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: In this group of 45 patients under protection with MESNA there were 5 complete remissions and 9 partial remissions ( total 31 % ) .
### Output Text:
In this group of 45 patients under protection with <span class="chemical">MESNA</span> there were 5 complete remissions and 9 partial remissions ( total 31 % ) . 