Rubrocinctal esters

Recently, we have isolated the aldehyde rubrocinctal A (7.5), the carboxymethyl ester rubrocinctal B (7.7), and the corresponding 6-oxostearoyl esters 7.6 and 7.8 from Lactarius rubrocinctus (Section Ichorati) (23) (Table 7). These compounds are the first examples of 12-oxygenated isovellerol derivatives from a Lactarius species. 

The only two known natural glutinopallane sesquiterpenes (8.2,8.3) have been isolated from Lactarius glutinopallens (42) (Table 8). Their structures are strictly related to velutinal esters (7.14, 7.15) for the presence of the cyclopropane ring and the 7a,8a-epoxyde, and to rubrocinctals 7.7 and 7.8 for the carbomethoxy group at C-3. 

Fatty acid esters of other marasmane sesquiterpenoids, as the two rubrocinctal derivatives 7.6 and 7.8, have been isolated so far only from L. rubrocinctus (23). Of limited distribution are also the farnesane fatty acid esters 1.3-1.9 (8), drimenol (3.2-3.6) and uvidin A (3.16-3.20) esters (11), violascensol lactarinate 5.2 (23), and the two glutinopallane esters 8.2 and 8.3 (42). Further unprecedented sesquiterpenoids are the guaiane esters 4.10-4.13 contained in intact specimens of Lactarius species of the Section Dapetes (14, 16, 21, 22). Various mixtures of yellow esters 4.12 and 4.13, red stearoylsangol (4.11), and blue stearoyldeterrol (4,10) are responsible for the beautiful colours of the latex of these species. 

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... 

The aldehyde rubrocinctal A (7.4), the 12-carboxymethyl ester rubrocinctal B (7.16), and the corresponding 6-oxostearoyl esters 7.27 and 7.31 were isolated from Lactarius rubrocinctus Section Ichorati (2), (69). They are of special interest because they are, along with glutinopallal esters 8.2 and 8.3, the only examples of 12-oxygenated sesquiterpenes isolated from Lactarius species. 

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