Poly acetylenes from the Higher Fungi

Several polyacetylenes have antibiotic properties and some are phytotoxic. Agrocybin (4.105), originally isolated from Agrocybe dura, is also formed by the fairy-ring fungus, Marasmius oreades, and it may be responsible for the death of grass. Their production as extracellular mycelial metabolites may thus facilitate the spread of the mycelium in a hostile environment. The dry-rot 

Terpenoids are widespread natural products that are formed from C5 isoprene units leading to their characteristic branched chain structure. Terpenoids are divided into families on the basis of the number of isoprene units from which they are formed. Thus there are monoterpenoids (Cio), sesquiterpenoids (C15) diterpenoids (C20), sesterterpenoids (C25), triterpenoids (C30) and carotenoids (C40). The isoprene units are normally linked together in a head-to-tail manner. However, the C30 triterpenoids and C40 carotenoids are formed by the dimerization of two Ci5 and C20 units, respectively. Hence, in these cases the central isoprene units are linked in a head-to-head manner. The presence of tertiary centres in the isoprenoid backbone of the terpenoids facilitates skeletal rearrangements in the biosynthesis of these natural products. As a consequence, on first inspection some structures appear not to obey the isoprene rule. 

The Chemistry of Fungi By James R. Hanson James R. Hanson, 2008 

which undergoes decarboxylation to form isopentenyl diphosphate (5.5). (3i )-Mevalonic acid contains three prochiral centres, C-2, C-4 and C-5. Each of these is involved in the biosynthesis of the terpenes. Samples of mevalonic acid have been prepared in which each of these centres has been 

The head-to-head coupling of two famesyl diphosphate units to form squalene is discussed later in the section on triterpenoids (Section 5.7). 

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