Andrena wilkella

11 Preparation of a pure sample for bioassay (3). pheromone of the palaearctic bee, Andrena wilkella 

The hydroxy ester (S)-B (92% ee) was converted to iodide (S)-C (4 steps). Inversion of the configuration of (S)-B to (-R)-D was possible by means of Mitsunobu inversion, which was further converted to (R)-C. Accordingly, both the enantiomers of C were prepared from the single enantiomer (S)-B. Alkylation of the dianion of methyl acetoacetate with (S)-C gave E, whose further alkylation with (S)-C afforded F. Successive treatments of F with base followed by acid effected hydrolysis, decarboxylation and acetaliza-tion to give (2S,6R,8S)-88 as a volatile oil. Similarly, (R)-C afforded (2R,6S,8R)-88. Both 88 and 88 were purified by chromatography and distillation, and they showed [a]o23 -51.6 (pentane) and +51.7 (pentane), respectively. 

In 1984 Isaksson et al. in Sweden separated the enantiomers 88 and 88 by chromatography over a triacetylcellulose column. Their 88 and 88 were of 98% ee, and showed [a]o24 -44.3 0.7 (pentane) and +44.6 0.7 (pentane), respectively. They questioned the higher rotation values of our 88 and 88, since we employed ethyl (S)-3-hydroxybutanoate of only 92% ee as our starting material. They said The reason for this is not clear to us. 66 Apparently, they thought that our starting material with 92% ee should have generated 88 and 88 of 92% ee. 

When the synthesis was repeated by starting from (S)-A of 85% ee, the resulting (2.S ,6R,8.S )-88 exhibited the rotation value of —56.0 (pentane). Simple comparison of these two values indicated that the enantiomeric purity of the resulting 88 was (56.0/57.6) x 100 = 97.2% ee, which was definitely larger than that (85% ee) of the starting (S)-A. 

Isaksson et al. reported the specific rotation of (2R,6.S ,8R)-88 as [a]o24 +44.6 (pentane), while our pure (2R,6S,8R)-88 showed [a]D21 +57.6 (pentane). Isaksson s value was too small. The reason for this was not clear to me. Perhaps they did not purify their samples by final distillation. Without distillation an oily sample can be contaminated with the solvents, which lower the [a]o value of the sample. 

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Male palaearctic bees (Andrena wilkella) in Sweden produce 2,8-dimethyl-l,7-dioxaspiro[5.5]undecane (88, Figure 4.34) as their pheromone. Its (25, 6R,83 )-isomer is pheromonally active, while the opposite enantiomer (2R,6S,8R)-88 is inactive.63 There are six stereoisomers of 2,8-dimethyl-1,7-dioxaspiro[5.5]undecane (88), three as shown in Figure 4.34 and their opposite enantiomers. Due to the oxygen-anomeric effect, (2S,6R,8S)-88 and its opposite enantiomer are the stable isomers. 

Figure 4.34 Pheromone of Andrena wilkella and its stereoisomers. Reprinted with permission of Shokabo Publishing Co., Ltd...

The conformation of 17-cp/-deoxysalinomycin (a close relative of the antibiotic) has a definite form in solution but it cannot exist as a head-to-tail hydrogen-bonded structure. The relevance of these deductions to its biological role has been discussed. One of the constituents of the secretion of the bee Andrena wilkella is the bis-spiropyran (7), and this has been synthesized from ethyl (+)-(5 )-3-hydroxybutenoate, obtained from the reduction of ethyl acetoacetate by yeast. ... 

Nitro compounds are also able to be reduced by stannanes under free-radical conditions. For example, Kitayama described the reduction of the nitro moiety in 74 by the action of BubSuH during his preparation of pheromones for Bactrocera Nigrotibialis, Andrem Wilkella and Andrena Haemorrhoa (equation 47). Petrini and coworkers reported the selective reduction of the nitro group in a series of ft), ft)-dichloro-ft)-alkanoates (75) it is interesting to note that the chlorine atoms remain intact during the reaction with Bu3SnH (equation 48). Witczak and coworkers described the reduction of substrate (76)... 

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