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 peptide CCK - 5 - 8 had weak anticonvulsant activity in comparison to the octapeptides , 3 . 2 mumol / kg and larger doses of the reference drug , diazepam , totally prevented picrotoxin - induced seizures and mortality .
### Output Text:
The peptide CCK - 5 - 8 had weak anticonvulsant activity in comparison to the octapeptides , 3 . 2 mumol / kg and larger doses of the reference drug , <span class="chemical">diazepam</span> , totally prevented <span class="chemical">picrotoxin</span> - induced seizures and mortality . 