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: Amifostine subsequently was shown to protect normal tissues from the toxic effects of alkylating agents and cisplatin without decreasing the antitumor effect of the chemotherapy .
### Output Text:
<span class="chemical">Amifostine</span> subsequently was shown to protect normal tissues from the toxic effects of <span class="chemical">alkylating agents</span> and <span class="chemical">cisplatin</span> without decreasing the antitumor effect of the chemotherapy . 