Microorganisms, sesquiterpenoids

Besides warburganal (1), muzigadial (2) and polygodial (3), none of the other sesquiterpenoids (4-11) isolated, showed any noticeable antifungal activity up to 100 /jg/ml, although they were all isolated from the active fractions. Nevertheless, most of the purified sesquiterpenoids were tested against eleven additional microorganisms. The results are listed in Table 1. 

Albicanal (288) and (-)-drimenol (289) are simple drimane sesquiterpenoids isolated from the liverwort, Diplophyllum serrulatum, and many other liverworts and higher plants. The latter compound was incubated with M. plumbeus and R. arrhizus. The former microorganism converted 289 to 6,7a-epojQ - (290), 3p-hydroxy- (291), and 6a-drimenol (292) in the yields of 2%, 7%, and 50%, respectively. On the other hand, the latter species produced only 3p hydroxy derivative (291) in 60% yield (Aranda et al., 1992) (Figure 20.90). 

In conclusion, a number of sesquiterpenoids were biotransformed by various fungi and mam mals to afford many metabolites, several of which showed antimicrobial and antifungal, antiobe sity, cytotoxic, neurotrophic, and enzyme inhibitory activity. Microorganisms introduce oxygen atom at allylic position to give secondary hydroxyl and keto groups. Double bond is also oxidized... 

Hashimoto, T., S. Kato, M. Tanaka, S. Takaoka, and Y. Asakawa, 1998a. Biotransformation of sesquiterpenoids by microorganisms (4) Biotransformation of hinesol by Aspergillus niger. Proceedings of 42nd TEAC, pp. 127-129. 

Similar results were obtained with acyclic mono- and sesquiterpenoid compounds containing an allylic alcohol group, either in a primary or a tertiary position. For example, linalool 9, nerolidol 10, geraniol 11, citronellol (or their estem) are hydroxylated by A. niger [5-7] and many other microorganisms [8-10] in terminal position, concurrently with epoxidation (followed by hydrolysis) at the remote double bond ... 

Much effort has been concentrated on microbial hydroxylations of dimethylcyclo-propane-containing sesquiterpenoids, the chemical oxidation of which is particularly delicate due to the instability of the strained cyclopropane ring. Calarene 110 was used as a substrate in die first experiments [138] but very low yields were observed in its biotransformation. By contrast, functionalized aristolenepoxide 111 [139] or the sesquiterpenoid enone 117 [140] was more easily oxidized by a number of strains, affording in moderate yields some new and selectively hydroxylated derivatives 112-116 or 118-120, respectively, depending on the microorganism used. 

Other related dimethylcyclopropane sesquiterpenoids, globulol (127) and 7-epiglob-ulol (128), are more efficiently transformed by various microorganisms [138] into similar products such as 129, mainly hydroxylated (and sometimes further oxidized) on one (or... 

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