B

FIGURE 4.5 Prenylated C6-C3 compounds 37-40 occurring in I. tashiroi and I. arborescens

O
O

och3

och3 'och3

och3

och3

och3

oh 45

FIGURE 4.6 Prenylated C6-C3 compounds 41-45 isolated from I. tashiroi and I. anisatum catalyst to yield 80a and 80b, which in turn were converted into p-bromobenzoyl derivatives 81a and 81b, respectively, with p-bromobenzoyl chloride-pyridine. The relative configurations of the p-bromobenzoyl groups in 81a and 81b were determined on the basis of NOEs, as shown in Figure

4.11. These results disclosed that the p-bromobenzoyl group is cis to the methylenedioxy group in 81a and trans in 81b. Thus, the relative configurations of 81a and 81b are ready to refer to their CD spectra. The CD spectra of 81a and 81b showed a negative Cotton effect at 240 nm and a positive Cotton effect at 239 nm, respectively, thereby allowing us to assign the absolute configuration at C-1 in 81a and 81b to R and S, respectively. Accordingly, the absolute configuration for illicinone E was determined to be (4S), (5S), and (11R) (Fukuyama et al., 1992).

(2R)-2,3-Dihydroillicinone E (72) and (2S)-2,3-dihydroillicinone E (75) were hydrogenated to yield the reduced products 72a and 75a, which were identical in all respects to each of the tetrahydro-derivatives transformed from illicinone E (68), respectively (Scheme 4.6). The chemical correlation indicated that 72 and 75 are stereoisomers with regard to C-2 in 2,3-dihydroillicinone E. Finally, NOE experiments could readily make a stereochemical difference to C-2 between 72 and 75. However, the structure of illicinol E (77) was assigned as 1R and 2R on the basis of the following data: the relative stereochemistry of the acetate 77a was elucidated as depicted in Figure

4.12, and the spectral data of 77 were identical with those of one of two products that were obtained by NaBH4 reduction of (2R)-2,3-dihydroxyillicinone E (72).

Illicium plants biosynthesize not only simple prenylated C6-C3 compounds (Kouno et al., 1990; Hano et al., 1992; Kaku et al. 1993) but also illicinone E (68) and its analogues 69-78, which contain the methylenedioxy group in the molecule. Illicinone E (68) and its variants are chemical

49a 49b

SCHEME 4.2 Absolute configuration at C-4 in illicinone A (37)

components characteristic of Illicium plants, which have not been so far found in the other plants (Fukuyama et al., 1994).

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