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 pilot study leads to the conclusion that glutamate supplementation at the chosen regimen fails to protect against peripheral neurotoxicity of PAC .
### Output Text:
This pilot study leads to the conclusion that <span class="chemical">glutamate</span> supplementation at the chosen regimen fails to protect against peripheral neurotoxicity of <span class="chemical">PAC</span> . 