Protoilludane sesquiterpenes

ViDARi, G., L. Garlaschelli, A. Rossi, and P. Vita-Finzi New Protoilludane Sesquiterpenes from Lactarius violascens. Tetrahedron Letters, 39, 1957 (1998). 

Several sesquiterpene skeletons include cyclobutane rings [78]. Some representative examples are summarized in Sch. 20. As can be easily seen, syntheses of caryophyllanes 78 and panasinsanes 79 are based on photocycloadditions to 2-methylpropene, those of tritomaranes (kelsoanes) 80, protoilludanes 81, and sterpuranes 82 are based on photocycloadditions to ethylene, while the bourbonane skeleton 83 is accessible via... 

Drimane, farnesane, glutinopallane, protoilludane, isolactarane, and guaiane sesquiterpenes have been isolated so far in a few Lactarius species therefore, they may be considered chemotaxonomic markers. By contrast, large quantities of marasmane, lactarane and secolactarane metabolites occur in almost all Sections, as reported in Table 24. 

Recently, for the first time among the Lactarius sesquiterpenes, the protoilludane skeleton has been assigned to two metabolites of Lactarius violascens (23) (Table 5). Also this mushroom contains a sesquiterpene alcohol (5.1) and the corresponding 6-oxostearic acid ester 5.2. It is worth noting that this fatty acid (also named lactarinic acid) is peculiar to Lactarius mushrooms where it has been isolated in the form of many sesquiterpenoid esters. 

Furantriol (18.27), isolated from L. mitissimus (84), is one of the few lactarane sesquiterpenes in which one of the gem-methyl groups at C-11 is oxidized and it was chemically correlated (82) with lactarorufin B (11.71), another example of this kind. The Polish authors suggested that lactone 11.71 was enzymatically formed from furan 18.27, and that a C-15 oxidized sesquiterpene of the velutinal type was the common precursor of both compounds in the mushroom (84). Actually, the possibility for the C-15 methyl group to be oxidized at an early stage of the lactarane biosynthesis seems to be confirmed by the recent finding of C-15 hydroxylated protoilludane sesquiterpenoids (5.1 and 5.2) in L. violascens (23) (Table 5). 

C,5H24, Mr 204.36, colorless oil, bp. 123°C(1.33 kPa). Monocyclic sesquiterpene from the essential oils of many plants such as, e.g., cloves, hops, and various Didymocarpus species. a-H. is often accompanied by the isomeric /5-humulene. The completely hydrogenated, monocyclic derivative of H. is humulane. H. is the biosynthetic precursor of various sesquiterpenoids, see hirsutanes, protoilludanes, etc. formed by basidi-omycetes. 

Sesquiterpenes (sesquiterpenoids). A structurally highly diverse class of terpenoids with 15 carbon atoms skeleton derived biosynthetically from famesyl pyrophosphate (FPP) ( famesol, isoprene rule, ter-penes). More than 70 different ring systems are formed by enzyme-catalyzed cyclization of the linear parent structure these cyclic structures can be further modified by 1,2- and 1,3-hydride shifts, renewed cycliza-tions, hydroxylations, and other subsequent reactions. S. are widely distributed in plants, fiingi, and animals but are less common in bacteria. Specific biosynthetic routes are often characteristic for certain organisms. Thus, basidiomycetes preferentially use humulene as the basis for the syntheses of protoilludanes, illu-danes, lactaranes, hirsutanes, and related S. skeletons. Individual S. systems are also known for liverworts and marine organisms. In addition, liverworts often contain the optical antipodes of S. known from plants. 

Marasmane sesquiterpenes, possibly resulting from contraction of the cyclobutane ring of the protoilludane skeleton (Scheme 1), can be divided into two groups tricyclic (Part 6) and heterocyclic (tetracyclic) (Part 7). The tricyclic constituents were divided into three subgroups simple marasmanes (6.1-6.8), isomarasmanes (6.9-6.11) and 13-normarasmanes (6.12-6.22). 

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