You can search ChEMBL open data base for looking into bioactive copmpounds of your interest. Or you can try with ZINC- a free database for commercially available bioactive copmpounds.

PubChem https://pubchem.ncbi.nlm.nih.gov/ 

ChemSpider http://www.chemspider.com/

and ZINC database are for commercially available bioactive copmpounds.

But you can't download all the files from any single database simultaneously.  

Can we use Zinc or ChemSpider for searching the reported inhibitors against a particular drug target?  

you can use DockBlaster http://blaster.docking.org/ for searching the reported inhibitors against a particular drug target which gives compounds from ZINC database with their ZINC id's 

you can search ChEBI, ZINC database, sureChEMBL etc

Dear Anu Manha,

SwissSimilarity server (http://www.swisssimilarity.ch/) could predict the bioactive compounds from different database, and it is possible to download all the compound features by excel. Also, we can retrieve the .sdf or simile files from individual compound ftp sites.

Thanku @ Dr. D. Rajesh