29 ニガキの苦味成分

概要

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Three new bitter principles, nigakilactone A, B and C and a known bitter principle, quassin (nigakilactone D), were isolated from Picrasma ailanthoides Planchon (Japanese name: nigaki, Simaroubaceae). Nigakilactone A, B and C were shown to be closely related lactones in the following way. Methylation of nigakilactone A (I), C_<21>H_<30>O_6, m.p. 237.5-238°, with CH_3I-Ag_2O-DMF gave nigakilactone B (II), C_<22>H_<30>O_6, m.p. 278.5°, which was formed by alkaline hydrolysis of nigakilactone C (III), C_<24>H_<34>O_7, m.p. 252.5-253°. The latter compound (III) was obtained on acetylation of II with Ac_2O-pyridine. Nigakilactone A (I) afforded a monoacetate (IV) by acetylation with Ac_2O-pyridine. On oxidation with Na_2Cr_2O_7 in acetic acid, IV yielded a keto-acetate (V). Oxidation of I with CrO_3-pyridine gave an α-ketol (VI), which was oxidized with Bi_2O_3 to afford a diosphenol (VII). On methylation with dimethyl sulfate and alkali, VII gave a methylated diosphenol (VIII), which was shown to be identical with quassin (XI). From these findings, along with the PMR spectrum of I, the structure of nigakilactone A is established as I. PMDR experiment on III, afforded the evidence for the presence of a partial structure (C). These observations lead to the structure III for nigakilactone C and the structure II for nigakilactone B. Nigakilactone D was found to be identical with quassin.
1969-09-01