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: INTRODUCTION : Cyclophosphamide is an alkylating agent given frequently as a component of many conditioning regimens .
### Output Text:
INTRODUCTION : <span class="chemical">Cyclophosphamide</span> is an alkylating agent given frequently as a component of many conditioning regimens . 