w, 3-Ethenoguanosine has not been reported as a product of guanosine reaction with haloacetaldehydes. This is in contrast to the reaction of the ribosides yielding the well- known etheno compounds l, N% Ado, 3, iV4-&yd, and 1, IP-tGuo. The base,@, 3- ethenoguanine was, however, synthesized, but not by direct reaction. We now report the synthesis of the nucleoside via reaction of 06-benzylguanosine with bromoacetaldehyde ...