To best way to get started is to have a look at some example URLs requesting data from the ChEMBL web services. The table below provides a list of examples and a description of the data being returned.
It is now possible to download all data from a specific ChEMBL web service resource. This is made possible by returning responses from the web services in 'pages', which can be navigated through using a 'page_meta' section. The 'page_meta' section includes information about total number of hits, total number of pages and links to the next and previous pages. An example 'page_meta' section is displayed below:
The 'Substructure' and 'Similarity' web service resources allow for the chemical content of ChEMBL to be searched. Similar to the other resources, these search based resources except filtering, paging and ordering arguments. These methods accept SMILES, InChI Key and molecule ChEMBL_ID as arguments and in the case of similarity searches an additional identity cut-off is needed. Some example molecule searches are provided in the table below.
Chemical Search Description
Substructure search for against ChEMBL using aspirin SMILES string
Searching with InChI key is only possible for InChI keys found in the ChEMBL database. The system does not try and convert InChI key to a chemical representation.
The Image resource returns a graphical representation of a ChEMBL molecule. Unlike the other resources it does not except filtering and paging arguments, but does except image specific arguments. These are defined in the table below.
In GET request all the parameters has to be encoded into URL. Because there is a limitation of how long a URL can be it's often more convenient to use POST requests instead. POST parameters are embedded into request body and can be of any size. This is especially important when retrieving a long list of entities identified by (random) IDs.
ChEMBL API supports both GET and POST but since POST has a special meaning in REST protocol (CREATE), a special header has to be added to every POST request:
Another issue is character encoding. SMILES strings often contain characters (such as #, % or \) that have a special meaning in URLs. This is why when using GET, all parameters should be percent-encoded.
To help users get started with using the updated ChEMBL web services the existing web service client has also been released. This is written in the Python programming language and is available to install from Python Package Index by typing: