Angular: Trying to use Observable.from, exported from rxjs/observable, with no luck

seems to be related to #5283?

this code used to work

import from 'angular2/angular2';
Observable.from([
new Response(new ResponseOptions({
body: {
message: "color:red"
}
}))
]);

now after an upgrade to alpha-0.0.50, it stopped working (from 0.0.46).

Observable from angular2 seems to be trimmed down as in #5283.
But would expect the code below still to work as it is not part of angular2:

import from 'rxjs/observable';
Observable.from([
new Response(new ResponseOptions({
body: {
message: "color:red"
}
}))
]);