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: Moreover , all adenosine receptor agonists : 2 - p - ( 2 - carboxyethyl ) phenethylamino - 5 ' - N - ethylcarboxamidoadenosine ( CGS 21680 ) , A2A receptor agonist , N6 - cyclopentyladenosine ( CPA ) , A1 receptor agonist , and 5 ' - N - ethylcarboxamidoadenosine ( NECA ) , A2 / A1 receptor agonist significantly and dose - dependently decreased cocaine - induced locomotor activity .
### Output Text:
Moreover , all <span class="chemical">adenosine</span> receptor agonists : <span class="chemical">2 - p - ( 2 - carboxyethyl ) phenethylamino - 5 ' - N - ethylcarboxamidoadenosine</span> ( <span class="chemical">CGS 21680</span> ) , A2A receptor agonist , <span class="chemical">N6 - cyclopentyladenosine</span> ( <span class="chemical">CPA</span> ) , A1 receptor agonist , and <span class="chemical">5 ' - N - ethylcarboxamidoadenosine</span> ( <span class="chemical">NECA</span> ) , A2 / A1 receptor agonist significantly and dose - dependently decreased <span class="chemical">cocaine</span> - induced locomotor activity . 