Ep4 receptor antagonists

A method of treating a condition which can be alleviated by antagonism of an EP4 receptor, which method comprises administering to a patient in need of treatment an effective amount of a compound of claim formula (I),

• or a pharmaceutically acceptable salt thereof, wherein:
• either R2 is H or an optionally substituted C1-4 alkyl group and R5 is an optionally substituted C5-7 aryl;
• or
• R5 is H or an optionally substituted C1-4 alkyl group and R2 is an optionally substituted C5-7 aryl;
• m and n can be 0 or 1, and m+n=1 or 2
• RN is H or optionally substituted C1-4 alkyl
• R3 is either:
• (i) carboxy;
• (ii) a group of formula (II):
• (iii) a group of formula (III):
• wherein R is optionally substituted C1-7 alkyl, C5-20 aryl, or NRN3RN4, where RN3 and RN4 are independently selected from optionally substituted C1-4 alkyl;
• or
• (iv) tetrazol-5-yl.