Arun K. Shaw

A Chiron Approach to Aminocytitols by Petasis-Borono-Mannich Reaction: Formal Synthesis of (+)-Conduramine E and (−)-Conduramine E

A chiron approach to a stereoselective route for the synthesis of aminocytitols from carbohydrates is described. The formal synthesis of (+)-conduramine E and (-)-conduramine E was achieved by utilizing this strategy. The key features of the synthetic strategy include one-pot three-component Petasis-Borono-Mannich reaction to introduce the syn-β-amino alcohol functionality of conduramine E and ring-closing metathesis to construct its carbocyclic core. The present synthetic approach paves the way for stereoselective synthesis of several conduramines starting from carbohydrates.

First total synthesis of (+)-varitriol.

A highly stereoselective total synthesis of (+)-varitriol, an antitumor natural product, has been achieved for the first time from commercially available methyl alpha,D-mannopyranoside and 2,6-dihydroxybenzoic acid.

Baylis–Hillman Reaction: Convenient Ascending Syntheses and Biological Evaluation of Acyclic Deoxy Monosaccharides as Potential Antimycobacterial Agents

A series of acyclic deoxy carbohydrate derivatives from easily available carbohydrate enals 1, 2, 3 or 5 were prepared involving the Baylis-Hillman reaction. These newly formed carbohydrate based Baylis-Hillman adducts and their amino derivatives were evaluated for their antimycobacterial activity against Mycobacterium tuberculosis H(37)R(v). Among the compounds evaluated for their antimycobacterial activity, compound (10) showed the desired activity in the range of 3.125 microg/mL.

Facile Synthesis of Enantiomerically Pure 2‐ and 2,3‐Disubstituted Furans Catalysed by Mixed Lewis Acids: An Easy Route to 3‐Iodofurans and 3‐(Hydroxymethyl)furans

Simple and efficient syntheses, catalysed by a mixed Lewis acid system (ZrCl(4)/ZnI(2)), of enantiomerically pure 2- and 2,3-disubstituted furan derivatives--including important synthons such as 3-iodofuran and 3-(hydroxymethyl)furan derivatives--from commercially available 3,4,6-tri-O-acetyl-D-glucal are described. The transformation is achieved through a synergistic interaction between ZrCl(4) and ZnI(2) in catalytic amounts.

Diastereoselective one-pot Wittig olefination–Michael addition and olefin cross metathesis strategy for total synthesis of cytotoxic natural product (+)-varitriol and its higher analogues

A stereoselective route for the total synthesis of anticancer marine natural product (+)-varitriol (1) is detailed herein. The impressive biological activity and interesting structural features of natural (+)-varitriol fuelled us to undertake the synthesis of some higher analogues (1a-j) of this molecule. The key features of the synthetic strategy include one-pot Wittig olefination followed by a highly diastereoselective oxa-Michael addition to assemble stereochemically pure tetrasubstituted THF moiety of the natural varitriol and olefin cross metathesis to couple the aromatic part with tetrasubstituted THF moiety. The total synthesis of title natural product is efficient with 21.8% overall yield for 9 linear steps from D-ribose and thus facilitates the more scaled-up practical route for the synthesis of 1 and its analogues as well. The synthetic (+)-varitriol (1) and its analogues were screened for their cytotoxicity. The present synthetic approach paves the way for preparation of numerous analogues of the title natural product for drug development.

Chain extension of acyclic sugar derivatives via the Baylis–Hillman reaction

Abstract Baylis–Hillman reactions on α,β-unsaturated sugar aldehydes with methyl vinyl ketone in the presence of Me 2 S–TiCl 4 have been carried out to provide a convenient strategy for extending the sugar chain in its open form. The resulting Baylis–Hillman adducts have been further used as synthons for synthesising chain extended amino polyols.

A chiron approach to the total synthesis of cytotoxic (+)-muricatacin and (+)-5-epi-muricatacin from d-ribose ☆

A chiron approach strategy toward the total synthesis of (+)-muricatacin and (+)-5-epi-muricatacin starting from commercially available and inexpensive d-ribose through the key intermediate (S)-5-((R)-1-hydroxyallyl)furan-2(5H)-one has been disclosed.

Higher acyclic nitrogen containing deoxy sugar derivatives: a new lead in the generation of antimycobacterial chemotherapeutics.

Syntheses of higher acyclic nitrogen containing deoxy sugar derivatives via nitroaldol reaction of different nitroalkanes with 2,3-dideoxy-alpha,beta-unsaturated aldehydo sugars obtained from glycals namely acetylated glucal and galactal and their in vitro antimycobacterial activity are presented.

Overexpression of Rv3097c in Mycobacterium bovis BCG abolished the efficacy of BCG vaccine to protect against Mycobacterium tuberculosis infection in mice.

Rv3097c of Mycobacterium tuberculosis encoding lipase (LipY) was overexpressed in Mycobacterium bovis BCG. Efficacy of recombinant BCG to protect against infection of M. tuberculosis was evaluated in mice. Whereas the parent BCG vaccine protected the mice against infection, recombinant BCG overexpressing LipY offered no protection as judged by viable counts of tubercule bacilli in lungs, weight of infected mice, pathology of lungs and survival of challenged mice. Downregulation of overexpression of LipY by antisense approach considerably restored protection of infected mice as observed with parent BCG vaccine. Overexpression of lipase in BCG caused extensive hydrolysis of triacylglycerol (TG) as identified by TLC, HPLC and NMR spectroscopy. A good correlation could be inferred between hydrolysis of TG and decrease in Th1 secreted IFNγ and IL-2, proinflammatory cytokines and survival of infected mice. Mice immunized with purified LipY antigen were protected and both proinflammatory and Th1 specific cytokines were augmented. TG was found to be a poor vaccine providing no protection, which appears to be due to attenuation of Th1 and proinflammatory immune responses. In conclusion this is the first experimental report to show that immunogenicity of BCG vaccine was impaired by LipY-induced hydrolysis of specific lipids leading to suppression of host immune responses.

Glycal approach to the synthesis of macrolide (−)-A26771B

A convergent total synthesis of a 16-membered macrolactone natural product (−)-A26771B 1 starting from 3,4,6-tri-O-acetyl-D-glucal 7 is reported. The Ferrier rearrangement of acetylated glucal 7, cross metathesis between chiral fragments 3 and 4, Yamaguchi macrolactonization and selective oxidation of the allylic alcohol are the key features of the synthesis.