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: UM - 272 ( N , N - dimethylpropranolol ) , a quaternary antiarrhythmic agent , was administered sublingually to dogs with ouabain - induced ventricular tachycardias .
### Output Text:
<span class="chemical">UM - 272</span> ( <span class="chemical">N , N - dimethylpropranolol</span> ) , a quaternary antiarrhythmic agent , was administered sublingually to dogs with <span class="chemical">ouabain</span> - induced ventricular tachycardias . 