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: Phenylpropanolamine ( PPA ) , a synthetic sympathomimetic that is structurally similar to amphetamine , is available over the counter in anorectics , nasal congestants , and cold preparations .
### Output Text:
<span class="chemical">Phenylpropanolamine</span> ( <span class="chemical">PPA</span> ) , a synthetic sympathomimetic that is structurally similar to <span class="chemical">amphetamine</span> , is available over the counter in anorectics , nasal congestants , and cold preparations . 