Abstract:The syntheses of some new sugar-based monocyclic β-lactams possessing several other functionalities in addition to the carbohydrate moiety are described. The key step was the Staudinger [2+2] cycloaddition of chiral carbohydrate Schiff base 5 with phthalimidoacetyl chloride to yield the sugar-based monocyclic β-lactam 6 as a single isomer. Treatment of protected β-lactams 6 and 8 with methylhydrazine afforded the free amino β-lactams 9 and 10. Acylation of these free amino β-lactams with benzoyl, phenoxyacetyl, cinnamoyl and phenylacetyl chloride in the presence of pyridine afforded β-lactams 11a-d and 12a-d. Some of these novel β-lactams were found to be active against Staphilococcus citrus, Klebsiella pneumoniae, Escherichia coli and Bacillus subtilis.
Abstract:Reaction of the amino acid D-phenylalanine ethyl ester (4) with cinnamaldehyde gave chiral Schiff base 5, which underwent an asymmetric Staudinger [2+2] cycloaddition reaction with phthalimidoacetyl chloride to give the monocyclic β-lactam 6 as a single stereoisomer. Ozonolysis of 6 followed by reduction with lithium aluminum tri(tert-butoxy) hydride afforded the hydroxymethyl β-lactam 8. Treatment of 8 with methansulfonyl chloride gave the mesylated monocyclic β-lactam 9, which was converted to the bicyclic β-lactam 10 upon treatment with 1,8-diazabicyclo[5,4.0] undec-7-ene (DBU). Deprotection of the phthalimido group in β-lactams 6 and 10 by methylhydrazine and subsequent acylation of the free amino β-lactams with different acyl chlorides in the presence of pyridine afforded mono and bicyclic β-lactams 14a-d and 15a-d respectively. The compounds prepared were tested against Escherichia coli, Staphilococcus citrus, Klebsiella pneumanie and Bacillus subtillis. Some of these compounds showed potential antimicrobial activities.
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