Koichiro Naemura

Synthesis and Association Behavior of [4.4.4.4.4.4]Metacyclophanedodecayne Derivatives with Interior Binding Groups

Intriguing association behavior in solution is exhibited by the rigid macrocycle 1. For instance, it reacts with organic cations to give ternary complexes of the composition (1⋅cation)⋅1, and with analogous macrocycles without cyano groups it forms heteroaggregates. R=CO2 C8 H17 .

Enantioselective acylation of primary and secondary alcohols catalyzed by lipase QL from Alcaligenes sp.: A predictive active site model for lipase QL to identify which enantiomer of an alcohol reacts faster in this acylation

Abstract Lipase QL (from Alcaligenes sp.)-catalyzed acylation of alcohols using isopropenyl acetate as the acylating agent in diisopropyl ether converted preferentially primary alcohols with an S configuration and secondary alcohols with an R configuration into the corresponding homochiral acetates. On the basis of observed enantiomer selectivities, a predictive active site model for lipase QL is proposed for identifying which enantiomer of a primary or a secondary alcohol reacts faster in this acylation.

Lipase-catalyzed enantioselective acylation of alcohols: a predictive active site model for lipase YS to identify which enantiomer of an alcohol reacts faster in this acylation

Abstract Primary alcohols having a hydroxymethyl group at an S stereogemic center and secondary alcohols with an R configuration are preferentially acylated to give the corresponding acetates by lipase YS (from Pseudomonas fluorescens )-catalyzed acylation using isopropenyl acetate as the acylating agent in diisopropyl ether. On the basis of enantiomer selectivities observed, a predictive active site model for lipase YS is proposed for identifying which enantiomer of a primary or a secondary alcohol reacts faster in this acylation.

Preparation of chiral and meso-crown ethers incorporating cyclohexane-1,2-diol derivatives as a steric barrier and their complexation with chiral and achiral amines

Abstract The design and synthesis of chiral crown ethers possessing a chiral recognition ability which carry great potential for separation of enantiomers and analytical purpose has become an important and rapidly growing field of host-guest chemistry. One of the advantages of crown ethers constructed using a synthetic chiral building block is that it is rather easy to modify the chiral cavity resulting in the improvement in enantiomer selectivity. Cyclohexane-1,2-diol derivatives such as cis -1-phenylcyclohexane-1,2-diol, trans -1-phenylcyclohexane-1,2-diol and trans - 1,2-diphenylcyclohexane-1,2-diol are of interest as chiral building blocks of crown ethers, because incorporation of these subunits into the 18-crown-6 framework causes a reduction in conformational flexibility of the chiral cavity and fixes the phenyl chiral barrier perpendicularly above the face of crown ring to modify enantiomer recognition ability. Chiral crown ethers of the 18-crown-6 type were synthesized using these building blocks and their chiral recognition behaviour in differential enantiomer transport through bulk liquid membranes were examined. Chiral azophenolic crown ethers containing cis -1-phenylcyclohexane-1,2-diol or cis -cyclohexane-1,2-diol which can bind neutral amines to form a stable complex and exhibit enantiorecognitive coloration in complexation with chiral amines were prepared and the association constants for their complexes with chiral ethylamine and ethanolamine derivatives were determined on the basis of UV-visible absorbance. The observed enantioselectivity is rationalized in terms of complementarity between a host and a guest as indicated by CPK molecular model examination. The alternation of the position of chiral barriers resulted in a reversal of the enantioselectivity. Crown ethers with diastereotopic faces can bind a guest to each side of the diastereotopic faces to form diastereoisomeric complexes which occasionally cause troublesome “sidedness” problems. In order to avoid the problems, most crown ethers previously prepared contained at least one C 2 axis of symmetry. However, diastereotopic face selectivity in complexation does provide helpful information on the complexing behaviour of crown ethers to assist in the design of more elaborate and structured host molecules. meso -Crown ethers having cis-1-phenylcyclohexane-1,2-diol were prepared and the diastereotopic face selectivity by their diastereotopic faces in complexation with achiral amines was examined by temperature-dependent 1H nuclear magnetic resonance. Ethanolamine is attached stereoselectively to one of the faces to give one of diastereoisomeric complexes and the alternation of the position of steric barriers led to reversal of the diastereotopic face selectivity. A prediction of which diastereoisomeric complex is formed is made on the basis of CPK molecular model.

Preparation and temperature-dependent enantioselectivities of homochiral phenolic crown ethers having aryl chiral barriers: thermodynamic parameters for enantioselective complexation with chiral amines

Abstract Homochiral crown ether ( S , S )- 1 containing 1-naphthyl groups as chiral barriers together with the phenol moiety was prepared by using ( S )- 3 as a chiral subunit which was resolved in enantiomerically pure form by lipase-catalyzed enantioselective acylation of (±)- 3 . Homochiral phenolic crown ether ( S , S )- 2 , containing phenyl groups as chiral barriers, was also prepared from ( S )- 5 which was derived from ( S )-mandelic acid. The association constants for their complexes with chiral amines in CHCl 3 were determined at various temperatures by the UV–visible spectroscopic method demonstrating that the crown ethers ( S , S )- 1 and ( S , S )- 2 displayed the large Δ R − S Δ G values of 6.2 and 6.4 kJ mol −1 , respectively, towards the amine 21 at 15°C. Thermodynamic parameters for complex formation were also determined and a linear correlation between T Δ R − S Δ S and Δ R − S Δ H values was observed.

Synthesis and self-association properties of diethynylbenzene macrocycles

We synthesized diethynylbenzene macrocycles (DBMs), cyclic oligomers of diethynylbenzene, having functional groups in the periphery of the macrocyclic framework and investigated their self-association properties in solution resulting from π-π stacking interaction. The tetrakis-DBM having hexadecyl ester groups showed dimerization behavior not only in chloroform-d, but also in o-dichlorobenzene-d4.

Polyyne cyclization to form carbon cages: [16.16.16](1,3,5)cyclophanetetracosayne derivatives C60H6 and C60Cl6 as precursors to C60 fullerene

Abstract [16.16.16](1,3,5)Cyclophanes fused by six [4.3.2]propellatriene units, which would serve as precursors to cage polyyne C 60 H 6 and its perchloro derivative C 60 Cl 6 , respectively, were prepared. In the negative mode laser desorption mass spectra of the cyclophanes, the polyyne anions C 60 H 6 − and C 60 Cl 6 − were detected. Moreover, size-selective formation of C 60 + as well as C 60 − was also observed, indicating the possible polyyne cyclization mechanism to form the fullerene cage.

Enantioselective acylation of alcohols catalyzed by lipase QL from Alcaligenes sp.: A predictive active site model for lipase QL to identify the faster reacting enantiomer of an alcohol in this acylation

Abstract Lipase QL-catalyzed acylation of secondary alcohols using isopropenyl acetate as the acylating agent in diisopropyl ether gave preferentially the corresponding acetate with an R configuration. On the basis of the results, a predictive active site model for lipase QL is proposed for identifying which enantiomer of a secondary alcohol reacts faster in this reaction.

Synthesis of butadiyne-bridged [4n] metacyclophanes having exo-annular t-butyl groups

Abstract Butadiyne-bridged [4 4 ]- and [4 8 ]metacyclophanes having exo -annular t -butyl groups were prepared by intermolecular Eglinton coupling of the dimeric unit or by intramolecular ring closure of the linear tetramer. Comparison of the 1 H and 13 C NMR spectra of [4 4 ]metacyclophane with those of [4 8 ]cyclophane and diphenylbutadiyne revealed its prominent geometrical feature due to deformation of the triple bonds from linearity. The [4 4 ]Metacyclophane was converted into [0 8 ]thiophenometacyclophane in good yield by treatment with sodium sulfide.

Enzyme-catalyzed asymmetric acylation and hydrolysis of cis-2,5-disubstituted tetrahydrofuran derivatives: Contribution to development of models for reactions catalyzed by porcine liver esterase and porcine pancreatic lipase

Abstract Pig liver esterase, lipase from porcine pancreas, lipase from Pseudomonas sp. (lipase YS), and lipase from Candida cylindracea catalyzed hydrolyses of the cis -diacetate 1 and the trans -diacetate (±)- 4 to give the cis -monoacetate 3 and the trans -monoacetate 6 in optically active forms, respectively. Lipase YS-catalyzed acylations of the cis -diol 2 and the trans -diol (±)- 5 with an acylating agent in cyclohexane yielded (−)- 3 and (−)- 6 , respectively. The group adjacent to the R stereogenic center preferentially reacted in lipase YS-catalyzed hydrolyses of 1 and (±)- 4 and acylations of 2 and (±)- 5 , and the enantioselectivities are rationalized by our rule recently proposed for lipase YS.