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: Via the sequential isolation of Pueraria thunbergiana , the active component was ultimately identified as daidzein ( 4 ' , 7 - dihydroxy - isoflavone ) .
### Output Text:
Via the sequential isolation of Pueraria thunbergiana , the active component was ultimately identified as <span class="chemical">daidzein</span> ( <span class="chemical">4 ' , 7 - dihydroxy - isoflavone</span> ) . 