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: To begin addressing this need , we characterized UMB24 ( 1 - ( 2 - phenethyl ) - 4 - ( 2 - pyridyl ) - piperazine ) and ( + / - ) - SM 21 ( 3alpha - tropanyl - 2 - ( 4 - chorophenoxy ) butyrate ) in receptor binding and behavioral studies .
### Output Text:
To begin addressing this need , we characterized <span class="chemical">UMB24</span> ( <span class="chemical">1 - ( 2 - phenethyl ) - 4 - ( 2 - pyridyl ) - piperazine</span> ) and ( + / - ) - <span class="chemical">SM 21</span> ( <span class="chemical">3alpha - tropanyl - 2 - ( 4 - chorophenoxy ) butyrate</span> ) in receptor binding and behavioral studies . 