B R1 R3 H R2 OH 124a R1 Bz R2 OH R3 H 125a R1 Ac R2 OH R3 Bz 126a R1 Bz R2 R3 H

FIGURE 4.18 Pseudoanisatin-type sesquiterpenes (compounds 118-126)

The compounds are proposed presumably derived from the majucin-type sesquiterpene as follows: the ring construction occurs between C-7 and C-8 in the majucin-type compound, followed by the bond formation of C-6 and C-8, and then hydroxylation at C-8. In this case, C-7 should become a methyl group. Although this seems to be a better explanation for converting from the majucin-type compound to anislactones, inversion of the C-9 configuration still has remained ambiguous.

Other new skeletal sesquiterpenes, named illicinolides A (155) and B (156) and tashironin (157), were isolated from I. tashiroi. The structure of illicinolide A was elucidated on the basis of the spectral data, and then its absolute configuration was established by x-ray crystallographic analysis of the p-bromobenzoyl derivative 155a (Fukuyama et al., 1990). The structure of Illicinolide B was assigned as 6a-hydroxyillicinolide A by spectral data compared with those of illicinolide A, and its absolute structure was determined by applying the CD dibenzoate rule to the p-bromobenzoyl derivative 156a (Fukuyama et al., 1992). Although illicinolides A and B appear to be closely related to the previously reported anisatin (107) and majucin (137), the structural feature that contains the Y-lactone ring closed between C-7 and C-9 is rather similar to noranisatin (107a) (Yamada et al., 1965), an oxidatively degraded product of anisatin. This highly oxygenated abnormal structure may be rationalized biogenetically by assuming that the C-11 carbon in compounds 155 and 156 would originate from the C-11 in normal anisatin skeleton through, for example, a tetracyclic intermediate C, as shown in Scheme 4.10.

ho oh i OH 118

OH I OH 128

OH I OH 128

OH i OH

OH i OH

FIGURE 4.19 Ketone and hemiacetal equilibrium of pseudoanisatin-type sesquiterpenes and an unusual sesquiterpene 132

In contrast, the structure of tashironin (157) was elucidated by extensive analysis of spectroscopic data (Fukuyama et al., 1995). Tashironin consists of a 2-oxatricyclo [4.3.1.049] heptane skeleton and can be regarded as a rare allocedrane-type sesquiterpene. Although anisatin (107) and its congeners have been postulated to be biosynthesized from a tricarbocyclic precursor A (Tomita and Hirose, 1973), the biosynthetic route leading to an anisatin skeleton has been still obscure because any tricarbocyclic sesquiterpenes made up by the same carbon skeleton of A have not been found in Illicium species. Tashironin (157) possesses the precise carbon skeleton corresponding

2 R3

2 R3

0 0

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