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: Although the neuroactive steroids were considerably less potent than the benzodiazepine clonazepam in protecting against pilocarpine seizures , steroids with the 5 alpha , 3 alpha - configuration had comparable or higher protective index values ( TD50 for motor impairment divided by ED50 for seizure protection ) than clonazepam , indicating that some neuroactive steroids may have lower relative toxicity .
### Output Text:
Although the neuroactive <span class="chemical">steroids</span> were considerably less potent than the <span class="chemical">benzodiazepine</span> <span class="chemical">clonazepam</span> in protecting against <span class="chemical">pilocarpine</span> seizures , <span class="chemical">steroids</span> with the 5 alpha , 3 alpha - configuration had comparable or higher protective index values ( TD50 for motor impairment divided by ED50 for seizure protection ) than <span class="chemical">clonazepam</span> , indicating that some neuroactive <span class="chemical">steroids</span> may have lower relative toxicity . 