Research
The synthesis of structurally complex natural products provides not only stringent tests of known methods and reactions but also opportunities to devise new synthetic methods and strategies. It also has the ability to make contributions in biology by making designed analogues as well as by providing the natural substance. Our research is focused on the synthesis of architecturally novel, biologically active natural products, and the development of new reactions and strategies for organic synthesis.
１．Total Synthesis of Marine Toxins with a Spiroimine Moiety
Pinnatoxins, considered as culprits in shellfish poisoning, are reported to activate calcium channels. We completed the total synthesis of pinnatoxin A, wherein key features include (1) the tandem double hemiketal formation/intramolecular hetero-Michael addition sequence, (2) the exo-selective Diels−Alder reaction, (3) the Ru-catalyzed cycloisomerization, and (4) the formation of the seven-membered cyclic imine by self-catalyzed dehydration. Efforts toward a total synthesis of spirolides, nicotinic acetylcholine receptor antagonists, are currently underway.
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Total Synthesis of Pinnatoxin A
２．Total Synthesis of Polygalolides
Polygalolides A and B were isolated from a medical plant used as tonics and antihepatitis drugs in China. We accomplished the first total synthesis of these natural products by a tandem carbonyl ylide formation/intramolecular 1,3-dipolar cycloaddition approach. Comparison of specific rotations of the synthetic materials and natural products suggests that polygalolides are biosynthesized in nearly racemic forms through a [5+2] cycloaddition between a fructose-derived oxypyrylium zwitterion with an isoprene derivative.
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Total Synthesis of Polygalolides A and B
３．Studies toward the Total Synthesis of Antitumor Saponins
Scillascillosides, eucosterol oligoglycosides isolated from a traditional Chinese medicine, were found to exhibit cytotoxicity against several tumor cells. We have already synthesized the oligosaccharide subunit of scillascilloside E-1, and our efforts are currently focused on the synthesis of its aglycon.
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Structure of Scillascilloside E-1
Laboratory of Synthetic Organic Chemistry
Graduate School of Pharmaceutical Sciences
Nagoya City University
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