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Organocatalytic Site-Selective Acylation of Avermectin B2a, a Unique Endectocidal Drug
Takeshi Yamada1, Koh Suzuki, Tomoyasu Hirose
1Kitasato Institute for Life Sciences, Kitasato University.
Abstract:
The organocatalytic site-selective monoacylation of avermectin B2a, an insecticidal and anti-parasitic drug, was accomplished. Although an acetylation of avermectin B2a using a 4-dimethylaminopyridine (DMAP) as a catalyst gave poor site-selectivity, use of our organocatalyst increased site-selectivity of the acylation at the C-5-OH as well as the yield of monoacetate. This catalyst was also effective in other acylations. Interestingly, trihaloacetylation under same conditions gave poor site-selectivity. However, the use of an enantiomer of our organocatalyst provided the C-4″-O-trihaloacetyl avermectin B2a with excellent site-selectivity. These results indicate that the site-selective acylation of avermectin B2a can be controlled by the combination of a suitable organocatalyst and an acid anhydride.
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