1. Natural Products and Organic Synthesis Research Unit (NPOS), Department of Chemistry, Faculty of Science, Kasetsart University, Bangkok, 10900, Thailand, Molecular Innovation, Diversity and Automated Synthesis (MIDAS) Centre, School of Chemistry, Leeds University, Leeds, LS2 9JT, U.K., Department of Chemistry, Faculty of Science, Mahidol University, Bangkok, 10400, Thailand, and Natural Products Research Section, Research Division, National Cancer Institute, Bangkok, 10400, Thailand