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: These effects were completely antagonized by pretreatment with a glutamate / N - methyl - D - aspartate antagonist , aminophosphonovaleric acid .
### Output Text:
These effects were completely antagonized by pretreatment with a <span class="chemical">glutamate</span> / <span class="chemical">N - methyl - D - aspartate</span> antagonist , <span class="chemical">aminophosphonovaleric acid</span> . 