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: YMDD motif mutants were not detected in any of the patients despite the liver enzyme levels and the presence of HBeAg or anti - HBe .
### Output Text:
YMDD motif mutants were not detected in any of the patients despite the liver enzyme levels and the presence of <span class="chemical">HBeAg</span> or anti - HBe . 