1. Department of Chemistry, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
2. Chemistry Division, Centre for Foundation Studies in Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
3. 1Department of Chemistry, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia 2Centre for Natural Products and Drug Discovery (CENAR), Universiti Malaya, 50603 Kuala Lumpur, Malaysia