Some constituents of Alyxia olivaeformis Gaud

Abstract

The endemic Hawaiian plant Alyxia olivaeformis Gaud. (Apocynaceae) had given an apparently satisfactory response to screening tests for the presence of alkaloids. Since earlier studies of Hawaiian Apocynaceae had yielded a number of new alkaloids, an exhaustive attempt was made to isolate alkaloids from A. olivaeformis. Repeated attempts to obtain alkaloids from this plant, employing different isolation procedures, were unsuccessful, and it was concluded that in A. olivaeformis alkaloids are either absent, or present in only trace quantities. During the course of these investigations, however, two non-nitrogenous compounds were obtained. One compound was shown to be coumarin (I) by comparison with an authentic sample. An examination of the volatile extract from fresh A. olivaeformis showed that coumarin is also the major volatile principle of this plant. The second compound, m. p. 143-145°C., [α]^27.5 + 33.7° was soluble in sodium hydroxide and in pyridine. Functional group analysis showed l1.94% methoxyl and 1.06% C-methy1. There was 1.53% active hydrogen. No uptake of hydrogen was observed under conditions Which would result in reduction of olefinic centers. Two empirical formulas were obtained from elemental analyses of the compound: C16H20O8 from samples which were dried under mild conditions, and C16H18O7 from those dried in vacuo at l00°C. Color tests and spectral data indicated that the compound is a catechin or flavan-3-ol (II). This catechin is a trihydroxymonomethoxyflavan-3-ol crystallizing with either one or two molecules of water of hydration, depending on the method of drying the solid. Interpretation of spectral and rotation data and of chemical evidence allows the proposal of a tentative structure III. This structure represents a naturally occurring methoxylated catechin, which is a type of compound not previously reported. The name mailein is proposed for III.