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 vitro , at a concentration of 100 mumol / L , BAU possesses minimal anti - HIV activity and has no effect on the ability of AZT to reverse the HIV - induced cytopathic effect in MT4 cells .
### Output Text:
In vitro , at a concentration of 100 mumol / L , <span class="chemical">BAU</span> possesses minimal anti - HIV activity and has no effect on the ability of <span class="chemical">AZT</span> to reverse the HIV - induced cytopathic effect in MT4 cells . 