engleski

Ring Expansion of Penicillins to Cephalosporins

The ring expansion of penicillin N to deacetoxycephalosporin C and its subsequent hydroxylation to deacetylcephalosporin C are the key steps in the biosynthesis of cephalosporin C. This ring expansion could be beneficial as possible biomimetic process. Our studies concerning chemistry of the penicillanic acid have yielded in the ring expansion of various penam systems in the corresponding cepham and cephem systems, via chemical synthesis. Accordingly, we would like to report the structural evidence for this observed ring interconversion, utilizing the transformation of 3-benzylcarboxy-6,6-dibromopenicillanic acid sulfoxide (penam) into 7,7-dibromo-2-cephem. Crystals of compound 7,7-dibromo-2-cephem (PLR-1274) were obtained by slow evaporation of petroleum ether solution. Crystallographic data were collected using PHILIPS PW1100/Stoe&Cie diffractometer and corrected, in addition to standard Lp-correction, for absorption effects using semi-empirical y-scan method. The crystal structure was solved using direct methods implemented in SHELXS-97 and refined on F2 by SHELXL-97 program. Crystal Data: C7H7Br2NOS, Mr = 313.02, orthorhombic, space group P212121 (No.19), Z = 4, a = 6.1724(12), b = 12.0791(16), c = 13.863(2) A, V = 1033.6(3) A3, Dx = 2.012 gcm-3, F(000) = 600, mu(MoKalpha) = 7.999 mm-1. wRF2 = 0.1148 and S = 1.065 for 110 parameters and 1749 unique reflections, while RF = 0.0548 for 668 observed reflections with I > 2s(I) criterion. Refined Flack parameter x = -0.08(3).

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