METHOD OF SYNTHESIS OF (S)-(-)- AND (R)-(+)-ISOMERS OF (5-AMINO-1,2-DIHYDRO-2-METHYL-3-PHENYLPYRIDO-[3,4-B]-PYRAZINE- -7-YL)-CARBAMIDE ACID ETHYL ESTER OR THEIR PHARMACEUTICALLY ACCEPTABLE SALTS AND INTERMEDIATE (S)-(-)- AND (R)-(+)-ISOMERS OF [6-AMINO-4-[[2-(ALKOXYALKYLAMINO)-1-METHYL-2-OXOETHYL]-AMI- -NO]-5-NITRO-2-PYRIDINYL]-CARBAMIDE ACID ETHYL ESTER Russian patent published in 1997 - IPC

FIELD: organic chemistry. SUBSTANCE: products: (S)-(-)- and (R)-(+)-isomers of (5-amino-1,2-dihydro)-2-methyl-3-phenylpyrido-[3,4-b]-pyrazi- -ne-7-yl)-carbamide acid ethyl ester of the formula were synthesized by interaction of 2-amino-3-nitro-4-chloropyridine-6-carbamide acid ethyl ester with (R)- or (S)-2-amino-N-alkoxy-N-alkylpropaneamide of the formula (V) where R and R′ - lower alkyl; product of amination (VI) is interacted with phenol-containing Grignard reagent and (S)- or (R)-[6-amino-4-[(1-(methyl-2-oxo- -2-phenylethyl)amino] -5-nitro-2-pyridinyl]-carbamide acid ester of the formula (IV) is obtained that is subjected for reductive cyclization; and an intermediate product (S)-(-)- and (R)-(+)-isomers of [6-amino-4-[[2-(alkoxyalkyl)-1-methyl-2-oxoethyl] amino] -5-nit- -ro-2-pyridinyl] -carbamide acid of the formula (VI). EFFECT: improved method of synthesis. 6 cl