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: This latter effect is thought to be due to drug precipitation within the renal tubule as a result of the poor solubility of CB 3717 under acidic conditions .
### Output Text:
This latter effect is thought to be due to drug precipitation within the renal tubule as a result of the poor solubility of <span class="chemical">CB 3717</span> under acidic conditions . 