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At least 451 records · Page 25Linked to original sources
PubMed2006

Reaction of azides with dichloroindium hydride: very mild production of amines and pyrrolidin-2-imines through possible indium-aminyl radicals.

Organic azides are easily reduced to the corresponding amines by reaction with dichloroindium hydride under very mild conditions and in a highly chemoselective fashion. Gamma-azidonitriles give rise to outstanding five-membered cyclizations affording pyrrolidin-2-imines. A rationalization of the overall experimental data cannot exclude the occurrence of competitive radical and nonradical pathways, but certain results are, however, soundly consistent with the intermediacy of indium-bound nitrogen-centered radicals. [reaction: see text]

Journal Article↗
PubMed2006

l-Piperazine-2-carboxylic acid derived N-formamide as a highly enantioselective Lewis basic catalyst for hydrosilylation of N-aryl imines with an unprecedented substrate profile.

[reaction: see text] l-Piperazine-2-carboxylic acid derived N-formamides have been developed as highly enantioselective Lewis basic catalysts for the hydrosilylation of N-aryl imines with trichlorosilane. The arene sulfonyl group on N4 was found to be critical for the high enantioselectivity of the catalyst. High isolated yields (up to 99%) and enantioselectivities (up to 97%) were obtained for a broad range of substrates, including aromatic and aliphatic ketimines, particularly those with R(2) as relatively bulky alkyl groups.

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PubMed2006

Theoretical rationale for regioselection in phosphine-catalyzed allenoate additions to acrylates, imines, and aldehydes.

[reaction: see text] A rationale for regioselection in phosphine-promoted annulations of acrylates, imines, and aldehydes with allenoates has been developed using computation at the B3LYP/6-31G(d) level of theory. The computed transition states revealed that Lewis acid activation, strong hydrogen bonding (H-bonding), and minimization of unfavorable van der Waals contacts are the guiding factors responsible for regioselection. An excellent level of correlation between the calculated regioselectivities and experiment was observed.

Journal Article↗
PubMed2006

Use of alpha-chlorinated N-(tert-butanesulfinyl)imines in the synthesis of chiral aziridines.

[reaction: see text] Reaction of chiral alpha-chloro tert-butanesulfinyl aldimines with Grignard reagents efficiently afforded beta-chloro N-sulfinamides in high diastereomeric excess. The latter compounds were cyclized toward the corresponding chiral aziridines in a high-yielding one-pot reaction or after separate treatment with base. The diastereoselectivity obtained in the newly synthesized beta-chloro sulfinamides is explained via the coordinating ability of the alpha-chloro atom with magnesium resulting in the opposite stereochemical outcome as generally observed for nonfunctionalized N-sulfinyl imines.

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PubMed2006

Room-temperature highly diastereoselective Zn-mediated allylation of chiral N-tert-butanesulfinyl imines: remarkable reaction condition controlled stereoselectivity reversal.

[reaction: see text] An efficient method for the highly diastereoselective synthesis of chiral homoallylic amines by Zn-mediated allylation of chiral N-tert-butanesulfinyl imines at room temperature was developed. By simply tuning the reaction conditions, the method allows the achievement of a highly remarkable opposite stereocontrol, affording the desired stereochemical outcome in good yield and with excellent diastereoselectivity (up to 98% dr). With N-sulfinyl ketimines, the corresponding quaternary carbon-containing chiral homoallylic amines could also be produced.

Journal Article↗
PubMed1998

Oxidation of acetaminophen to its toxic quinone imine and nontoxic catechol metabolites by baculovirus-expressed and purified human cytochromes P450 2E1 and 2A6.

Acetaminophen (APAP), a widely used analgesic and antipyretic agent, is bioactivated by cytochromes P450 to cause severe hepatotoxicity. APAP is oxidized by two pathways to form a toxic intermediate, N-acetyl-p-benzoquinone imine (NAPQI), and a nontoxic catechol metabolite, 3-hydroxy-APAP (3-OH-APAP). We investigated the role of P450 2E1 and 2A6 in APAP oxidation by using baculovirus-expressed and highly purified forms of human P450 2E1 and 2A6. An electrochemical HPLC assay was developed to quantify both oxidative metabolites simultaneously. For the first time, it was demonstrated that human P450 2E1 selectively oxidized APAP to NAPQI (assayed as its glutathione conjugate, GS-APAP), whereas human P450 2A6 selectively oxidized APAP to 3-OH-APAP. At 1 mM APAP, the relative ratio for the formation of GS-APAP vs 3-OH-APAP with human P450 2E1 was approximately 6:1, whereas the ratio with human P450 2A6 was 1:3. Apparent Km and Vmax values for the formation of GS-APAP by human P450 2E1 were 1.3 mM and 6.9 nmol/min/nmol of P450, respectively, whereas they were 4.6 mM and 7.9 nmol/min/nmol of P450 for P450 2A6. Apparent Km and Vmax values for the formation of 3-OH-APAP by human P450 2E1 were 4.0 mM and 2.5 nmol/min/nmol of P450, respectively, whereas they were 2.2 mM and 14.2 nmol/min/nmol of P450, respectively, for P450 2A6. Thus, although at toxic doses of APAP P450 2E1 is the more efficient catalyst for the formation of the toxic metabolite NAPQI, P450 2A6 also can contribute significantly to NAPQI production.

Acetaminophen↗
PubMed2002

The structure of PEG-modified poly(ethylene imines) influences biodistribution and pharmacokinetics of their complexes with NF-kappaB decoy in mice.

PURPOSE: To study the relationship between structure of poly(ethylene imine-co-ethylene glycol), PEI-PEG, copolymers and physicochemical properties as well as in vivo behavior of their complexes with NF-kappaB decoy. METHODS: A variety of copolymers of PEG grafted onto PEI as well as PEI grafted onto PEG were synthesized and their complexes with a double stranded 20mer oligonucleotide were examined regarding size, surface charge, biodistribution and pharmacokinetics. RESULTS: Polyplexes of copolymers were smaller compared to polyplexes formed by non-PEGylated PEI 25 kDa (58 - 334 nm vs. 437 nm for a nitrogen/phosphate ratio of 3.5 and 85 - 308 nm vs. 408 nm for N/P 6.0) and showed reduced zeta potential (-2.5 - 6.4 mV vs. 14.5 mV for N/P 6.0). IV injection into mice revealed liver (35-76% of injected dose), kidney (3 - 22%) and spleen (2 - 16%) to be the main target organs for all injected complexes. Complexes formed by copolymers with few PEG blocks of higher molecular weight (5 kDa and 20 kDa) grafted onto PEI 25 kDa did not show different blood levels from PEI 25 kDa. In contrast, a copolymer with more short PEG blocks (550 Da) grafted onto PEI showed elevated blood levels with an increase in AUC of 62 %. CONCLUSIONS: A sufficiently high density of PEG molecules is necessary to effectively prevent opsonization and thereby rapid clearance from blood stream.

Animals↗
PubMed2002

Semiconductor photocatalysis type B: synthesis of unsaturated alpha-amino esters from imines and olefins photocatalyzed by silica-supported cadmium sulfide.

Novel unsaturated N-phenyl-alpha-amino esters were synthesized in isolated yields of 50 to 10% by visible light irradiation of methanolic suspensions of silica-supported cadmium sulfide in the presence of methyl (2Z)-phenyl(phenylimino)acetate and various cyclic olefins. A semiconductor photocatalysis mechanism is proposed for this linear addition reaction. The light-generated electron-hole pair in the oxidative step induces a dissociative electron transfer from the olefin to CdS affording a proton and an allylic radical, whereas in the reductive step an alpha-aminobenzyl radical is formed in a proton coupled reaction. Heterocoupling of these intermediate radicals leads to the corresponding addition products. As the only by-product the hydrogenated imine is obtained in comparable amounts through the subsequent photoreduction of the alpha-aminobenzyl radical. Supporting the catalyst on silica made the reaction three times faster as compared to neat CdS. When the surface OH groups of CdS were removed through alkylation, the reaction between ArCH=NAr (Ar = p-C1C6H4) and cyclopentene was completely inhibited, but occurred again upon replacing the aldimine by its hydrochloride salt. This indicates that the protonated aldimine is involved in the reductive reaction step. Protonation makes this reduction easier by 0.1 V as indicated by the shift of the reduction potential of methyl (2Z)-phenyl(phenylimino)acetate upon addition of glacial acetic acid to the acetonitrile solution.

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