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: A selective dopamine D4 receptor antagonist , NRA0160 : a preclinical neuropharmacological profile .
### Output Text:
A selective <span class="chemical">dopamine</span> D4 receptor antagonist , <span class="chemical">NRA0160</span> : a preclinical neuropharmacological profile . 