Customizing ngb-typeahead button (dropdown-item) in anglular

Question

<ng-template #userTypeaheadTemplate let-r="result" let-t="term">
    <ngb-highlight [result]="r.value" [term]="t"
             [ngClass]="r.roleId == 6 ? 'disabled-user' : ''">
    </ngb-highlight>
</ng-template>

Added above template for customized template for angular bootstrap typahead but not being able to add class to it's parent which is button.dropdown-item. Can I get any reference or anything for the same?