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: Toleration of high doses of angiotensin - converting enzyme inhibitors in patients with chronic heart failure : results from the ATLAS trial .
### Output Text:
Toleration of high doses of <span class="chemical">angiotensin - converting enzyme inhibitors</span> in patients with chronic heart failure : results from the ATLAS trial . 