Naphthyridine derivatives as alpha v beta 6 integrin antagonists for the treatment of e.g. fibrotic diseases

A compound of formula (I) or a pharmaceutically acceptable salt thereof:

• wherein
• R1 is an optionally substituted five-membered aromatic heterocycle,
• wherein the optionally substituted five-membered aromatic heterocycle is selected from an optionally substituted N- or a C-linked pyrazole, an optionally substituted N- or a C-linked triazole, and an optionally substituted N- or C-linked imidazole,
• wherein the optionally substituted N- or a C-linked pyrazole, the optionally substituted N- or a C-linked triazole, and the optionally substituted N- or C-linked imidazole is optionally substituted by 1 or 2 substituents independently selected from methyl, ethyl, fluoro, hydroxymethyl, 2-hydroxypropan-2-yl, trifluoromethyl, difluoromethyl, and fluoromethyl;
• provided that when R1 is an optionally substituted N-linked pyrazole, Ri does not represent 3,5-dimethyl-1H-pyrazol-1-yl, 5-methyl-1H-pyrazol-1-yl, 5-ethyl-3-methyl-1H-pyrazol-1-yl, 3,5-diethyl-1H-pyrazol-1-yl, 4-fluoro-3,5-dimethyl-1H-pyrazol-1-yl, 3-methyl-1H-pyrazol-1-yl, or 1H-pyrazol-1-yl.