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Diphenylmethyl (6R,7S)-7-amino-7-methoxy-3-{[(1-methyl-1H-tetrazol-5-yl)thio]methyl}-Δ3-cephem-4-carboxylate (9) is obtained from a cephamycin C derivative by treatment of an imino chloride intermediate with o-aminobenzenethiol.

The o-nitrobenzeneselenenamides were oxidized with active manganese dioxide to give the irnines, which were converted to the 7α-methoxycephalosporins 3 by the reaction with lithium methoxide. The selenenamides 3 were acylated with phenoxyacetyl chloride to afford the desired cephamycin derivatives 4 via tertiary amide 5, which was not isolable. This methoxylation reaction was also carried out in penicillin series to give the desired 6α-methoxypenicillin 8 although the ring opening compound 9 was a major product. The difference between sulfenamides and selenenamides in their acylation reactions was discussed.

The sulfinamides 3 were transformed to sulfenimines 4 by treatment with thionyl chloride and a weak base such as quinoline (or triethylamine). The sulfenimines 4 were methoxylated with lithium methoxide to give 7α-methoxysulfenamides 5, which were directly acylated with an acyl chloride to furnish cephamycin derivatives 6. There was a major difference between the acylation of 7α-methoxysulfenamides 5 and that of the 7α-H derivatives 7. Reduction of the imines 4a with metal hydrides gave 7β-sulfenaminocephalosporins 12 together with a small amount of the 7α-isomers 13. The synthetic sequence 4a→12→14 provides a useful method for the isomerization of 7α-aminocephalosporins 17 to the corresponding 7β-isomers 18.

The C-3 side chain moiety of C-2801X, a new cephamycin-type antibiotic, was almost quantitatively obtained by Dowex 50-catalyzed hydrolysis, and its structure was established as 3,4-dihydroxy-α-methoxycinnamic acid (I) by spectroscopic analyses and synthesis. The full structure of C-2801X was also assumed to be XIII by NMR analysis.

Die Isothiazole (I) lagern sich in Gegenwart von wasrigem Natriumbicarbonat oder Triethylamin in die Dithietane (II) um und konnen aus diesen durch Behandlung mit einer starken Base wieder erhalten werden.