Typescript definitions for sendgrid

I am trying to write a typescript app that uses sendgrid, but unlike with other definitions I got from typings the one from typings install sendgrid --ambient is causing me some headaches:

I am able to instantiate the client like so:

import * as sendgrid from 'sendgrid';
import Email = Sendgrid.Email;
import Instance = Sendgrid.Instance;
...
private client: Instance;
...
this.client = sendgrid(user, key);

And then later in the code I am trying to send an email, which is why ts is forcing me to import the EMail interface in the first place.

var email = new Email();
...
this.client.send(email, (err, data) => {
        if (err) {
            throw err;
        }
    });

tslint doesn't throw any error, but when I build and run the program (or just my tests), I get this:

Mocha exploded! ReferenceError: Sendgrid is not defined at Object. (/Users/chrismatic/codingprojects/weview/weview-node/build/server/components/mail/clients/sendgrid.js:4:13)

Has anybody a working implementation to showcase, or do I have to write my own interface? Thanks in advance for the help

EDIT:

The generated js file looks something like this:

var sendgrid = require('sendgrid');
var Email = Sendgrid.Email;

If I decapitalize "Sendgrid", then the error disappears, but I can't do so in the ts file

This should give you an idea on how to use SendGrid's typescript definitions.

import * as SendGrid from 'sendgrid';

export class SendGridMail extends SendGrid.mail.Mail {}
export class SendGridEmail extends SendGrid.mail.Email {}
export class SendGridContent extends SendGrid.mail.Content {}

export class SendGridService {
  private sendGrid;

  constructor(private sendgridApiKey: string) {
    this.sendGrid = SendGrid(sendgridApiKey);

  }

  send(mail: SendGridMail): Promise<any> {

    let request = this.sendGrid.emptyRequest({
      method: 'POST',
      path: '/v3/mail/send',
      body: mail.toJSON()
    });

    return this.sendGrid.API(request);
  }

}

Here is how I used the class above:

let mail = new SendGridMail(
      new SendGridEmail('from@example.com'),
      'Sending with SendGrid is Fun',
      new SendGridEmail('to@example.com'),
      new SendGridContent('text/plain', 'Email sent to to@example.com'));


return this.sendgridService.send(mail);