// A *self-contained* demonstration of the problem follows...

// There doesn't seem to be an API to create an Interface in the AST programmatically
const _implementsClause = ts.createHeritageClause(ts.SyntaxKind.ImplementsKeyword, [
    ts.createExpressionWithTypeArguments([], ts.createIdentifier('MyInterface'))
]);
const _exportModifier = ts.createToken(ts.SyntaxKind.ExportKeyword);
const _classExpression = ts.createClassExpression([_exportModifier], 'MyClass', [], [_implementsClause], []);
const _classStatement = ts.createStatement(_classExpression);

let src = ts.createSourceFile('output.ts', '', ts.ScriptTarget.ES5, false, ts.ScriptKind.TS);
src = ts.updateSourceFileNode(src, [_classStatement]);