A compound of formula: wherein: X is absent and Y is -CHR 3 CH 2 -, -CH 2 CHR 3 -, -CHR 3 CHR 4 CH 2 -, -CH 2 CHR 3 CHR 4 -, -CH 2 CH 2 CHR 3 -, -CR 3 =CHCH 2 -, -CH=CHR 3 CH 2 - or -CH 2 CH=CR 3 -; or X is -CHR 5 and Y is -CHR 3 -, -CHR 3 CHR 4 -, -CHR 3 CR 4 =, -CH 2 CHR 3 -, -CR 3 =CH-or -CH=CR 3 -, wherein when Y is -CHR 3 CR 4 =, R 2b is absent, or X is -CH 2 CHR 5 - or C(=O)CHR 5 - and Y is -CHR 3 -; R 1 is -C(=O)CH(aryl)(aryl), -C(=O)CH(aryl)(cycloalkyl), -C(=O)CH(cycloalkyl)(cycloalkyl), -C(=O)N(aryl)(aryl), -C(=O)N(aryl)(cycloalkyl) or -C(=O)N(cycloalkyl)(cycloalkyl); R 2 is heterocyclyl, heteroaryl, -C 1-4 alkylenearyl, -OC 1-3 alkylenearyl, -OC 2-3 alkenylenearyl, -OC 2-3 alkynylenearyl, -OC 1-3 alkylenecycloalkylaryl, -OarylOaryl, -SC 1-3 alkylenearyl, -SO 2 C 1-3 alkylenearyl, -NHC 1-8 alkyl, -NHC 1-3 alkylenearyl, -NHC 1-3 alkyleneheteroaryl, -NHC 2-3 alkynylenearyl, -N(CH 3)C 1-8 alkyl,-N(CH 3)C 1-3 alkylenearyl,-N(CH 3)C 1-3 alkyleneheteroaryl, -N(CH 3)C 2-3 alkynylenearyl, -CH 2 OC 1-3 alkylenearyl, -N(CH 3)C 1-3 alkylenecycloalkyl or -NHC 1-3 alkylenecycloalkyl; R 2b is hydrogen; R 3 is CO 2 H, -CH 2 CO 2 H, -C(=O)C(=O)OH, -C(=O)NHSO 2 C 1-6 alkyl, -C(=O)NHSO 2 phenyl, -C(=O)NHSO 2 CF 3 -SO 3 H or -PO 3 H 2; R 4 is hydrogen or R 3 and R 4 together form a group: R 5 is hydrogen; and wherein each cycloalkyl, cycloalkenyl, aryl, heterocyclyl and heteroaryl may be optionally substituted with one or more optional substituents selected from the group consisting of C 1-6 alkyl, C 2-6 alkenyl, C 3-6 cycloalkyl, oxo (=O), -OH, -SH, C 1-6 alkylO-, C 2-6 alkenylO, C 3-6 cycloalkylO-, C 1-6 alkylS-, C 2-6 alkenylS-, C 3-6 cycloalkylS-, -CO 2 H, -CO 2 C 1-6 alkyl, -NH 2, -NH(C 1-6 alkyl), -N(C 1-6 alkyl) 2, -NH(phenyl), -N(phenyl) 2, -CN, -NO 2, -halogen, -CF 3, -OCF 3, -SCF 3, -CHF 2, -OCH F 2, -SCHF 2, -phenyl, -heterocyclyl, -heteroaryl, -Oheteroaryl, -Oheterocyclyl, -Ophenyl, -C phenyl, -C C 1-6 alkyl; wherein heterocyclyl is selected from the group consisting of azetidine, tetrahydrofuranyl, tetrahydrothiophenyl, pyrrolidinyl, 2-oxopyrrolidinyl, pyrrolinyl, pyranyl, dioxolanyl, piperidinyl, 2-oxopiperidinyl, pyrazolinyl, imidazolinyl, thiazolinyl, dithiolyl, oxathiolyl, dioxanyl, dioxinyl, dioxazolyl, oxathiozolyl, oxazolonyl, piperazinyl, morpholino, thiomorpholinyl, 3-oxomorpholinyl, dithianyl, trithianyl and oxaziny; or a pharmaceutically acceptable salt thereof. X is absent and Y is -CHR 3 CH 2 -, -CH 2 CHR 3 -, -CHR 3 CHR 4 CH 2 -, -CH 2 CHR 3 CHR 4 -, -CH 2 CH 2 CHR 3 -, -CR 3 =CHCH 2 -, -CH=CHR 3 CH 2 - or -CH 2 CH=CR 3 -; or X is -CHR 5 and Y is -CHR 3 -, -CHR 3 CHR 4 -, -CHR 3 CR 4 =, -CH 2 CHR 3 -, -CR 3 =CH-or -CH=CR 3 -, wherein when Y is -CHR 3 CR 4 =, R 2b is absent, or X is -CH 2 CHR 5 - or C(=O)CHR 5 - and Y is -CHR 3 -; R 1 is -C(=O)CH(aryl)(aryl), -C(=O)CH(aryl)(cycloalkyl), -C(=O)CH(cycloalkyl)(cycloalkyl), -C(=O)N(aryl)(aryl), -C(=O)N(aryl)(cycloalkyl) or -C(=O)N(cycloalkyl)(cycloalkyl); R 2 is heterocyclyl, heteroaryl, -C 1-4 alkylenearyl, -OC 1-3 alkylenearyl, -OC 2-3 alkenylenearyl, -OC 2-3 alkynylenearyl, -OC 1-3 alkylenecycloalkylaryl, -OarylOaryl, -SC 1-3 alkylenearyl, -SO 2 C 1-3 alkylenearyl, -NHC 1-8 alkyl, -NHC 1-3 alkylenearyl, -NHC 1-3 alkyleneheteroaryl, -NHC 2-3 alkynylenearyl, -N(CH 3)C 1-8 alkyl,-N(CH 3)C 1-3 alkylenearyl,-N(CH 3)C 1-3 alkyleneheteroaryl, -N(CH 3)C 2-3 alkynylenearyl, -CH 2 OC 1-3 alkylenearyl, -N(CH 3)C 1-3 alkylenecycloalkyl or -NHC 1-3 alkylenecycloalkyl; R 2b is hydrogen; R 3 is CO 2 H, -CH 2 CO 2 H, -C(=O)C(=O)OH, -C(=O)NHSO 2 C 1-6 alkyl, -C(=O)NHSO 2 phenyl, -C(=O)NHSO 2 CF 3 -SO 3 H or -PO 3 H 2; R 4 is hydrogen or R 3 and R 4 together form a group: R 5 is hydrogen; and wherein each cycloalkyl, cycloalkenyl, aryl, heterocyclyl and heteroaryl may be optionally substituted with one or more optional substituents selected from the group consisting of C 1-6 alkyl, C 2-6 alkenyl, C 3-6 cycloalkyl, oxo (=O), -OH, -SH, C 1-6 alkylO-, C 2-6 alkenylO, C 3-6 cycloalkylO-, C 1-6 alkylS-, C 2-6 alkenylS-, C 3-6 cycloalkylS-, -CO 2 H, -CO 2 C 1-6 alkyl, -NH 2, -NH(C 1-6 alkyl), -N(C 1-6 alkyl) 2, -NH(phenyl), -N(phenyl) 2, -CN, -NO 2, -halogen, -CF 3, -OCF 3, -SCF 3, -CHF 2, -OCH F 2, -SCHF 2, -phenyl, -heterocyclyl, -heteroaryl, -Oheteroaryl, -Oheterocyclyl, -Ophenyl, -C phenyl, -C C 1-6 alkyl; wherein heterocyclyl is selected from the group consisting of azetidine, tetrahydrofuranyl, tetrahydrothiophenyl, pyrrolidinyl, 2-oxopyrrolidinyl, pyrrolinyl, pyranyl, dioxolanyl, piperidinyl, 2-oxopiperidinyl, pyrazolinyl, imidazolinyl, thiazolinyl, dithiolyl, oxathiolyl, dioxanyl, dioxinyl, dioxazolyl, oxathiozolyl, oxazolonyl, piperazinyl, morpholino, thiomorpholinyl, 3-oxomorpholinyl, dithianyl, trithianyl and oxaziny;