Enantiomerically pure dihydropyrimidones (DHPMs) were prepared by lipase-catalyzed enzymatic resolution of two types of activated DHPM esters. In the first model series, pivaloyloxymethyl-activated DHPM C5-esters 10a-c were resolved on an analytical scale by various lipases in two different solvent systems with selectivities E < 50. Alternatively, attachment of an acetoxymethyl residue at the N3 position of the DHPM scaffold led to activated ester 15, which was selectively cleaved by Thermomyces lanuginosus lipase (E > 200) to furnish, after deprotection, DHPMs (R)-and (S)-13 on a semi-preparative scale. Treatment of (R)-13 with trichloroacetyl isocyanate produced the antihypertensive agent (R)-SQ 32926.
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