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Cleavage of 7α-methoxycephalosporin c derivatives with phosphorus pentachloride

✍ Scribed by W.H.W. Lunn; R.W. Burchfield; T.K. Elzey; E.V. Mason

Book ID
104234804
Publisher
Elsevier Science
Year
1974
Tongue
French
Weight
181 KB
Volume
15
Category
Article
ISSN
0040-4039

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✦ Synopsis

Reports of naturally occurring 7a-methoxycephalosporin compounds (1) and a procedure for converting them to other 7a-methoxy-76-amidocephalosporanic acids (2) have recently appeared in the literature.

There are many instances of phosphorus pentachloride being used to convert 76-amidocephalosporins and Cfl-amidopenicillins to their imidoyl chlorides, and then cleaving these to the corresponding amines (3). In some unpublished work at these laboratories this sequence was applied to 7a-methoxycephalosporins and, while paper chromatography indicated cleavage, the low yields made isolation of products extremely difficult.

We outline below studies of the phosphorus pentachloride cleavage which have led to a ready procedure for replacing the aminoadipoyl side chain of 7amethoxycephalosporin C derivatives with other acyl functions. Appropriate conditions were determined by carrying out the reactions in nmr tubes and following their course by nmr spectroscopy.

Using N-phthaloyl cephalosporin C esters as models, we found we could follow imidoyl chloride formation (occurring on treatment with phosphorus pentachloride and pyridine in methylene chloride) by observing the characteristic downfield shift of the signal for the methylene group, -CH2CONH-, of the adipoyl side chain. This signal appears as part of a broad 4-proton resonance centered at about 6 2.35 in the amides and as a 2-proton triplet, at 6 2.74 Q+7 cps), in the imidoyl chloride spectra.

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