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 H2O was effective to remove the bornyl group and the benzyl group on the amino group to provide the β-amino ester derivative.

A practical method for the synthesis of chiral β2,3-amino esters having various substituents was developed, which is characterized by an asymmetric Michael addition reaction of a chiral lithium amide with trisubstituted (E)-α,β-unsaturated esters. We found that a highly face-selective protonation occurred by the quick addition of water to the enolate intermediate derived from the Michael addition reaction to afford N-protected β2,3-amino esters in moderate to excellent yields. This finding was made possible by the facile preparation of geometrically pure trisubstituted (E)-α,β-unsaturated esters, which was established recently by our group. The subsequent deprotection of the amino group in the Michael adduct by using N-iodosuccinimide (NIS) efficiently provided β2,3-amino esters having various substituents.

A tandem "quadruple" Michael addition reaction of (+)-borny-lamide with two equivalents of a Michael acceptor having two alpha, beta-unsaturated ester moieties spontaneously proceeded to afford one diastereomer with seven contiguous chiral centers in 27% yield. Meanwhile, a stepwise "double-double" Michael addition, in which the very slow addition of the first one equivalent of the acceptor substrate to the bornylamide was followed by a further addition of another Michael acceptor bearing two alpha, beta-unsaturated ester moieties, provided a compound with a similar set of seven contiguous chiral centers on a different carbon skeleton in 48% yield. Both quadruple and double-double Michael adducts were one of 128 possible diastereomers, namely, each Michael addition in those two reactions proceeded in 72% and 83% yields on average, respectively. We showed the importance of adding speed of the Michael acceptor to the bornylamide in controlling the quadruple and double-double Michael addition reactions.

An asymmetric intramolecular Heck reaction that involves the dynamic kinetic resolution of an atropisomer as the substrate furnished a product in high yield with high enantioselectivity. DFT calculations (Spartan'10, B3LYP/6-31G*) confirmed that the reaction proceeded via atropisomerization involving a conformational transformation (half-chair form/distorted-boat form) of the substrate.

Abstract Trisubstituted (E)-α,β-unsaturated esters bearing various substituents were synthesized with high geometrical selectivity by using three reactions: an aldol reaction, acetylation of the hydroxy group at the β-position, and an E1cB reaction induced by 1,8-diazabicyclo[5.4.0]undec-7-ene. The method does not require separation of the diastereoisomeric mixture of β-hydroxy ester intermediates before the E1cB reaction, and is usable for gram-scale syntheses of trisubstituted (E)-α,β-unsaturated esters.

The first asymmetric total synthesis of (+)-taiwaniaquinol D and (−)-taiwaniaquinone D isolated from Taiwania cryptomerioides was attained by using the intramolecular asymmetric Heck reaction. The reaction provided a tricyclic intermediate that would be available for the asymmetric total synthesis of various abeo-abietane-type diterpenoids.

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.

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. Simple accumulation of (11)C in the brain was measured in an in vivo biodistribution study using mice, whilst donepezil was used as a blocking agent in analogous in vivo blocking studies. In vitro autoradiography of rat brain tissue was performed to investigate the distribution of (-)-[(11)C]galanthamine, and confirmed the results of PET studies in mice. The radiochemical yields of N-methylation of (-)- and (+)-norgalanthamines were 13.7% and 14.4%, respectively. The highest level of accumulation of (11)C in the brains of mice was observed at 10 min after administration (2.1% ID/g). Intravenous pretreatment with donepezil resulted in a 30% decrease in accumulation of (-)-[(11)C]galanthamine in the striatum; however, levels in the cerebellum were unchanged. In contrast, use of (+)-[(11)C]galanthamine led to accumulation of radioactivity in the striatum equal to that in the cerebellum, and these levels were unaffected by pretreatment with donepezil. In in vitro autoradiography of regional radioactive signals of brain sections showed that pretreatment with either (-)-galanthamine or donepezil blocked the binding of (-)-[(11)C]galanthamine to the striatum, while sagittal PET imaging revealed accumulation of (-)-[(11)C]galanthamine in the brain. These results indicate that (-)-[(11)C]galanthamine showed specific binding to AChE, whereas (+)-[(11)C]-galanthamine accumulated in brain tissue by non-specific binding. Thus, optically pure (-)-[(11)C]galanthamine could be a useful PET tracer for imaging cerebral AChE.

Circular dichroism (CD) spectra of the 2,2′-binaphthyl ester derived from Δ5-sterols showed not bisignate CD but diagnostic CD bands at around 210 and 240nm. 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. As a result, CD spectra of the binaphthyl derivatives of the saturated sterols showed bisignate curves centered at 240nm (3S(β): positive chirality; 3R(α): negative one). This suggested a straightforward and practical method for discriminating the absolute stereogenic center at the C-3 positions of sterols based on an induced CD. This finding should contribute significantly to the analysis of metabolites of various types of sterols.

Induced circular dichroism (ICD) was observed in binaphthyl N-methyl amides of chiral primary amines. The CD spectra showed split curves centered at 225nm. A good correlation was found between the sign of the exciton chirality of the binaphthyl derivative and the absolute configuration of the original amine. Furthermore, the screw sense of the two naphthyl groups in the most stable conformer obtained from molecular mechanics (MM) calculation was in agreement with those expected from the exciton chirality, indicating that the method based on MM calculations can be used to determine unknown absolute configurations of aliphatic chiral amines. The practical use of the present method was demonstrated by the determination of the absolute configurations of the natural products, d- and l-cycloserines.

A radioiodinated artificial substrate of N-acetylglucosaminyltransferase V (GnT-V), 2-(4-iodophenyl)ethyl 2-acetamido-2-deoxy-beta-D-glucopyranosyl-(1 -> 2)-alpha-D-mannopyranosyl-(1 -> 6)-beta-D-glucopyranoside (([I-125]1a), was alternatively synthesized by using the glycosylation reaction from the non-reducing end, in which a glycosyl sulfoxide and a thioglycoside were employed as the glycosyl acceptor and donor, respectively. In addition, two derivatives of [I-125]1a having different lengths of alkyl chain ([I-125]1b, [I-125]1c) were prepared in the same way to increase the permeability of the substrates through the cell membrane and into the Golgi apparatus, where GnT-V acts to modify glycoconjugates by transferring N-acetylglucosamine units from UDP-GIcNAc.

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. The iododestannylation of 21 using hydrogen peroxide as an oxidant followed by deacetylation yielded [(125)I]1. When [(125)I]1 was incubated in GnT-V-expressing cells with a UDP-GlcNAc donor, the production of β1-6GlcNAc-bearing IPGMG (IPGGMG, 2) was confirmed by radio-HPLC. In kinetic analysis, 1 was found to be a good substrate with a K(m) of 23.7 μM and a V(max) of 159 pmol/h. μg protein. [(125)I]1 would therefore be a useful synthetic substrate for the quantitative determination of GnT-V activity.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A straightforward strategy is reported for chiral discrimination in a specified carotenoid using a CD band, which is insensitive to conformational changes, computed by quantum chemical calculation.

3alpha-methoxyserrat-14-en-21beta-ol (1) and 3beta-methoxyserrat-14-en-21beta-ol (2) and their conjugates with curcumin, kojic acid, quercetin, and baicalein (3-18), as well as new analogs (19-24) derived from 1 and 2, were tested for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). The inhibitory effects of 16 (IC50=330 mol ratio/32 pmol/TPA), 9 (IC50=335), 10 (IC50=338), and 15 (IC50=350) were stronger than those of the other compounds and the positive control, oleanolic acid (IC50=449). Compounds 15 and 16, which are conjugates of one molecule each of 1 or 2 and quercetin, inhibited mouse skin tumor promotion in an in vivo two-stage carcinogenesis model. The in vivo two-stage mouse skin carcinogenesis test employed 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and TPA as a promoter.

Asymmetric Michael addition of zinc enolate to a chiral nitroolefin was improved and the method was applied to the synthesis of (-)-Δ 9(12) -Capnellene [(-)-6], (-)-aphanorphine [(-)-7], and (-)-eptazocine [(-)-8]. Whisky lactone (28) was also prepared by taking advantage of tandem Michael addition-MPV-reduction, which was capable of constructing three contiguous chiral centers of 1,3-mercaptoalcohols. In addition, (+)-negamycin [(+)-35] was synthesized by using the Michael addition of a chiral amine [(-)-31] as a key step with the best overall yield and with shortest steps to date. Efficient synthesis of galanthamine [(-)-51] was attained by a novel strategy of remote asymmetric control of intramolecular Michael addition of phenolic hydroxyl group to the dienone moiety. Moreover, epibatidine [(-)-42] was synthesized by using the Diels-Alder reaction, of which the dienophile, chiral allene dicarboxylate, was prepared by asymmetric crystallization. Finally, the first synthesis of naturally occurring form of dichroanal B (71), dichroanone (72), and taiwaniaquinone H (73) were achieved by using intramolecular asymmetric Heck reaction.

Multiple contiguous chiral centers were constructed in one pot using three types of multistep reactions initiated with the Michael addition of N-benzyl-2(R)-methoxy-(+)-10-bornylamide to alpha,beta-unsaturated esters, i.e., asymmetric Michael-aldol reaction, double Michael addition, and double Michael-aldol reaction. The chiral 2-methoxy-10-bornyl group as well as the benzyl group on the amino group of the products in the Michael-aldol reaction could be easily cleaved by treatment with NIS (4 equiv), and beta-amino esters with multiple contiguous chiral centers were obtained in good yield. As an application, the beta-amino-beta'-hydroxy ester obtained in the asymmetric Michael-aldol reaction was converted to the beta-lactam derivative in good yield.

AbstractTandem Michael—aldol, double Michael, and double Michael—aldol reactions with the chiral amine (I) allow efficient and stereoselective access to functionalized amines with up to five contiguous chiral centers in one pot.

In this article, we describe asymmetric syntheses taking advantage of chiral auxiliary characteristics. In the asymmetric Michael addition reaction of chiral thiol, we developed a novel tandem Michael-MPV (Meerwein-Ponndorf-Verley) reaction, which provided the 1,3-mercapto-alcohols with two or three chiral centers. Moreover, multi-contiguous chiral centers were finely constructed in one pot utilizing three types of Michael addition-initiated reactions, i.e., tandem Michael-aldol reaction, double Michael addition reaction, double Michael-aldol reaction, which were triggered by a nucleophilic attack of a novel recyclable chiral amine. Asymmetric syntheses of a number of biologically active compounds such as captopril, gamma-lactone natural products, (+) -negamycin and beta-lactam were achieved as an application of our reactions.