Hai-Bo Tan

Visible-Light-Promoted Vinylation of Tetrahydrofuran with Alkynes through Direct C–H Bond Functionalization

Mild and direct C-H bond functionalizations and vinylations of tetrahydrofuran with alkynes have been accomplished through visible light photocatalysis, yielding a range of vinyl tetrahydrofurans under the synergistic actions of organic dye-type photocatalyst eosin Y, tert-butyl hydroperoxide (t-BuOOH), and a 45 W household lightbulb. A significant kinetic isotope effect (KIE) was recorded, which helps shed light on the mechanistic course.

Enantioselective Organocatalytic Mannich Reactions with Autocatalysts and Their Mimics

The Mannich reactions previously extensively investigated with organocatalysis of l-proline and other related small molecules were reinvestigated with detailed stereochemical analysis of their autocatalysis pathways, through employment of both the products themselves and their close structural mimics as the catalysts. These organo-autocatalytic processes function as meaningful molecular models toward understanding the origin and maintenance of homochirality under biologically relevant conditions.

Isolation and biomimetic total synthesis of tomentodiones A–B, terpenoid-conjugated phloroglucinols from the leaves of Rhodomyrtus tomentosa

Tomentodiones A (1) and B (2), a pair of C-11′ epimers of caryophyllene-conjugated phloroglucinols with an unprecedented skeleton, were isolated from the leaves of Rhodomyrtus tomentosa. Their structures were elucidated through the application of extensive spectroscopic measurements with the absolute configuration of 1 determined by single-crystal X-ray diffraction analysis and electronic circular dichroism (ECD) calculations. The biogenetic pathways of 1 and 2 were proposed to involve an intermolecular, inverse electron demand Diels–Alder cycloaddition reaction as the key step, and their biomimetic total synthesis was accomplished.

Isolation, synthesis, and biological activity of tomentosenol A from the leaves of Rhodomyrtus tomentosa

Tomentosenol A (1), along with a pair of epimers, 4S-focifolidione (2) and 4R-focifolidione (3), were isolated from the leaves of Rhodomyrtus tomentosa. 1 was the first example of a new meroterpenoid class with a unique skeleton that contained a free syncarpic acid coupled with a terpenoid unit, and showed excellent antimicrobial and cytotoxic activities. The absolute configuration of 1 was unambiguously determined by a chemical conversion between 1 and the predetermined 2. In contrast to the common hetero Diels–Alder cycloaddition embodied in previously reported meroterpenoid biosynthesis, an Alder-ene reaction was proposed as the key transformation to account for the biosynthesis of 1, which was confirmed by a biomimetic total synthesis.

Antimicrobial acylphloroglucinols from the leaves of Rhodomyrtus tomentosa

Abstract Phytochemical study on the leaves of Rhodomyrtus tomentosa resulted in the isolation of fourteen compounds including a new acylphloroglucinol, named tomentosone C (1), and a new flavonol glycoside, namely myricetin-3,7,3′-trimethyl ether-5′-O-β-glucopyranoside (2). Their structures were characterized by spectral data interpretation for new structures and in comparison with published data for known compounds. The antimicrobial activity evaluation revealed that 1 and the known acylphloroglucinol rhodomyrtone (3) exhibited significant antimicrobial activity with MIC 3.66 and 1.83 μg ml−1, respectively, toward Staphylococcus aureus, responsible for the antimicrobial activity observed with the n-hexane and EtOAc-soluble fraction of the ethanol extract of R. tomentosa leaves.

Acylphloroglucinols from the leaves of Callistemon viminalis

A phytochemical study on the leaves of Callistemon viminalis, a widely distributed ornamental and medicinal plant of agricultural importance in China, resulted in the isolation of eleven acylphloroglucinols, including six new ones named callistenones F-K (1-6), as well as five known congeners. Their structures were fully characterized using spectral data interpretation for the new structures and compared to published data for the known ones. All the isolated compounds were evaluated for in vitro antimicrobial activity and growth inhibitory activity against four tumor cell lines (MCF-7, NCI-H460, SF-268 and HepG-2).

Callviminols A-E, new terpenoid-conjugated phloroglucinols from the leaves of Callistemon viminalis.

Callviminols A-E (1-5), five rare phloroglucinols bearing a framework embodying a hexahydrodibenzo[b,d]furan or 2-phenylcyclohexanol nucleus derived from a phloroglucinol-monoterpene adduct, were isolated from the leaves of Callistemon viminalis. Their structures were established via extensive spectroscopic measurements, with the absolute configuration of 5 determined by electronic circular dichroism (ECD) calculations. The plausible biogenetic pathway suggested that a unique oxidative radical addition and classic cationic cyclization were key biosynthetic steps.

Biomimetic Total Syntheses of Linderaspirone A and Bi-linderone and Revisions of Their Biosynthetic Pathways

Simple exposure to sunlight is sufficient for triggering photochemical [2 + 2] cycloaddition-Cope or radical rearrangement cascades in the naturally occurring methyl linderone, leading to efficient biomimetic total syntheses of linderaspirone A and bi-linderone, two recently discovered bioactive spirocyclopentenedione natural products.

Three new highly-oxygenated metabolites from the endophytic fungus Cytospora rhizophorae A761

Cytosporaphenones A-C, one new polyhydric benzophenone and two new naphtopyrone derivatives, along with eight known ones, were isolated from Cytospora rhizophorae, an endophytic fungus from Morinda officinalis. Their structures were fully characterized by means of detailed spectroscopic analysis and X-ray single crystal diffraction. To our knowledge, the three new compounds were the most highly oxygenated metabolites of their families discovered in nature. Moreover, all of the compounds were evaluated for in vitro cytotoxic activities against MCF-7, NCI-H460, HepG-2 and SF-268 tumor cell lines, and the new compound 1 exhibited weak growth inhibitory activity against the tumor cell lines MCF-7 and HepG-2 with IC50 values of 70 and 60μM, respectively.

Biomimetic-Inspired Syntheses of Myrtucommuacetalone and Myrtucommulone J

Driven by bioinspiration and appreciation of their structures, the first biomimetic total syntheses with structural revision of the acylphloroglucinols myrtucommulone J and myrtucommuacetalone, two biologically meaningful natural products, were achieved through a biosynthetic hemiacetalization/dehydration/[3 + 3]-type cycloaddition domino sequence with high step efficiency. These syntheses result in a corrected structure for myrtucommulone J.