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 possible influence of the hepatic damage , mainly hyperammonemia , upon the development of valproate encephalopathy is discussed .
### Output Text:
The possible influence of the hepatic damage , mainly hyperammonemia , upon the development of <span class="chemical">valproate</span> encephalopathy is discussed . 