Platanionosides D—J: Megastigmane Glycosides from the Leaves of Alangium platanifolium (SIEB. et ZUCC.) HARMS var. platanifolium SIEB. et ZUCC
Chemical and pharmaceutical bulletin
There are three Alangiaceous plants in Japan. 1) Alangium premnifolium grows in the southernmost part and A. platanifolium var. trilobum in wide areas of the northern to southern parts of Japan, and the title plant is restricted to the areas of western Yamaguchi and Fukuoka Prefectures. In a previous work, considerable numbers of megastigmane glycosides were isolated from the leaves of A. premnifolium. 2) At first, investigation of Alangiaceae plants was performed in order to isolate ipecac
... loids. 3) However, this has not been successful so far, except for the isolation of alangiside. 4) Phytochemical isolation work on the title plant has afforded three megastigmane glycosides 5) and several phenolic glycosides. 6) Further investigation yielded seven new megastigmane glycosides ( Fig. 1 ) along with five known compounds (Fig. 2) . This paper deals with the structural elucidation of these new megastigmane glycosides. Results and Discussion Air-dried leaves of A. platanifolium var. platanifolium were extracted with MeOH, followed by partitioning between solvents of increasing polarity, namely, n-hexane, EtOAc and n-BuOH. The n-BuOH-soluble fraction was purified using a highly porous synthetic resin, octadecyl silica (ODS), and silica gel column chromatographies, and then subjected to droplet counter-current chromatography (DCCC) to give 12 pure megastigmane glycosides. Five of them were known glycosides, being identified as (6S,9R)-roseoside, 7) alangionosides A, 8) H 7) and K, 7) and linarionoside C. 9) Platanionoside D (1), [a] D Ϫ25°, was isolated as an amorphous powder and its elemental composition, C 25 H 44 O 12 , was deduced from the observation of a quasi-molecular ion peak in negative-ion high-resolution (HR) FAB-mass spectrometry. The IR spectrum indicated that 1 was a glycosidic compound. The 1 H-NMR spectrum showed the presence of two singlet and two doublet methyls, and two doublet signals (d H 4.335, d, Jϭ8 Hz and 4.338, d, Jϭ8 Hz), which were assigned as two anomeric protons of sugar moieties. The 13 C-NMR spectrum of 1 indicated the presence of two terminal b-glucopyranose units, and the remaining 13 signals were expected to present a megastigmane skeleton. These signals were assigned to four methyls, four methylenes, four methines, two of which were substituted by oxygen atoms (d C 75.8, 76.2), and one quaternary carbon. These functionalities and the relative arrangement of the ring protons, deduced From the leaves of Alangium paltanifolium var. platanifolium, collected in Fukuoka Prefecture, twelve further megastigmane glycosides were isolated. Seven of them, named platanionosides D-J (1-7), were found to be new compounds. Their structures were elucidated from spectroscopic evidence and their absolute structures were determined from b b-D-glucosylation-induced shift trends of 13 C-NMR and by application of a modified Mosher's method.