Biomedical subjects

N Koumura

Publications and source records attributed to N Koumura.

3 recordsLinked to original sources

PubMed2000

Chiral overcrowded alkenes; asymmetric synthesis of (3S,3'S)-(M, M)-(E)-(+)-1,1',2,2',3,3',4,4'-octahydro-3,3',7,7'-tetramethyl-4, 4'-biphenanthrylidenes.

An asymmetric synthesis route towards (3S,3'S)-(M,M)-(E)-(+)-1,1',2, 2',3,3',4,4'-octahydro-3,3',7,7'-tetramethyl-4,4'-biphenanthrylidene was developed using the Evans procedure as a key step. The absolute configurations of the title compound and of its parent ketone were determined by CD spectroscopy and could be correlated with the stereochemical results of the asymmetric alkylation. Furthermore, a comparison was made with the known (3R,3'R)-(P,P)-(E)-(-)-1,1',2,2', 3,3',4,4'-octahydro-3,3',7,7'-dimethyl-4,4'-biphenanthrylidene. Finally, the X-ray crystallographic analysis of (3S,3'S)-(M, M)-(E)-(+)-1,1',2,2',3,3',4,4'-octahydro-3,3',7,7'-tetramethyl-4, 4'-biphenanthrylidene is presented.

Alkenes↗

PubMed2000

Synthesis, circular dichroism and absolute stereochemistry of 1,1',2,2',3,3',4,4',-octahydro-3,3'-dimethyl-4,4'-biphenanthryl

In the course of synthetic studies of chiral olefins, (3R,3'R)-(P,P)-(E)-(-)-1,1',2,2',3,3',4,4'-octahydro3,3'-dimethyl-4,4'-biphenanthrylidene (1) and its (3R, 3'R)-(P,P)-(Z)-(+)-isomer (2), chiral (3R,3'R,4R,4'R)-(-)-1,1',2,2',3,3',4,4'-octahydro-3,3'-dimethyl-4,4'-biphenanthryl (3) was obtained as a by-product in the McMurry reaction of (3R)-(-)-2,3-dihydro-3-methyl-4(1H)-phenanthrenone (4). The relative and absolute stereostructures of (-)-3 were fully determined by NMR, X-ray crystallographic, and CD spectral analyses.

Journal Article↗

PubMed1999

Light-driven monodirectional molecular rotor.

Attempts to fabricate mechanical devices on the molecular level have yielded analogues of rotors, gears, switches, shuttles, turnstiles and ratchets. Molecular motors, however, have not yet been made, even though they are common in biological systems. Rotary motion as such has been induced in interlocked systems and directly visualized for single molecules, but the controlled conversion of energy into unidirectional rotary motion has remained difficult to achieve. Here we report repetitive, monodirectional rotation around a central carbon-carbon double bond in a chiral, helical alkene, with each 360 degrees rotation involving four discrete isomerization steps activated by ultraviolet light or a change in the temperature of the system. We find that axial chirality and the presence of two chiral centres are essential for the observed monodirectional behaviour of the molecular motor. Two light-induced cis-trans isomerizations are each associated with a 180 degrees rotation around the carbon-carbon double bond and are each followed by thermally controlled helicity inversions, which effectively block reverse rotation and thus ensure that the four individual steps add up to one full rotation in one direction only. As the energy barriers of the helicity inversion steps can be adjusted by structural modifications, chiral alkenes based on our system may find use as basic components for 'molecular machinery' driven by light.

Alkenes↗