D-Threonine (I) was esterified by means of thionyl chloride in methanol, and the resultant amino ester (II) was subsequently acylated with 3,5-dinitrobenzoyl chloride (III) to afford amide (IV). Conversion of (IV) to the acetoacetate ester (VI) was effected by reaction with the diketene precursor 2,2,6-trimethyl-4H-1,3-dioxin-4-one (V) in boiling xylene. Treatment of keto ester (V) with ammonia in the presence of p-toluenesulfonic acid produced the aminocrotonate ester (VI). Dihydropyridine (IXa-b) was then obtained as a diastereomeric mixture by a modified Hantzsh condensation between enamine (VI), 2-trifluoromethylbenzaldehyde (VII) and nitroacetone. After chromatographic separation of the isomers, the chiral auxiliary group was removed by methanolysis in the presence of DBU. The desired (+)-(S)-dihydropyridinecarboxylic acid (X) was finally converted to the nitrooxyethyl ester by reaction with 2-bromoethyl nitrate (XI).

D-Threonine (I) was esterified by means of thionyl chloride in methanol, and the resultant amino ester (II) was subsequently acylated with 3,5-dinitrobenzoyl chloride (III) to afford amide (IV). Conversion of (IV) to the acetoacetate ester (VI) was effected by reaction with the diketene precursor 2,2,6-trimethyl-4H-1,3-dioxin-4-one (V) in boiling xylene. Treatment of keto ester (V) with ammonia in the presence of p-toluenesulfonic acid produced the aminocrotonate ester (VI). Dihydropyridine (IXa-b) was then obtained as a diastereomeric mixture by a modified Hantzsh condensation between enamine (VI), 2-trifluoromethylbenzaldehyde (VII) and nitroacetone. After chromatographic separation of the isomers, the chiral auxiliary group was removed by methanolysis in the presence of DBU. The desired (+)-(S)-dihydropyridinecarboxylic acid (X) was finally converted to the nitrooxyethyl ester by reaction with 2-bromoethyl nitrate (XI).