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 mode of action was said to be comparable to that of the synthetic compound ' carbamylcholin ' ; that is , carbachol .
### Output Text:
The mode of action was said to be comparable to that of the synthetic compound ' <span class="chemical">carbamylcholin</span> ' ; that is , <span class="chemical">carbachol</span> . 