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: VPU was more potent than VPA , exhibiting the median effective dose ( ED ( 50 ) ) of 49 mg / kg in protecting rats against pilocarpine - induced seizure whereas the corresponding value for VPA was 322 mg / kg .
### Output Text:
<span class="chemical">VPU</span> was more potent than <span class="chemical">VPA</span> , exhibiting the median effective dose ( ED ( 50 ) ) of 49 mg / kg in protecting rats against <span class="chemical">pilocarpine</span> - induced seizure whereas the corresponding value for <span class="chemical">VPA</span> was 322 mg / kg . 