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PHYTOCHEMICAL INVESTIGATION OF CORCHOURS DEPRESSUS AND ASYMMETRIC SYNTHESES WITH CHIRAL YLIDENDIOXANONES

Ali, Akbar (2004) PHYTOCHEMICAL INVESTIGATION OF CORCHOURS DEPRESSUS AND ASYMMETRIC SYNTHESES WITH CHIRAL YLIDENDIOXANONES. PhD thesis, University of Karachi, Karachi.

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Abstract

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.

Item Type:Thesis (PhD)
Uncontrolled Keywords:corchours depressus, asymmetric syntheses, chiral ylidendioxanones, saponins, corchorus acutangulus, corchorus olitorius l., corchorus capsularis l., depressoside
Subjects:Physical Sciences (f) > Chemistry(f2)
ID Code:1136
Deposited By:Mr. Muhammad Asif
Deposited On:03 Jan 2007
Last Modified:04 Oct 2007 21:04

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