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 concluded that WR242511 should not be pursued as a pretreatment for CN poisoning unless the anti - CN characteristics of this compound can be successfully dissociated from those producing undesirable toxicity .
### Output Text:
It is concluded that <span class="chemical">WR242511</span> should not be pursued as a pretreatment for CN poisoning unless the anti - CN characteristics of this compound can be successfully dissociated from those producing undesirable toxicity . 