Isolation of the β-lactam function of penicillins

Abstract

A convenient method for the isolation of the p-lactam function of penicillins has been developed, involving cleavage across the thiazolidine ring.

Mechanism of the pyrolysis of C2HCl5, molecular and radical steps

“…The energetics of the elementary steps involved in the pyrolysis of pentachloroethane (Table 111) support the heterogeneous C-C1 bond breaking (lw) as chain initiation [7,8], confirm the main chain (7), (8) carried by C1 and CzC15 [4-91 accounting for -99% of reaction, suggest the occurrence of a minor propagation step generating C2HC13 and C12 (7'), (4), and support the heterogeneous C1 atom recombination (1lw) as chain termination [7,8] and the heterogeneous Clz dissociation (llw) as reaction autoacceleration [7,8]. The back reactions (-8), (-4) become as fast as the forward ones (8),(4) only after -50% conversion.…”

“…The pyrolysis of pentachloroethane was first studied by Barton in 1949 [4] who identified the main products: CzC14 and HC1. Then Houser and Bernstein [5,6], in a cyclone stirred-flow reactor with helium as carrier, identified C12, found an autoacceleration in the reaction and inhibition by propylene, and recognized, on these bases, the chain character of the reaction.…”

Structure du chiorhydrate de norgalanthamine

“…= +38 °, un quasi-rac+mique par association ~quimol6culaire, auquel ces deux auteurs donnent le nom de narcissamine (Boit & Ehmke, 1956;Fales, Giuffrida & Wildman, 1956;Boit, D6pke & Beitner, 1957). I1 est fi noter, que d6s 1960, Boit et D6pke avaient mis en 6vidence une forme naturelle rac6mique de la galanthamine qui requt le nom de bodamine, et que Barton & Kirby (1962) avaient synth&is~ la (+)-galanthamine.…”

“…Dans notre cas, on peut faire logiquement intervenir une rac6misation au cours de l'extraction, avec rupture de la liaison C(4a)-O(5) et passage par un inter-m6diaire d+sm6thyl~ identique fi celui propos6 par Barton & Kirby (1960, 1962 pour la galanthamine (II), ou bien invoquer une cristallisation privil~gi6e des cristaux de rac6mique par rapport fi celle de leurs 6nantiom+res d6doubl~s. Dans ce dernier cas, il y aurait eu une variation du pouvoir rotatoire de la solution s'enrichissant en Fun des 6nantiom6res, ce que nous n'avons pu contr61er.…”

A rapid and simple one-pot procedure for the synthesis of 3β-acetoxy-5α-hydroxy-6-oxo steroids

“…Barton reported that treatment of steroid sapogenins with CrO 3 in acetic acid yielded the corresponding sapogenoic acid as a result of the oxidative opening of the spirostanic side chain (equation 1). 8 On the other hand, we described that treatment of furostanols with the KMnO 4 /Fe 2 (SO 4 ) 3 cleaved the E-ring to afford 16,22-diones, (equation 2). 9 As a part of our project on the synthesis of bioactive compounds, we have directed our attention to a series of 3β-acetoxy-5α-hydroxy-6-oxo steroids bearing different oxygenated side chains as starting materials in the preparation of potentially bioactive compounds.…”