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A roselle (Hibiscus sabdariffa Linn.) tea extract was found to have high inhibitory activity against porcine pancreatic alpha-amylase. Hibiscus acid and its 6-methyl ester were respectively isolated as active principles from the 50% methanol and acetone extracts of roselle tea. The activity of each isolate was compared to that of structurally related citric acid, a previously known inhibitor of fungal alpha-amylase.

[Structure: see text]. Citrinadin A (2) is a pentacyclic indolinone alkaloid isolated from the cultured broth of a fungus, Penicillium citrinum, which was separated from a marine red alga. The absolute stereochemistry of the pentacyclic core in 2 and its new congener, citrinadin B (1), was elucidated by analysis of the ROESY spectrum for the chlorohydrin derivative (3) of 1 as well as comparison of the electronic circular dichroism (ECD) spectra for 1 and 2 with those of known spirooxiindole alkaloids. On the other hand, the absolute configuration at C-21 bearing an epoxide ring was assigned as S by comparison of the vibrational circular dichroism (VCD) spectra of 1 with those of model compounds 2S- and 2R-2,3-epoxy-3,3-dimethyl-1-phenylpropan-1-one (4a and 4b, respectively).

Five antioxidative caffeoylquinic acid derivatives were isolated from the roots of burdock (Arctium lappa L.), an edible plant in Japan. Their structures were established as 1-0-,5-O-dicaffeoylquinic acid (1), l-0-,5-0-dicaffeoyl-3-0-succinylquinic acid (2), l-0-,5-0-dicaffeoyl-4-0-succinylquinic acid (3), l-0-,5-0-dicaffeoyl-3-0-,4-0-disuccinylquinic acid (4), and 1-0-,3-0-,5-0-tricaffeoyl-4-0-succinylquinic acid (5) on the basis of chemical and spectral (NMR, MS) evidence. The antioxidant activities were measured in a hexane/2-propanol solution of methyl linoleate in the presence of a radical initiator. The antioxidant efficiency increased in the order of -tocopherol < chlorogenic acid < caffeic acid < (1) = (2) = (3) = (4) < (5).

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Two novel bromophenols (1 and 2) were isolated from an extract of a red alga, Odonthalia corymbifera, together with a known bromophenol (3). The novel bromophenols were determined as 4-bromo-2, 3-dihydroxy-6-hydroxymethylphenyl 2, 5-dibromo-6-hydroxy-3-hydroxymethylphenyl ether (1) and bis(2, 3-dibromo-4,5-dihydroxybenzyl) ether (2), from spectroscopic evidence. Compounds 1-3 were found to be inactivators of alpha-glucosidase.

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