The antimicrobial activity of 6 beta -aminopropio-phenones (I), 4 alpha -phenyl-beta -aminopropiophenones (II), and 2 alpha -phenyl-beta -aminoketones (III) increased with increasing in-stability in aq. solns. at pH 7.35 and 37 Deg. Compds. which did not decomp. under these physiol. conditions also showed no biol. activity. The effect of I and III was due to release of an alpha ,beta -unsatd. ketone, whereas II formed CH2O and alpha ,beta -unsatd. ketones under physiol. conditions
