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: The liver levels of beta - oxidation metabolites of VPA were decreased by day 14 , while the levels of 4 - ene - VPA and ( E ) - 2 , 4 - diene - VPA were not elevated throughout the study .
### Output Text:
The liver levels of beta - oxidation metabolites of <span class="chemical">VPA</span> were decreased by day 14 , while the levels of <span class="chemical">4 - ene - VPA</span> and ( E ) - <span class="chemical">2 , 4 - diene - VPA</span> were not elevated throughout the study . 