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: Control was defined as MSDBP < 90 mm Hg compared with baseline .
### Output Text:
Control was defined as MSDBP < 90 mm Hg compared with baseline . 