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: Both anti - asthmatic and tremorgenic effects of procaterol were dose - related .
### Output Text:
Both anti - asthmatic and tremorgenic effects of <span class="chemical">procaterol</span> were dose - related . 