Aziridinium Ion Research Articles

Nicotine improves AF64A-induced spatial memory deficits in Morris water maze in rats

Ethylcholine mustard aziridinium ion (AF64A) is a neurotoxic derivative of choline that produces not only long-term presynaptic cholinergic deficits, but also various memory deficits in rats similar to some characteristics observed in Alzheimer's disease patients. This study investigated whether nicotine (NCT) administration attenuated spatial learning deficits induced by intracerebroventricular AF64A treatment. AF64A (6nmol/6μl)-or saline (SAL)-treated rats were trained in Morris water maze task. NCT (0.025–0.25mg/kg) was subcutaneously injected 5min before the training every day. The results showed that moderate dose (0.10mg/kg) of NCT attenuated AF64A-induced prolongation of escape latency. Furthermore, NCT dose-dependently recovered the AF64A-induced decrease of time spent in the target quadrant in the probe test. These results suggest that NCT improves AF64A-induced spatial memory deficits, and thus it is a potential therapeutic agent for the treatment of memory deficits in dementia.

Investigating the interaction of McN-A-343 with the M 2 muscarinic receptor using its nitrogen mustard derivative

We investigated whether the aziridinium ion formed from a nitrogen mustard derivative (4-[(2-bromoethyl)methyl-amino]-2-butynyl N-(3-chlorophenyl)carbamate; BR384) structurally related to McN-A-343 (4-(trimethyl-amino)-2-butynyl N-(3-chlorophenyl)carbamate) interacts allosterically or orthosterically with the M 2 muscarinic receptor. Chinese hamster ovary cells expressing the human M 2 muscarinic receptor were incubated with the aziridinium ion of BR384 in combination with McN-A-343 or other known orthosteric and allosteric ligands for various incubation times. After removing unreacted ligands, we measured the binding of [ 3H]N-methylscopolamine to residual unalkylated receptors. Affinity constants, rate constants for alkylation, and cooperativity constants were estimated for the interacting ligands using a mathematical model. Receptor alkylation by BR384 was consistent with a two-step process. After rapidly equilibrating with the receptor (step one), the aziridinium ion–receptor complex became covalently linked with a first order rate constant of about 0.95 min −1 (step two). McN-A-343, acetylcholine and N-methylscopolamine competitively protected the M 2 receptor from irreversible alkylation by BR384. In contrast, the allosteric modulators, gallamine and WIN 51,708 (17-β-hydroxy-17-α-ethynyl-5-α-androstano[3,2-β]pyrimido[1,2-α]benzimidazole), allosterically inhibited or had no effect on, respectively, receptor alkylation by BR384. There was good agreement between affinity constants estimated from the kinetics of receptor alkylation and by displacement of [ 3H]N-methylscopolamine binding. Our results suggest that BR384 covalently binds to the orthosteric site of the M 2 receptor and that McN-A-343 binds reversibly at the same locus. Our method of analyzing allosteric interactions does not suffer from the limitations of more conventional approaches and can be adapted to detect allosteric interactions at receptors other than the muscarinic subtypes.

Cognitive enhancement and neuroprotective effects of Bacopa monnieri in Alzheimer's disease model

Ethnopharmacological relevance Bacopa monnieri (L.) Wettst., a plant belonging to the family Scrophulariaceae, has been used in the traditional system of Ayurvedic medicine to improve intelligence and memory for a long time. Therefore, the potential of this plant to protect against Alzheimer's disease has been raised but less supported document is available. Aim of the study To determine the effect of alcoholic extract of Bacopa monnieri on cognitive function and neurodegeneration in animal model of Alzheimer's disease induced by ethylcholine aziridinium ion (AF64A). Materials and methods Male Wistar rats were orally given the alcoholic extract of Bacopa monnieri at doses of 20, 40 and 80 mg/kg BW via feeding needle for a period of 2 weeks before and 1 week after the intracerebroventricular administration of AF64A bilaterally. Rats were tested for spatial memory using Morris water maze test and the density of neurons and cholinergic neurons was determined using histological techniques 7 days after AF64A administration. Results Bacopa monnieri extract improved the escape latency time ( p < .01) in Morris water maze test. Moreover, the reduction of neurons and cholinergic neuron densities were also mitigated. Conclusion These findings suggest that Bacopa monnieri is a potential cognitive enhancer and neuroprotectant against Alzheimer's disease.

Facile and practical synthesis of a cannabinoid-1 antagonist via regio- and stereoselective ring-opening of an aziridinium ion

A scalable synthetic strategy of a chiral, trisubstituted imidazolidinone ( 1), a novel cannabinoid-1 antagonist, starting from a commercially available mandelic acid ( 5) is described. The key step involves a regio- and stereoselective ring-opening of an aziridinium ion by an aniline nucleophile ( 3). A mechanistic study revealed the insight into rate amplification at a lower temperature for vicinal diamine 12 formation via a aziridinium ion 14. Although most intermediates are not isolable by crystallization due to their intrinsic physical properties (oil or foamy solid), the reported synthesis furnished pure 1 without any chromatography purification throughout the entire synthesis. Employing green chemistry principles, this novel synthesis appears to be highly efficient for the manufacturing of multi-kilogram quantities of an optically-pure active pharmaceutical ingredient.

Iodine-mediated ring-closing iodoamination with concomitant N-debenzylation for the asymmetric synthesis of polyhydroxylated pyrrolidines

Treatment of a range of homochiral unsaturated β-amino esters (containing a cis-dioxolane unit) with iodine promotes a novel ring-closing alkene iodoamination reaction which proceeds with concomitant N-debenzylation, providing a simple and stereoselective route to iodomethyl pyrrolidines. Functional group interconversion of the resulting iodomethyl pyrrolidines upon treatment with AgOAc proceeds via the corresponding aziridinium ion, with subsequent deprotection giving access to polyhydroxylated pyrrolidines.

Use of Acetylcholine Mustard to Study Allosteric Interactions at the M2Muscarinic Receptor

We explored the interaction of a nitrogen mustard derivative of acetylcholine with the human M(2) muscarinic receptor expressed in Chinese hamster ovary cells using the muscarinic radioligand, [3H]N-methylscopolamine (NMS). Acetylcholine mustard caused a concentration-dependent, first-order loss of [3H]NMS binding at 37 degrees C, with the half-maximal rate constant occurring at 24 microM and a maximal rate constant of 0.16 min(-1). We examined the effects of various ligands on the rate of alkylation of M(2) receptors by acetylcholine mustard. N-methylscopolamine and 4-(trimethylamino)-2-butynyl-(3-chlorophenyl)carbamate (McN-A-343) competitively slowed the rate of alkylation, whereas the inhibition by gallamine reached a plateau at high concentrations, indicating allosteric inhibition. In contrast, 17-beta-hydroxy-17-alpha-ethynyl-5-alpha-androstano[3,2-beta]-pyrimido[1,2-alpha]benzimidazole (WIN 51708) had no effect. We also measured the inhibition of [3H]NMS binding by acetylcholine mustard at 0 degrees C, conditions under which there is little or no detectable covalent binding. In these experiments, the dissociation constant of the aziridinium ion of acetylcholine mustard was estimated to be 12.3 microM. In contrast, the parent mustard and alcoholic hydrolysis product of acetylcholine mustard were without effect. Our results show that measurement of the effects of ligands on the rate of inactivation of the orthosteric site by a small site-directed electrophile is a powerful method for discriminating competitive inhibition from allosterism.

Ring Expansion of 2‐(α‐Hydroxyalkyl)azetidines: A Synthetic Route to Functionalized Pyrrolidines

AbstractA series of 2‐(α‐hydroxyalkyl)azetidines synthesized from enantiomerically pure β‐amino alcohols and presenting various patterns both on the four‐membered ring and on the adjacent hydroxy group were treated with either thionyl chloride or methanesulfonyl chloride in the presence of triethylamine. The thus‐prepared 2‐(α‐chloro‐ or α‐methanesulfonyloxyalkyl)azetidines were shown to rearrange stereospecifically into 3‐(chloro‐ or methanesulfonyloxy)pyrrolidines. When this rearrangement is conducted in the presence of an added nucleophile (NaN3, KCN, KOH, or NaOAc), the produced pyrrolidine incorporates the added nucleophile at C‐3 stereospecifically. The relative configuration of the substituents in the formed pyrrolidines is consistent with a mechanism involving the formation of an intermediate bicyclic aziridinium ion, which is opened regioselectively at the bridgehead carbon atom. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

Use of 4‐[(2‐bromoethyl)methyl‐amino]‐2‐butynyl N‐(3‐chlorophenyl)carbamate (BR 384), to study allosteric interactions at M2 muscarinic receptor

We explored the interaction of a nitrogen mustard derivative of McN‐A‐343 (BR 384) with the human M2 muscarinic receptor expressed in CHO cells using the muscarinic radioligand, [3H]N‐methylscopolamine ([3H]NMS). BR 384 caused a concentration‐dependent, first order loss of [3H]NMS binding at 37°C, with the half maximal rate constant occurring at 8.6 μM BR 384. We examined the effects of various ligands on the rate of alkylation of M2 receptors by BR 384. NMS competitively slowed the rate of alkylation, whereas the inhibition by gallamine and McN‐A‐343 reached a plateau at high concentrations, indicating an allosteric inhibition. In contrast, WIN51708 had no effect. We also measured the inhibition of [3H]NMS binding by BR 384 at 0°C, conditions under which covalent binding is reduced. In these experiments, the dissociation constants of NMS, gallamine, McN‐A‐343 and the aziridinium ion of BR 384 for their binding sites were 0.0001, 0.64, 18 and 3.7 μM, respectively. In contrast, the parent mustard and alcoholic hydrolysis product of BR 384 were without effect. Our results show that the aziridinium ion of BR 384 binds covalently to the orthosteric site of the M2 receptor, whereas McN‐A‐343 binds to an allosteric site. Measurement of the effects of ligands on the rate of inactivation of muscarinic receptors by a covalent orthosteric ligand is a powerful method for detecting allosterism.Supported by a NIH Grant GM 69829.

Formate ester synthesis via reaction of 2-bromoethylamines with dimethylformamide

2-Bromoethylamines are converted to the corresponding formate esters in the presence of DMF. Both primary and secondary bromides are smoothly transformed to the esters in satisfactory yields. The reaction mechanism involves the formation of an aziridinium ion, which upon reaction with DMF forms a Vilsmeier-type intermediate that is further hydrolyzed to the corresponding formates. Participation of the β-amino group appears to control not only the regioselectivity but also the stereoselectivity of the reaction. Application of the reaction conditions to chiral substrates indicated that non-rearranged products are formed with retention of configuration at the reacting center.

Reactions of DNA bases with the anti-cancer nitrogen mustard mechlorethamine: A quantum chemical study

Reactions of the aziridinium ion of mechlorethamine ( A Z + 1 ) at the N7, N3 and O6 sites of guanine, N7, N3 and N1 sites of adenine, O2 and N3 sites of cytosine, and O2 and O4 sites of thymine were studied using density functional theory (B3LYP) and the MP2 method in gas phase and aqueous media. The calculations explain the mechanism of alkylation of the DNA bases and show that the reactions of the A Z + 1 ion would be most likely to occur at the N7 site of guanine and the N3 site of adenine while it would be much less likely to occur at the carbonyl oxygen sites of the DNA bases.

Dynamic Biphasic Counterion Exchange in a Configurationally Stable Aziridinium Ion: Efficient Synthesis and Isolation of a Koga C2-Symmetric Tetraamine Base

An efficient synthetic process for chiral tetraamine base (R,R)-5 is reported that leverages mechanistic understanding to enable control over key transformations. Specifically, a configurationally stable and observable aziridinium ion intermediate was found to undergo counterion exchange impacting the feasibility of the process. Mechanistic investigations revealed that both counterion exchange and trapping of the aziridinium ion were biphasic events and that the former could be suppressed at lower temperatures, facilitating the reaction on both small and large scales. The mechanistic insights gained have led to the development of an efficient one-pot process that enables preparation of multiple kilograms of (R,R)-5 as a crystalline solid without chromatography in excellent chemical and chiral purity.

Proposed Biogenetic Origin of Secu'amamine A from Allosecurinine: A Model Study To Support the Intermediacy of the Putative Aziridinium Ion

Proposed Biogenetic Origin of Secu'amamine A from Allosecurinine: A Model Study To Support the Intermediacy of the Putative Aziridinium Ion

Opposite Regioselectivity in the Sequential Ring-Opening of 2-(Alkanoyloxymethyl)aziridinium Salts by Bromide and Fluoride in the Synthesis of Functionalized β-Fluoro Amines

1-Arylmethyl-2-(bromomethyl)aziridines were converted into the corresponding 2-(alkanoyloxymethyl)aziridines upon treatment with potassium 2-methylpropanoate or potassium 2-­methylbutyrate in DMSO in excellent yields, following regio­selective ring-opening towards N-(2-bromo-3-alkanoyloxy­propyl)amines ­using allyl bromide or an arylmethyl bromide in acetonitrile. Treatment of the latter β-bromo amines with tetrabutyl­ammonium fluoride in acetonitrile afforded 2-amino-1-fluoro­propanes as the major compounds (72-86%) besides the isomeric 1-amino-2-fluoropropanes in minor quantities (14-28%). The ring-opening of the intermediate aziridinium salts by bromide and ­fluoride in acetonitrile resulted in a different regioselectivity with a preferential attack of bromide at the more hindered carbon atom and of fluoride at the less hindered carbon atom of the aziridinium ion.

Proposed Biogenetic Origin of Secu'amamine A from Allosecurinine: A Model Study To Support the Intermediacy of the Putative Aziridinium Ion

[reaction: see text] A model study to support the intermediacy of the aziridinium ion in the proposed biogenetic origin of secu'amamine A from allosecurinine is described.

Cover Picture: Design, Synthesis, and Preliminary Biological Evaluation of a DNA Methyltransferase‐Directed Alkylating Agent (ChemBioChem 2/2006)

The cover picture shows the envisioned pathways for how the DNA methyltransferase, M.HhaI, can use either S‐adenosyl‐L‐methionine (SAM; left) or an unnatural aziridinium cofactor (right). The aziridinium ion is proposed to arise in situ from the appropriately functionalized 5′ N‐mustard precursor. By virtue of its structural similarity to SAM, this highly reactive alkylating agent is bound by a methyltransferase (MTase) and delivered to a specific DNA nucleobase (extrahelical cytosine colored by atom). The stick structures (center) depict the envisioned approach of SAM vs. the proposed aziridinium intermediate to an M.HhaI DNA substrate within the M.HhaI active site. We thank Peter Anderson for assistance in generating the modeling images. The DNA substrate and cofactor structures were adapted from coordinates for the ternary structure of M.HhaI in complex with duplex DNA and S‐adenosyl‐homocysteine (RCSB PDB). Detailed information regarding this new synthetic DNA alkylating agent and MTase‐driven DNA alkylation is reported by S. Rajski and R. Weller on p. 243 ff.

Use of the intramolecular Heck reaction for forming congested quaternary carbon stereocenters. Stereocontrolled total synthesis of (+/-)-gelsemine.

Intramolecular Heck reactions of alpha,beta-unsaturated 2-haloanilides derived from azatricyclo[4.4.0.0(2,8)]decanone 5 efficiently install the congested spirooxindole functionality of gelsemine. Depending upon the Heck reaction conditions and the nature of the beta-substituent, either products having the natural or unnatural configuration of the spirooxindole group are formed predominantly. Efforts to elaborate the hydropyran ring of gelsemine from the endo-oriented nitrile substituent of pentacyclic Heck product 18 were unsuccessful. Important steps in the ultimately successful route to (+/-)-gelsemine (1) are as follows: (a) intramolecular Heck reaction of tricyclic beta-methoxy alpha,beta-unsaturated 2-iodoanilide 68 in the presence of silver phosphate to form pentacyclic product 69 having the unnatural configuration of the spirooxindole fragment, (b) formation of hexacyclic aziridine 80 from the reaction of cyanide with intermediate 79 containing an N-methoxycarbonyl-beta-bromoethylamine fragment, (c) introduction of C17 by ring-opening of the aziridinium ion derived from aziridine 80, and (d) base-promoted skeletal rearrangement of pentacyclic equatorial alcohol 82 to form the oxacyclic ring and invert the spirooxindole functional group to provide hexacyclic gelsemine precursor 83.

DNA Damage by Fasicularin

Fasicularin is a structurally novel thiocyanate-containing alkaloid isolated from the ascidian Nephteis fasicularis. Early biological experiments suggested that this compound's cytotoxic properties may stem from its ability to damage cellular DNA. Sequence gel analysis reveals that treatment of a 5'-32P-labeled DNA duplex with fasicularin in pH 7.0 buffer causes strand cleavage selectively at guanine residues. Further experiments indicate that production of these base-labile lesions in DNA involves alkylation of guanine residues by a fasicularin-derived aziridinium ion. This work reveals fasicularin as the first natural product found to generate a DNA-alkylating aziridinium ion via a mechanism analogous to the clinically used anticancer drugs mechlorethamine, melphalan, and chlorambucil.

N‐Cyanomethyl‐β‐chloroamines: A Convenient Source of Aziridinium Ions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The Combination of 2‐NsNH2/NCS and MeCN as the Nitrogen Sources for the Regio‐ and Stereoselective Formation of Imidazolines from α,β‐Unsaturated Ketones.

Abstract A new nitrogen source combination was found for the regio- and stereoselective diamination of α,β-unsaturated ketones. This combination employs the readily available and inexpensive combination of NCS and 2-NsNH 2 as the electrophilic nitrogen source, and acetonitrile as the nucleophilic nitrogen source, respectively. The reaction is easily performed by mixing olefin, 2-NsNH 2 , NCS and 4 A molecular sieves in freshly distilled acetonitrile at room temperature. The reaction is chemoselective without the formation of any haloamine side products. A new aziridinium ion formed from enones and 2-NsNHCl is suggested to exist and to react with nitrile via a [2+3] cycloaddition mechanism, which is responsible for the excellent regio-, stereoselectivity of the resulting diamination products.

Synthesis of novel DNA cross-linking antitumour agents based on polyazamacrocycles

We are seeking to develop more effective alkylating agents as antitumour agents. In previous work conformationally restricted nitrogen mustards were synthesised containing piperidine or pyrrolidine rings. The free bases were designed to be bifunctional alkylating agents via aziridinium ion formation and the effects of varying the distances between the two alkylating sites were studied. Some efficient cross-linkers of naked DNA were prepared but few of these compounds exhibited significant cytotoxicity in human tumour cells in vitro. We have extended this work by making tri- and tetra-azamacrocyclic compounds containing two to four potential alkylating sites. Most of these compounds were powerful DNA alkylating agents and showed cytotoxicity (IC 50 values 6–100 μM) comparable with chlorambucil (45 μM) and melphalan (8.5 μM). In particular the cyclen derivative 2a was more than 10 4 times more effective at cross-linking DNA ( 2a XL 50 ≪ 10 nM) than chlorambucil (XL 50 100 μM), and showed significant cytotoxicity in human tumour cells in vitro.