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: This report describes a patient with mild language delay and mental retardation , who was found to have nonketotic hyperglycinemia following her presentation with acute encephalopathy and chorea shortly after initiation of valproate therapy .
### Output Text:
This report describes a patient with mild language delay and mental retardation , who was found to have nonketotic hyperglycinemia following her presentation with acute encephalopathy and chorea shortly after initiation of <span class="chemical">valproate</span> therapy . 