Marasmane sesquiterpenes

Other highly oxygenated bicyclic marasmane sesquiterpenes have been isolated from an EtOH extract of L. vellereus, which for many aspects seems an inexhaustible mine of Lactarius sesquiterpenes of any kind (see Table 24). The very unstable 5,10a,13-trihydroxymarasm-7(8)-ene (6.7) is accompanied by the 13-normarasmane isomers 6.12 and 6.13 (32) The latter ketones can derive from lactaropallidine (6.6) by (J-elimination and oxidation at C-7. 

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). 

The group of heterocyclic marasmane sesquiterpenes includes hemi-acetals velutinal (7.12), isovellerol (7.11), rubrocinctal A (7.4), and their derivatives and lactones which are unsubstituted or possess up to three hydroxy groups. Velutinal esters 7.28 and 7.30 have already been illustrated. The free hemiacetal velutinal (7.12) does not occur in intact fruiting bodies where, instead, is contained in the form of esters (see above) however, small amounts of 7.12 were detected by tic in a hexane extract of injured L. vellereus within the first minutes after grinding at 4° (7). Moreover, velutinal could be obtained by ethanolysis at 25° of... 

De Bernardi, M., G. Fronza, A.P. Gatti, G. Vidari, and P. Vita-Finzi New Marasmane Sesquiterpenes from Lactarius rubrocinctus (Basidiomycetes). 15th lUPAC International Symposium on the Chemistry of Natural Products, PA 75 (1986). 

Hansson, T, R. Bergman, O. Sterner, and B. Wickberg The Mechanism of the Thermal Rearrangement of the Marasmane Sesquiterpene (+) Isovelleral. Cyclopropane Ring Closure via an Intramolecular Ene Reaction. J. Chem. Soc., Chem. Commun., 1260 (1990). 

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. 

Rearranged marasmane skeletons glutinopallane and isolactarane sesquiterpenes... 

Flavidulol D was isolated from L. flavidulus, and its structure was identified as the stearate of flavidulol A (22.8) on the basis of spectroscopic data (147). The new marasmane lactone P3 and diketopiperazine P4 were isolated from the most polar fraction of an ethanolic extract of L. vellereus (148). The structures of compounds P3 and P4 were established by extensive NMR studies together with acetylation reactions. The isolation of lactone P3 suggested that the possible oxidation of the 15-methyl group, typical of a few lactarane sesquiterpenes, could take place at the early velutinal stage... 

Follotving the quite recent discovery of the broad range of biological activities exhibited by members of the sesquiterpene-based drimane family, namely mnio-petals, kuehneromycins, and marasmanes, a solid-phase approach towards a common key intermediate has recently been disclosed [408]. This supported synthesis offers the additional advantage of potential access to libraries of compounds with the same sesquiterpenoid skeleton. 

Froborg, j., and G. Magnusson Fungal Extractives-XI. On the Biogenetic Interrelationship between the Marasmane- and Vellerane Sesquiterpene Skeletons. Tetrahedron, 34, 2027 (1978). 

---