Synthesis and antimicrobial activities of some new tetrahydro-2H-1,3,5-thiadiazine-2-thione derivatives of amoxicillin.

A number of 6-[2-(dihydro-5-substituted-6-thioxo-2H-1,3,5-thiadiazine-3( 4H)-yl)-2-(4-hydroxyphenyl)acetamido]penicillanic acids has been synthesized as prodrugs by incorporating the amine group of amoxicillin trihydrate into tetrahydro-2H-1,3,5-thiadiazine-2-thione ring. The compounds have been prepared by the reaction of various alkyl or aralkyl amines with potassium hydroxide, carbon disulfide, formaldehyde and amoxicillin trihydrate. The structures of the compounds have been elucidated by UV, IR, 1H-NMR spectra and elementary analysis. The in vitro activity of these compounds against gram-positive bacteria (Staphylococcus aureus, Streptococcus faecalis), gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and yeast-like fungi (Candida albicans, C. parapsilosis, C. stellatoidea, C. pseudotropicalis) was investigated by the tube dilution method and compared with the activity of amoxicillin trihydrate. By this way their minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and minimal fungicidal concentration (MFC) values were determined. Compound I and Compound VII were significantly more effective than amoxicillin trihydrate against S. aureus (MBC: 6.25 micrograms/ml). Compound VI and Compound XI were effective against S. faecalis (MBC: 6.25 micrograms/ml) and Compound I and Compound VI were effective against E. coli (MBC: 12.5 micrograms/ml). All of the compounds and amoxicillin trihydrate were ineffective against P. aeruginosa (MIC: greater than 100 micrograms/ml). Compound IX and Compound X were the most active derivatives against yeast-like fungi; the MFC values for these compounds ranged between 6.25 and 37.5 micrograms/ml.