The absolute stereochemistry of brusatol has been confirmed to be 55, 1R, 8R,9R, 105, 11R, 125, 135, 145, 15R by a combination of 2D nmr ['H-'H and 'H-^C (onebond and long-range) COSY], nOe, and cd spectroscopic analyses.In our studies on biologically active natural products, an antitumor quassinoid, brusatol [1], was recently isolated from the traditional Chinese medicine "Yandanzi," Brucea javanica (L.)Merr (Simaroubaceae) (1). Sim etal. (2) had previously reported that 1 was a bitter principle of Brucea sumatrana and that 2', 3' -dihydrobrusatol, which was obtained by the hydrogenation of 1, was identical with bruceine A [2], It is known that bruceines A [2], B [3], and C [4], bruceantarin [5], bruceantin [6], and bruceantiol [7] are the C20 quassinoids with the same basic skeleton as that of 1 and only differ in the nature of 15-ester grouping (3-7). The absolute stereochemistry of bruceine C [4} was elucidated on the basis of X-ray analysis of its tetraacetate by Polonsky et al. ( 7). Thus, the absolute stereochemistry of the basic skeleton of these quassinoids was assumed to be the same as that of 4. This paper is concerned with an approach to the absolute stereochemistry of 1 by a combination of high-resolution ('H, 400 MHz; 13C, 100.6 MHz) nmr and cd spectroscopic analyses.
RESULTS AND DISCUSSIONNmr spectroscopy.-The nmr spectra were taken in pyridine-
