Kazuo Nakai

Unprecedented rearrangement reaction of 2-aziridinemethanols with lower order lithium methylcyanocuprate

Abstract Complementary selectivity can be achieved in ring opening reactions of 2-aziridinemethanols by using either the Gilman reagent or lower order cyanocuprate. In the former case, the usual attack of the Gilman reagent to the substrates 1 and 2 results in the formation of the expected ring opening products ( 3 and 4 ) and ( 7 and 8 ), respectively. In contrast, exposure of both 1 and 2 to the lower order cyanocuprate proceeds in an unprecedented fashion, presumably via epoxides D and G , to yield unexpected secondary alcohols ( 11 and 12 ) as the major products.

SN2′ Ring opening of aziridines bearing an α,β-unsaturated ester group with organocopper reagents. A new stereoselective synthetic route to (E)-alkene dipeptide isosteres

Regio- and stereo-selective synthesis of (E)-alkene dipeptide isosteres has been successfully achieved by exposing both (E)- and (Z)-N-(4-methylphenyl)sulfonyl-γ,δ-epimino-α,β-enoates to organocopper reagents at –78 °C for 30 min.

A one-pot aza-Payne rearrangement-epoxide ring opening reaction of 2-aziridinemethanols: A regio- and stereoselective synthetic route to diastereomerically pure 1,2-amino alcohols

Abstract A regio- and stereoselective synthetic route to diastereomerically pure 1,2-amino alcohols via a one-pot aza-Payne rearrangement — epoxide ring opening reaction of 2-aziridinemethanols is reported. Satisfactory yields are obtained in excellent diastereoisomeric excesses by successive exposure of 2-aziridinemethanols to potassium hydride and nucleophilic reagents in a one-pot manner.

Effect of a new bombesin receptor antagonist, (E)-alkene bombesin isostere, on amylase release from rat pancreatic acini

The short-chain pseudopeptide, [d-Phe6, Leu13Φ(CH2NH)Leu14]bombesin(6–14) (RDI), is reported to be a potent antagonist of bombesin, and development of this type of compound has greatly contributed to the investigation of biological actions of bombesin and its related peptides. We recently synthesized (E)-alkene bombesin isostere by replacing the peptide bond with an (E)-double bond: [d-Phe6, Leu13Φ[(E)CH = CH]Leu14] bombesin(6–14) (EABI). The present study examined the effect of EABI on amylase release from rat pancreatic acini. EABI showed no agonistic activity at concentrations up to 1 μM, and RBI showed slight agonistic activity at concentrations >10 nM. EABI caused a dose-dependent inhibition of amylase release stimulated by 0.1 nM bombesin, with an IC150 of 6.7 ± 1.7 nM, and induced almost-complete inhibition at 0.3 μM. RDI caused a dosedependent inhibition of amylase release, with an IC50 of 68.7 ± 16 nM. EABI caused a parallel and rightward shift of the entire dose-response curve of bombesin-stimulated amylase release, and the degree of the shift was dependent on the concentrations of EABI. EABI (100 nM) and RDI (100 nM) inhibited amylase releases stimulated by gastrin-releasing peptide (1 nM) and neuromedin-C (1 nM). In contrast, amylase release stimulated by cholecystokinin octapeptide (0.1 nM), carbachol (10 μM), vasoactive intestinal peptide (1 nM), and gastrin-17 (10 nM) was not inhibited by EABI and RDI. The results indicate that EABI is a potent and specific bombesin receptor antagonist. EABI was 10 times more potent than RDI in terms of inhibition of bombesin-stimulated amylase release. Thus, EABI can be a useful probe for studying the biological roles of bombesin and related peptides in a basic and clinical sense.

SN2′ selective alkylation of allylic chlorides and mesylates with RZnX reagents generated from Grignard reagents, zinc chloride, lithium chloride, and Cu(II)-salts

Abstract Treatment of RMgX (1 equiv. R = alkyl; X = Cl, Br) with ZnCl 2 (1 equiv.) in a mixed solvent of THF and Et 2 O leads to a highly turbid white suspension. Addition of LiCl (1∼2 equiv.) solubilizes the insoluble species to yield a colorless clear solution. Addition of a catalytic amount of a Cu(II)-salt followed by allylic halides or mesylates at 0 °C ∼ room temperature yielded S N 2′products in high yields. Application for the synthesis of ( E )-alkene dipeptide isosteres is also reported.

An aza-Payne rearrangement-epoxide ring opening reaction of 2-aziridinemethanols in a one-pot manner: A regio- and stereoselective synthetic route to diastereomerically pure N-protected 1,2-amino alcohols

Abstract A regio- and stereoselective synthetic route to diastereomerically pure 1,2-amino alcohols via a one-pot aza-Payne rearrangement - epoxide ring opening reaction of 2-aziridinemethanols is reported.

Effects of structural modulation on biological activity of bombesin analogues with (E)-alkene bond

The specific bombesin receptor antagonist, (E)-alkene bombesin isostere (EABI-1), [D-Phe6,Leu13psi[(E)CH=CH]Leu14]bombesin(6-14) is a potent antagonist in terms of inhibition of bombesin-stimulated amylase release from rat pancreatic acini. This study examined the effects of EABI-1 (L-L diastereomer) and three novel bombesin analogues on amylase release in rat pancreatic acini. EABI-2 is a L-D diastereomer of EABI-1. EABI-3 is an analogue, of which leucine at position 13 of EABI-1 was replaced with valine. EABI-4 is a L-D diastereomer of EABI-3 (L-L). The order of agonist potency was EABI-2>EABI-3>EABI-4. EABI-1 showed no agonist activity at concentrations up to 100nM. On the other hand, all of four analogues had antagonist activity. The order of antagonist potency was EABI-1>EABI-3>EABI-4>EABI-2. EABI-1 was a complete antagonist, EABI-2 and EABI-3 were partial agonists, and EABI-4 had a weak agonist effect. The present study provides a useful information on the future development of peptide analogues for anticancer agents and biological tools for investigating actions of bombesin family peptides.

Involvement of cholinergic processes in cholecystokinin (CCK) release by luminal oleic acid

Cholecystokinin (CCK) is an important bioactive peptide that stimulates pancreatic enzyme secretion. Circulating CCK is secreted from endocrine cells in the upper small intestine in response to various luminal stimuli and to vascular administration of gastrin releasing peptides. However, the mechanism of its release has not been fully elucidated. In the present study, the vascularly perfused duodenojejunum was isolated from male Wistar rats. The effects of luminal infusion of sodium oleate (2 or 0.4%) or intra-arterial infusion of neuromedin C(10(-7) M) with or without atropine and with a recently synthesized specific bombesin antagonist (EABI) were examined. The CCK release produced by intra-arterial infusion of neuromedin C was inhibited by EABI in a dose-dependent manner. The CCK release produced by luminal sodium oleate was inhibited by atropine, but not affected by EABI. The CCK release stimulated by luminal sodium oleate is mediated, at least in part, by a cholinergic mechanism, but neuromedin C directly stimulates CCK release via its receptor on CCK-producing cells.

A thermodynamic preference of chiral cis-γ,δ-epimino-(E)-α,β-unsaturated esters over other stereoisomers: Synthetically useful Pd(0)-catalyzed equilibrated reactions of aziridines bearing an α,β-unsaturated ester group

Abstract A practical synthesis of chiral N -arylsulfonyl- cis - γ , δ -epimino-( E )- α , β -enoates, key intermediates for the synthesis of ( E )-alkene dipeptide isosteres via Pd(0)-catalyzed equilibrated reactions, has been successfully achieved by exposing N -arylsulfonyl-γ,δ-epimino-α,β-unsaturated esters to a catalytic amount of Pd(PPh 3 ) 4 in THF at 0 ∼ 20 °C.

Remarkable difference in reactivity of ordinary vinylcopper reagents and vinylzinc halide containing a copper salt towards γ-mesyloxy-α, β-enoates. Synthesis of homochiral 1,4-dienes

Abstract Whereas the reaction of γ-mesyloxy α,β-enoates with vinyl-Cu(CN)M or (vinyl) 2 Cu(CN)M 2 (M = Li or MgX) yielded a reduction product with an ( E )-double bond at the β,γ-position, treatment of the same substrates with “higher order” zinc cuprate reagents or vinyl-ZnCl by the addition of a catalytic amount of Cu(I) or Cu(II) salt afforded α- and γ-vinylation products. Both vinylation products were stable 1,4-diene derivatives that are only more difficulty accessed by more traditional means.