in hexane under N2; dry hexane; refluxed for 2 h; orange soln. became burgundy red; whitish ppt. sepd.; dissolved in warm CH2Cl2; slow cooling at 0°C; identified as biuret by IR, (1)H NMR, MS; red supernatant liquid was syringed off; TLC showed one band; soln. was concd. and cooled to -20°C; elem. anal.;