Akio Murai

Convergent and short-step syntheses of dl-Cypridina luciferin and its analogues based on Pd-mediated cross couplings

Abstract dl -Cypridina luciferin and its analogues were synthesized from 2-aminopyrazine by an eight-step method that included two regio-selective Pd-mediated cross couplings, and their chemi- and bioluminescent activities were compared. Analogues having a 3-benzofuranyl or a 3-benzothienyl group in the place of a 3-indolyl group showed luciferase affinities similar to Cypridina luciferase but with a lower luminescent efficiency, suggesting that the NH group is unimportant for molecular recognition whereas the indolyl group is crucial for efficient luminescence.

Total synthesis of (+)-laurencin

Abstract The first total synthesis of (+)-laurencin (1), which is the most representative marine natural product isolated from red algae, is described via intermediates 2–18. Key steps in the synthesis include a facile oxidative preparation of 2, an effective conversion of 9a to 11, and a SmI2-catalyzed elongation reaction of 15, providing 16a.

CONVERSION OF PRELAUREATIN INTO LAURALLENE, A BROMO-ALLENE COMPOUND, BY ENZYMATIC AND CHEMICAL BROMO-ETHERIFICATION REACTIONS

Abstract Studies on biomimetic conversion of prelaureatin into laurallene were reported. This unique bromo-allene compound has been assumed to be biogenetically synthesized by bromo-cationic reaction of prelaureatin, an eight-membered ether, containing an enyne unit. The electrophilic bromination afforded laurallene chemically and enzymatically.

Chemi- and bioluminescence of coelenterazine analogues with a conjugated group at the C-8 position

Abstract The chemiliminescent compound coelenterazine is involved in various bioluminescence reactions as the substrates, causing the luminescence with an emission peak in the range of 450–475 nm. Anticipating the introduction of a bathochromicshift of the luminescence, several new coelenterazine analogues that have conjugated olefins or aromatic groups at the 8-position of imidazopyrazinone ring were synthesized. In the chemiluminescence reaction, the emission spectra of a majority of the compounds synthesized showed a bathochromic shift, giving an emission peak in the range of 520–580 nm. In the bioluminescence catalyzed by Oplophorus luciferase, the bisthienyl analogue of coelenterazine emitted a moderate intensity of luminescence (5% of coelenterazine) with an emission maximum at 528 nm, which was the longest wavelength of all the analogues tested.

Synthetic studies on ciguatoxin [1]; construction of the spiro acetal part (C46-C55)

Abstract The spiro acetal part (C46–C55) of ciguatoxin was synthesized stereoselectively.

Zooxanthellatoxin-B, vasoconstrictive congener of zooxanthellatoxin-A from a symbiotic dinoflagellate Symbiodinium sp

Abstract Zooxanthellatoxin-B was isolated from a symbiotic marine alga, Symbiodinium sp. and the structure of zooxanthellatoxin-B was determined to be a 62-membered lactone by comparing spectral data and degradation products with those of zooxanthellatoxin-A.

Efficient Bioluminescence of Bisdeoxycoelenterazine with the Luciferase of a Deep-Sea Shrimp Oplophorus

Abstract The luminescence of the bisdeoxy analogue of coelenterazine ( 1b : X=Y=H) catalyzed by Oplophorus luciferase was highly efficient (0.19 quanta/molecule), almost comparable to the luminescence of unmodified coelenterazine ( 1a : X=Y=OH), whereas the luminescence of 1b was very inefficient when catalyzed by apoaequorin or Renilla luciferase and when the aequorin regenerated with 1b was luminesced with Ca 2+ .

Isolation of zooxanthellatoxins, novel vasoconstrictive substances from the zooxanthella Symbiodinium sp.

Isolation of zooxanthellatoxins, novel vasoconstrictive substances from the zooxanthella Symbiodinium sp. Toxicon 31, 371-376, 1993. New polyhydroxypolyenes with potent vasoconstrictive activity, zooxanthellatoxin-A and -B, were isolated from a symbiotic marine alga Symbiodinium sp. These compounds caused sustained contractions of isolated rabbit aorta at concentrations above 7 x 10(-7) M; this effect was abolished in Ca(2+)-free solution or in the presence of verapamil. Both compounds were relatively large molecules (mol. wt about 2900), containing a large number of oxygen atoms and olefinic carbons, thus differing from two other vasoconstrictive marine toxins, palytoxin and maitotoxin, in containing more olefins than palytoxin, and fewer ethereal rings than maitotoxin.

LA(OTF)3-CATALYZED 7-ENDO AND 8-ENDO SELECTIVE CYCLIZATIONS OF HYDROXY EPOXIDES

Abstract Endo selective intramolecular cyclization has been achieved in 5, 6-epoxy-5-methoxymethyl-1-heptanol and 6, 7-epoxy-6-methoxymethyl-3-octen-1-ol systems by the chelation of La(OTf) 3 between the oxygen atoms of the epoxide and methoxymethyl groups, affording 3-hydroxyoxepane and 3-hydroxy-5-oxocene derivatives, respectively.

Synthetic studies on ciguatoxin [2]; synthesis of the A,B,C-ring system

Abstract The synthesis of the A,B,C-ring system having all the natural substituents of ciguatoxin was achieved from D-glucose.