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: Grape seed extract , primarily a mixture of proanthocyanidins , has been shown to modulate a wide - range of biological , pharmacological and toxicological effects which are mainly cytoprotective .
### Output Text:
<span class="chemical">Grape seed extract</span> , primarily a mixture of <span class="chemical">proanthocyanidins</span> , has been shown to modulate a wide - range of biological , pharmacological and toxicological effects which are mainly cytoprotective . 