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: NRA0160 has negligible affinity for the human cloned dopamine D3 receptor ( Ki = 39 nM ) , rat serotonin ( 5 - HT ) 2A receptors ( Ki = 180 nM ) and rat alpha1 adrenoceptor ( Ki = 237 nM ) .
### Output Text:
<span class="chemical">NRA0160</span> has negligible affinity for the human cloned <span class="chemical">dopamine</span> D3 receptor ( Ki = 39 nM ) , rat <span class="chemical">serotonin</span> ( <span class="chemical">5 - HT</span> ) 2A receptors ( Ki = 180 nM ) and rat alpha1 adrenoceptor ( Ki = 237 nM ) . 