Acylphloroglucinol-monoterpene meroterpenoids from Eucalyptus tereticornis and their inhibitory activity against ATP citrate lyase

Biomimetic Synthesis and Chemical Proteomics Reveal the Mechanism of Action and Functional Targets of Phloroglucinol Meroterpenoids

Natural products perennially serve as prolific sources of drug leads and chemical probes, fueling the development of numerous therapeutics. Despite their scarcity, natural products that modulate protein function through covalent interactions with lysine residues hold immense potential to unlock new therapeutic interventions and advance our understanding of the biological processes governed by these modifications. Phloroglucinol meroterpenoids constitute one of the most expansive classes of natural products, displaying a plethora of biological activities. However, their mechanism of action and cellular targets have, until now, remained elusive. In this study, we detail the concise biomimetic synthesis, computational mechanistic insights, physicochemical attributes, kinetic parameters, molecular mechanism of action, and functional cellular targets of several phloroglucinol meroterpenoids. We harness synthetic clickable analogues of natural products to probe their disparate proteome-wide reactivity and subcellular localization through in-gel fluorescence scanning and cell imaging. By implementing sample multiplexing and a redesigned lysine-targeting probe, we streamline a quantitative activity-based protein profiling, enabling the direct mapping of global reactivity and ligandability of proteinaceous lysines in human cells. Leveraging this framework, we identify numerous lysine-meroterpenoid interactions in breast cancer cells at tractable protein sites across diverse structural and functional classes, including those historically deemed undruggable. We validate that phloroglucinol meroterpenoids perturb biochemical functions through stereoselective and site-specific modification of lysines in proteins vital for breast cancer metabolism, including lipid signaling, mitochondrial respiration, and glycolysis. These findings underscore the broad potential of phloroglucinol meroterpenoids for targeting functional lysines in the human proteome.

Camaldulensals A-C, the First Meroterpenoids Possessing Two Spatially Separated Formyl Phloroglucinols Conjugated to a Terpene Core from the Leaves of Eucalyptus camaldulensis Dehnh

Three new bis-formyl phloroglucinol-meroterpenoids (1-3), three new euglobal type formyl phloroglucinol-meroterpenoids (4-6), and one new dimeric formyl phloroglucinol (7) were isolated from the leaves of Eucalyptus camaldulensis. Camaldulensal A (1) is the first bis-isovaleryl-formyl-phloroglucinol-sesquiterpenoid. It features a novel 6/6/10/3/6/6 fused ring system and contains six stereogenic centers. Camaldulensals B (2) and C (3) are the first bis-isovaleryl-formyl-phloroglucinols, each conjugated to a monoterpene. Formyl phloroglucinol compounds (FPCs) containing two spatially separated formyl phloroglucinols conjugated to a terpene core such as 1-3 have not been reported previously. The structures of these compounds were elucidated by spectroscopic methods and computational analysis. Camaldulensals B (2) and C (3) exhibited significant antibacterial activity against methicillin-susceptible and methicillin-resistant Staphylococcus aureus. Structure activity relationships are discussed in relation to previously reported antibacterial activities of other molecules from the FPC structure class.