Scheme 1. Mechanism of cyclisation vs. transfer in the cyanate- or cyanogen-mediated activation of 2 and 1H NMR spectra of the mixtures. (a) 1H NMR spectrum after 20 h following incubation of 2 (50 mM), CuCl2 (25 mM) and cyanate 7 (100 mM) at pH 4, 40 °C, showing the formation of 3 and 9a; (b) 1H NMR spectrum after 1 h following incubation of 2 (12.5 mM), Gly (50 mM) CuCl2 (25 mM) and cyanogen 8 (100 mM) at pH 5.5, RT, showing the formation of 3 and 9b; (c) as (b) but without CuCl2. N.B. conditions are different to Table 1.
