Velutinal esters

Catalytic transesterification of esters 7.14 or 7.15 in EtO /EtOH afforded the free hemiacetal velutinal (7.11) (38), while both velutinal esters gave the methyl acetal 7.13 (38, 40) in HPLC grade methanol. 

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. 

Attempted formation of the bromide from the furanosesquiterpene 18.10 with Ph3P and CBr4 gave furanether A (18.5) and pyrovellerofuran (18.3), as main products (93). The latter compound had previously been obtained by thermal rearrangement of isovelleral (6.1) (90), while furanol 18.10, isolated from L. vellereus (93), was also formed when velutinal derivatives were decomposed on silica gel (85). This experiment correlated the absolute configuration of isovelleral (6.1) with that of velutinal esters and, indirectly, with the stereostructures of many other Lactarius... 

In conclusion, while the first steps of the velutinal ester conversions arc rather certain, the details of further enzymatic transformations are still hypothetical, and their investigation will require more sophisticated experiments, possibly with isolated enzymes and labelled advanced intermediates. 

Conversion of velutinal esters in the fruit bodies of Russula cuprea, M. Cler-icuzio and O. Sterner, Phytochemistry, 1997, 45, 1569. 

Introduction to Parts 6 and 7 - Velutinal Esters and Related Sesquiterpenes. 85... 

Velutinal esters are the only observable sesquiterpenes occurring in undamaged fruiting bodies, when worked up under carefully controlled conditions (see introductory remarks). If extraction is not carried out properly, they are rapidly degraded and artifacts are formed (vide infra). 

It is worth noting that Lactarius sesquiterpenes derived from velutinal esters (7.28, 7.30) have the same configuration of the related... 

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... 

Lactaranolide derivatives included in Part 12 are produced by silica gel degradation of velutinal esters (7.28, 7.30), methylvelutinal (7.17) or free velutinal itself (for a discussion of these transformations see the chapter on chemical interconversions of Lactarius sesquiterpenes). The compounds upon acidification underwent aromatization to form furanoid derivatives (see Part 18). Under these conditions dehydration reactions took place and also dienes were formed (72). 

Three sesquiterpenes (14.1, 14.2, and 14.3) of this group are considered genuine metabolites of Lactarius and blennin C (14.3) is apparently one of the most frequently isolated. The structure initially assigned to blennin C had the lactone carbonyl at C-13 (50, 99), but was later revised to 14.3 on the basis of chemical and spectroscopic evidence 103). Lactardial (14.2), formally a 1,4-dialdehyde possessing a pungent taste and antimicrobial activity, is formed from velutinal esters (7.28 and 7.30) both through enzymatic and chemical routes (72). 

Having read the review, which described the constituents of Lactarius mushrooms we can realize that the mushrooms possess a very potent biochemical system, which produces a big variety of compounds. Enzymatic system of majority of species is capable of transforming the velutinal esters into a series of biologically active compounds, which can serve a particular species as defense weapons. 

Sterner, O., R. Bergman, E. Kesler, L. Nilsson, J. Oluwadiya, and B. Wick-berg Velutinal Esters of Lactarius vellereus and Lactarius necator. The Preparation of Free Velutinal. Tetrahedron Letters, 24, 1415 (1983). 

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