L.Yeap Foo

Rosmarinic acid derivatives from Salvia officinalis

Abstract Sagerinic acid, a novel cyclobutane and salvianolic acid K, derived from rosmarinic acid,were isolated together with the parent compound from polar solvent extracts of Salvia officinalis .Their chemical structures were elucidated by NMR and, for sagerinic acid, the stereochemistry ofthe substituents on the cyclobutane moiety was established as 3 β ,4a-diaryl-1a,2 β -dicarboxylicacid diester (m-truxinate form).

Amariin, a di-dehydrohexahydroxydiphenoyl hydrolysable tannin from Phyllanthus amarus

Abstract Amariin, a novel hydrolysable tannin together with geraniin, corilagin, 1,6-digalloylglucopyranoside as well as rutin and quercetin-3- O -glucopyranoside were isolated from the polar fraction of Phyllanthus amarus . On the basis of spectroscopic data and inverse long range 1 H, 13 C correlation experiments on its phenazine derivative, the structure of amariin was established as 1-galloyl-2,4: 3,6-bis-DHHDP-glucopyranoside in which the cyclohexenetrione portion of the DHHDP moieties were linked to the O-3 and O-4 of the glucose moiety.

Proanthocyanidin dimers and polymers from Quercus dentata

Abstract In a chemical investigation of the bark of Quercus dentata gallic acid, (+)-catechin, (+)-gallocatechin, hexagalloyl glucose and five proanthocyanidin dimers namely catechin-(4α → 8)-catechin, gallocatechin-(4α → 8)-gallocatechin, gallocatechin-(4α → 8)-catechin, gallocatechin-(4α → 6)-catechin and 3- O -galloylepigallocatechin-(4β → 8)-catechin were identified. The proanthocyanidin polymers also isolated from the same extract have been shown to consist of monomeric and terminal units identifiable with the corresponding units of all the five co-occurring proanthocyanidin dimers.

Phyllanthusiin D, an unusual hydrolysable tannin from Phyllanthus amarus

Abstract An unusual ellagitannin was isolated from the biologically active polar fraction of Phyllanthus amarus. Its structure was established as 1-galloyl-2,4-(acetonyl-dehydrohexahydroxydiphenoyl)-3,6-hexahydroxydiphenoylglucopyranoside by chemical and spectroscopic methods.

Sagecoumarin, a novel caffeic acid trimer from Salvia officinalis

Three structurally related caffeic acid trimers, melitric acid A, methyl melitrate A and the novel sagecoumarin, were isolated from sage and their chemical structures elucidated by means of NMR spectroscopy and mass spectroscopy. The mechanism for their formation from salvianolic acid K was proposed.

Nigrumin-5-p-coumarate and nigrumin-5-ferulate, two unusual nitrile-containing metabolites from black currant (Ribes nigrum) seed

Two novel nitrile-containing compounds, nigrumin-5-p-coumarate and nigrumin-5-ferulate, together with six known flavonoids, were isolated from the seed of black currant (Ribes nigrum). The chemical structures of nigrumin-5-p-coumarate and 5-ferulate were elucidated using NMR spectroscopy as 2-trans-p-coumaroyloxymethyl-4-beta-D-glucopyranosyloxy-2(E)-butenenitrile and 2-trans-feruloyloxymethyl-4-beta-D-glucopyranosyloxy-2(E)-butenenitrile, respectively.

Biphenyl-linked biflavanoids from grape pomace

Abstract Two novel biphenyl linked biflavanoids commonly associated with polyphenol oxidase-coupled products were isolated from Chardonnay grape pomace. Their chemical structures were established by long-range H,C couplings as epicatechin [6′ → 8]-epicatechin and epicatechin [6′ → 8] catechin. The disproportionate representation of the epicatechin unit as compared with catechin among the isolated biflavanoids could not be accounted for by their relative concentration in the pomace and suggested that the 2,3-trans configuration provided more steric constraints than the 2,3-cis one during grape polyphenol enzymatic oxidation of the B-ring leading to the quinone intermediate.

New pyranoanthocyanins from blackcurrant seeds

Four new pyranoanthocyanins, namely pyranocyanin C and D and pyranodelphinin C and D, possessing the pyrano[4,3,2-de]-1-benzopyrylium core structure were isolated from an extract of blackcurrant seeds. Their chemical structures were elucidated by spectral methods and confirmed by chemical synthesis involving blackcurrant anthocyanins and p-coumaric acid. It is postulated that this condensation reaction plays a significant part in the evolution of red wine colour.

Isolation of the first C-2 addition products of anthocyanins

Abstract Addition of anthocyanins with nucleophilic agents normally occurs at the C-4 centre and the isolation of C-2 adducts between acetone and cyanidin-3- and delphinidin-3-rutinosides is the first definitive demonstration of the reactivity of this carbon site. These C-2 addition products were isolated as diastereoisomers and their chemical structures elucidated by 1D and 2D NMR spectroscopy.