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: It is thought that the clinico - pathological features and chronology of this case bore the hallmarks of the so - called " 3 - week sulphasalazine syndrome " , a rare , but often fatal , immunoallergic reaction to sulphasalazine .
### Output Text:
It is thought that the clinico - pathological features and chronology of this case bore the hallmarks of the so - called " 3 - week <span class="chemical">sulphasalazine</span> syndrome " , a rare , but often fatal , immunoallergic reaction to <span class="chemical">sulphasalazine</span> . 