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: Above mentioned AZT incorporation may have induced an ineffective hemopoiesis in the primitive hemopoietic progenitor cells , which is known to be seen commonly in the myelodysplastic syndrome .
### Output Text:
Above mentioned <span class="chemical">AZT</span> incorporation may have induced an ineffective hemopoiesis in the primitive hemopoietic progenitor cells , which is known to be seen commonly in the myelodysplastic syndrome . 