Interfaces are only at compile time. This allows only you to check that the expected data received follows a particular structure. For this you can cast your content to this interface:
this.http.get('...')
.map(res => <Product[]>res.json());
See these questions:
You can do something similar with class but the main differences with class are that they are present at runtime (constructor function) and you can define methods in them with processing. But, in this case, you need to instantiate objects to be able to use them:
this.http.get('...')
.map(res => {
var data = res.json();
return data.map(d => {
return new Product(d.productNumber,
d.productName, d.productDescription);
});
});