Massenspektrometrische Untersuchungen an 4-Benzyl-1.2.3.4-tetrahydroisochinolinen

Mass-Spectrometric Studies on 4-Benzyl-1,2,3,4-tetrahydroisoquinolines The electron-impact induced decomposition of the 4-benzyl-1,2,3,4-tetrahydro-N-methylisoquinolines 1–3 proceeds mainly in three competing ways: 1. By retro-Diels-Alder reaction and successive fragmentations, 2. by loss of C₆H₅X with [1,3]H shift, and 3. by loss of C₇H₇X with [1,5]H shift. The unexpected explusion of the ortho substituent × from M^+· is highly specific as shown by comparison of the isomeric chlorobenzyl compounds 1f, 2 and 3 . In striking contrast to the behavior of the 1-isomers, simple fission of the benzylic bond is of minor importance.     

Synthesis of C‐14 and C‐13, H‐2‐labeled IKK inhibitor: [14C] and [13C4,D3]‐N‐(6‐chloro‐7‐methoxy‐9H‐pyrido[3,4‐b]indol‐8‐yl)‐2‐methyl‐3‐pyridinecarboxamide

[¹⁴C]‐N‐(6‐Chloro‐7‐methoxy‐9H‐pyrido [3,4‐b]indol‐8‐yl)‐2‐methyl‐3‐pyridinecarboxamide (5B ), an IKK inhibitor, was synthesized from [¹⁴C]‐barium carbonate in two steps in an overall radiochemical yield of 41%. The intermediate, [carboxyl‐¹⁴C]‐2‐methylnicotinic acid, was prepared by the lithiation and carbonation of 3‐bromo‐2‐methylpyridine. [¹³C₄,D₃]‐N‐(6‐chloro‐7‐methoxy‐9H‐pyrido [3,4‐b]indol‐8‐yl)‐2‐methyl‐3‐pyridinecarboxamide (5C ) was synthesized from [1,2,3,4‐¹³C₄]‐ethyl acetoacetate and [D₄]‐methanol in six steps in an overall yield of 2%. [¹³C₄]‐2‐methylnicotic acid, was prepared by condensation of [¹³C₄]‐ethyl 3‐aminocrotonate and acrolein, followed by hydrolysis with lithium hydroxide. Copyright © 2006 John Wiley & Sons, Ltd.     

Syntheses of perdeuterated indoles and derivatives as probes for the biosyntheses of crucifer phytoalexins

A simple two‐step preparation of [²H₄]indole, a starting material necessary for the synthesis of various crucifer metabolites, starting with readily available ¹H NMR solvent [²H₅]nitrobenzene (99% deuterated) was developed. [4,5,6,7‐²H₄]Indole 99% deuterated at the specified positions was then used to synthesize [4′,5′,6′,7′‐²H₄]indolyl‐3‐acetaldoxime, [4′,5′,6′,7′‐²H₄]1‐methoxyindolyl‐3‐acetaldoxime, [1″,1″,1″,4′,5′,6′,7′‐²H₇]1‐methoxyindolyl‐3‐acetaldoxime, [4′,5′,6′,7′‐²H₄]1‐methoxybrassinin, and [3,3,3,4′,5′,6′,7′‐²H₇]1‐methoxybrassinin. Copyright © 2005 John Wiley & Sons, Ltd.     

Massenspektrometrie einiger substituierter α-Ethoxy-Pyridine und -Pyrimidine

Mass Spectrometry of Substituted α-Ethoxypyridines and -Pyrimidines The molecular ions of the α-ethoxy heterocycles 1–8 lose * CH₃ and C₂H₄ or * C₂H₅ from the α-ethoxy group. Also, fragmentation of the esters 2b, 3b, 4–8 occurs by degradation of the ethoxycarbonyl group.     

Cyclophosphamide analogues: synthesis, spectroscopic study, and antitumor activity of diazaphosphorinanes

Some diazaphosphorinanes were synthesized and characterized by ¹H, ¹³C, ³¹P NMR and IR spectroscopy and elemental analysis. The antitumor activity of cyclophosphamide (CP) and its nine analogoues with formula , R = OC₆H₅CH₃-4 (1), NHC₆H₄S(O)₂NH₂-4 (2), NHC(O)NHC₆H₄-CH₃-2 (3), NHC(O)NHC₆H₄-NO₂-2 (4), NHC(O)NHC₆H₄-NO₂-3 (5), NHC(O)NHC₆H₄-NO₂-4 (6), NHC(O)C₆H₄-NO₂-2 (7), NHC(O)C₆H₄-NO₂-3 (8), and NHC(O)C₆H₄-NO₂-4 (9) were evaluated by cell culture on K562 cell line using MTT cell proliferation assay. The IC₅₀ values for CP and the compounds 1–9 were in the range of 0.140 (for 3) to 58.250 μM (for 2). It was found that compounds 3–6 are the best candidates for antitumor activity close to CP. Compound 2 containing aminosulfonamide substituent is very much less toxic among these compounds.     

In-vitro Characterization of YM872, a Selective,Potent and Highly Water-soluble α-Amino-3-hydroxy-5-methylisoxazole-4-propionate Receptor Antagonist

The in-vitro pharmacological properties of (2,3-dioxo-7-(1H-imidazol-***1-yl)-6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl)-acetic acid monohydrate, YM872, a novel and highly water-soluble α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)-receptor antagonist were investigated. YM872 is highly water soluble (83 mg mL^?1 in Britton-Robinson buffer) compared with 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX), 6-(1H-imidazol-1-yl)-7-nitro-2,3(1H,4H)-quinoxalinedione hydrochloride (YM90K) or 6-cyano-7-nitroquinoxa-line-2,3-dione (CNQX). YM872 potently inhibits [³H]AMPA binding with a K_i (apparent equilibrium dissociation constant) value of 0.096 ± 0.0024 μM. However, YM872 had very low affinity for other ionotropic glutamate receptors, as measured by competition with [³H]kainate (high-affinity kainate binding site, concentration resulting in half the maximum inhibition (IC50) = 4.6 ± 0.14 μm), [³H]glutamate (N-methyl-D-aspartate (NMDA) receptor glutamate binding site, IC50 > 100 μM) and [³H]glycine (NMDA receptor glycine-binding site, IC50 > 100 μM). YM872 competitively antagonized kainate-induced currents in Xenopus laevis oocytes which express rat AMPA receptors, with a pA₂ value of 6.97 ± 0.01. In rat hippocampal primary cultures, YM872 blocked a 20-μM AMPA-induced increase of intracellular Ca²⁺ concentration with an IC50 value of 0.82 ± 0.031 μM, and blocked 300-μM kainate-induced neurotoxicity with an IC50 value of 1.02 μM. These results show that YM872 is a potent and highly water-soluble AMPA antagonist with great potential for treatment of neurodegenerative disorders such as stroke.     

Synthesis and Antifungal Activity of 1‐Aryl‐3‐phenethylamino‐1‐propanone Hydrochlorides and 3‐Aroyl‐4‐aryl‐1‐phenethyl‐4‐piperidinols

Mono‐Mannich bases, 1‐aryl‐3‐phenethylamino‐1‐propanone hydrochlorides, 1a, 2a , 3a , 4a , 5a , 6a , 7a , 8a , 9a , and semi‐cyclic mono‐Mannich bases, 3‐aroyl‐4‐aryl‐1‐phenethyl‐4‐piperidinols, 1b , 2b , 3b , 4b , 5b , 6b , 7b , 8b , 9b , were synthesized by a non‐classical Mannich reaction. The aryl part was: C₆H₅ for 1a , 1b ; 4‐CH₃C₆H₄ for 2a , 2b ; 4‐CH₃OC₆H₄ for 3a , 3b ; 4‐ClC₆H₄ for 4a , 4b ; 4‐FC₆H₄ for 5a , 5b ; 4‐BrC₆H₄ for 6a , 6b ; 2,4‐(Cl)₂C₆H₃ for 7a , 7b ; 4‐NO₂C₆H₄ for 8a , 8b ; and C₄H₃S(2‐yl) i. e., 2‐thienyl for 9a , 9b . Piperidinol compounds 2b , 3b , 4b , 5b , 7b , 8b , and 9b are reported here for the first time. The synthesized compounds were tested against seven types of plant pathogenic fungi and three types of human pathogenic fungi using the agar dilution assay. Itraconazole was tested against Candida parapsilosis as the reference compound, while Nystatin was tested as the reference compound against the other fungi. Compounds 1a , 1b , 2a , 4a , 4b , 5a , 5b , 6a , 7a , 8a , 9a , and 9b can be selected as model compounds to develop new antifungal agents against the human pathogen Microsporum canis. Compounds 8a and 8b , which had a similar antifungal activity compared with the reference compound Nystatin against the plant pathogen Aspergillus flavus, can serve as model compounds to develop new antifungal agents to solve agricultural problems.     

Synthesis of highly potent lymphocyte function‐associated antigen‐1 antagonists labeled with carbon‐14 and with stable isotopes,part 3

The drug candidates ( 2 ) and ( 3 ) are highly potent LFA‐1 inhibitors. They were efficiently prepared labeled with carbon‐14 using a palladium‐catalyzed carboxylation of an iodo‐precursor ( 5 ) and sodium formate‐¹⁴C to afford acid [¹⁴C]‐( 6 ), which was coupled via an amide bond to chiral amines ( 7 ) and ( 8 ) in 52% and 48% overall yield, respectively, and with specific activities higher than 56 mCi/mmol and radiochemical purities of 99%. For stable isotopes synthesis, the amine [²H₈]‐( 7 ) was synthesized in three steps from 2‐cyanopyridine‐²H₄ using Kulinkovich‐Szymonik aminocyclopropanation, followed by coupling to L ‐alanine‐2,3,3,3‐²H₄‐N‐t‐BOC, and then removal of the BOC‐protecting group. Amide bond formation with acid ( 6 ) gave [²H₈]‐( 2 ) in 36% overall yield. The amine [¹³C₄,¹⁵N]‐( 8 ) was obtained in two steps using L‐threonine‐¹⁴C₄,¹⁵N and then coupled to acid [¹³C]‐( 6 ) to give [¹³C₅,¹⁵N]‐( 3 ) in 56% overall yield.     

Tritiation of CEP‐1347 at high specific activity using several methods

[Thiomethylenes‐³H] CEP‐1347 ( 5 ) was synthesized by the tritiation of diformyl precursor 3 with NaB³H₄ followed by treatment with ethanethiol. [Methyl ester‐³H] CEP‐1347 ( 7 ) was prepared at even higher specific activity by the alkylation of precursor 6 with C³H₃I. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparison of early injury to liver endoplasmic reticulum by halomethanes,hexachloroethane, benzene,toluene, bromobenzene,ethionine, thioacetamide and dimethylnitrosamine

This study compares the effects in vivo of CH₂Cl₂, CH₂Br₂, CHCl₃, CH₂I₂, CHBr₃, CCl₄, CHI₃, CBr₄, CI₄, C₂Cl₆, C₂HCl₅, C₆H₆, C₇H₈, C₆H₅Br, ethionine, thioaeetamide and dimethylnitrosamine on the functions and composition of liver endoplasmic reticulum 2 hr after poisoning. Within the halomethane series, the effects on lipid diene conjugate content, oxidative demethylase, ¹⁴C-glycine incorporation into protein and glucose 6-phosphatase of liver microsomes and cell sap RNA content, increase with decreasing effective negative charge on the halogen atoms (?), an indicator of increasing halomethane free radical reactivity (cf.B. P. Dailey, J. chem. Phys.33, 1641,1960). Peak toxic effect is reached following CCl₄ and CHI₃. Glycine incorporation into protein is also decreased 2 hr after thioacetamide and dimethylnitrosamine. After dimethylnitrosamine, suppression of protein synthesis is concomitant with increases in lipid diene conjugate content and cell sap RNA. C₆H₅Br and ethionine, both known hepatotoxins, do not effect microsomal composition and function at this time, nor do C₆H₆ or C₇H₈ both organic solvents with solubility properties similar to CCl₄. The findings support the hypothesis that free radical halomethane metabolites injure the endoplasmic reticulum by reacting with and chemically altering its constituents. While dimethylnitrosamine may act similarly, thioaeetamide, bromobenzene and ethionine apparently do not.     

Guanidinium-carboxylate interactions

The crystal structures of the 1:1 complexes methylguanidinium benzylhydrogenmalonate, (C₂N₃H₈)⁺(C₁₀H₉O₄)^?, MGD.BMAL, and methylguanidinium ethylhydrogenmalonate, (C₂N₃H₈)⁺(C₅H₇O₄)^?, MGD.EMAL, and of the 2:1 complex methylguanidinium sulfate, (C₂N₃H₈)₂SO₄, have been determined from three-dimensional X-ray data. For MGD.BMAL, the complex crystallizes in the triclinic space group P with two formula units in a cell of dimensions a = 6.277(5), b = 8.470(3), c = 13.191(6)Å, α= 91.01(1), β= 99.64(9), γ= 90.83(5)°. The structure has been refined to a final value of R = 0.061 based on 1511 intensities. The MGD.EMAL complex is also triclinic, space group P with two molecules in a cell of dimensions a = 9.254(7), b = 9.625(6), c = 6.778(2) Å, α= 109.6(1), β= 100.8(1), γ= 62.7(1)Å. The crystals of this compound are of low quality, and the final value is R = 0.109 based on 706 intensities. (MGD)₂SO₄ is orthorhombic, space group P2₁2₁2₁, with four molecules in a cell of dimensions a = 7.100(4), b = 12.151(3), c = 13.108(2) Å. Refinement has converged to R = 0.054 based on 907 data. All three crystals exhibit extensive interionic hydrogen bonding. The hydrogen bonding in MGD.BMAL includes a Type B interaction and a Type 1 interaction, the latter being a pairwise interaction from both amino nitrogen atoms on the cation to two carboxylate oxygen atoms from the two different carboxylate groups in an anion. In MGD.EMAL, the anion participates in both a Type A and a Type B pairwise interaction with two neighboring cations. The possible implications of the hydrogen bonding patterns in these two compounds for the role of arginyl side chains in protection of γ-carboxyglutamate residues from decarboxylation are discussed.     

A gram‐scale synthesis of [3,4‐13C2,1α,7‐2H2]cortisone

A gram‐scale synthesis of [3,4‐¹³C₂,1α,7‐²H₂]cortisone from prednisone was developed. The deuterium atom at the C‐1 position was introduced through a regioselective and stereoselective deuteration of the 1,2‐double bond of the 1,4‐diene‐3‐one using Wilkinson's catalyst. After the oxidative cleavage of the A‐ring, two carbon‐13 atoms were introduced via acetylation of an A‐ring enol lactone with [1,2‐¹³C₂]acetyl chloride. The steroidal A‐ring was then reconstructed to incorporate the carbon‐13 atoms into the C‐3 and C‐4 positions. The deuterium atom at C‐7 was introduced through a regioselective deuteration of the 6,7‐double bond of a 4,6‐diene‐3‐one intermediate using palladium on strontium carbonate. The M + 4 stable isotope labeled cortisone was thus prepared in ca. 4% overall yield. In addition, [3,4‐¹³C₂,1α,7‐²H₂]‐11‐dehydrocorticosterone, [3,4‐¹³C₂,1α,7‐²H₂]cortisol, and [3,4‐¹³C₂,1α,7‐²H₂]corticosterone were also prepared. Copyright © 2011 John Wiley & Sons, Ltd.     

Channel‐forming,self‐assembling,bishelical amphiphilic peptides: design,synthesis and crystal structure of Py(Aibn)2, n = 2, 3, 4

Abstract: The design, synthesis, characterization and self‐assembling properties of a new class of amphiphilic peptides, constructed from a bifunctional polar core attached to totally hydrophobic arms, are presented. The first series of this class, represented by the general structure Py(Aib_n)₂ (Py = 2,6‐pyridine dicarbonyl unit; Aib = α, α′‐dimethyl glycine; n = 1–4), is prepared in a single step by the condensation of commercially available 2,6‐pyridine dicarbonyl dichloride with the methyl ester of homo oligoAib peptide (Aib_n‐OMe) in the presence of triethyl amine. ¹H NMR VT and ROESY studies indicated the presence of a common structural feature of 2‐fold symmetry and an NH…N hydrogen bond for all the members. Whereas the Aib3 segment in Py(Aib3)₂ showed only the onset of a 3₁₀‐helical structure, the presence of a well‐formed 3₁₀‐helix in both Aib4 arms of Py(Aib4)₂ was evident in the ¹H NMR of the bispeptide. X‐ray crystallographic studies have shown that in the solid state, whereas Py(Aib2)₂ molecules organize into a sheet‐like structure and Py(Aib3)₂ molecules form a double‐stranded string assembly, the tetra Aib bispeptide, Py(Aib4)₂, is organized to form a tetrameric assembly which in turn extends into a continuous channel‐like structure. The channel is totally hydrophobic in the interior and can selectively encapsulate lipophilic ester (CH₃COOR, R = C₂H₅, C₅H₁₁) molecules, as shown by the crystal structures of the encapsulating channel. The crystal structure parameters are: 1b , Py(Aib2)₂, C₂₅H₃₇N₅O₈, sp. gr. P2₁2₁2₁, a = 9.170(1) Å, b = 16.215(2) Å, c = 20.091(3) Å, R = 4.80; 1c , Py(Aib3)₂, C₃₃H₅₁N₇O₁₀·H₂O, sp. gr. P, a = 11.040(1) Å, b = 12.367(1) Å, c = 16.959(1) Å, α = 102.41°, β = 97.29°, γ = 110.83°, R₁ = 6.94; 1 da, Py(Aib4)₂?et ac, C₄₁H₆₅N₉O₁₂?1.5H₂O·C₄H₈O₂, sp. gr. P, a = 16.064(4) Å, b = 16.156 Å, c = 21.655(5) Å, α = 90.14(1)°, β = 101.38(2)°, γ = 97.07(1)°, Z = 4, R₁ = 9.03; 1db, Py(Aib4)₂?amylac,C₄₁H₆₅N₉O₁₂?H₂O ·C₇H₁₄O₂, P2₁/c, a = 16.890(1) Å, b = 17.523(1) Å, c = 20.411(1) Å, β = 98.18 °, Z = 4, R = 11.1 (with disorder).     

Effects of Aroclor 1254 on disposition and hepatotoxicity of ethylene in the rat

The purpose of this study was to investigate the disposition of ethylene (C₂H₄) in the F344 rat and to determine the effects of pretreatment of animals with Aroclor 1254 on the disposition and hepatotoxicity of ethylene. Control or Aroclor 1254-pretreated (500 mg/kg, 5 days before exposure) male rats were exposed to ¹⁴C₂H₄ (10,000 ppm, 0.04–0.11 μCi/μmol) for 5 hr. Urine, feces, expired CO₂, and expired ¹⁴C₂H₄ were collected for 36 hr following the exposure. Aroclor pretreatment did not affect the amount of C₂H₄ expired (17–18 μmol/rat) but did cause a 4-fold increase in expired ¹⁴CO₂ and a doubled urinary excretion of radioactivity. In control animals the blood, gut, kidney, liver, and lung all had detectable ¹⁴C concentrations (20, 83, 14, 77, and 6 nmol-eq of C₂H₄, respectively) 36 hr after exposure. Aroclor pretreatment increased the concentrations in these tissues by factors of 1.5-, 8-, 6-, 17-, and 6-fold, respectively. In contrast to control rats. Aroclor-pretreated animals had detectable concentrations of radioactivity in brain, fat, heart, and muscle. Rats exposed to 10,000 ppm C₂H₄ exhibited no light microscopic evidence of hepatotoxicity. However, Aroclor-pretreated animals had centrolobular hepatic necrosis as assessed microscopically 36 hr after exposure to C₂H₄. These results demonstrate that the metabolism of C₂H₄ is stimulated by Aroclor pretreatment, and that the hepatic necrosis seen in Aroclor-pretreated rats is the result of a greater amount of metabolism or the production of a metabolite(s) not seen in control animals.     

Synthesis and deuterium labelling of the pure selective estrogen receptor modulator (SERM) acolbifene glucuronides

Acolbifene (EM‐652·HCl, SCH 57068·HCl), a highly potent and orally active selective estrogen receptor modulator (SERM), is at late stage clinical development for the treatment of estrogen‐sensitive breast cancer. Acolbifene‐7‐glucuronide 1 (major) and acolbifene‐4′‐glucuronide 2 (minor) were identified as metabolites of acolbifene in the human. The two monoglucuronides and a diglucuronide 3 as well as the corresponding ²H‐labelled derivatives 4 – 6 were synthesised for use as preclinical and clinical standards for LC–MS/MS analysis. All glucuronides were prepared by the Schmidt glycosylation of monoprotected acolbifene with a glucuronyl imidate at ?10°C to prevent epimerisation at the C‐2 position. The two monoglucuronides 1 and 2 of acolbifene were separated by semi‐preparative HPLC. Incorporation of three deuteriums was achieved by alkylation of chromanone 15 with C²H₃MgI followed by dehydration with C²H₃CO₂ ²H/²H₂O. After chemical resolution and salt neutralisation, [²H₃]acolbifene 19 was obtained with 99.4% enantiomeric purity and >98% isotopic purity. Copyright © 2007 John Wiley & Sons, Ltd.     

Characterizing the effect of UDP-glucuronosyltransferase (UGT) 2B7 and UGT1A9 genetic polymorphisms on enantioselective glucuronidation of flurbiprofen

Flurbiprofen (FPF), available commercially as a racemic mixture, is a propionic acid derivative of non-steroidal anti-inflammatory drugs (NSAIDs) with known stereoselective glucuronidation. The major enzyme catalyzing this conjugation reaction is UDP-glucuronosyltransferase (UGT) 2B7, with minor contributions by UGT1A9. This study examines the role of the genetic variants of UGT2B7 and 1A9 enzymes involved in the formation of acyl glucuronides (FPFGs). Variants caused by three single nucleotide polymorphisms (SNPs) (A71S, 211G>T; H268Y, 802C>T; and D398N, 1192G>A) in UGT2B7 and three SNPs (C3Y, 8G>A; M33T, 98T>C; D256N, 766G>A) in UGT1A9 showed activity changes toward different substrates. However the functional impacts of these SNPs on chiral substrates were not examined. Upon stable expression in Bac-to-Bac system, UGT2B7*71S (A⁷¹S), UGT2B7*2 (H²⁶⁸Y) and UGT2B7*5 (D³⁹⁸N) were all associated with a decrease in the formation of FPFGs. Compared with UGT2B7*1 (wild-type), UGT2B7*71S exhibited a >2-fold lower intrinsic clearance mainly by altered capacities (V_max). Furthermore, a >14-fold decreased intrinsic clearance of the *1 protein was produced by UGT2B7*2 and UGT2B7*5. However, no significantly stereoselective difference for the formation of (R)- and (S)-FPFG was found among these UGT2B7 allozymes. UGT1A9*2 (C³Y) exhibited a higher V_max (3.2-fold), K_m (2.1-fold) and intrinsic clearance (1.6-fold) toward (S)-FPF than UGT1A9*1 (wild-type). UGT1A9*3 (M³³T) almost lost the catalytic activity to FPF. A significantly stereoselective difference on the glucuronidation of rac-FPF was seen between the two variants compared with the wild type of UGT1A9.     

Synthesis of tritium labelled (R) and (S)-3-aminoquinuclidine: A ubiquitous component of serotonin receptor ligands,part II

(S)-3-Aminoquinuclidine-³H 10c-S having a specific activity of 66 Ci/mmol was prepared in eight steps from Isonicotinic acid ( 2 ). Reduction of 2 with carrier free tritium gas over PtO₂ in DMF gave isonipecotic acid-³H 3c . Conversion to α-bromo ketone 5c followed by cyclization afforded 3-quinuclidone-³H 6c . Racemic 3-aminoquinuclidine-³H 8c was prepared by conversion of 6c to oxime 7c followed by reduction with NaBH₄/NiCl₂·6H₂O. Racemic 8c was resolved with (R)-methylbenzyl isocyanate. Hydrolysis of 9c-S.R afforded (S)-3-aminoquinuclidine-³H 10c-S . The enantiopurity was >99.5% (S).     

Structure and conformation of peptides involving prolyl residue III. L-Prolyl-L-isoleucine monohydrate

The dipeptide, L-prolyl-L-isoleucine monohydrate (C₁₁ H₂₀N₂O₃· H₂O, molecular weight 246.3) crystallizes in the monoclinic space group P2₁, with a = 6.601(3)Å, b = 5.413(3) Å, c = 19.128(6) Å, β= 98.1(1)°, Z = 2, Do = 1.20g·cm^-3 and Dc = 1.208g·cm^-3. The structure was solved by MULTAN–80 and refined to a final R-factor of 0.081 for 594 reflections measured on a Enraf Nonius CAD-4 diffractometer. The peptide linkage exists in the trans conformation. The pyrrolidine ring is disordered with two alternate envelope conformations for the C^γ atom. The values of the sidechain torsion angles are: χ₁₁=– 63.6(17)°, χ₁₂= 171.1(16)° and χ₂=– 59.6(21)° for isoleucine (C-terminal). The crystal structure is stabilized by a three-dimensional network of N—H ? O, O—H ? O and C—H ? O hydrogen bonds. The dipeptide exists in the extended Conformation.     

Synthesis and evaluation of conformationally restricted pyridino N‐alkylated nicotine analogs as nicotinic acetylcholine receptor antagonists

Previous work has shown that quaternization of the pyridine‐N atom of S‐(–)‐nicotine (NIC) affords compounds such as N‐n‐octylnicotinium iodide (NONI) and N‐n‐decylnicotinium iodide (NDNI) that act as competitive nicotinic acetylcholine receptor (nAChR) antagonists at α3β2* and α4β2* subtypes, respectively. To ascertain the rotameric preference about the C3‐C2′ bond of NONI and NDNI for interaction with several nAChR subtypes, two classes of bridged analogs representing extreme rotameric conformations (syn and anti) of NONI and NDNI were synthesized. NIC‐evoked [³H]dopamine ([³H]DA) release from superfused rat striatal slices was used to determine the activity of the analogs at the α3β2* nAChR. [³H]NIC and [³H]methyllycaconitine ([³H]MLA) binding to rat brain membranes were used to determine affinity for α4β2* and α7* nAChRs, respectively. With the exception of BCDD (IC₅₀ value = 1,580 nM), all analogs potently and selectively inhibited NIC‐evoked [³H]DA release (IC₅₀ values = 30–660 nM), indicating antagonism of α3β2* nAChRs. None of the analogs inhibited either [³H]NIC or [³H]MLA binding, indicating a lack of interaction with α4β2* and α7* nAChR subtypes. Interestingly, the C_{10 N}‐alkyl chain analogs, ACD and BCD, had negligible affinity for the α4β2* subtype compared to the high affinity exhibited by NDNI, suggesting that the α4β2* subtype does not recognize the unique stereochemistry of these conformationally restricted analogs. Thus, conformational restriction of N‐n‐alkylnicotinium iodides eliminated inhibitory activity at α4β2* nAChRs, but more importantly afforded high affinity and selectivity for α3β2* nAChRs. Conformational restriction of N‐n‐alkyl analogs of NIC appears to be a viable approach for the development of α3β2*‐selective nAChR antagonists. Drug Dev. Res. 55:172–186, 2002. © 2002 Wiley‐Liss, Inc.     

Membrane lesions in cultured mouse neuroblastoma cells exposed to metal compounds

Tritiated 2-deoxy-D-glucose (dGlc) was rapidly taken up into cultured mouse neuroblastoma C1300 cells (clone 41A₃). Upon perfusion the pre-loaded cultures slowly released radioactivity as [³H]2-deoxy-D-glucose-6-phosphate ([³H]dGlc-6-P) (rate const. = 0.017 min^?1) from a pool corresponding to 74% (t1/2 = 41 min) of the total radioactivity incorporated. Destruction of the plasma membrane of the cells by means of Triton X-100 (1.0%) resulted in a rapid and total release of the radioactivity. CH₃HgCl, HgCl, (C₂H₅)₃SnCl and K₂Cr₂O₇ all caused an increase in the passive cell membrane permeability to [³H]dGlc-6-P. A membrane toxic concentration (MTC) was defined as the concentration of the tested metal compound giving rise to an increase in the relative efflux from 1.0 to 1.2 during 60 min perfusion. Using this MTC-value, the membrane toxicity of the compounds could be ranked in the following order: CH₃HgCl (MTC = 9 × 10^?7 M >; HgCl (MTC = 6 × 10^?6 M) > (C₂H₅)₃SnCl (MTC = 3 × 10^?4 M) > K₂Cr₂O₇ (MTC = 7 × 10^?4 M. Since this differential toxicity is in accordance with other reports it is concluded that 2-deoxy-D-glucose (dGlc) may be used together with 41A₃ cells to screen metal compounds for their membrane toxicity.