It looks like this guy used T4 to generate a TypeScript proxy to his Web API service. http://galador.net/codeblog/post/2013/11/12/Client-Side-Web-Application-primer.aspx
However, if your only client will be from the browser, you may want to consider using SignalR instead with this T4 template. https://gist.github.com/robfe/4583549
There are also a few libraries that generate TypeScript definition files from CLR types: