The Part A of the present Ph. D. dissertation describes the isolation and structure elucidation of four new cyeloartane triterpene glucosides, depressoside A-D, from Corchorus depressus L. The glycoside depressoside C contains a novel carbon skeleton. The structures of the new compounds have been elucidated as 9,19-cyclolanosta- 22 (R) ,25-epoxy-3 β,16 β, 24(S)-triol 3-O-B-D-glucopyranoside, 9,19-cyclolanosta-22(R),25-epoxy-24(S)-acetoxy-3 β,16 β-diol3-O- β-D-glucopyranoside, 9,19-cyclolanosta-22(R)-epoxy-3 β,26-dihydroxy-24E-ene 3,26-di0O- β-D-glucopyranoside and 9,19-cyclolanosta-16 β,22(R)-,25-epoxy-3 β,16, β ,24(S)-trihydroxy 3,24-di-O- β-D-glucopyranoside, respectively, with the help of extensive spectroscopic studies and chemical analysis. The aglycone of depressoside A and D, a new cycloartane triterpene named as depressogenin, has also been fully characterized as 9,19-cyclolanosta-22(R),25-epoxy-3 β, 16 β,24(S)-triol. Depressoside A is a potent inhibitor of a-gluccsidase, IC50=0.236 mM………………………………………….
The Part B of the present Ph.D. dissertation describes asymmetric synthesis of 3,4-disubstituted pyroglutamates, 2,3-dihydro-benzothiazepin-4-ones and thiochroman-4-ones using readily available (E)-and (Z)-5-ylidene-1,3-dioxan-4-ones as starting chiral substrates. The conjugate addition of carbon and sulfur nucleophiles occurred stereoselectively and the resulting Michael adducts underwent ring transformation reactions. The lithium enolate of N-(Diphenylmethylene)- glycinate gave stereoselective conjugate addition to ylidenedioxanones. Hydrolytic cleavage of the imine functionality of the resulting Michael-adducts caused ring transformation to new, optically active 3,4-disubstituted pyroglutamats. Optically active cis-and trans-3-(1-hydroxyethyl)-1,5-benzothiazepin-4-ones have been synthesized by conjugate addition followed by ring transformation of ylidenedioxanones with 2-aminothiophenol Stereoselective conjugate addition of 2-bromothiophenol to ylidenedioxanones followed by bromo-lithium exchange with n-Buli provided a now access to optically active thiochroman-4-ones by the attack of the lithiated phenyl ring at the dioxanone carbonyl carbon atom, splitting off pivalaldehyde.