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: Such organophosphorus ( OP ) compounds as diisopropylfluorophosphate ( DFP ) , sarin and soman are potent inhibitors of acetylcholinesterases ( AChEs ) and butyrylcholinesterases ( BChEs ) .
### Output Text:
Such <span class="chemical">organophosphorus</span> ( <span class="chemical">OP</span> ) compounds as <span class="chemical">diisopropylfluorophosphate</span> ( <span class="chemical">DFP</span> ) , <span class="chemical">sarin</span> and <span class="chemical">soman</span> are potent inhibitors of acetylcholinesterases ( AChEs ) and butyrylcholinesterases ( BChEs ) . 