I= PHYTOCHEMICAL INVESTIGATION OF CORCHOURS DEPRESSUS AND ASYMMETRIC SYNTHESES WITH CHIRAL YLIDENDIOXANONES
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Title of Thesis
PHYTOCHEMICAL INVESTIGATION OF CORCHOURS DEPRESSUS AND ASYMMETRIC SYNTHESES WITH CHIRAL YLIDENDIOXANONES

Author(s)
Akbar Ali
Institute/University/Department Details
H.E.J. Research Institute of Chemistry/ University Of Karachi
Session
2004
Subject
Chemistry
Number of Pages
157
Keywords (Extracted from title, table of contents and abstract of thesis)
corchours depressus, asymmetric syntheses, chiral ylidendioxanones, saponins, corchorus acutangulus, corchorus olitorius l., corchorus capsularis l., depressoside

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.

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1403.9 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
94.79 KB
2 1 Introduction 2
64.38 KB
  1.1 Saponins 3
3 2 Biosynthesis 4
66.62 KB
  2.1 Biosynthesis Of Cycloartanes And Cycloartane Glycosides 7
  2.2 Biosynthesis Of Squalene And 2 ,3 -Oxidosqualene To 7
  2.3 Cyclization Mechanisms Of 2 ,3 -Oxidosqualene To Lanosterol And Cyloartenol 10
  2.4 Biosynthesis Of Saponins 12
4 3 Literature Review 14
90.43 KB
  3.1 The Genus Corchorus 14
  3.2 Corchorus Depressus L. 14
  3.3 Corchorus Acutangulus 16
  3.3 Corchorus Olitorius L. 17
  3.4 Corchorus Capsularis L. 22
5 4 Results And Discussion 24
296.38 KB
  4.1 Present Work 24
  4.2 Structure Elucidation Of Depressoside A And The Aglycone Depressogenin 25
  4.3 Structure Elucidation Of Depressoside B 35
  4.4 Structure Elucidation F Depressoside C 41
  4.5 Structure Elucidation Of Depressoside D 50
  4.6 Enzyme Inhibition Activity Of Depressoside A 56
6 5 Experimental 58
108.64 KB
  5.1 Experimental 58
  5.2 General Remarks 58
  5.3 Plant Material 59
  5.4 Extraction And Isolation. 59
  5.5 Characterization Of Depressoside A 61
  5.6 Characterization Of Depressoside B 62
  5.7 Characterization Of Depressoside C 62
  5.8 Characterization Of Depressoside D 63
  5.9 Enzyme Inhibition Activity Of Depressoside A 63
  5.10 References 64
7 6 Introduction 69
48.22 KB
  6.1 Introduction 69
  6.1 Asymmetric Synthesis, Epc - Synthesis 69
8 7 Synthesis And Known Reactions Of Ylidenedioxanones 74
122.43 KB
  7.1 Synthesis Of Enantiomerically Pure 5-Ylidene-1 ,3 -Dioxan-4-Ones 74
  7.2 General Reaction Behavior Of 5-Ylidene-1 ,3 -Dioxan-4-Ones 78
9 8 Results And Discussion 87
298.79 KB
  8.1 Conjugate Addition Reactions Of 5-Ylidene-1 ,3 -Dioxan-4-Ones 87
  8.2 Michael Addition Of N-( Diphenylmethylen )- Glycinate To 5-Ylidene-1 ,3 -Dioxan-4-Ones 87
  8.3 Conjugate Addition Of Thiols To 5-Ylidene-1 ,3 -Dioxan-4-Ones 98
  8.4 Summary 114
10 9 Experimental 119
431.78 KB
  9.1 Experimental 119
  9.2 General Remarks 119
  9.3 General Procedure For The Preparation Of 5-Ylidene-1 ,3 -Dioxan-4-Ones From Dioxanone 120
  9.4 General Procedure For The Michael Addition Of Ethyl N-( Diphenylmethylene )- Glycinate To 5-Ylidene-1 ,3 -Dioxan-4-Ones 122
  9.5 General Procedure For The Transformation Of Michael Adducts To Pyroglutamates 127
  9.6 General Procedure For The Conjugate Addition Of 2-Aminothiophenol To 5-Ylidene-1 ,3 -Dioxan-4-Ones 131
  9.7 General Procedure For The Transformation Of Adducis To 2 ,3 -Dihydro-1,5-Benzothiazepin-4(5h)-Ones With Etmgbr 135
  9.8 General Procedure For The Conjugate Addition Of 2-Bromothiophenol To 5-Ylidene-1 ,3 -Dioxan-4-One 114
  9.9 General Procedure For The Transformation Of Adducts To Thiochroman-4-Ones Via Bromo -Lithium Exchange 147
  9.10 References 152
  9.11 Abbreviations 157