Showing papers by "Susumu Kobayashi published in 1987"

An enantioselective synthesis of (−)-fortamine

Abstract: The aminocyclitol moiety of fortimicin A, (−)-fortamine, was synthesized in an enantioselective manner starting from the chiral half ester, easily available by the enantioselective hydrolysis of a symmetrical diester with pig liver esterase. The present approach provides a general and efficient route to variously substituted 1,4-diaminocyclitol-derivatives.

A Molecular Design toward Biologically Significant Compounds based on PAF Structures

Abstract: Since the identification of platelet activating factor (PAF) as alkylacetylglycerophosphocholine, a number of constitutional analogues have been prepared by many laboratories including ours. However those simple constitutional modification of PAF could not make any substantial advance toward the discovery of any useful compounds. At least, one of the most important synthetic goals may be the elaboration of a more selective analogue that keeps good antihypertensive activity with lower platelet aggregation. A molecular design was carried out in such a way to lock or localize the conformational isomers of PAF by introducing methyl group in the glycerine moiety. Thus, tartaric acid strategy allowed us to introduce methyl group at C1 or C3 diastereoselectively and enantioselectively to afford all isomers. Among them, 1 S -Me-PAF has been shown to be the first selective agonist, possessing much stronger antihypertensive activity than PAF itself by oral dose, and rather low platelet activation. The results will be discussed.

Monocyclic .BETA.-lactam antibiotics: Synthesis and antibacterial activity of 4-(substituted ethyl)-2-azetidinone-1-sulfonic acid derivatives.

Abstract: The synthesis and antibacterial activity of sodium (3S,4R)-3-[2-(2-aminothiazol-4-yl)-(Z)-2-(O-substituted oxyimino)acetamido]-2-azetidinone-1-sulfonates having various substituted ethyl groups at the C-4 position are described. Among various substituents explored, the (substituted isothiuronio)ethyl groups were found to have strong antibacterial activity against a variety of Gram-negative bacteria, and moreover, the ethylene isothiuronium derivative exhibited moderate antibacterial activity against Staphylococcus aureus.

Power enhancement in argon II narrow-tube lasers due to zeeman effect by a transverse magnetic field

Abstract: The role of the Zeeman effect for the power enhancement of a small-bore argon ion laser (488.0 nm) by applying the transverse magnetic field has been investigated both experimentally and theoretically. The σ-polarized laser has a larger output power than the π-polarized laser in the wide range of magnetic field strength. Specifically, at weak magnetic fields, enhancement occurred only for the σ-polarized laser. The experimental results are interpreted in terms of the semiclassical theory of the Zeeman laser. A narrow spectrum envelope is observed in the σ-polarized laser. In the case of internal mirrors without Brewster window, it is demonstrated experimentally that π and σ polarization coexist and compete with each other.

Synthesis and biological activity of fluorine-modified platelet activating factors.

Abstract: Fluorine-modified acetyl glyceryl ether phosphorylcholines (platelet activating factors; PAFs) were efficiently synthesized in an enantioselective manner by the coupling of a D-threitol.derivative with fluorinated long-chain alkoxy methanesulfonates. The introduction of a trifluoromethyl group at the terminal of the alkyl ether chain decreased the hypotensive activity and platelet activation considerably. As the number of fluorine atoms in the alkyl ether chain was increased, both activities were gradually restored, but no selective agonist was obtained from among the fluorinated PAFs.

Molecular Design Toward Biologically Significant Compounds Based on Platelet Activating Factor: A Highly Selective Agonist as a Potential Antihypertensive Agent.

Abstract: Synthese enantioselective de S- et R-[trimethylammonio-2ethyl] phosphate de (O-acetyl-3 desoxy-1 O-palmityl-2) tetritol

An Enantioselective Synthesis of (-)-Fortamine.

Abstract: The aminocyclitol moiety of fortimicin A, (−)-fortamine, was synthesized in an enantioselective manner starting from the chiral half ester, easily available by the enantioselective hydrolysis of a symmetrical diester with pig liver esterase. The present approach provides a general and efficient route to variously substituted 1,4-diaminocyclitol-derivatives.

Stereocontrolled Synthesis of 6-epi-D-Purpurosamine B by Iodocyclocarbamation of a Chiral Z-Olefin Derived from L-Alanine and L-Malic Acid.

Abstract: 6-epi-D-Purpurosamine B was synthesized efficiently through a chiral Z-olefin 8 derived from L-alanine and L-malic acid under complete stereochemical control by using iodocyclocarbamation as the key reaction.

Synthesis of cis-Substituted β-Lactams, Potential Intermediates for cis-Carbapenems, from L-Aspartic Acid.

Abstract: (3S)-3-Benzyloxycarbonylamino-γ-butyrolactone was prepared by the regioselective reduction of L-aspartic acid. Alkylation and aldol condensation of the γ-butyrolactone afforded the trans isomer selectively. The resulting 2, 3-trans γ-butyrolactone was hydrolyzed and then cyclized to give the 3, 4-cis β-lactam. By taking advantage of this strategy, key intermediates of epi-PS-5 and carpetimycins were synthesized.