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Synthetic urea's are known constituent of several natural products and pharmaceutical preparation. Urea derivatives are widely used in medicinal chemistry because this moiety is involved in bio chemical process in drug development. This structural component is very good building blocks in solid phase synthesis and act as precursor for synthesis of pharmacological active molecules. In present work a glycosyl urea derivative was synthesized and screened for its biological activity.

Glycosyl ureas are known to have antibacterial and antidiabetic activity. These compounds are pharmacologically important because of their biological activity. Therefore present study involves synthesis of N1, N3 substituted Glycosyl ureas for investigation of its biological activity.

After covid-19 pandemic new cases  of tuberculosis have been increased globally. Multiple drug resistant (MDR) tuberculosis and its combination with HIV and mycotic infections particularly due to Candida sp. like Candida albicans, and Cryptococcus neoformans in patients with weak immune system have worsened the problem. [4-7]. Among various targets mycobacterium cell wall was chosen as unique target for development of new class of antituberculosis agents. Since the mycobacterium cell wall is composed of various glycosyl polymers like mAGP complex (mycolylated arabinogalactan peptidoglycan) complex, therefore the enzymes involved in biosynthesis of cell wall polymers are very selective target  to derive new chemotherapeutic agents. In general the  derivatives of  glycosyl urea  particularly with respect to their  roles as artificial receptors are important in this respect. [8]  Many glycohybrid molecules having condensed structure of urea are known for inhibitory activity against enzymes like glycosidase, glycogen phosphorylases etc. [9, 10] Glycosidase and glycosyl transferases are two important enzymes  involved in biosynthesis of mycobacterium cell wall. Some glycosyl ureides have shown  antileishmanial  and antimycobacterial activity. [11, 12]  Limitations of the existing drugs, prolong treatment as well as emergence of resistance  has led to the scientific community to discover new chemical entities (NCE) as antitubercular agents with novel mode of action. 

-D-xylofuran-1,5-dialdose. [15, 16] This glycosyl aldehyde on Wittig reaction with carbethoxy methylene triphenyl phosphorane or triethyl phosphonoacetate resulted into respective glycosyl olefinic ester as a mixture of E and Z isomer . The glycosyl olefinic ester on conjugate addition reaction with 1, 5 dimethylhexyl amine led to the formation of corresponding glycosyl amino ester as a mixture of diasteroisomers. [17] The major isomer was separated by column chromatography and this was used as starting material for the formation of glycosyl urea compound. Hence the synthetic strategy involves the reaction of glycosyl amino ester with benzyl isocyanate in anhydrous dichloromethane (DCM) resulted in the formation of N1, N3-substituted glycosyl urea compound as shown below in (Scheme). The compound was characterized with help of elemental analysis, IR, 1H NMR, 13C NMR and MS FAB spectroscopy techniques. Further the synthesized compound was investigated for its biological activity against M. tuberculosis. Such compounds attracts the attention of scientific community to develop pharmacologically active compounds such as antibacterial, antifungal, and anti-inflammatory compounds. [18]a-D-glucofuranose which on oxidation with sodium metaperiodate yielded 3-O-methyl-1,2-O-isopropylidene- a-D-glucofuranose in good yield as shown in scheme. [13, 14] The later on methylation with methyl iodide and selective deprotection gave 3-O-methyl-1,2- O-isopropylidene- aThe glycosyl ureas have been synthesized as possible inhibitors of mycobacterium cell wall polymers. Sugar based complex molecules like glycosidase, glycosyl transferase and enzymes responsible for mycolic acid biosynthesis have been taken into consideration. Glycohybrid compounds are a new class of molecules of great medicinal value and are very important in design and development of novel class of antimycobacterial agents. The synthesized compound was screened for its biological activity against Mycobacterium tuberculosis. The synthesis of glycosyl urea compound starts with easily available D-glucose which on protection with acetone in presence of sulphuric acid followed by methylation gives 1,2,5,6,-di-O-isopropyledene-

Experimental:

Ethyl-[(1R, 2R, 3S, 4S, 5S)-5-{N³-benzyl-N¹-(1, 5-dimethylhexyl)-5, 6-dideoxy-1, 2-O- isopropylidene-3-O-methyl-1-ureidyl}-1, 4-heptofuranos-5-yl]-uronoate :

This glycosyl  urea compound was obtained by the reaction of glycosyl amino ester  (1.5 g, 3.74 mmol) on benzyl isocyanate (0.46 mL, 3.74 mmol) in solvent dry dichloromethane  for 6-8 hours . After completion of reaction the crude product obtained was dried and weighed. The desired compound was purified by column chromatography over SiO₂ using the solvent gradient of hexane:ethyl acetate (4:1) as eluent which afforded the glycosyl urea compound as colorless foam. Yield (1.38g, 91%), [ɑ]_D²⁵ -25 (c 0.15, CH₃OH); MS FAB m/z = 535 [M+H]⁺; IR (neat): v_max cm^-1 3371 (NH), 2930 (CH), 1730 (C=O), 1639 (NC=O); ¹H NMR (CDCl₃, 200 MHz) δ =7.29 (m, 5H, Ar-H), 5.83 (d, J = 3.7 Hz, 1H, H-1), 4.51 (d, J = 3.7 Hz, 1H, H-2), 4.39 (d, J = 5.38 Hz, NCH₂Ph), 4.10 (m, 3H, H-4 and OCH₂CH₃), 3.19 (d, J = 3.0 Hz, 1H, H-3), 3.17 (s, 3H, OCH₃), 3.10 (m, 1H, H-5), 2.80 (m, 1H, H-6_A), 2.67 (m, 1H H-6_B), 1.55 (d, 3H, NCH(CH₃)), 1.47 and 1.34 [each s, each 3H, C(CH₃)₂], 1.30 (m, 10H, OCH₂CH₃ and CH₂ s and CH(CH₃)₂). 0.86 (d, J = 6.5 Hz, 6H, CH(CH₃)₂); ¹³C NMR (CDCl₃, 50 MHz): δ=172.4 (OC=O); 158.5 (NC=O); 140.4 (Ar-C); 128.7, 128.0, 127.9, 127.2, 127.1 (Ar-CH); 112.2 [>C(CH₃)₂]: 105.1 (C-1); 84.5 (C-2): 81.2 (C-4): 81.0 (C-3); 61.1 (OCH₂CH₃): 57.7 (OCH₃): 57.5 (C-5), 45.1 (NCH₂Ph), 35.9 (C-6); 36.6, 30.7 (-CH₂’s), 28.3 (NCH); 27.1, 26.5 [>C(CH₃)₂]: 25.7 (- CH₂CH(CH₃)₂); 23.0 (CH(CH₃)₂); 20.2, 19.4 (CH(CH₃)₂); 14.5 (OCH₂CH₃); Elemental Analysis for C₂₉H₄₆N₂O₇: C, 65.16; H, 8.61; N, 5.24; Found: C, 65.44; H, 9.01; N, 5.63%.

Bioevaluation:                                                               

The synthesized glycosyl urea compound [ Ethyl-[(1R, 2R, 3S, 4S, 5S)-5-{N³-benzyl-N¹-(1, 5-dimethylhexyl)-5, 6-dideoxy-1, 2-O- isopropylidene-3-O-methyl-1-ureidyl}-1, 4-heptofuranos-5-yl]-uronoate] has been taken as test compound and our earlier reported glycosyl urea compound is taken as reference sample. Both were evaluated for  antitubercular activities against M. tuberculosis H37Ra and H37Rv. The results are depicted as shown below in Table. The bioevaluation methods used for screening of the above compound against M. tuberculosis are Micro Alamar Blue Assay and Agar Micro dilution techniques.[19, 20]

Table: Inhibitory activity of N¹, N³-substituted Glycosyl Ureas

1^# test compound, 2^*= reference sample, MIC = Minimum Inhibitory Concentration 

The glcosyl urea compound with 1,5 dimethyl hexyl substituent at N¹ position was synthesized to see the structure activity relationship. The table  shows comparative study of antitubercular activity of glycosyl ureas. The earlier  prepared compound with twelve carbon chain showed activity against the virulent strain H37Rv at MIC  12.5 µg /ml and showed inhibition against the strain H37Ra of  M. tuberculosis at MIC >25 µg /ml while the glycosyl urea compound having 1,5 dimethyl hexyl chain at N-1 position and benzyl substituent at N³ position  showed inhibition at MIC  >25 µg /ml against both the strains H37Ra and H37Rv of M. tuberculosis. Although, this test compound has shown activity to some extent and this led us to further optimize the compound for better biological activity. 

In conclusion it can be stated that glycosyl ureas might be useful compounds to search lead molecules against M. tuberculosis. As per earlier reported work such compounds have shown -glucosidase inhibitory activity and their transformation in C- nucleosides shows their potential in the field of pharmaceuticals and medicinal chemistry. Author thanks to medicinal and process chemistry division of CDRI for all experimental work and biological activity.

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