Using the model deployment and prediction service, I put up the two linear regression models I had built so far (described in more detail here) While REST is nice, a simple web page that allows you to paste a set of SMILES and get back predictions is handy. So I whipped together a simple interface to the prediction service, allowing one to select a model, view the author-generated description and a get a nice (sortable!) table of predicted values. View it here. As noted in my previous post it’s not going to be very fast, but hopefully that will change in the future.
Posts Tagged ‘REST’
Over the past few days I’ve been developing some predictive models in R, for the solubility data being generated as part of the ONS Solubility Challenge. As I develop the models I put up a brief summary of the results on the wiki. In the end however, we’d like to use these models to predict the solubility of untested compounds. While anybody can send me a SMILES string and get back a prediction, it’s more useful (and less work for me!) if a user can do it themselves. This requires that the models be deployed and made available as a web page or a service. Last year I developed a series of statistical web services based on R. The services were written in Java and are described in this paper. Since I’m working more with REST services these days, I wanted to see how easy it’d be to develop a model deployment system using Python, thus avoiding a multi-tiered system. With the help of rpy2, it turns out that this wasn’t very difficult.
The current version of the REST interface to the CDK descriptors allowed one to access descriptor values for a SMILES string by simply appending it to an URL, resulting in something like
This type of URL is pretty handy to construct by hand. However, as Pat Walters pointed out in the comments to that post, SMILES containing ‘#’ will cause problems since that character is a URL fragment identifier. Furthermore, the presence of a ‘/’ in a SMILES string necessitates some processing in the service to recognize it as part of the SMILES, rather than a URL path separator. While the service could handle these (at the expense of messy code) it turned out that there were subtle bugs.
Based on Pats’ suggestion I converted the service to use base64 encoded SMILES, which let me simplify the code and remove the bugs. As a result, one cannot append the SMILES directly to the URL’s. Instead the above URL would be rewritten in the form
All the example URL’s described in my previous post that involve SMILES strings, should be rewritten using base64 encoded SMILES. So to get a document listing all descriptors for “c1ccccc1COCC” one would write
and then follow the links therein.
While this makes it a little harder to directly write out these URL’s by hand, I expect that most uses of this service would be programmatic – in which case getting base64 encoded SMILES is trivial.
As part of my work at IU I have been implementing a number of cheminformatics web services. Initially these were SOAP, but I realized that REST interfaces make life much easier. (also see here) As a result, a number of these services have simple REST interfaces. One such service provides molecular descriptor calculations, using the CDK as the backend. Thus by visiting (i.e., making a HTTP GET request) a URL of the form
you get a simple XML document containing a list of URL’s. Each URL represents a specific “resource”. In this context, the resource is the descriptor values for the given molecule. Thus by visiting
one gets another simple XML document that lists the names and values of the AlogP descriptor. In this case, the CDK implementation evaluates AlogP, AlogP2 and molar refractivity – so there are actually three descriptor values. On the other hand something like the molecular weight descriptor gives a single value. To just see the list of available descriptors visit
which gives an XML document containing a series of links. Visiting one of these links gives the “descriptor specification” – information on the vendor, version, reference to a descriptor ontology and so on.
(I should point out that the descriptors available in this service are from a pretty old version of the CDK. I really should update the descriptors to the 1.2.x versions)
This type of interface makes it easy to whip up various applications. One example is the PCA analysis of compound collections. Another one I put together today based on a conversation with Jean-Claude was a simple application to plot pairs of descriptor values for a collection of SMILES.
The app is pretty simple (and quite slow, since it uses synchronous GET’s to the descriptor service for each SMILES and has to make two calls for each SMILES – hey, it was a quick hack!). Currently, it’s a bit restrictive – if a descriptor calculates multiple values, it will only use the first value. To see how many values a molecular descriptor calculates, see the list here.
With a little more effort one could easily have a pretty nice online descriptor calculation application rivaling a standalone application such as the the CDK descriptor GUI
Which XRay ligands are closest to the Fontaine et al. structure-activity relationship data for allowing structure-based drug design?
using Blue Obelisk tools and ChemSpider and where Fontaine et al. refers to the Fontaine Factor Xa dataset. You should read his post for a nice analysis of the problem. I just wanted to consider two points he had raised.
I recently described a REST based service for performing PCA-based visualization of chemical spaces. By visiting a URL of the form
one would get a HTML, plain text or JSON page containing the first two principal components for the molecules specified. With this data one can generate a simple 2D plot of the distributions of molecules in the “default” chemical space.
However, as Andrew Lang pointed out on FriendFeed, one could use SecondLife to look at 3D versions of the PCA results. So I updatesd the service to allow one to specify the number of components in the URL. The above form of the service will still work – you get the first two components by default.
To specify more components use an URL of the form
where mol1, mol2, mol3 etc should be valid SMILES strings. The above URL will return the first three PC’s. To get just the first PC, replace the 3 with 1 and so on. If more components are requested than available, all components are returned.
Currently, the only available space is the “default” space which is 4-dimensional, so you can get a maximum of four components. In general, visit the URL
to obtain a list of currently available chemical spaces, their names and dimensionality.
While it’s easy to get all the components and visualize them, it doesn’t always make sense to do so. In general, one should consider those initial principal components that explain a significant portion of the variance (see Kaisers criterion). The service currently doesn’t provide the eigenvalues, so it’s not really possible to decide whether to go to 3, 4 or more components. For most cases, just looking at the first two principal components will sufficient – especially given the currently available chemical space.
Update (Jan 13, 2009)
Since the descriptor service now requires that Base64 encoded SMILES, the example usage URL is now invalid. Instead, the SMILES should be replaced by their encoded versions. In other words the first URL above becomes
http://rguha.ath.cx/~rguha/cicc/rest/chemspace/default/ YzFjY2NjYzE=,YzFjY2NjYzFDQw==,YzFjY2NjYzFDQ0M=, Qyg9TylDKD1PKQ==,Q0MoPU8pTw==
I met with Jean-Claude Bradley yesterday and we had a pretty useful hack session, allowing him to easily incorporate chemical and cheminformatics functionality into a GoogleDocs spreadsheet.
A common task that Jean-Claude wanted to automate was the calculation of milligrams (or milliliters) of a chemical required for a certain molarity. So what we need for this calculation is the compound name, desired molarity, molecular weight and the density. Importantly, the people who’d like to use this will provide compound names and not a directly parseable SMILES. So we’d also like to (optionally) get the SMILES. Finally, he wanted to be able to do this in a Google spreadsheet – rather than a specific web page or stand alone program.