Hiroshi Suemune

Stabilized α-Helix-Catalyzed Enantioselective Epoxidation of α,β-Unsaturated Ketones

Chiral cyclic alpha-amino acid containing oligopeptide catalyzed highly enantioselective epoxidation of alpha,beta-unsaturated ketones and the alpha-helical secondary structure of the peptide catalyst were revealed by X-ray crystallographic analysis.

A novel synthesis of cis-3,4-disubstituted cyclopentanones

Abstract A new method for the stereospecific synthesis of cis-3,4-disubstituted cyclopentanones is described.

One‐Handed Helical Screw Direction of Homopeptide Foldamer Exclusively Induced by Cyclic α‐Amino Acid Side‐Chain Chiral Centers

Chiral cyclic α,α-disubstituted amino acids, (3S,4S)- and (3R,4R)-1-amino-3,4-(dialkoxy)cyclopentanecarboxylic acids ((S,S)- and (R,R)-Ac(5)c(dOR); R: methyl, methoxymethyl), were synthesized from dimethyl L-(+)- or D-(-)-tartrate, and their homochiral homoligomers were prepared by solution-phase methods. The preferred secondary structure of the (S,S)-Ac(5)c(dOMe) hexapeptide was a left-handed (M) 3(10) helix, whereas those of the (S,S)-Ac(5)c(dOMe) octa- and decapeptides were left-handed (M) α helices, both in solution and in the crystal state. The octa- and decapeptides can be well dissolved in pure water and are more α helical in water than in 2,2,2-trifluoroethanol solution. The left-handed (M) helices of the (S,S)-Ac(5)c(dOMe) homochiral homopeptides were exclusively controlled by the side-chain chiral centers, because the cyclic amino acid (S,S)-Ac(5)c(dOMe) does not have an α-carbon chiral center but has side-chain γ-carbon chiral centers.

Asymmetric conjugate addition of organometallic reagents to chiral α, β-unsaturated esters

Abstract Asymmetric conjugate addition to α,β-unsaturated ester was studied using four kinds of cyclic diols ( 1c–4c ) as chiral auxiliaries. Among the tested substrates, ( R,R )-cyclohexane-1,2-diol derivatives ( 6a–c ) and (1 R ,2 S )-2-hydroxymethylcyclopentanol derivative ( 7a ) showed high and reverse diastereoselectivity in conjugate addition by organocuprates (R 2 CuLi) and/or Grignard reagents in the presence of copper iodide (RMgBr + CuI), respectively.

Stereochemical observation on the enantioselective hydrolysis using Pseudomonas fluorescens lipase

Abstract Three-site model concerning the hydrolysis of acetate on the mono-cyclic or bicyclic ring using Pseudomonas fluoresence lipase (PFL) could be simplified to a two site model, and the R-preference of hydrolysed alcohol could be predicted by the analysis of a proposed stereomodel. Optically pure (+)-( 3 ) was readily converted to (−)-( 17 ), which is an important precursor for the synthesis of isocarbacyclin.

Synthesis of [5]helicenes with a substituent exclusively on the interior side of the helix by metal-catalyzed cycloisomerization

[5]Helicenes with a substituent exclusively oriented toward the interior curvature of the helix are synthesized by metal-catalyzed cycloisomerization. In addition, novel azulene-fused helicenes have been found through cycloisomerization studies. These [5]helicenes shows a high enough configurationally stability to allow resolution by HPLC on a chiral stationary phase.

Synthesis of chiral building blocks using Pseudomonas Fluorescens lipase catalyzed asymmetric hydrolysis of Meso diacetates

Abstract Two chiral building blocks were prepared using a lipase-catalyzed asymmetric hydrolysis of the corresponding meso-diacetates. The chirality in the hydrolyzed products was conveniently incorporated into that of(R)-muscone and hunger modulator.

Novel ring expansion of cyclopentanones to seven membered rings

Abstract By treatment with BF 3 /ethyleneglycol, cyclopentanones with the carbonyl function at the C 3 -position of α-side chain undergo the ring cleavage to build up the seven membered rings, and this novel ring expansion was applied to the synthesis of bulnesol.

Conformations of peptides containing a chiral cyclic α, α‐disubstituted α‐amino acid within the sequence of Aib residues

A single chiral cyclic α,α‐disubstituted amino acid, (3S,4S)‐1‐amino‐(3,4‐dimethoxy)cyclopentanecarboxylic acid [(S,S)‐Ac5cdOM], was placed at the N‐terminal or C‐terminal positions of achiral α‐aminoisobutyric acid (Aib) peptide segments. The IR and 1H NMR spectra indicated that the dominant conformations of two peptides Cbz‐[(S,S)‐Ac5cdOM]‐(Aib)4‐OEt (1) and Cbz‐(Aib)4‐[(S,S)‐Ac5cdOM]‐OMe (2) in solution were helical structures. X‐ray crystallographic analysis of 1 and 2 revealed that a left‐handed (M) 310‐helical structure was present in 1 and that a right‐handed (P) 310‐helical structure was present in 2 in their crystalline states. Copyright

Ring cleavage and reconstruction of five and six membered ring

Abstract Under the acetalization conditions using BF 3 -etherate/ethylene glycol, cyclopentanones and cyclohexanones with the carbonyl function at the C 3 - or C 4 -position of the β-side chain undergo the facile ring cleavage to reconstruct the new ring.