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: CONCLUSION : In conclusion , the demonstration of an inverse relationship between infusion time of a fixed and convulsive dose of bupropion and the risk of convulsions in a prospective study is novel .
### Output Text:
CONCLUSION : In conclusion , the demonstration of an inverse relationship between infusion time of a fixed and convulsive dose of <span class="chemical">bupropion</span> and the risk of convulsions in a prospective study is novel . 