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: Characterization of a novel BCHE " silent " allele : point mutation ( p . Val204Asp ) causes loss of activity and prolonged apnea with suxamethonium .
### Output Text:
Characterization of a novel BCHE " silent " allele : point mutation ( p . Val204Asp ) causes loss of activity and prolonged apnea with <span class="chemical">suxamethonium</span> . 