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: A phase I clinical study of the antipurine antifolate lometrexol ( DDATHF ) given with oral folic acid .
### Output Text:
A phase I clinical study of the <span class="chemical">antipurine</span> antifolate <span class="chemical">lometrexol</span> ( <span class="chemical">DDATHF</span> ) given with oral <span class="chemical">folic acid</span> . 