Cxo-Brevicomin

Figure 2. Representative chromatograms of the urinary volatiles from dominant (upper) and subordinate (lower) male mice. The peaks marked as 1 and 2 correspond to 3,4-dehydro-cxo-brevicomin and 2-.yec-butyl-4,5-dihy-drothiazole, respectively. Reproduced from Experientia (Novotny, Harvey Jemiolo, 1990) with permission of Birkhauser Verlag Basel, Switzerland.

Fig. 12.1 Aggregation pheromones of (a) Ips paraconfusus, three male-produced synergistic components - (+ )2-methyl-6-methylene-2,7-octadien-4-ol (ipsdienol) (-)2-methyl-6-methylene-7-octen-4-ol (ipsenol) and cw-verbenol. (b) Dendroctonus brevicomisj three attractive components, cxo-7-ethyl-5-methyl-6,8-dioxabicyclo-[3.2.1] octane (cxo-brevicomin) from the female l,5-dimethyl-6,8-dioxabicyclo-[3.2.1] octane (frontalin) from the male and myrcene released from the host tree. Verbenone and trans-verbenol, released after a male locates the female, interrupts response to the attractant blend.

A mixture of epimeric epoxyketals (148 a and 148 b), separable by preparative GC, was obtained by Silverstein et al. (62, 117) upon treatment of the isomeric mixture of (147 a and 147 b) with m-chloroper-benzoic acid (Scheme 28). Acid hydrolysis of (148 a) gave the intermediate ketodiol (149 a), which spontaneously cyclized to racemic cxo-brevicomin (150). Similarly, (148b) afforded racemic entlo-brevicomin (151). Stereoselective syntheses of (147 a) and/or (147 b) have been achieved by Bellas et al. (117), Kocienski and Ostrow (118), and Mori (119) (Schemes 29—31, respectively). Knolle and Schaefer (120) prepared the carbon skeleton (162 a) in one step via Kolbe electrolysis (Scheme 32). 

Wasserman and Barber (123) observed that heating the ketoepoxides (184 a and 184 b) in a sealed tube stereospecifically gave exo- and endo-brevicomin, respectively (Scheme 35). A similar synthesis of the endo-epimer has been reported by Look (124). Acetylenic ketone (157) was prepared by Coke et al. (125) after treatment of chloride (186) with methyl lithium and thermal cleavage of the resultant intermediate (Scheme 36). Catalytic reduction to the E olefinic ketone (162 a) was followed by epoxidation and thermolysis to give exo-brevicomin. Rodin et al. (126) obtained cxo-brevicomin from acid catalyzed cyclization of ketoepoxide (184a). 

The Western pine beetle, D. brevicomis, responds maximally to a ternary mixture of (lR,5S,7R)-(-l-)-cxo-brevicomin, (15, 5R)-(—)-frontalin, and the host-produced alicyclic terpene myrcene (320). Mixtures containing the antipodes of exo-brevicomin and frontalin were much less attractive. 

Successful host colonization depends on recruiting a minimum number of Dendroctonus pon-derosae to attack the tree and overcome its defenses," a process that is completed within 2-3 weeks. As the abundance of colonizing male Dendroctonus ponderosae increases, levels of male-secreted cxo-brevicomin and frontalin increase " " - while concentrations of the aggregation pheromones trans- and cis-verbenol and host monoterpenes decline."" This reduces the attractiveness of the target tree and commences latter stages of tree colonization. The secretion of 2-phenylethanol by males" " and the release of l-octen-3-ol by females may further reduce attraction to the target tree. 

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