Showing papers by "Masahiro Murakami published in 1999"

Cleavage of Carbon—Carbon Single Bonds by Transition Metals

Abstract: Cleavage of carbon-carbon bonds by transition metals under homogeneous conditions has recently received much scientific and technological interest. In this review, an overview of this field is presented. The first part deals with stoichiometric reactions involving carbon-carbon bond breaking. The second part features catalytic reactions, especially those related to organic synthesis.

Catalytic asymmetric 4 + 1 cycloaddition of vinylallenes with carbon monoxide : reversal of the induced chirality by the choice of metal

Abstract: Rhodium(I) and platinum(0) complexes having a chiral ligand, 1,2-bis(2,5-dialkylphosphorano)benzene, effected an asymmetric carbonylative [4 + 1] cycloaddition reaction of vinylallenes. Useful levels of asymmetric induction were attained even with substrates lacking directive heteroatom functionalities. The highest enantioselectivity of 95.0% ee was achieved in the rhodium-catalyzed reaction of a vinylallene bearing an ester group. Whereas the enantioselectivities of the rhodium-catalyzed reactions were significantly affected by the substrate structures, the platinum-catalyzed reactions generally presented good enantioselectivities over 70% ee. In particular, the observed absolute configurations were opposite to those observed in the rhodium-catalyzed reactions. The reversal of the induced chirality according to the center metal employed was interpreted mechanistically.

Five new cyanobacterial peptides from water bloom materials of lake Teganuma (Japan)

Abstract: Five new cyanobacterial peptides, named microginins T1 (1) and T2 (2), micropeptins T1 (3) and T2 (4) and anabaenopeptin T (5), were isolated from cyanobacterial water bloom materials of lake Teganuma (Japan), collected in 1994, 1995 and 1997. Their structures were determined by two-dimensional 1H-1H and 1H-13C NMR correlation experiments and confirmed by mass spectral and amino acid analyses. Their stereochemistries were deduced by spectral and chemical studies. The peptides showed a unique pattern of inhibition when tested in assays for trypsin, plasmin, chymotrypsin, leucine aminopeptidase, carboxypeptidase A and angiotensin-converting enzyme. Each peptide inhibited at least one and sometimes two proteases with characteristic IC50 values.

Goniodomin A induces modulation of actomyosin ATPase activity mediated through conformational change of actin

Abstract: Goniodomin A induced a potent stimulation of the actomyosin ATPase activities of actin-myosin reconstituted system and natural actomyosin. Interestingly, these stimulatory effects of goniodomin A were significantly inhibited by troponin-tropomyosin complex. The ATPase activity of skeletal muscle myofibrils and the contractile response of skinned fibers to Ca2+ were never activated and were decreased by this compound, suggesting inhibition by troponin-tropomyosin complex. In the analysis of the far-ultraviolet circular dichroism spectra, goniodomin A caused a concentration-dependent increase in alpha-helical content of actin. Goniodomin A inhibited the ATPase activities of atrial myofibrils, naural actimyosin and reconstituted actomyosin. Interestingly, these ATPase activities of ventricular muscle were enhanced by goniodomin A. The stimulatory effect of goniodomin A was significantly inhibited by troponin-tropomyosin complex. Goniodomin A increased the intracellular content of F-actin and caused the change in its distribution in 1321N1 cells. Goniodomin A-induced inositol phosphates accumulation in 1321N1 cells was reduced by C3 exoenzyme but was not affected by pertussis toxin. These results suggest that goniodomin A affects actin directly to modify the actin-myosin interaction and that goniodomin A-induced activation of the actomyosin ATPase activity may be physiologically significant because its activation is sensitive to the regulatory protein system, troponin-tropomyosin complex.

Prenylagaramides A and B, new cyclic peptides from two strains of oscillatoria agardhii

Abstract: Prenylagaramides A (1) and B (2), two new cyclic peptides, were isolated from the cultured cyanobacteria Oscillatoria agardhii (NIES-205) and O. agardhii (NIES-596), respectively. The structures of 1 and 2, which both contain a rare O-prenyltyrosine (Ptyr) unit, were established as cyclo(-Ptyr1-Gly2-Thr3-Gly4-Glu5-Phe6-Phe7-Asn8-Pro9-) and cyclo(-Ptyr1-Leu2-Tyr3-Pro4-Ile5-Asn6-Pro7-), respectively, by spectroscopic analysis and chemical degradation.

Powerful activation of skeletal muscle actomyosin ATPase by goniodomin A is highly sensitive to troponin/tropomyosin complex.

Abstract: Goniodomin A has been shown to cause the conformational change of actin to modify actomyosin ATPase activity. Goniodomin A induced a potent stimulation of the actomyosin ATPase activities of the actin-myosin reconstituted system and natural actomyosin in the range of 10−8 to 10−7 M. When the concentration was increased above 10−7 M, actomyosin ATPase activity was decreased. Interestingly, the troponin/tropomyosin complex caused a concentration-dependent inhibition of the goniodomin A-induced stimulation of actomyosin ATPase activity. In the presence of a high concentration of the troponin/tropomyosin complex, goniodomin A decreased actomyosin ATPase activity in a concentration-dependent manner. The enhancement of the ATPase activity of troponin/tropomyosin-free natural actomyosin by goniodomin A was larger than that obtained with natural actomyosin. Goniodomin A at lower concentrations enhanced the superprecipitation of natural actomyosin but decreased it at higher concentrations. The ATPase activity of skeletal muscle myofibrils and the contractile response of skinned fibers to Ca2+ were never activated and were decreased by this compound, suggesting an inhibition by the troponin/tropomyosin complex. In the far ultraviolet circular dichroism, goniodomin A above 10−8 M increased the negative ellipticity at 220 nm, suggesting an increase in the α-helical content of actin. These results suggest that goniodomin A increases and decreases actomyosin ATPase activity, probably through the stimulatory and inhibitory sites on actin, respectively. It is also suggested that the troponin/tropomyosin complex binds to actin to inhibit the goniodomin A-induced enhancement of actomyosin ATPase activity, probably by affecting the stimulatory site on the molecule.

Occurrence and identification of UDP-N-acetylmuramyl-pentapeptide from the cyanobacterium Anabaena cylindrica.

Abstract: UDP-N-acetylmuramyl-pentapeptide (UDP-MurNAc-pentapeptide) is well known to be a key intermediate of bacterial peptidoglycan biosynthesis. We first detected the occurrence of UDP-MurNAc-pentapeptide in the cyanobacterium Anabaena cylindrica (NIES-19), and identified the structure of this pentapeptide by two-dimensional 1H-1H and 1H-13C NMR correlation experiments and mass spectra.

Rhodium-Catalyzed Intermolecular [4 + 2] Cycloaddition of Unactivated Substrates.

Abstract: No electron-withdrawing or electron-releasing substituents are necessary for the substrates in the rhodium-catalyzed [4+2] cycloaddition reaction between a vinylallene and an ordinary alkyne under mild conditions [Eq. (1)]. The use of the strongly electron-accepting P[OCH(CF3 )2 ]3 ligand affords the optimal rhodium catalyst. cod = 1,5-cyclooctadiene.