Enolic acid are a group of FANS (non steroidal antiinflammatory). They react with COX 1 as well as COX 2 (which is not a constitutive enzyme but peculiar of the inflammatory phenomenon).
The key factor is that they are weak acids, extremely weaker than, say, aspirin or ibuprofen. This means they give less gastric problems.
We can divide enolic acids in two groups, according to their structures: in the former we have phenylbutazone, oxyphenylbutazone, feprazone and sulfinpyrazone. In the latter (aka OXICAMS), there are: piroxicam, isoxicam, tenoxicam and meloxicam.
If you need, I can post pictures from both groups in order to stress the differences and similarities.