FIGURE 15.52 Biotransformation of atractylon (163) and costunolide (165) by Aspergillus niger.

Aspergillus niger converted ß-cyclocostunolide (170) to 2-oxygenated metabolites (173, 174, 178 -181) of which 173 was predominant. It is suggested that compound 173 and 174 might be formed during biotransformation period since metabolite media after 7 days was acidic (pH 2.7). Surprisingly, Aspergillus cellulose gave a sole 11ß,13-dihydro-ß-cyclocostunolide (182), which was abnormally folded in the mycelium of Aspergillus cellulosae as a crystal form after biotransformation of 170. On the other hand, the metabolites were normally liberated in medium outside of the mycelium of Aspergillus niger and Botryosphaeria dothidea (Hashimoto et al., 1999a, 2001) (Figure 15.56).

Botryosphaeria dothidea has no stereoselectivity to reduce C11-C13 double bond of ß-cyclocos-tunolide (170) since this organism gave two dihydro derivatives 182 (16.7%) and 183 (37.8%), respectively, as shown in Figure 15.57.

It is noteworthy that both a- and ß -cyclocostunolides were biotransformed by Aspergillus niger to give the sulfur-containing metabolites (176, 181). Possible biogenetic pathway of 170 is shown in Figure 15.58.

When g-cyclocostunolide (171) was cultivated in Aspergillus niger to give dihydro-a-santonin (187, 25%) and its related C11,C13 dihydro derivatives (184-186, 188, 189) were obtained as a small amount. Compound 186 was recultivated for 2 days by the same organism as mentioned above to afford 187 (25%) and 5ß -hydroxy- a-cyclocostunolide (189, 54%). Recultivation of 185 for 2 days by Aspergillus niger afforded compound 187 as a sole metabolite. During the biotransformation of 171, no sulfur-containing product was obtained. Both Aspergillus cellulosae and Botryosphaeria dothidea produced only dihydro-g-cyclocostunolide (184) from the substrate (171) (Hashimoto et al., 1999a, 2001) (Figure 15.59).

Santonin (190) has been used as vermicide against round warm. Cunninghamella blakesleeana and Aspergillus niger converted 190-187 (Atta-ur Rahman et al., 1998). When 187 was fed by Aspergillus niger for one week to give 2ß -hydroxy-1,2-dihydro-a-santonin (188, 39%) as well as 1ß -hydroxy-1,2-dihydro-a-santonin (195, 6.5%), 9ß-hydroxy-1,2-dihydro-a-santonin (196, 6.9%), and a-santonin (190, 5.4%), which might be obtained from dehyroxylation of 188, as a minor

HO - H î = O-

168a O

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