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 study of 4 ' - 0 - tetrahydropyranyladriamycin .
### Output Text:
A phase I study of <span class="chemical">4 ' - 0 - tetrahydropyranyladriamycin</span> . 