Patent ID: 7553812

Claim:
A compound of formula (I): wherein R 1 is H, (C 1- C 4 )alkyl, (C 3- C 6 )cycloalkyl, hydroxy(C 1- C 4 )alkyl, benzoyl(C 1- C 4 )alkyl or phenyl; R 2 is H or hydroxy(C 1- C 4 )alkyl; R 3 is H, (C 1- C 4 )alkyl or hydroxy(C 1- C 4 )alkyl; R 4 is -Q-X-Y-Z (n) -R; each Q is independently S or O; each X, Y and Z is independently Met, Val, Thr, Tyr, Trp, Ser, Ala or Gly; each R is independently H or an amino-protecting group; and n is 0 or 1; or a pharmaceutically acceptable salt thereof.