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: Alternating sinus rhythm and intermittent sinoatrial ( S - A ) block was observed in a 57 - year - old woman , under treatment for angina with 80 mg propranolol daily .
### Output Text:
Alternating sinus rhythm and intermittent sinoatrial ( S - A ) block was observed in a 57 - year - old woman , under treatment for angina with 80 mg <span class="chemical">propranolol</span> daily . 