Substituted acetic acid derivatives

A compound having the formula.

• wherein:
• R1 is —OH or —OC1-C8 alkyl;
• R2 and R3 are, independently, hydrogen or C1-C8 alkyl;
• R4 is hydrogen or C1-C8 alkyl;
• R21 is —(CH2)p—O-phenyl;
• W is phenyl;
• and
• p is an integer from 1 to 5;
• wherein the alkyl, and phenyl groups are each optionally substituted by one or more substituents, or a pharmaceutically acceptable salt or ester form thereof.