Isolactaranes

A stereoselective electroreductive cyclization has been used in the synthesis of /-sterpurene, an isolactarane-type sesquiterpene 95). 

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... 

The fascinating lactone isolactarorufin (9.5) (Table 9) is the only example of isolactarane sesquiterpenes isolated from a Lactarius specie (43-45). The structure of isolactarorufin has been elucidated by spectroscopic data and confirmed by X-ray analysis of its p-bromobenzoate 9.8 (45). 

CijHzoOj, Mr 248.32, cryst., mp. 99°C, [aJo -154° (CHjOH). A sesquiterpenoid of the isolactarane type from cultures of Merulius tremellosus (Basidiomy-cetes). M. is active against bacteria, fungi, and yeasts. It also has cytotoxic activity against ascites cells of the Ehrlich carcinoma and shows strong mutagenicity in the Ames test. 

The fascinating lactone isolactarorufin (9.4), at first discovered in an EtOH extract of L. rufus (75, 76, 77) and later also in L. vellereus (5S) and L. necator, is the only known isolactarane sesquiterpene so far isolated from Lactarius species. Other compounds listed in Part 9 are synthetic derivatives that were prepared for structure elucidation of the parent compound or for investigation of their biological properties. 

When the few y-hydroxy aldehydes possessing the marasmane, isolactarane, or lactarane skeletons are compared, some interesting observations can be made. In principle, open y-hydroxy aldehydes should exist as an equilibrium mixture with their two cyclic stereo-isomeric hemiacetals. In fact, NMR spectra indicate that in common organic solvents isovellerol 7.11 exists as a mixture of approximately equal amounts of the three forms shown in Scheme 3 (7). 

Daniewski, W.M., M. Gumueka, E. Beoszyk, U. Jacobsson, and T. Norin Isovellerol and New Isolactarane Sesquiterpenes, Their Structure and Antifeedant Activity. Polish J. Chem., 71, 1254 (1997). 

Gianetti, B., B. Steffan, and W. Steglich Antibiotics from Basidiomycetes. Part 23. Merulidial, an Isolactarane Derivative from Merulius tremellosus. Tetrahedron, 42, 3579 (1986). 

Culture of the phytopathogenic fungus Stereum purpureum (Basidomycetae), a parasite of some trees, produces unsaturated and hydroxylated sesquiterpenes wifli the tricyclic skeleton of sterpurane, formally arising from isolactarane by opening the C-5-C-6- and closing the C-4-C-5 bond, or directly from famesane by Unking the bonds C-l-C-11, C-2-C-9 and C-4-C-7. 

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