Novel total syntheses of (±)-oxerine by intramolecular Heck reaction

Discovery of antibacterial agents targeting biofilm formation: total synthesis and in vitro investigation of amycolasporins

Three monoterpene alkaloids amycolasporin A and (±) amycolasporins B and C have been synthesized for the first time from commercially available materials in yields of 31%, 14% and 21%, respectively. Their six analogues (18, 19, 30a and 30d-30f) were synthesized through a similar protocol. Meanwhile, the antibacterial activity of all synthesized molecules was evaluated, showing different levels of bioactivity. Among them, analogue 30d was screened as the most effective antibacterial candidate against E. coli (MIC value, 12.5 μg mL^-1) and S. aureus (MIC value, 12.5 μg mL^-1). Further investigation showed that 30d obviously inhibited biofilm formation and disrupted the preformed biofilm of E. coli and S. aureus by promoting intracellular ROS release.

Isolation and structure elucidation of pyridine alkaloids from the aerial parts of the Mongolian medicinal plant Caryopteris mongolica Bunge

The seven pyridine alkaloids 1–7, the flavonoid acacetin (8), and L-proline anhydride (9) have been isolated from the aerial parts of the Mongolian medicinal plant Caryopteris mongolica Bunge. The structures of the natural products 1–9 have been assigned by MS, as well as IR, 1D NMR (¹H, ¹³C, DEPT), and 2D NMR (COSY, HSQC, HMBC, NOESY) spectroscopic methods. The compounds 2 and 4–7 represent new chemical structures. Acacetin (8) and L-proline anhydride (9) have been obtained from C. mongolica for the first time.

Four-component bicyclization approaches to skeletally diverse pyrazolo[3,4-b]pyridine derivatives

A novel four-component bicyclization strategy has been established, allowing a flexible and practical approach to 37 examples of multicyclic pyrazolo[3,4-b]pyridines from low-cost and readily accessible arylglyoxals, pyrazol-5-amines, aromatic amines, 4-hydroxy-6-methyl-2H-pyran-2-one, and cyclohexane-1,3-diones. The polysubstituted cyclopenta[d]pyrazolo[3,4-b]pyridines were stereoselectively synthesized through a microwave-assisted special [3+2+1]/[3+2] bicyclization with good control of the spatial configuration of exocyclic double bonds. The novel [3+2+1]/[2+2+1] bicyclization resulted in 17 examples of unreported pyrazolo[3,4-b]pyrrolo[4,3,2-de]quinolones. Reasonable mechanisms for forming two new types of multicyclic pyrazolo[3,4-b]pyridines are also proposed.

Use of the Oxazole-Olefin Diels-Alder Reaction in the Total Synthesis of the Monoterpene Alkaloids (-)-Plectrodorine and (+)-Oxerine

A full account of the total synthesis of two monoterpene alkaloids, (-)-plectrodorine [(-)-1] and (+)-oxerine [(+)-3], is presented. The key steps involved are the formation of the oxazole alcohol 10 from the gamma-butyrolactone 9 and the intramolecular Diels-Alder reaction of the oxazole-olefins 13a, b. Since the sign of specific rotation for the synthetic (+)-3 was different from that reported for natural oxerine, the absolute configuration of this alkaloid is not yet fully understood.