A series of β-lactam derivatives were synthesized and tested to determine the structure- activity relationship for inhibition of human leukocyte elastase (HLE), a serine protease involved in several degenerative lung and tissue diseases. The most potent IC50 values were obtained with neutral hydrophobic 7α-methoxy cephalosporanic acid derivatives. Tryptophanyl-9-fluorenylmethyl ester and N-benzhydryl piperazine derivatives of 7α- ...