NOVELTY - (2R)-2-(((Tert-butoxy)carbonyl)amino)-3-(methylcarbamoyl)propanoic acid (II) is activated, to obtain benzyl (2S,5R,6R)-6-(2-((2R)-2-(((tert-butoxy)carbonyl)amino)-N-methylbutanediamido)-2-(4-hydroxyphenyl)acetamido)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo(3.2.0)heptane-2-carboxylate (IV). The obtained product is decarboxylated, and tert-butoxycarbonyl protection group of obtained ((2R)-2-(((tert-butoxy)carbonyl)amino)-N-methylbutanediamido)-2-(4-hydroxyphenyl)acetamido)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo(3.2.0)heptane-2-carboxylic acid (V) is removed, to obtain aspoxicillin (VI).    USE - Synthesis of aspoxicillin (claimed).    ADVANTAGE - The method enables quick and environmentally-friendly synthesis of aspoxicillin with reduced by-products, with nontoxic intermediate products.    DETAILED DESCRIPTION - (2R)-2-Amino-3-(methylcarbamoyl)propanoic acid of formula (I) is reacted with di-tert-butyl dicarbonate under alkaline conditions, to obtain (2R)-2-(((tert-butoxy)carbonyl)amino)-3-(methylcarbamoyl)propanoic acid of formula (II). The obtained product is activated by (1-(bis(dimethylamino)methylene)-1H-1,2,3-triazolo(4,5-b)pyridinium 3-oxid hexafluorophosphate), and then reacted with benzyl (2S,5R,6R)-6-(2-amino-2-(4-hydroxyphenyl)acetamido)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo(3.2.0)heptane-2-carboxylate of formula (III) under alkaline conditions, to obtain benzyl (2S,5R,6R)-6-(2-((2R)-2-(((tert-butoxy)carbonyl)amino)-N-methylbutanediamido)-2-(4-hydroxyphenyl)acetamido)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo(3.2.0)heptane-2-carboxylate of formula (IV). The obtained product is decarboxylated on benzyl protecting group in presence of palladium catalyst, to obtain (2S,5R,6R)-6-(2-((2R)-2-(((tert-butoxy)carbonyl)amino)-N-methylbutanediamido)-2-(4-hydroxyphenyl)acetamido)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo(3.2.0)heptane-2-carboxylic acid of formula (V). Tert-butoxycarbonyl protection group of obtained product is removed in hydrochloric acid/dioxane solvent, to obtain aspoxicillin of formula (VI).