Protoilludane

The epoxyketone 3 is a versatile precursor for a variety of tricycloundecane systems having a p,y-unsaturated carbonyl chromophore, which are not so readily accessible. The contiguous epoxy ketone functionality and the double bond present in the five-membered ring provide opportunities for further manipulation. Adduct 3 may be transformed into a variety of molecular frameworks such as linearly fused cis anti cis tricyclopentanoids, protoilludanes, and marasmanes in a stereoselective fashion after suitable chemical and photochemical manipulation.13... 

Scheme 23. A schematic representation of the postulated involvement of a protoilludane intermediate (213) in the biosynthesis of various sesquiterpenoid...

Intramolecular [2 + 2 + 2] cycloadditions belong to the same type of valence isomerization as those of 1,5-unsaturated compounds to cyclobutanes.70 The cobalt-mediated cyclization of l-en-5-ynes stereoselectively converts enediynes directly to bicyclo[4.2.0]hexa-l,3-dienes, as single diastereomers, when a stoichiometric amount of dicarbonyl(cyclopentadienyl)cobalt is used. This cyclization90 has a high efficiency (92%). An example is the synthesis of the protoilludane framework 23 from the enediyne precursor 22.71... 

Singh, V. and Porinchu, M. (1996) Sigmatropic 1,2- and 1,3-acyl shifts in excited states a novel, general protocol for the synthesis of tricyclopentanoids and protoilludanes. Tetrahedron, 52, 7087-7126. 

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... 

Photochemical transformations of bicyclo[2.2.2]octenones derived from Diels-Alder reaction of spiroepoxycyclohexa-2,4-dienones 116 have been exploited by Singh s group in their synthetic studies towards triquinane 119 and oxa-triquinane 121, protoilludane 120, and oxa-sterpurane 122 frameworks (Figure 30) [120, 154]. Spiroepoxycyclohexa-2,4-... 

An expeditious stereospecific synthesis of the protoilludane skeleton has been actively pursued by Matsumoto s group. In his first approach (Scheme 42),307 bicyclooctanone 274 was smoothly elaborated in classical fashion. Using a five-step sequence to effect a 1,2-carbonyl transposition with retention of a hydroxyl group at the original carbonyl site, these workers then prepared 275. Oxidation of this intermediate followed by end acetylation afforded 276. When this enone was irradiated... 

Caryophyllane, Humulane, Africane, Illudalane, Protoilludane, Hirsutane, Vellerane, Pentalane, Senoxydane... 

A number of compounds with the protoilludane skeleton have been synthesized (Scheme 40). The two keto-esters (279) and (280) have been converted by standard methods into a variety of tricyclic analogues. In addition, the bicyclic enone (281), obtained from 4,4-dimethylcyclopentene and acetyl-acetone by a similar procedure, has been converted into protoillud-7-ene (282) (Scheme 41). A long and rather low-yield synthesis of (283), a possible precursor of illudinine (284), has been reported. ... 

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). 

Humulane, Caryophyllane, Protoilludane, Illudane, Marasmane, Hirsutane... 

The proposed intermediacy of humulene (218) in the biosynthesis of sesquiterpenoids belonging to various structural groups (caryophyllane, protoilludane, etc.)... 

A protoilludane intermediate (225) (c/. Vol. 4, p. 113) has been implicated in the biosynthesis of protoilludane, illudane, illudalane, and marasmane sesquiterpenoids... 

The fungus Fames annosus is the cause of another serious root decay of trees, particularly conifers. The phytotoxic metabolite, fomannosin (5.81) also arises by cleavage of a protoilludane, this time of the six-membered ring. The cleavage is followed by a lactonization. Labelling studies with [l,2- C2]acetate have confirmed this biosynthetic route. 

The silver-leaf disease of fruit trees is caused by the fungus Stereum pur-pureum. The phytotoxic metabolites such as sterpuric acid (5.82) possess the sterpurane skeleton which may also be derived from a protoilludane by a series of rearrangements. 

The hirsutane carbon skeleton, which is found in some other antibiotics produced by the Basidiomycetes, is also formed by a sequence of Wagner-Meerwein rearrangements of a protoilludane carbocation via 5.58. Hirsutic acid... 

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