Sesquiterpenoids, definition

The structure and stereochemistry of cis-sativenediol (111) and trans-sativenediol (112) have been established57 by n.m.r. spectroscopy and, in the case of the ris-isomer, by conversion into the diethyl acetal (113) of helminthosporal (115). Both diols co-occur with prehelminthosporol (114), helminthosporal (115), and helminthosporol (116) in Helminthosporium sativum and Cochliobolus setariae and a definitive statement on the possible biosynthetic relationship between these compounds is expected in the near future. Two related sesquiterpenoids, (117) and (118), having the isosativane skeleton have also been identified as metabolites of H. sativum.5 The structures assigned to these compounds are based on chemical correlation with cis-sativenediol (111) (cf. Scheme 16) and it is reasonable to... 

A reinvestigation of the structures of the two marine metabolites lemnalactone and 7-epilemnalactone has resulted in definitive evidence in favour of (645) and (646) respectively. The three aromadendrane sesquiterpenoids (647)—(649)... 

The synthesis of sesquiterpenoids has aroused much attention, not only because it constitutes a method for obtaining these interesting bioactive compounds that are often found in only small amounts in nature, but also because they constitute definitive proof of the structures elucidated by spectroscopic methods [2]. 

By definition, sesquiterpenoids contain 15 carbon atoms. This results in their having lower volatilities and hence higher boiling points than monoterpenoids. Therefore, fewer of them (in percentage terms) contribute to the odor of essential oils but those that do often have low-odor thresholds and contribute significantly as end notes. They are also important as fixatives for more volatile components. 

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