(3-amino-1,2,3,4-tetrahydro-9

1. A compound of Formula I:

wherein

R 1 , R 2 , R 3 and R 4 are independently hydrogen, C 1-5 -alkyl, C 1-5 -alkoxy, alkenyl, halogen, nitro, cyano, halo-C 1-6 -alkoxy, halo-C 1-6 -alkyl, C 1-6 -alkylsulfonyl, or formyl;

R 5 is a hydrogen, alkenyl, C 1-6 -alkyl, cycloalkyl-C 1-4 -alkyl, C 1-3 -alkoxy-C 1-4 -alkyl, aryl-C 1-4 -alkyl, or aryloxy-C 1-4 -alkyl; wherein the aryl is unsubstituted, mono- or di-substituted by C 1-2 -alkylendioxy, C 1-4 -alkoxy, C 1-4 -alkyl, halogen, trifluoromethyl, or trifluoromethoxy; and

R 6 is a C 1-9 -alkylaminocarbonyl; C 1-9 -alkylaminothiocarbonyl; C 1-9 -alkylcarbonyl; C 1-9 -alkoxycarbonyl; arylalkenylcarbonyl; arylaminocarbonyl; arylaminothiocarbonyl; aryl-C 1-3 -alkoxy-C 1-3 -alkoxycarbonyl; aryl-C 1-3 -alkoxycarbonyl; aryl-C 1-3 -alkylaminocarbonyl; aryl-C 1-6 -alkylcarbonyl; aryl-C 1-3 -alkoxy-C 1-3 -alkylcarbonyl; arylcarbonyl; arylcarbonyl-C 1-4 -alkylcarbonyl; aryloxy-C 1-3 -alkylcarbonyl; arylsulfonylaminocarbonyl; cycloalkyl-C 1-3 -alkylcarbonyl; diaryl-C 1-3 -alkylcarbonyl; heterocyclylcarbonyl; heteroaryl-C 1-3 -alkylcarbonyl; heteroarylcarbonyl; aryl-C 3-6 -cycloalkylcarbonyl; cycloalkylcarbonyl; or R 7 —C 1-4 -alkylcarbonyl wherein the bridging C 1-4 -alkyl group of the R 7 —C 1-4 -alkylcarbonyl may additionally be mono-substituted with an aryl or disubstituted with a hydroxy, and wherein R 7 is an arylaminocarbonyl, heteroarylaminocarbonyl, C 1-6 -alkylaminocarbonyl, or aryl-C 1-3 -alkylaminocarbonyl;

further wherein the aryl is unsubstituted, mono- or di-substituted with a C 1-2 -alkylendioxy; C 1-6 -alkoxy; C 1-6 -alkyl; C 1-6 -alkylsulfonyl; phenyl which is unsubstituted, mono- or di-substituted by a halogen, trifluoromethyl, methoxy or methyl; naphthyl; phenyl-C 1-3 -alkyl, wherein the phenyl group is unsubstituted, mono- or di-substituted independently with a halogen, trifluoromethyl, methoxy or methyl; naphthyl-C 1-3 -alkyl; phenoxy, wherein the phenyl group is unsubstituted, mono- or di-substituted independently with a halogen, trifluoromethyl, methoxy or methyl; naphthyloxy; halogen; hydroxy; halo-C 1-6 -alkyl; halo-C 1-6 -alkoxy; C 1-6 -alkylthio; or C 1-4 -alkoxycarbonylamino;

or a salt thereof.

2. The compound according to claim 1 , wherein R 1 , R 3 and R 4 are hydrogen; or a salt thereof.

3. The compound according to claim 1 , wherein R 2 is a hydrogen, trifluoromethyl, or halogen;

or a salt thereof.

4. The compound according to claim 1 , wherein R 5 is a hydrogen; C 1-3 -alkyl; cyclopropylmethyl; 2-methoxyethyl; phenyl-C 2-3 -alkyl; or phenoxyethyl,

wherein the phenyl group is unsubstituted or mono-substituted with C 1-2 -alkylendioxy, C 1-4 -alkoxy, C 1-4 -alkyl, halogen, trifluoromethyl, or trifluoromethoxy;

or a salt thereof.

5. The compound according to claim 1 , wherein R 6 is a C 1-9 -alkylaminocarbonyl; C 1-9 -alkylcarbonyl; C 1-9 -alkoxycarbonyl; arylalkenylcarbonyl; arylaminocarbonyl; aryl-C 1-3 -alkoxy-C 1-3 -alkoxycarbonyl; aryl-C 1-3 -alkoxycarbonyl; aryl-C 1-3 -alkylaminocarbonyl; aryl-C 1-6 -alkylcarbonyl; aryl-C 1-3 -alkoxy-C 1-3 -alkylcarbonyl; arylcarbonyl; arylcarbonyl-C 1-4 -alkylcarbonyl; aryloxy-C 1-3 -alkylcarbonyl; arylsulfonylaminocarbonyl; cycloalkyl-C 1-3 -alkylcarbonyl; diaryl-C 1-3 -alkylcarbonyl; heterocyclylcarbonyl; heteroaryl-C 1-3 -alkylcarbonyl; heteroarylcarbonyl; aryl-C 3-6 -cycloalkylcarbonyl; cycloalkylcarbonyl; or R 7 —C 1-4 -alkylcarbonyl, wherein the bridging C 1-4 -alkyl group of the R 7 —C 1-4 -alkylcarbonyl may additionally be mono-substituted with aryl, and R 7 is an arylaminocarbonyl, heteroarylaminocarbonyl, C 1-6 -alkylaminocarbonyl, or aryl-C 1-3 -alkylaminocarbonyl;

further wherein the aryl is unsubstituted, mono- or di-substituted independently with a C 1-2 -alkylendioxy, C 1-6 -alkoxy, C 1-6 -alkyl, C 1-6 -alkylsulfonyl, halogen, hydroxy, halo-C 1-6 -alkyl, halo-C 1-5 -alkoxy, C 1-6 -alkylthio, or C 1-4 -alkoxycarbonylamino;

or a salt thereof.

6. The compound according to claim 1 , wherein R 6 is an aryl-C 1-2 -alkoxycarbonyl; aryl-C 1-2 -alkylaminocarbonyl; aryl-C 1-4 -alkylcarbonyl; aryloxy-C 1-2 -alkylcarbonyl; diaryl-C 2-3 -alkylcarbonyl; or R 7 —C 2-4 -alkylcarbonyl, wherein the bridging C 2-4 -alkyl group may additionally be mono-substituted with aryl, and R 7 is an arylaminocarbonyl or C 1-4 -alkylaminocarbonyl;

further wherein the aryl is unsubstituted, mono- or di-substituted independently with a C 1-2 -alkylendioxy, C 1-6 -alkoxy, C 1-6 -alkyl, C 1-6 -alkylsulfonyl, halogen, hydroxy, trifluoromethyl, or trifluoromethoxy;

or a salt thereof.

7. The compound according to claim 1 , wherein,

if R 6 is a group comprising a carbonyl group and one or more aryl moieties,

then R 6 comprises a bridging group between said carbonyl group and said one or more aryl moieties, further wherein said carbonyl moiety and at least one of said one or more aryl moieties are directly attached to different atoms of said bridging group;

or a salt thereof.

8. The compound according to claim 1 , wherein

R 6 is a C 1-4 -alkylcarbonyl or aryl-C 2-4 -alkylcarbonyl, wherein the aryl is unsubstituted, mono- or di-substituted independently with a C 1-4 -alkoxy, C 1-4 -alkyl, halogen, or trifluoromethyl; and

R 5 is a phenyl-C 2-3 -alkyl;

or a salt thereof.

9. The compound according to claim 1 , wherein the compound is

(3S)-[3-(3,3-diphenyl-propionylamino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{3-[2-(3-chloro-phenoxy)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[6-fluoro-3-(3-phenyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{3-[2-(4-chloro-phenoxy)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(2-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-(3-isobutoxycarbonylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-[6-fluoro-3-(3-phenyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{3-[3-(4-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-(3-benzyloxycarbonylamino-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-benzyloxycarbonylamino-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{3-[2-(4-chloro-phenoxy)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{3-[2-(2-chloro-phenoxy)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(3-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[6-fluoro-3-(4-oxo-4-phenyl-butyrylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[6-fluoro-3-(2-indan-2-yl-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{3-[(2,3-dihydro-1H-indole-2-carbonyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(3-{[2-(4-chloro-phenyl)-acetyl]-ethyl-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-(3-propoxycarbonylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-[6-fluoro-3-(2-p-tolyloxy-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-fluoro-3-[methyl-(3-phenyl-propionyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[6-fluoro-3-(3-1H-indol-3-yl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(3-benzo[1,3]dioxol-5-yl-propionylamino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-fluoro-3-[ethyl-(3-phenyl-propionyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[2-(4-chloro-phenyl)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(2,3-diphenyl-propionylamino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-[6-fluoro-3-(2-phenoxy-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{3-[3-(3,4-difluoro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(3-phenyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-[3-(2-benzyloxy-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-fluoro-3-[3-(2-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-fluoro-3-[propyl-(3-phenyl-propionyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(2-benzyloxy-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-(3-benzyloxycarbonylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-{6-fluoro-3-[2-(4-methoxy-phenyl)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{3-[3-(4-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[4-(4-bromo-phenyl)-4-oxo-butyrylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(3-{[2-(4-chloro-phenyl)-acetyl]-propyl-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-(3-phenyl acetylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-{3-[3-(2-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-fluoro-3-[2-(4-trifluoromethyl-phenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-(6-fluoro-3-phenylacetylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{6-fluoro-3-[3-(2-hydroxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(3-1H-benzoimidazol-2-yl-propionylamino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-fluoro-3-[3-(4-hydroxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[6-fluoro-3-(2-p-tolyloxy-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-[6-fluoro-3-(2-p-tolyl-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{3-[3-(3-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-[3-(2-phenoxy-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[6-fluoro-3-(3-p-tolyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-(3-benzyloxycarbonylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-[6-fluoro-3-(2-p-tolyl-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(3-phenethyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-fluoro-3-[3-(3-hydroxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-[3-(2-benzyloxy-ethoxycarbonylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[6-fluoro-3-(3-naphthalen-2-yl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-fluoro-3-[4-(4-methanesulfonyl-phenyl)-4-oxo-butyrylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(3-{[2-(4-chloro-phenyl)-acetyl]-methyl-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-[3-(3-phenylsulfonyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-fluoro-3-[3-(4-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-[3-(3-phenyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{3-[2-(4-chloro-phenyl)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-[6-fluoro-3-(3-p-tolyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{6-fluoro-3-[3-(4-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-fluoro-3-[3-(4-hydroxy-3-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-fluoro-3-[2-(3-trifluoromethyl-phenyl)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-fluoro-3-[2-(4-methoxy-phenyl)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{3-[2-(3-chloro-phenyl)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-fluoro-3-[2-(4-trifluoromethyl-phenyl)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-(3-tert-butoxycarbonylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-{3-[2-(3,4-dichloro-phenyl)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(3-isobutoxycarbonylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{6-fluoro-3-[3-(3-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[6-fluoro-3-(2-phenoxy-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{3-(3-phenethyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(2-benzyloxy-ethoxycarbonylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(2-phenoxy-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-(3-propoxycarbonylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-[3-(2-thiophen-2-yl-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-(3-phenylacetylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-[3-(3-phenylsulfonyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(3-benzyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-[3-(3-naphthalen-1-yl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-(3-decanoylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-[6-fluoro-3-(3-naphthalen-2-yl-acryloylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]acetic acid;

(3S)-{3-[2-(4-tert-butyl-phenyl)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-(3-benzyloxycarbonylamino-8-chloro-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-benzyloxycarbonylamino-8-chloro-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-[6-fluoro-3-(3-pyridin-3-yl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-[3-(3-benzyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(3-methyl-butyrylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{6-fluoro-3-[2-(4-trifluoromethyl-phenyl)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(3-phenyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(3-cyclopentyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-[3-(2-thiophen-2-yl-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-(3-butyrylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-(3-benzyloxycarbonylamino-8-chloro-5-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-benzyloxycarbonylamino-8-chloro-5-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-heptanoylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-[3-(3-cyclopentyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-(3-decanoylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-(3-benzoylamino-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-[3-(3-butyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{6-fluoro-3-[(1H-indole-2-carbonyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-[3-(3-methyl-butyrylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid; or

(3S)-[3-(3-butyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

or a salt thereof.

10. The compound according to claim 1 , wherein the compound is:

(3R)-[3-(3-Benzyl-ureido)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(3-Benzyl-ureido)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[6-Fluoro-3-(3-phenethyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-[3-(3-Benzyl-ureido)-8-chloro-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(3-Benzyl-ureido)-8-chloro-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-[8-Chloro-6-fluoro-3-(3-phenethyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[8-Chloro-6-fluoro-3-(3-phenethyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-(3-Benzyloxycarbonylamino-6-trifluoromethyl-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-Benzyloxycarbonylamino-6-trifluoromethyl-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-(3-Benzyloxylcarbonylamino-8-bromo-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-Benzyloxycarbonylamino-8-bromo-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-(3-Benzyloxycarbonylamino-6-fluoro-8-vinyl-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-Benzyloxycarbonylamino-6-fluoro-8-vinyl-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-(3-Benzyloxycarbonylamino-6-fluoro-8-methanesulfonyl-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-Benzyloxycarbonylamino-6-fluoro-8-methanesulfonyl-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-Benzyloxycarbonylamino-6-fluoro-8-methyl-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-Benzyloxycarbonylamino-7-chloro-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(8-Allyl-3-benzyloxycarbonylamino-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-(3-Benzyloxycarbonylamino-8-chloro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3R)-{3-[3-(2,4-Dimethoxy-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[6-Fluoro-3-(3-naphthalen-1-yl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{6-Fluoro-3-[2-(2-methoxy-phenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[2-(2-methoxy-phenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{6-Fluoro-3-[3-(2-methylphenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(2-methylphenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{6-Fluoro-3-[3-(3-methylphenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(3-methylphenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{6-Fluoro-3-[3-(3-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(3-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{6-Fluoro-3-[2-(3-methoxy-phenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[2-(3-methoxy-phenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{6-Fluoro-3-[2-(2-methylphenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[2-(2-methylphenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(2,5-Dimethoxy-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(4-trifluoromethyl-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(2,6-Dichloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(2,5-Bis-trifluoromethyl-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(4-methylsulfanyl-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(4-iodo-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(4-isopropyl-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(3-trifluoromethyl-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(2,4-Dichloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(4-fluoro-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(3,5-Bis-trifluoromethyl-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(4-Ethyl-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(3-iodo-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(4-methanesulfonyl-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(2,3-Dimethoxy-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(2-Bromo-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(3-trifluoromethoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(2,4-Dimethyl-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(3-Bromo-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-(3-tert-Butoxycarbonylamino-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[(S)-3-(4-fluoro-phenyl)-2-phenyl-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[(S)-3-(4-methoxy-phenyl)-2-phenyl-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[3-(2-fluoro-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(6-Fluoro-3-{[(2RS)-1,2,3,4-tetrahydro-naphthalene-2-carbonyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{[(2RS)-8-methoxy-1,2,3,4-tetrahydro-naphthalene-2-carbonyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{(2RS)-2-[(4-fluoro-phenylcarbamoyl)-methyl]-3-phenyl-propionylamino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{3-[(2RS)-2-Benzyl-3,3-dimethyl-butyrylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(6-Fluoro-3-{[(2RS)-8-methoxy-1,2,3,4-tetrahydro-naphthalene-2-carbonyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{6-Fluoro-3-[3-(3-fluoro-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(6-Fluoro-3-{[(2RS)-8-methoxy-1,2,3,4-tetrahydro-naphthalene-2-carbonyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{6-Fluoro-3-[(2R)-2-methyl-3-phenyl-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(2,2-Dimethyl-3-phenyl-propionylamino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[6-Fluoro-3-(3-methyl-3-phenyl-butyrylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-Fluoro-3-[(3S)-3-phenyl-butyrylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(2-Benzyloxy-acetylamino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[6-Fluoro-3-(4-phenyl-butyrylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{3-[(2R,3R)-2,3-Dihydroxy-3-(2-methoxy-phenylcarbamoyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-6-fluoro-3-[3-(2-methylphenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-6-fluoro-3-[3-(2-methylphenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-6-fluoro-3-[2-(2-methoxy-phenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-6-fluoro-3-[2-(2-methoxy-phenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-6-fluoro-3-[3-(3-hydroxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-6-fluoro-3-[3-(3-hydroxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-6-fluoro-3-[3-(3-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-6-fluoro-3-[3-(3-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-6-fluoro-3-[3-(3-methylphenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-6-fluoro-3-[3-(3-methylphenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-6-fluoro-3-[3-(2-hydroxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-6-fluoro-3-[3-(2-hydroxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-[8-Chloro-6-fluoro-3-(3-phenyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[8-Chloro-6-fluoro-3-(3-phenyl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{8-Chloro-6-fluoro-3-[3-(2-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-6-fluoro-3-[3-(2-methoxy-phenyl)-propionylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-3-[3-(3-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-3-[3-(3-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-[8-Chloro-6-fluoro-3-(3-1H-indol-3-yl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[ 8 -Chloro-6-fluoro-3-(3-1H-indol-3-yl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{8-Chloro-3-[2-(2-chloro-phenoxy)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-3-[2-(2-chloro-phenoxy)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-6-fluoro-3-[2-(2-methylphenyl)-oxy-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-6-fluoro-3-[2-(2-methylphenyl)-oxy-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-[3-(3-Benzo[1,3]dioxol-5-yl-propionylamino)-8-chloro-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(3-Benzo[1,3]dioxol-5-yl-propionylamino)-8-chloro-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-{8-Chloro-6-fluoro-3-[2-(3-methoxy-phenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-6-fluoro-3-[2-(3-methoxy-phenoxy)-acetylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-3-[2-(3-chloro-phenoxy)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-3-[2-(3-chloro-phenoxy)-acetylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-{8-Chloro-3-[3-(2-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{8-Chloro-3-[3-(2-chloro-phenyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3R)-[8-Chloro-6-fluoro-3-(2-indan-2-yl-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[8-Chloro-6-fluoro-3-(2-indan-2-yl-acetylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3R)-[6-Fluoro-3-(1-methyl-3-phenethyl-ureido)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{3-[3-(2-Chloro-benzyl)-1-methyl-ureido]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(3-Benzyl-1-methyl-ureido)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(Benzyloxycarbonyl-methyl-amino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

{(3S)-3-[(2-Chloro-benzyloxycarbonyl)-methyl-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(6-Fluoro-3-{[2-(4-methoxy-phenyl)-acetyl]-methyl-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{methyl-[2-(4-methylphenyl)-acetyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{[2-(2-methoxy-phenyl)-acetyl]-methyl-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{6-Fluoro-3-[(2-indan-2-yl-acetyl)-methyl-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(3-{[2-(3-Chloro-phenyl)-acetyl]-methyl-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{methyl-[2-(3-methylphenyl)-acetyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{[2-(3-methoxy-phenyl)-acetyl]-methyl-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-{[2-(2-Chloro-phenoxy)-acetyl]-methyl-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-{[2-(4-Chloro-phenoxy)-acetyl]-methyl-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{[3-(3-methoxy-phenyl)-propionyl]-methyl-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{methyl-[2-(2-methylphenyl)-acetyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{3-[(3,3-Diphenyl-propionyl)-methyl-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(6-Fluoro-3-{[3-(2-methoxy-phenyl)-propionyl]-methyl-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{6-Fluoro-3-[(3-1H-indol-3-yl-propionyl)-methyl-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[(2-Benzyloxy-acetyl)-methyl-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[(2,3-Diphenyl-propionyl)-methyl-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[[3-(2-methoxy-phenyl)-propionyl]-(3-phenyl-propyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[Acetyl-(3-phenyl-propyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-Benzyl-(1-cyclopropylmethyl)-ureido]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(Benzyloxycarbonyl-cyclopropylmethyl-amino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{3-[Cyclopropylmethyl-(3-phenyl-propionyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[Cyclopropylmethyl-((S)-2-methyl-3-phenyl-propionyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(3-{Cyclopropylmethyl-[3-(2-methoxy-phenyl)-propionyl]-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{3-[2-(3-Chloro-phenoxy)-acetyl]-cyclopropylmethyl-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{3-[Cyclopropylmethyl-(3,3-diphenyl-propionyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[Cyclopropylmethyl-(2-naphthalen-1-yl-acetyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(3-{Benzyloxycarbonyl-[2-(4-trifluoromethyl-phenoxy)-ethyl]-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-{Acetyl-[2-(4-trifluoromethyl-phenoxy)-ethyl]-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{propionyl-[2-(4-trifluoromethyl-phenoxy)-ethyl]amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{(3-phenyl-propionyl)-[2-(4-trifluoromethyl-phenoxy)-ethyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{[3-(2-methoxy-phenyl)-propionyl]-[2-(4-trifluoromethyl-phenoxy)-ethyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{6-Fluoro-3-[(2-phenoxy-ethyl)-(3-phenyl-propionyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[((S)-2-methyl-3-phenyl-propionyl)-(2-phenoxy-ethyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[[3-(2-methoxy-phenyl)-propionyl]-(2-phenoxy-ethyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[Acetyl-(2-phenoxy-ethyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[3-Benzyl-1-(2-methoxy-ethyl)-ureido]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[Benzyloxycarbonyl-(2-methoxy-ethyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[(2-methoxy-ethyl)-(3-phenyl-propionyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[(2-methoxy-ethyl)-((S)-2-methyl-3-phenyl-propionyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(6-Fluoro-3-{(2-methoxy-ethyl)-[3-(2-methoxy-phenyl)-propionyl]-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{3-[[2-(3-Chloro-phenoxy)-acetyl]-(2-methoxy-ethyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[(3,3-Diphenyl-propionyl)-(2-methoxy-ethyl)-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[(2-methoxy-ethyl)-(2-naphthalen-1-yl-acetyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(6-Fluoro-3-{[(2S)-2-methyl-3-phenyl-propionyl]-phenethyl-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(6-Fluoro-3-{[3-(2-methoxy-phenyl)-propionyl]-phenethyl-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-[3-(Acetyl-phenethyl-amino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-Fluoro-3-[(2-naphthalen-1-yl-acetyl)-phenethyl-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[phenethyl-(3-phenyl-propionyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(3-Benzyl-1-naphthalen-1-ylmethyl-ureido)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[3-(Benzyloxycarbonyl-naphthalen-1-ylmethyl-amino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-Fluoro-3-[naphthalen-1-ylmethyl-(3-phenyl-propionyl)-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{6-Fluoro-3-[((S)-2-methyl-3-phenyl-propionyl)-naphthalen-1-ylmethyl-amino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-(6-Fluoro-3-{[3-(2-methoxy-phenyl)-propionyl]-naphthalen-1-ylmethyl-amino}-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-{3-[(3,3-Diphenyl-propionyl)-naphthalen-1-ylmethyl-amino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(Acetyl-naphthalen-1-ylmethyl-amino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[6-Fluoro-3-(naphthalen-1-ylmethyl-propionyl-amino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{3-[(RS)-2-Benzyl-3-(2-methylphenyl)-carbamoyl-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[(RS)-2-Benzyl-3-(3-methoxy-phenylcarbamoyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[(RS)-2-Benzyl-3-(4-chloro-phenylcarbamoyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-{3-[(RS)-2-Benzyl-3-(4-fluoro-benzylcarbamoyl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

[(3S)-3-((RS)-2-Benzyl-3-propylcarbamoyl-propionylamino)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-[6-Fluoro-3-(3-thiophen-2-yl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{3-[3-(3-Chloro-isoxazol-5-yl)-propionylamino]-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[6-Fluoro-3-(3-pyrimidin-2-yl-propionylamino)-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-{6-Fluoro-3-[3-phenyl-4-([1,3,4]thiadiazol-2-ylcarbamoyl)-butyrylamino]-1,2,3,4-tetrahydro-9H-carbazol-9-yl}-acetic acid;

(3S)-[3-(1,3-Dibenzyl-ureido)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid;

(3S)-(3-{Acetyl-[2-(2-fluoro-phenyl)-ethyl]-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-(3-{Acetyl-[2-(3-fluoro-phenyl)-ethyl]-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

(3S)-[3-(3-Benzyl-1-cyclohexylmethyl-ureido)-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl]-acetic acid; or

(3S)-(3-{Cyclohexylmethyl-[3-(2-methoxy-phenyl)-propionyl]-amino}-6-fluoro-1,2,3,4-tetrahydro-9H-carbazol-9-yl)-acetic acid;

or a salt thereof.

11. A pharmaceutical composition, comprising a compound according to claim 1 , or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.

12. A medicament, comprising a compound according to claim 1 , or a pharmaceutically acceptable salt thereof.

13. A method of antagonizing a CRTH2 receptor, comprising the step of administering an effective amount of a compound according to claim 1 , or a pharmaceutically acceptable salt thereof, to a patient in need thereof.

14. The method of claim 13 , wherein said patient has a disease or disorder that comprises allergic asthma, rhinitis, allergic rhinitis, chronic obstructive pulmonary disease, dermatitis, inflammatory bowel disease, rheumatoid arthritis, allergic nephritis, conjunctivitis, atopic dermatitis, bronchial asthma, food allergy, systemic mast cell disorders, anaphylactic shock, urticaria, eczema, itching, inflammation, ischemia-reperfusion injury, cerebrovascular disorders, pleuritis, ulcerative colitis, an eosinophil-related disease, or a basophil-related disease.

15. The method of claim 14 , wherein said patient has an eosinophil-related disease comprising Churg-Strauss syndrome or sinusitis.

16. The method of claim 14 , wherein said patient has a basophil-related disease comprising basophilic leukemia or basophilic leukocytosis.

17. The compound according to claim 1 , wherein

R 5 is hydrogen, methyl, ethyl, or n-propyl;

or a salt thereof.

18. The compound according to claim 2 , wherein

R 5 is hydrogen, methyl, ethyl, or n-propyl;

or a salt thereof.

19. The compound according to claim 1 , wherein R 6 is aryl-C 1-3 -alkoxycarbonyl; aryl-C 1-3 -alkylaminocarbonyl; aryl-C 1-6 -alkylcarbonyl; aryl-C 1-3 -alkoxy-C 1-3 -alkylcarbonyl; arylcarbonyl-C 1-4 -alkylcarbonyl; aryloxy-C 1-3 -alkylcarbonyl; cycloalkyl-C 1-3 -alkylcarbonyl; diaryl-C 1-3 -alkylcarbonyl; aryl-C 3-6 -cycloalkylcarbonyl; or R 7 —C 1-4 -alkylcarbonyl wherein the bridging C 1-4 -alkyl group of the R 7 —C 1-4 -alkylcarbonyl may additionally be mono-substituted with an aryl, and wherein R 7 is an arylaminocarbonyl, heteroarylaminocarbonyl, C 1-6 -alkylaminocarbonyl, or aryl-C 1-3 -alkylaminocarbonyl; further wherein the aryl is unsubstituted, mono- or di-substituted with a C 1-2 -alkylendioxy; C 1-6 -alkoxy; C 1-6 -alkyl; C 1-6 -alkylsulfonyl; halogen; hydroxy; halo-C 1-6 -alkyl; halo-C 1-6 -alkoxy; C 1-6 -alkylthio, or C 1-4 -alkoxycarbonylamino;

or a salt thereof.

20. The compound according to claim 17 , wherein R 6 is aryl-C 1-3 -alkoxycarbonyl; aryl-C 1-3 -alkylaminocarbonyl; aryl-C 1-6 -alkylcarbonyl; aryl-C 1-3 -alkoxy-C 1-3 -alkylcarbonyl; arylcarbonyl-C 1-4 -alkylcarbonyl; aryloxy-C 1-3 -alkylcarbonyl; cycloalkyl-C 1-3 -alkylcarbonyl; diaryl-C 1-3 -alkylcarbonyl; aryl-C 3-6 -cycloalkylcarbonyl; or R 7 —C 1-4 -alkylcarbonyl wherein the bridging C 1-4 -alkyl group of the R 7 —C 1-4 -alkylcarbonyl may additionally be mono-substituted with an aryl, and wherein R 7 is an arylaminocarbonyl, heteroarylaminocarbonyl, C 1-6 -alkylaminocarbonyl, or aryl-C 1-3 -alkylaminocarbonyl; further wherein the aryl is unsubstituted, mono- or di-substituted with a C 1-2 -alkylendioxy; C 1-6 -alkoxy; C 1-6 -alkyl; C 1-6 -alkylsulfonyl; halogen; hydroxy; halo-C 1-6 -alkyl; halo-C 1-6 -alkoxy; C 1-6 -alkylthio, or C 1-4 -alkoxycarbonylamino;

or a salt thereof.

21. The compound according to claim 18 , wherein R 6 is aryl-C 1-3 -alkoxycarbonyl; aryl-C 1-3 -alkylaminocarbonyl; aryl-C 1-6 -alkylcarbonyl; aryl-C 1-3 -alkoxy-C 1-3 -alkylcarbonyl; arylcarbonyl-C 1-4 -alkylcarbonyl; aryloxy-C 1-3 -alkylcarbonyl; cycloalkyl-C 1-3 -alkylcarbonyl; diaryl-C 1-3 -alkylcarbonyl; aryl-C 3-6 -cycloalkylcarbonyl; or R 7 —C 1-4 -alkylcarbonyl wherein the bridging C 1-4 -alkyl group of the R 7 —C 1-4 -alkylcarbonyl may additionally be mono-substituted with an aryl, and wherein R 7 is an arylaminocarbonyl, heteroarylaminocarbonyl, C 1-6 -alkylaminocarbonyl, or aryl-C 1-3 -alkylaminocarbonyl; further wherein the aryl is unsubstituted, mono- or di-substituted with a C 1-2 -alkylendioxy; C 1-6 -alkoxy; C 1-6 -alkyl; C 1-6 -alkylsulfonyl; halogen; hydroxy; halo-C 1-6 -alkyl; halo-C 1-6 -alkoxy; C 1-6 -alkylthio, or C 1-4 -alkoxycarbonylamino;

or a salt thereof.

22. The compound according to claim 1 , wherein R 6 represents C 1-9 -alkylaminocarbonyl; C 1-9 -alkylcarbonyl; or C 1-9 -alkoxycarbonyl;

or a salt thereof.

23. The compound according to claim 2 , wherein R 6 represents C 1-9 -alkylaminocarbonyl; C 1-9 -alkylcarbonyl; or C 1-9 -alkoxycarbonyl;

or a salt thereof.