Patent ID: 8809529

Claim:
A compound of formula (Ia) or formula (Ib): wherein R 2 is selected from the group consisting of or C 2-5 straight chain alkyl; R 6 is selected from the group consisting of —H, —OH, —NH 2 , —OC(O)R or —OCH 2 OC(O)R; R 8 is selected from the group consisting of —CH 2 C 6 H 5 , H or lower cycloalkyl; W is —NH 2 , halo, —OH, —NHC(O)R, —CO 2 R; X is —S—, —O— or —NR 22 —; Y is —H, —OH, or —OR 11 ; Z is —CH— or —N—; each R 11 is independently —C(O)R″ or —CH 2 OC(O)R″; R 22 is H; each R is independently C 1-7 straight-chain alkyl or C 3-7 branched alkyl; R″ is C 1-7 straight-chain alkyl or C 3-7 branched alkyl; with the proviso that when R 2 is or R 8 is not —CH 2 C 6 H 5 ; with the proviso that when R 2 is —CH 2 C 6 H 5 , R 8 is lower cycloalkyl; and with the proviso that when R 6 is NH 2 , R 2 is, or C 2-5 straight chain alkyl; or R 8 is not —CH 2 C 6 H 5 .