Synthesis and conformations of α-aminoadipyl- and glycyl-α-aminoadipylthiazepine sulfoxides

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Abstract
The title compounds, having the R-absolute configurations at sulfur, and labelled with 14C at carbons 5, 6, and 7 of the seven-membered ring, have been synthesized by condensation of isotopically labelled 3D-benzhydryloxycarbonyl-6L-amino-2,2-dimethyl-5-oxoperhydro-1,4-thiazepine with N-Boc- and α-benzhydryl-protected L-α-aminoadipic acid and glycyl-L-α-aminoadipic acid, followed by oxidation with m-chloroperoxybenzoic acid and complete deprotection with formic acid. The conformations of the sulfoxides, and related thiazepines and thiazepine sulfoxides, have been examined by 1Hmr spectroscopy. All thiazepines, and the two title sulfoxides, appear to exist in a twist boat conformation. Most other sulfoxides exist in a chair conformation, which is stabilized by an internal hydrogen bond between the sulfinyl oxygen and the amide proton at C6; when this hydrogen bond is not present, both chair and twist boat conformations may be observable. The title compounds are of interest as possible intermediates in penicillin biosynthesis from glycyl-δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine (GACV) or ACV, according to a new theory, which deals, in particular, with the stereochemical course of the biosynthesis at the beta (β) carbon atom of valine.