Won Koo Lee

Selective Mono‐BOC Protection of Diamines

Abstract A facile route for mono‐BOC protection of symmetrical and unsymmetrical diamines was developed by sequential additions of 1 mol of HCl and 1 mol of (BOC)2O followed by neutralization.

Regiospecific reductive ring cleavage of N-substituted aziridine-2-carboxylates and an aziridine-2-methanol via catalytic hydrogenation using Pd as a catalyst

Regiospecific reductive ring cleavage was accomplished in the reaction of N-α-methylbenzyl substituted aziridine-2-carboxylate and aziridine-2-methanol under a catalytic hydrogenation condition. The regiospecificity was determined by the substituent at C-2.

Aminostyrylbenzofuran derivatives as potent inhibitors for Aβ fibril formation

The synthesis of a novel series of aminostyrylbenzofuran derivatives 1a-w and their inhibitory activities for Abeta fibril formation were described. All the synthesized compounds were evaluated by thioflavin T (ThT) assay and displayed potent inhibitory activities for Abeta fibril formation. Among them, compounds 1i and 1q exhibited excellent inhibitory activities (IC(50)=0.07 and 0.08 microM, respectively) than those of Curcumin (IC(50)=0.80 microM) and IMSB (IC(50)=8.00 microM) as reference compounds. Both compounds were selected as promising candidates for further biological evaluation.

Preparation of cysteinol derivatives by highly regioselective ring opening of nonactivated chiral aziridines by thiols

Various enantiomerically pure aziridine-2-methanol derivatives 3a-1 were reacted with thiophenol in methylene chloride at room temperature to obtain ring-opening products 4a-1 in high yields with excellent regioselectivity. The reaction procedure is very simple and it provides highly functionalized chiral molecules potentially useful for the synthesis of many biologically important compounds. The reaction rate was found to increase with the acidity of thiols.

New synthesis and ring opening of cis-3-alkylaziridine-2-carboxylates

Abstract Syntheses of cis-3-alkylaziridine-2-carboxylates including cis-3-benzyl- and cis-3-phenylaziridine-2-carboxylates were achieved from the reaction of α-aminonitrile and alkyldiazoacetate in the presence of a Lewis acid. Asymmetric version of this reaction with the chiral α-methylbenzylamine was also successful for the preparation of chiral aziridines that were used for the synthesis of various amino acids including homophenylalanine, β-amino-α-hydroxy acid, α,β-diamino acid, and α-amino-β-hydroxy acid via regioselective aziridine ring openings.

Stereoselective synthesis of protected threo-β-hydroxy-l-glutamic acid using a chiral aziridine

Abstract Threo -β-hydroxy- l -glutamic acid derivatives with different carboxylic acid protecting groups were stereoselectively prepared from a chiral aziridine-2-carboxylate using an aldol reaction, stereoselective ketone reduction, and aziridine ring transformation.

Dihydroxylation of 2-vinylaziridine: efficient synthesis of D-ribo-phytosphingosine

An efficient and highly stereoselective synthesis of D-ribo-(2S,3S,4R)-phytosphingosine was accomplished in 62% overall yield starting from commercially available (2S)-hydroxymethylaziridine via osmium-catalyzed asymmetric dihydroxylation as a key step.

The preparation of stable aziridinium ions and their ring-openings.

The reaction of enantiomerically pure 2-substituted 1-phenylethyl-aziridine with methyl trifluoromethanesulfonate generated a stable methylaziridinium ion, which was reacted with various external nucleophiles, including nitrile, to yield synthetically valuable and optically pure acyclic amine derivatives in a completely regio- and stereoselective manner.

Stereoselective synthesis of enantiomerically pure D-threo-PDMP; manipulation of a core 2,3-diamino alcohol unit

Abstract The C(3)N bond of various non-activated enantiomerically pure aziridine-2-methanols was regioselectively cleaved by nitrogen nucleophiles to provide a variety of β-aminoalanine derivatives in high yields.

Nucleophile-dependent regioselective ring opening of 2-substituted N,N-dibenzylaziridinium ions: bromide versus hydride

The ring opening of 2-substituted N,N-dibenzylaziridinium ions by bromide exclusively occurs at the substituted aziridine carbon atom in a stereospecific way, whereas the opposite regioselectivity was observed for hydride-induced ring opening at the unsubstituted position; furthermore, this unprecedented hydride-promoted reactivity was validated by means of Density Functional Theory (DFT) calculations.