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: We compared the potential beta - receptor blocker , B 24 / 76 i . e . 1 - ( 2 , 4 - dichlorophenoxy ) - 3 [ 2 - 3 , 4 - dimethoxyphenyl ) ethanolamino ] - prop an - 2 - ol , which is characterized by beta 1 - adrenoceptor blocking and beta 2 - adrenoceptor stimulating properties with propranolol .
### Output Text:
We compared the potential beta - receptor blocker , B 24 / 76 i . e . 1 - ( 2 , 4 - dichlorophenoxy ) - 3 [ 2 - 3 , 4 - dimethoxyphenyl ) ethanolamino ] - prop an - 2 - ol , which is characterized by beta 1 - adrenoceptor blocking and beta 2 - adrenoceptor stimulating properties with <span class="chemical">propranolol</span> . 