Mānuka Honey and Leaf Bioactives: A Review of Taonga Natural Products From Leptospermum scoparium

Mānuka ( Leptospermum scoparium Myrtaceae), a shrub that grows throughout Aotearoa New Zealand, is highly valued for the medicinal properties of its bioactive natural products. This first comprehensive review of mānuka chemistry examines traditional uses and cultural significance to Māori; botany and genetics showing its distinctness from Australian Leptospermum species and natural products chemistry and bioactivity. Mānuka nectar is a rich source of dihydroxyacetone (DHA), a precursor to the potent antibacterial methylglyoxal that is generated in mānuka honey. DHA has only been found in the nectar of mānuka and of some Australian Myrtaceae. The worldwide popularity of mānuka honey has led to high prices and honey fraud, so analytical markers for authentication and adulteration are discussed. Mānuka leaf oils have different bioactives from nectar and honey, with some rich in rare triketones active against antibiotic‐resistant Gram‐positive bacteria. These volatile triketones, which are also herbicidal, are high only in one regional chemotype. Unique nortriketones and unusual flavonoids with relaxant activity are found in other mānuka, all encapsulated within leaf oil glands. Advances in the knowledge of the genetics and biosynthesis of the valuable mānuka molecules in this ‘chemical crop' are summarised, and future research directions are proposed.