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: The effects of PG - 9 ( 3alpha - tropyl 2 - ( p - bromophenyl ) propionate ) , the acetylcholine releaser , on memory processes and nerve growth factor ( NGF ) synthesis were evaluated .
### Output Text:
The effects of <span class="chemical">PG - 9</span> ( <span class="chemical">3alpha - tropyl 2 - ( p - bromophenyl ) propionate</span> ) , the <span class="chemical">acetylcholine</span> releaser , on memory processes and nerve growth factor ( NGF ) synthesis were evaluated . 