To a solution of 0.18 ml. of aniline in 8 ml. of N HCl, cooled to 0°-5°C. in an ice bath was slowly added 150 mg. of NaNO2 in water chilled to the same temperature. To the above solution was added a cold methanolic solution of 550 mg. of crystalline antibiotic X-537A. The reaction mixture was kept at 3° to 5° for 15 minutes and then allowed to slowly reach room temperature. At the end of 2 hours, the reaction mixture was diluted with water and extracted with ethyl acetate. The solvent extract was washed with a saturated solution of Na2CO3, dried over NaSO4 and concentrated to a solid. The solid was chromatographed on a 30 g. silica gel (Grade 62) column eluting with a gradient between 300 ml. methylene chloride and 500 ml. ether. The product was eluted in the first peak and crystallized from methylene chloride/hexane, m.p. 212°-215°, [α] D25 -27.30° (0.586%, CH3OH).
