To a cold solution (~3°) of 6.12 g. of the sodium salt of antibiotic X-537A in 50 ml. of chloroform/3 ml. of carbon tetrachloride was slowly added 34 ml. of carbon tetrachloride saturated with 10 millimoles of chlorine gas. The reaction was continued for 1/2 hour after which the solution was filtered and the filtrate treated with a saturated aqueous solution of Na2CO3. The solvent layer was dried over Na2SO4 and concentrated to a small volume from which after addition of hexane the crystalline product was recovered. The crystalline material which had a tendency to incorporate the solvent of crystallization was twice recrystallized from methylene chloride/ether and acetone/hexane, m.p. 183°-185°, [α]D25 -44.31° (C, 0.99%, CHCl3).
