Yes, you can.
Go read this guide. Pressing the ES5 tab on the code examples will show you regular ES5 JavaScript, as apposed to TypeScript.
The API preview is, for obvious reasons, incomplete though. So you may not find the ES5 methods listed there yet, and some of it may change before release.
Current example of Angular 2.0 main component in ES5.
function AppComponent() {}
AppComponent.annotations = [
new angular.ComponentAnnotation({
selector: 'my-app'
}),
new angular.ViewAnnotation({
template: '<h1>My first Angular 2 App</h1>'
})
];
document.addEventListener('DOMContentLoaded', function() {
angular.bootstrap(AppComponent);
});