Bromination of N-(o-Aminophenyl)-cis-4-cyclohexene-1,2-dicarboximide and cis-2-(2-Benzimidazolyl)-4-cyclohexene-1-carboxylic Acid

Exhaustive oxidative bromination of N-(o-aminophenyl)-cis-4-cyclohexene-1'2-dicarboximide and2-(2-benzimidazolyl)-cis-4-cyclohexene-1-carboxylic acid results in bromine addition at the double bond.Under more severe conditions, the addition of bromine at the double bond is accompanied by bromination ofthe aromatic ring. The latter process does not occur in the exhaustive bromination of cis-2-(2-benzimidazolyl)-4-cyclohexene-1-carboxylic acid.     

Stereoselective total synthesis of polyketide lactone, (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone

The total synthesis of lactone 1 has been described. The convergent asymmetric synthesis relies on the use of an Evans’ syn-aldol, chain extension with lithio tert-butyl acetate, and the stereoselective reduction of a ketone as the key reactions.     

Practical enantioselective synthesis of (3S, 4R)-3-hydroxypiperidine-4-carboxylic acid

A practical enantioselective synthesis of (3S, 4R)-3-hydroxypiperidine-4-carboxylic acid was accomplished via an unconventional Evans anti-aldol reaction followed by a one-pot azide reduction/reductive cyclization.     

2, 4-Dimethyl -5 -nitrofuran -3 -carboxylic acid and its derivatives

It is found that 2, 4-dimethyl-5-nitrofuran-3-carboxylic acid and its methyl ester can give comparatively stable anionic groups, which are prepared electrochemically and investigated by EPR. Their lives (80–100 sec) are 4- 5 times greater than the lives of other anionic groups of the 5-nitrofuran series previously studied. Starting from 2, 4-dimethyl-5-nitrofuran-3-carboxylic acid and 2, 4-dimethylfuran-3-carboxylic acid, two new semisynthetic penicillins are prepared, with activities basically extending to Gram-positive microorganisms, including forms of staphylcocci resistant to benzylpenicillin. Introduction of the nitro group into the furan ring increases the stability of penicillin to acid 79-fold. Low toxicity penicillins are synthesized (LD₅₀ 1000–1500 mg/kg).     

Stereoselective synthesis of (2R,3S,4S,5R)-trans-3,4-dihydroxy-5-(4-fluorophenoxymethyl)-2-(1-N-hydroxyureidyl-3-butyn-4-yl)tetrahydrofuran and (2R,3S,4S,5R)-trans-5-ethynyl-2-(4-fluorophenoxymethyl)-3,4-O-isopropylidene tetrahydrofuran from mannose diacetonide

Stereoselective synthesis of pharmaceutically interesting chiral tetrahydrofurans starting from mannose diacetonide is reported. A 1,4-diol system derived from mannose diacetonide, through a Mitsunobu reaction was stereospecifically cyclized to give chiral tetrahydrofurans. Both the C-1 and C-4 centers of d-mannose are successfully exploited to install the requisite side chains.     

Stereoselective synthesis of the nonproteinogenic amino acid (2S,3R)-3-amino-2-hydroxydecanoic acid from (4S,5S)-4-formyl-5-vinyl-2-oxazolidinone

(4S,5S)-4-Formyl-5-vinyl-2-oxazolidinone (4b), which is readily obtained via a zinc-silver-mediated reductive elimination of alpha-d-lyxofuranosyl phenyl sulfone (3b), is successfully converted to the naturally occurring, nonproteinogenic amino acid (2S,3R)-3-amino-2-hydroxydecanoic acid (2). Also in this study, a facile "oxazolidinone rearrangement" reaction is uncovered during the attempted formation of the (methylthio)thiocarbonate derivative of the oxazolidinone alcohol 7.     

Synthesis of 1-[6-Fluoro-(2S)-3H,4H-dihydro-2H-2-chromenyl]-(1R)-1,2- ethanediol and 1-[6-Fluoro-(2R)-3H,4H-dihydro-2H-2-chromenyl]- (1R)-1,2-ethanediol

Benzopyran compounds possess diverse pharmacological properties such as β-blockade, anticonvulsant and antimicrobial.[1,2] Our interest has been focused on the synthesis of 1-[6-Fluoro-2S]-3H,4H-dihydro-2H-2-chromenyl]-(1R)-1,2-ethanediol (6) and 1-[6-fluoro-(2R)-3H,4H-dihydro-2H-2-chromenyl]-(1R)-1,2-ethanediol (7) which are particularly convenient precursor to (S,R,R,R)-NE (8). 8 containing four asymmetrical carbon atoms was reported to be the most active isomer.[3] Chandrasekhar[4] has reported on the synthesis of 8. The key step to synthesize this compound is to obtain the chiral chromanone 6 and 7. 6 was accomplished in 8 steps by the Clasien rearrangement and a one-pot Sharpless asymmetric epoxidation, but the compound 7 was accomplished in 10 steps. Johannes[5] used Zr-catalytic kinetic resolution of allylic ethers and Mo-catalyzed chromene formation to synthesize 8 in 14 steps. However both of the methods request many synthetic steps and expensive reagents.     

A new route to (2S,4R)- and (2R,4S)-4-hydroxypipecolic acid

Both enantiomers of cis-4-hydroxypipecolic acid have been prepared by asymmetric synthesis using (S)- or (R)-glycidol as the chiral source, and involving a stereoselective hydrogenation of a six-membered cyclic imine. The latter is obtained by reduction and cyclization of a cyano β-hydroxy ketone.     

Synthesis of (4S, 5R)-1,4,5-Hexanetriol and D-Amicetose

Starting from L-glutamic acid the synthesis of (4S, 5R),-1,4,5-hexanetriol and D-amicetose is described.