Biosynthesis Majucin

FIGURE 4.13 Neolignans (compounds 82-88)

K^ 0CH3

92 r=0ch3 94 r=0ch3

oCH3
FIGURE 4.14 Neolignans (compounds 89-98)

was correct, and the aforementioned spectral discrepancy could be attributed to a strong intramolecular hydrogen bond between the OH group attached to C-14 and C-3.

Some pseudoanisatin-type sesquiterpenes were found to coexist as a ketone and hemiacetal equilibrium (Figure 4.19), such as pseudoanisatin (118) and 4,7-hemiketal of pseudoanisatin (127), parviflorolide (128), cycloparviflorolide (129) (Schmidt et al., 1999), merrillianolide (130), and cyclomerrillianolide (131) (Huang et al., 1999). In addition, an unusual sesquiterpene neodunnianin (132) was isolated from the pericarps of I. dunnianum (Huang et al., 1997), featured by an 11,15-5-lactone. Pseudoanisatin derivatives, which have been so far checked, are nontoxic substances unlike anisatin, but it is worthy of note that isodunnianin (125) not only promotes neurite outgrowth

99 100

FIGURE 4.15 Neolignans (compounds 99-103)

in the primary culture of fetal rat cerebral hemisphere at 10 pM but also increases choline acetyl-transferase activity (Fukuyama et al., 1993).

The opening of the spiro P-lactone of anisatin-type sesquiterpene leads to minwanensin type. After the structure of minwanensin (133) from the pericarps of I. minwanense was elucidated (Figure 4.20), this type of compound such as 3-acetoxy-14-n-butyryloxy-10-deoxyfluoridanolide (134), 14-acetoxy-3-oxofloridanolide (135), 13-acetoxy-14-(n-butyryloxy)fluoridanolide (136), and debenzoyldunnianin (123) were also found in the fruits of I. floridanum (Schmidt et al., 1998). The structure of debenzoyldunnianin was first proposed as 123a and/or 123b (Kouno et al., 1991;

O

SCHEME 4.7 Possible biosynthesis of 103

HO A OH

FIGURE 4.16 Anisatin (107) and neoanisatin (108)

KMnO,

ho hvvoo

O 107

107a

AcOH

NaHCO3

CO2H

CO2H

107d

HO HO

co2h

OH/X=OOH

107e

SCHEME 4.8 Chemical characteristics of anisatin (107) (Yamada et al., 1968)

Schmidt and Peters, 1997), but the correct structure 123 was finally established by x-ray crystal-lographic analysis. The structure of minwanensin was considered to be similar to that of anisatin, but it does not show toxicity against mouse at the dose of 50 mg/kg. This indicates that the presence of P-lactone in a molecule may be responsible for toxicity.

A number of new majucin-type sesquiterpenes having a y-lactone ring, as shown in Figure 4.21, were found in the pericarps of I. majus, belong to one of the Chinese Illicium plants. Majucin (137) was assigned the structure by extensive spectroscopic analysis and by comparing its nuclear magnetic resonance data with those of anisatin as well as of neomajucin (138), established by an x-ray diffraction method (Yang et al., 1988; Kouno et al., 1989). More majucin-type sesquiterpene lactones, (2S*)-hydroxyneomajucin (139), 2-oxoneomajucin (142), 2,3-dehydromajucin (143), (2^*)-hydroxy-3,4-dehydroneomajucin (144), (1S*)-2-oxo-3,4-dehydroneomajucin (145), (1^*)-2-oxo-3,4-dehydroneomajucin (146), and (1R*, 10 S*) -2-oxo-3,4-dehydroneomajucin (147), were isolated (Kouno et al., 1989, 1990). It should be noted in particular that the compound bearing the (10S*)-hydroxyl group is only 147 among the anisatin-like sesquiterpenes. 6-Deoxyneomajucin (140), isolated from the seeds of I. anisatum, is the first example of majucin type found in Japanese star anise (Kouno et al., 1988). I. angustisepalum also contains majucin-type sesquiterpene like 10-benzoyl ester of neomajucin (141) (Sy and Brown, 1998).

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