Abstract: Alkenyl and alkinylureido cephalosporins of the formula ##STR1## wherein R is hydrogen, lower alkyl, phenyl-lower alkyl, diphenyl-lower alkyl, tri(lower alkyl)silyl, trihaloethyl, a salt forming ion, or the group ##STR2## R.sub.1 is hydrogen or methoxy; R.sub.2 is lower alkenyl or lower alkinyl, R.sub.3 is hydrogen or lower alkyl; R.sub.4 is hydrogen, lower alkyl, cycloalkyl, cycloalkenyl, cycloalkadienyl, phenyl, phenyl-lower alkyl, substituted phenyl, substituted phenyl-lower alkyl, or certain heterocyclic groups; R.sub.5 is hydrogen or lower alkyl; R.sub.6 is lower alkyl; and X is hydrogen, lower alkanoyloxy, ##STR3## or certain heterothio groups; are disclosed. These compounds are useful as antibacterial agents.

Abstract: Leurosine is converted to vincathicine by treatment with acid.