In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Urinary NGF , PGF2alpha and PGI2 did not correlate with urodynamic parameters in patients with OAB .
### Output Text:
Urinary NGF , <span class="chemical">PGF2alpha</span> and <span class="chemical">PGI2</span> did not correlate with urodynamic parameters in patients with OAB . 