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: These effects were not mediated by a dopaminergic mechanism as nefiracetam , at millimolar concentrations , failed to displace either [ 3H ] SCH 23390 or [ 3H ] spiperone binding from D1 or D2 dopamine receptor subtypes , respectively .
### Output Text:
These effects were not mediated by a dopaminergic mechanism as <span class="chemical">nefiracetam</span> , at millimolar concentrations , failed to displace either [ 3H ] <span class="chemical">SCH 23390</span> or [ 3H ] <span class="chemical">spiperone</span> binding from D1 or D2 <span class="chemical">dopamine</span> receptor subtypes , respectively . 