Sesquiterpenoids are built from three isoprene units and also contain a lactone ring. One eudesmanolide, 3-oxo-5αH,8βH-eudesma-1,4(15),7(11)-trien-8,12-olide.....usual name. 

Dear Anass,

Please, be more specific. Would you like to name a specific sesquiterpene lactone or to know in general how such compounds are given names?

Lactones are named using the 'olide' suffix together with two locants, the first being the locant for the carbonyl carbon, and this system is used even when a high-priority substituent (usually COOH) is also present, necessitating the appearance of two principal suffixes (and thus breaching the IUPAC rules).

Here are the link to the IUPAC site with the rules for naming natural products and specifically to the numbering schemes of the basic terpene (including sesquiterpene skeletons):

http://www.chem.qmul.ac.uk/iupac/sectionF/

http://www.chem.qmul.ac.uk/iupac/sectionF/terp1.html

Hope this helps!

All the best,

Niko

Dear Anass,

You can also contact Prof. Antonio Evidente (who is registered on RG; [email protected]) who is a specialist in the field.

Best regards

Robert

Interesting question

You'll find a good monograph on terpenes and terpene nomenclature in:

Chizzola R. (2013) Regular Monoterpenes and Sesquiterpenes (Essential Oils). In: Ramawat K., Mérillon JM. (eds) Natural Products. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-22144-6_130