text: user2945: If you're looking at the entry for a ligand, for example, adenosine, there's a link on the webpage to entries for which this entry exists as a free ligand. 
  However, I want to access this via the API and can't seem to find docs/info on how to do that. 
  I have been looking at the fields you can use to get custom reports.  
  
  user266: I'm not sure about the RCSB, but you can get such a list from the PDBe REST API, as documented in the compounds section:
  http://www.ebi.ac.uk/pdbe/api/pdb/compound/in_pdb/ADN
  Alternatively, from an older service:
  http://www.ebi.ac.uk/pdbe-srv/pdbechem/PDBEntry/download/ADN
  
original_text: 2945: <p>If you're looking at the entry for a ligand, for example, <a href="http://www.rcsb.org/ligand/ADN" rel="nofollow noreferrer">adenosine</a>, there's a link on the webpage to entries for which this entry exists as a free ligand. 
  However, I want to access this via the API and can't seem to find docs/info on how to do that. </p>
  
  <p>I have been looking at the fields you can use to get <a href="https://www.rcsb.org/pdb/results/reportField.do" rel="nofollow noreferrer">custom reports</a>.  </p>
   266: <p>I'm not sure about the RCSB, but you can get such a list from the PDBe REST API, as documented in the <a href="http://www.ebi.ac.uk/pdbe/api/doc/compounds.html" rel="nofollow noreferrer">compounds section</a>:</p>
  
  <p><a href="http://www.ebi.ac.uk/pdbe/api/pdb/compound/in_pdb/ADN" rel="nofollow noreferrer">http://www.ebi.ac.uk/pdbe/api/pdb/compound/in_pdb/ADN</a></p>
  
  <p>Alternatively, from an older service:</p>
  
  <p><a href="http://www.ebi.ac.uk/pdbe-srv/pdbechem/PDBEntry/download/ADN" rel="nofollow noreferrer">http://www.ebi.ac.uk/pdbe-srv/pdbechem/PDBEntry/download/ADN</a></p>
  