. . . . "???NR12COR13 in which R12 is a hydrogen or a (C1-C7)alkyl and R13 is a (C3-C7)cycloalkyl which is unsubstituted or substituted by one or more methyls; a phenyl; a benzyl; a vinyl; a pyridyl; a furyl; a thienyl; a pyrrolyl; or an imidazolyl; or R12 and R13 together are a group ???(CH2)u??? in which u is three or four;" .