Basic authentication http request

Ionic Framework ionic-v3
1

hi guys…i am having some issues with my authentications
i have tested the url in soapUI and it worked but did not work in postman though
here is the code
var headers = new Headers();
headers.append(‘Authorization’,'Basic '+ ‘username’ );
var options = new RequestOptions({headers:this.headers});
return new Promise(resolve => {
this.http.get(this.Url,options)
.subscribe((res) => {

        resolve(res.json());
    },
    err => {
      console.log(err);
      alert(err);
    });
})

can you guys help me please