Construction of Acyclic All-Carbon Quaternary Stereocenter Based on Asymmetric Michael Addition of Chiral Amine.

Acyclic asymmetric quaternary stereocenters, which are composed of four carbon-carbon bonds, were finely constructed by utilizing a face-selective alkylation of enolate intermediates derived from an asymmetric Michael addition reaction of a chiral lithium amide with trisubstituted (E)-α,β-unsaturated esters. The present face-selective alkylation was able to employ diverse alkyl halides as an electrophile to afford various Michael adducts having an all-carbon quaternary stereocenter. With regard to the deprotection of the chiral auxiliary, N-iodosuccinimide used in our previous study did not work in the present cases; however, we found that pyridine iodine monochloride in the presence of HO was effective to remove the bornyl group and the benzyl group on the amino group to provide the β-amino ester derivative.

Synthesis and evaluation of (-)- and (+)-[¹¹C]galanthamine as PET tracers for cerebral acetylcholinesterase imaging.

Improved radiopharmaceuticals for imaging cerebral acetylcholinesterase (AChE) are needed for the diagnosis of Alzheimer's disease (AD). Thus, (11)C-labeled (-)-galanthamine and its enantiomers were synthesized as novel agents for imaging the localization and activity of AChE by positron emission tomography (PET). C-11 was incorporated into (-)- and (+)-[(11)C]galanthamine by N-methylation of norgalanthamines with [(11)C]methyl triflate.

Novel design and synthesis of a radioiodinated glycolipid analog as an acceptor substrate for N-acetylglucosaminyltransferase V.

Guided by the known molecular recognition interactions between N-acetylglucosaminyltransferase V (GnT-V) and certain synthetic substrates, we synthesized a radiolabeled double-stranded glycolipid composed of a long-chain alkyl unit and a radioiodinated phenylalkyl unit, [(125)I]-2-[N-(2-hydroxy-3-hexadecyloxy)propyl-15-(4-iodophenyl)pentadecanecarboxamido]ethyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-D-mannopyranosyl-(1→6)-β-D-glucopyranoside ([(125)I]2), as a novel intravital glycolipid mimic substrate of GnT-V. The radioactive iodine ((125)I) was incorporated via iododestannylation of the phenyltributyltin derivative, 2-[N-(2-acetoxy-3-hexadecyloxy)propyl-15-(4-tributylstannylphenyl)pentadecanecarboxamido]ethyl 3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-3,4,6-O-acetyl-α-D-mannopyranosyl-(1→6)-2,3,4-tri-O-acetyl-β-D-glucopyranoside (26). Subsequent deacetylation at the final step afforded [(125)I]2.

Novel approach to determining the absolute configurations at the C3-positions of various types of sterols based on an induced circular dichroism.

Circular dichroism (CD) spectra of the 2,2'-binaphthyl ester derived from Δ(5)-sterols showed not bisignate CD but diagnostic CD bands at around 210 and 240 nm. These bands might be attributable to an interaction between an olefinic chromophore and a binaphthyl one. Various types of unsaturated sterols were thus derivatized followed by complete hydrogenation, to give saturated sterols.

Synthesis and evaluation of a radioiodinated trisaccharide derivative as a synthetic substrate for a sensitive N-acetylglucosaminyltransferase V radioassay.

N-acetylglucosaminyltransferase V (GnT-V) is one of the most relevant glycosyltransferases to tumor invasion and metastasis. Based on previous findings of molecular recognition between GnT-V and synthetic substrates, we designed and synthesized a p-iodophenyl-derivatized trisaccharide, 2-(4-iodophenyl)ethyl 6-O-[2-O-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-α-d-mannopyranosyl]-β-D-glucopyranoside (IPGMG, 1) and its radiolabeled form, [(125)I]IPGMG ([(125)I]1), for use in assays of GnT-V activity in vitro. The tributyltin derivative, 2-[4-(n-tributylstannyl)phenyl]ethyl 6-O-[2-O-(3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-glucopyranosyl)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl]-2,3,4-tri-O-acetyl-β-D-glucopyranoside (21), was synthesized as a precursor for the preparation of [(125)I]1.