(6) The N-acylamino acid (2.5 mmol) was added to a mixture of 1 mL of fuming 90% nitric acid (sp gr 1.5)(commercial sample used without purification) and 3 mL of acetic anhydride at-20 OC. The solution obtained after-10 min was warmed to 0 OC for-5 min and then worked up with ice and methylene chloride. 2a: 51%(from ether), mp 87-88 OC; IR (KBr) 3068, 1825. 1766. 1555. 1443 cm-l: WMH z'H NMR ICDCI,) 6 4.92 lo. J= 7.0