Efficient Total Synthesis of 12-oxo-PDA and OPC-8:0

Although the supply of 12-oxo-PDA (1) and OPC-8:0 (2), the metabolites in the linolenic acid cascade leading to epi-jasmonic acid, is in demand for biological investigations, the previous syntheses of these metabolites suffer from low efficiency. Recently, we established a reaction to install an alkyl group onto the ring of cyclopentene monoacetate 4 by using a reagent system consisting of RMgCl (3 equiv) and CuCN (cat). The reaction was applied to ClMg(CH2)8OTBDPS (11) with modification by which the quantity of 11 could be reduced to 2 equiv without decreasing efficiency. The product 12 obtained in 88% yield with 92% regioselectivity was successfully transformed into the key iodo-lactone 17 in good yield, from which 12-oxo-PDA (1) and OPC-8:0 (2) were synthesized as described in Schemes 3 and 5 through construction of the cis side chain by Wittig reaction. Note that the Wittig reaction proceeded with high cis selectivity of >95%, which is higher than in similar cases reported previously. Synthesis of the 13-isomers of 1 and 2 was also accomplished. With these compounds in hand, the epimerization speed of 1 and 2 was investigated to rule out overestimation of the finding in the literature that 1 and 2 change to the 13-epimers easily. Instead, we observed that the compounds are quite stable at room temperature for an extended period of days under slightly acidic and neutral conditions.