There is not currently anything that will map C# to TypeScript. If you have a lot of POCOs or you think they might change often, you could create a converter – something simple along the lines of…
public class MyPoco {
public string Name { get; set; }
}
To
export class MyPoco {
public Name: string;
}
There is also a discussion on Codeplex about auto-generating from C#.
Just to keep things updated, TypeLite can generate TypeScript interfaces from C#: