Two Methyl‐Substituted Carbapenem Antibiotic Precursors

Carbapenem antibiotics are characterized by the presence of the 7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid system. These new bicyclic β-lactam antibiotics are rapidly degraded by dehydropeptidase-I. The introduction of a methyl group at the C1 position of the carbapenem skeleton improves the dehydropeptidase stability. The crystal structure determinations of two synthetic methyl-substituted carbapenem precursors, 4-benzyl-6-methoxy-3-propylsulfonyl-2-{2,2,2',2'-tetramethyl-[4,4'-bi([1,3]dioxolanyl)-5-yl]}-1 -azabicyclo[3.2.0]heptane-7-one, C 27 H 39 NO 8 S, and 3-ethylthio-4-(2-furylmethyl)-6-methoxy-2-{2,2,2',2'-tetramethyl-[4,4'-bi([1,3]dioxolanyl)-5-yl]}-1-azabicyclo[3.2.0]heptane-7-one, C 24 H 35 NO 7 S, established their stereochemistry unambiguously. The absolute configuration was deduced from that of the chiral D-glucosamine auxiliary.