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: Synthesis of N - pyrimidinyl - 2 - phenoxyacetamides as adenosine A2A receptor antagonists .
### Output Text:
Synthesis of <span class="chemical">N - pyrimidinyl - 2 - phenoxyacetamides</span> as <span class="chemical">adenosine</span> A2A receptor antagonists . 