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: No necrosis was observed in cells treated with NCQ436 but NCQ344 had a biphasic effect in both cell types , inducing apoptosis at lower concentrations and necrosis at higher concentrations .
### Output Text:
No necrosis was observed in cells treated with <span class="chemical">NCQ436</span> but <span class="chemical">NCQ344</span> had a biphasic effect in both cell types , inducing apoptosis at lower concentrations and necrosis at higher concentrations . 