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: Among late - conversion patients , 37 ( 90 . 2 % ) had improvement / resolution ; in 4 ( 9 . 8 % ) , adverse effects persisted .
### Output Text:
Among late - conversion patients , 37 ( 90 . 2 % ) had improvement / resolution ; in 4 ( 9 . 8 % ) , adverse effects persisted . 