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: The muscarinic receptor antagonists atropine , 4 - diphenylacetoxy - N - methylpiperidine ( 4 - DAMP ) ( ' M ( 1 ) / M ( 3 ) / M ( 5 ) - selective ' ) , methoctramine ( ' M ( 2 ) - selective ' ) and pirenzepine ( ' M ( 1 ) - selective ' ) antagonized the tonic component of the electrical field stimulation - evoked contractile response more potently than the phasic component .
### Output Text:
The muscarinic receptor antagonists <span class="chemical">atropine</span> , <span class="chemical">4 - diphenylacetoxy - N - methylpiperidine</span> ( <span class="chemical">4 - DAMP</span> ) ( ' M ( 1 ) / M ( 3 ) / M ( 5 ) - selective ' ) , <span class="chemical">methoctramine</span> ( ' M ( 2 ) - selective ' ) and <span class="chemical">pirenzepine</span> ( ' M ( 1 ) - selective ' ) antagonized the tonic component of the electrical field stimulation - evoked contractile response more potently than the phasic component . 