1-phenethyl-1H-tetrazol-5-yl)piperidin-2-one (6h) N NN N N H O
The product was obtained using procedure 2 starting from 5h as a white solid (40%): 1H NMR (500 MHz, CDCl 3) δ 7.27 (d, J = 6.7, 3H), 7.06 – 6.91 (m, 3H), 4.65 – 4.46 (m, 2H), 4.28 (t, J = 5.8, 1H), 3.31 – 3.16 (m, 2H), 2.28 – 2.19 (m, 2H), 1.94 – 1.81 (m, 1H), 1.67 – 1.44 (m, 3H) ppm. 13C NMR (126 MHz, CDCl 3) δ 172.12, 155.36, 136.60, 129.23, 128.94, 127.66, 49.42, 46.67, 36.29, 31.01, 26.91, 18.83 ppm. MS (ESI) (m/z) 272.2 [M+H]+. 6-(1-benzyl-1H-tetrazol-5-yl)piperidin-2-one (6i) N NN N N H O
The product was obtained using procedure 2 starting from 5i as a white solid (99%): 1H NMR (500 MHz, CDCl 3) δ 7.44 – 7.33 (m, 3H), 7.24 (s, 1H), 7.23 – 7.17 (m, 2H), 5.66 (s, 2H), 4.91 – 4.81 (m, 1H), 2.37 – 2.21 (m, 2H), 1.98 – 1.82 (m, 2H), 1.77 – 1.59 (m, 2H). 13C NMR (125 MHz, CDCl3) δ 172.50, 155.12, 133.55, 129.47, 129.24, 127.67, 51.55, 47.37, 31.09, 26.95, 18.80 ppm. MS (ESI) (m/z) 258.1 [M+H]+. 6-(1-cyclohexyl-1H-tetrazol-5-yl)piperidin-2-one (6j) N NN N N H O
The product was obtained using procedure 2 starting from 5j as a white solid (79%): 1H NMR (500 MHz, CDCl 3) δ 7.50 (s, 1H), 4.95 (t, J = 5.6, 1H), 4.38 – 4.19 (m, 1H), 2.48 – 2.32 (m, 2H), 2.23 – 1.91 (m, 10H), 1.91 – 1.82 (m, 1H), 1.82 – 1.70 (m, 1H), 1.51 – 1.39 (m, 2H), 1.39 – 1.31 (m, 1H) ppm. 13C NMR (126 MHz, CDCl 3) δ 172.40, 154.11, 58.29, 46.90, 33.55, 32.87, 31.05, 27.48, 25.29, 25.26, 24.81, 18.86 ppm. MS (ESI) (m/z) 250.2 [M+H]+.
4
Exemplary 1H NMR and 13C NMR for the UT-4CR and intramolecular
cycliza-tion product 5b and 6b.
Compound 5b 1H NMR 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 f1 (ppm) -500 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 9.46 3.10 3.20 2.34 1.19 1.07 1.08 1.08 0.95 2.92 1.05 3.00 6.22 6.11 0.81 1.43 1.52 1.69 1.72 1.74 1.77 1.85 1.86 1.87 1.89 2.15 2.16 2.17 2.30 2.31 2.31 2.63 2.65 2.67 2.68 2.70 3.53 3.55 3.62 3.63 3.65 4.43 4.44 4.45 4.46 4.47 7.12 7.14 7.15 7.18 7.19 7.21 7.38 7.40 NH N N N N O O CH3 C H3 C H3 CH3 C H3 C H3 Compound 5b 13C NMR 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 f1 (ppm) -1000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 17000 18000 28.39 28.45 29.89 31.11 31.61 32.18 48.60 51.69 55.21 66.13 71.71 126.76 127.93 128.99 145.72 156.98 173.61 NH N N N N O O CH3 C H3 C H3 CH3 C H3 C H3
Compound 6b 1H NMR 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 f1 (ppm) -500 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 9.75 6.24 2.16 2.09 2.08 1.04 1.00 0.79 1.86 1.87 1.93 1.96 1.98 2.01 2.34 2.35 2.36 2.37 2.37 2.38 2.40 2.41 2.41 2.42 2.43 2.44 2.45 2.59 2.60 2.61 2.62 2.63 2.63 2.69 2.70 2.71 2.72 2.74 5.27 5.28 5.29 5.29 7.75 N N N N C H3 C H3 CH3 C H3 C H3 NH O Compound 6b 13C NMR 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 f1 (ppm) -500 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 28.20 29.38 30.53 30.78 31.84 49.28 54.34 64.96 156.33 178.67 N N N N C H3 C H3 CH3 C H3 C H3 NH O
4
Single Crystal X-Ray Structure Determination
Crystallographic data were collected on an X-ray single crystal diffractometer equipped with a CCD detector (Bruker APEX II, κ-CCD), a fine focus sealed tube (Bruker AXS, D8) with MoKα radiation (λ= 0.71073 Å), and a graphite mono-chromator by using the SMART software package. The measurements were per-formed on single crystals coated with perfluorinated ether. The crystals were fixed on the top of a cactus prickle (Opuntia ficus-india) with perfluorinated ether and transferred to the diffractometer. The crystals were frozen under a stream of cold nitrogen. A matrix scan was used to determine the initial lattice parameters. Reflections were merged and corrected for Lorenz and polarization effects, scan speed, and background using SAINT. Absorption corrections, including odd and even ordered spherical harmonics were performed using SADABS. Space group assignments were based upon systematic absences, E statistics, and successful refinement of the structures. Structures were solved by direct methods with the aid of successive difference Fourier maps, and were refined against all data using WinGX23 based on SIR-92. If not mentioned otherwise, non-hydrogen atoms were
refined with anisotropic displacement parameters. Hydrogen atoms could be lo-cated in the difference Fourier maps and were allowed to refine freely. Full-ma-trix least-squares refinements were carried out by minimizing Σw(Fo2-F
c2)2 with
SHELXL-97 weighting scheme. Neutral atom scattering factors for all atoms and anomalous dispersion corrections for the non-hydrogen atoms were taken from
International Tables for Crystallography. Images of the crystal structures were
gen-erated by PLATON. CCDC 961190 (6b), CCDC 961191 (6e), CCDC 961188 (6f), and CCDC 961189 (6j) contains the supplementary crystallographic data for this compound. This data can be obtained free of charge from The Cambridge Crys-tallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif or via https:// www.ccdc.cam.ac.uk/services/structure_deposit/
.
6b 6e
6f 6j
Figure 4. Ortep drawing drawings of compounds 6b, 6e, 6f and 6j with 50% ellipsoids. Table 2. Data collection and refinement parameters of obtained crystals
Data Collection
6b 6e 6f 6j
Molecular
For-mula C13H23N5O C11H17N5O C20H36N10O3 C12H19N5O
Molecular
Weight 265.36 g/mol 235.30 a.m.u. 464.59 a.m.u 249.32 a.m.u. Crystal Color/
size 0.20×0.25×0.43 mm 0.28×0.41×0.51 mm 0.10×0.30×0.36 mm 0.25×0.25×0.28 mm Space Group Monoclinic
4
Cell Constants a= 907.24 pm b= 1147.13pm β= 100.6508° c 1399.04 pm V= 1430.93∙106 pm3 Z = 4 Dcalc = 1.232 g∙cm-3 a = 654.62 pm α=65.9412° b = 925.70 pm β=81.5752° c = 1055.29 pm γ=89.9391° V = 576.41·106 pm3 Z = 2 Dcalc= 1.356 gcm-3 a =2660.36 pm b =630.28 pm β =109.7809° c =1546.66 pm V = 2440.37∙106 pm3 Z = 4 Dcalc = 1.265 gcm-3 a =991.62(3) pm b =1193.89(3) pm c =2152.52(7) pm V = 2548.34∙106 pm3 Z = 8 Dcalc = 1.300 gcm-3 F000: 576 252 1000 1072 Temperature (-173±1) °C (-173±1) °C (-150±1) °C (-150±1) °C Measurement Range 2.28° < θ < 25.46° h: -10/10, k: -13/13, l: -16/16 2.14 < θ < 25.38° h: -7/7, k: -11/11 l: -12/12 1.63° < θ < 25.55° h: -32/32 k: -7/7 l: -18/18 2.79° < θ < 25.40° h: -11/11 k: -14/14 l: -25/25 Refinement Refl. collected 48744 19536 35663 34576 Independentreflections 2636 Rint: 0,020 2111 Rint: 0,016 2264 Rint: 0,026 2338 Rint: 0,026 Extinction Cor-rection ε 0.0054refined to ε= No No No Goodness of fit 1.033 1.050 1.049 1.082 Resid. Electron Density +0.28 e/Å 3 -0.17 e/Å3 +0.26 e/Å 3 -0.23 e/Å3 +0.19 e/Å 3 -0.18 e/Å3 +0.24 e/Å 3 -0.24 e/Å3 R indices (all refelctions) R1=0.0320 wR2=0.0764 R1=0.0303 wR2=0.0774 R1=0.0348 wR2=0.0911 R1=0.0407 wR2=0.0994
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