¹H NMR‐Guided Isolation of Formyl‐Phloroglucinol Meroterpenoids from the Leaves of Eucalyptus robusta

Abstract

Nine formyl-phloroglucinolmeroterpenoids (FPMs), namely, eucalrobusones A-I (1-9), were isolated from the leaves of Eucalyptus robusta by tracking the phenolic hydroxyl (1) H NMR peaks. The Snatzke helicity rules for the Cotton effects of twisted benzene rings were applied to elucidate the absolute configurations of the FPMs. These findings, along with NMR spectroscopy, the circular dichroism (CD) exciton chirality method, and CD calculations, allowed complete structures for the FPMs to be assigned. Eucalrobusones A-F (1-6) are novel adducts formed between a formyl-derived carbon atom on the phloroglucinol ring and monoterpene and sesquiterpene components. Eucalrobusones G-I (7-9) are the first examples of FPMs with cubebane part structures connected by an unusual 1-oxaspiro[5.5]undecane subunit. Among these isolates, eucalrobusone C (3) showed significant cytotoxicity against HepG2, MCF-7, and U2OS cancer cell lines, with IC50 values less than 10 μm. Compound 3 significantly blocks cell proliferation in MCF-7 cells and induces MCF-7 cell death through apoptosis.

New Formyl Phloroglucinol Meroterpenoids from the Leaves of Eucalyptus robusta

“…The ROESY correlations of H-5/H-8 β , H-7/H-8 α , Me-12/H-5, Me-15/H-6, and H-6/H-1 indicated the α -orientations of H-1, H-6, and H-7 and the β -orientations of H-4 and H-5. The absolute configuration was determined by application of the Snatzke’s helicity rule1013141516. The P/M -helicity of the dihydropyran ring in FPMs controlled the signs of Cotton effects approximately between 270–310 nm (Fig.…”

“…Formyl phloroglucinol meroterpenoids (FPMs) are important derivatives of phloroglucinol. Through hetero Diels-Alder reaction678 or nucleophilic addition91011, phloroglucinol of FPMs could couple with different terpene moieties, mainly forming dihydropyran-fused or open-chain structures. In addition, reaction at the active sites of phloroglucinol (C-7′/C-12′/OH-3′) could also generate other coupling patterns, such as macrocarpal A 1 , eucalrobusone A 10 , and eucalyptal A 11 .…”

“…In addition, reaction at the active sites of phloroglucinol (C-7′/C-12′/OH-3′) could also generate other coupling patterns, such as macrocarpal A 1 , eucalrobusone A 10 , and eucalyptal A 11 . In our continuous 1 H NMR-guided isolation10, ten FPMs (Fig. 1) with various spiro-heterocycles and polycyclic systems were isolated from the leaves of Eucalyptus robusta .…”

Hybrid materials of ZnO nanostructures with reduced graphene oxide and gold nanoparticles: enhanced photodegradation rates in relation to their composition and morphology

“…19 In another case of RB degradation using rGO-ZnO NPs, complete degradation is achieved in 60 min. 32,33 However, a one to one comparison with literature values is difficult since the degradation rates are largely dependent on the irradiation power, amount of catalyst and dye concentration. We have provided a comparative table of the reported rate values for various systems in Table S2 (ESI †).…”

In Vitro Antibiofilm Activity of Eucarobustol E against Candida albicans

“…Formyl-phloroglucinol meroterpenoids (FPMs) are an important class of secondary metabolites that are widely available from the genera Eucalyptus and Psidium (14)(15)(16). The past decades have seen increasing reports on structurally diverse FPMs with various bioactivities, such as anti-HIV, antimicrobial, and antitumor effects (17)(18)(19)(20)(21).…”