Recently I started refactoring one of the Angular projects I am working on with TypeScript. Using TypeScript classes to define controllers is very convenient and works well
This article pretty much covers it and the answer from tanguy_k is pretty much verbatim the example given in the article. It also has all the motivation of WHY you would want to write the class this way. Inheritance, type checking and other good things...
http://blog.aaronholmes.net/writing-angularjs-directives-as-typescript-classes/