Novel elastase inhibitors

The present invention provides novel compounds of formula (I), hydrates, optical isomers and pharmaceutically acceptable salts thereof, wherein P3 is Ala, bAla, Leu, Ile, Val, Nva, Nlev or bVal; P2 is Pip, Aze, Pro (4-OH), Pro (4-OAc) or Pro (4-OBzl); R1 is the side chain of Ala, Leu, Ile, Val, Nva or bVal; and K is a group of the formula (f) wherein Z is a meanthene and B is a group of formula (j). The compounds of the invention are elastase inhibitors, particularly neutrophil elastase inhibitors and useful in medicine. ŕ