Gas Chromatography of Penicillin and Penicillanic Acid Esters

Abstract

WHILE preparing and investigating the properties of penicillanic acid (IVa) and its derivatives, we have found that it is possible to separate esters of penicillins and of penicillanic acids by gas chromatography. 6-Chloro-(IIa) and 6-bromo-penicillanic acid (IIa) were prepared by diazotization of 6-aminopenicillanic acid¹ (III) in dilute hydrochloric or hydrobromic acid². The dibenzylethylene-diamine salts, which were used for the isolation of these acids, were transformed into their potassium salts. By hydrogenolysis, in the presence of 10 per cent Pd/C, of the potassium salt of IIa, only partial hydrogenolysis of Ia was observed; in 1 M phosphate buffer at pH 7.6 or in water at a constant pH_ of 8 (a constant pH. was maintained by the addition of 0.5 N sodium hydroxide by means of pH. stat), penicillanic acid (IVa) was obtained in 80 per cent yield. The physical constants of the potassium salt of IVa were: [α]²⁰_D + 344 (about 1.0 in water); infra-red bands (potassium bromide disk) at 1,780 (β-lactam) and 1,610 cm.⁻¹ (COO−), and of the cyclohexyl-amine salt: m.p. 161° (dec.); [α]²⁰_D + 217 (about 1.0 in water) (all substances reported in this communication gave satisfactory carbon, hydrogen, nitrogen, sulphur and halogen analyses, where appropriate). Penicillanic acid is the basic nucleus of all penicillins³. However, just as with the 6-amino and 6-halogen-substituted derivatives, it is devoid of significant antibacterial activity.