Chemical nature of implant-derived titanium(IV) ions in synovial fluid

Previous investigations have indicated a deleterious leakage of Ti(III) and/or Ti(IV) species from Ti-Al-V alloy joint prostheses into adjacent tissue, synovium or synovial fluid (SF) in vivo. In view of the importance of the particular chemical nature of such complexes in determining their biological activity, we have employed high field proton (1H) NMR spectroscopy to "speciate" Ti(IV) in inflammatory SF. Treatment of osteoarthritic SF samples with increasing concentrations of Ti(IV) (0.10-1.03 mM [TiO(C2O4)2]2-) gave rise to a specific broadening of the citrate proton resonances, indicating that this bioavailable oxygen-donor ligand plays an important role in complexing implant-derived Ti(IV). 1H NMR analysis of Ti(IV)-loaded SF samples subsequently treated with a large excess of ascorbate (0.05 M) showed that this added Ti(IV) chelator was only poorly effective in removing this metal ion from Ti(IV)-citrate/Ti(IV)-oxycitrate complexes. The results obtained here provide evidence for complexation of the low-molecular-mass (non-protein-bound) fraction of implant-derived Ti(IV) by citrate in vivo.     

Enantioselective desymmetrization of meso-epoxides with anilines catalyzed by polymeric and monomeric Ti(IV) salen complexes

The active catalysts for the enantioselective ring opening (ARO) of meso-stilbene oxide, cis-butene oxide, cyclohexene oxide, cyclopentene oxide, and cyclooctene oxide with various substituted anilines were generated in situ by the reaction of Ti(O(i)Pr)(4) with poly-[(R,R)-N,N'-bis-{3-(1,1-dimethylethyl)-5-methylene salicylidene} cyclohexane-1,2-diamine]-1 and (1R,2R)-N,N'-bis[3,5-di(tert-butyl)salicylidene] cyclohexane-1,2-diamine-2. These catalysts in the presence of nonracemic imine as an additive provided β-amino alcohol in excellent yield (99%) and chiral purity (enantiomeric excess (ee) up to 99%) for the ARO of meso-stilbene oxide with aniline. The same protocol was less effective for the ARO of cyclic epoxides; however, when triphenylphosphine was used as an additive, there was a significant improvement in catalyst performance for the ARO of cyclohexene oxide (yield, 85-90%; ee, 63-67%). Both in situ generated polymeric and monomeric catalysts performed in a similar manner except that the polymeric catalyst Ti(IV)-1 was more active and recycled several times with retention of enantioselectivity when compared with the monomeric catalyst Ti(IV)-2, which was nonrecyclable.     

Etoxadrol-meta-isothiocyanate: a potent, enantioselective, electrophilic affinity ligand for the phencyclidine-binding site

Etoxadrol-meta-isothiocyanate (2S,4S,6S-2-ethyl-2-(3-isothiocyanatophenyl)-2-piperidyl)1,3-dioxolane, 4a) has been synthesized and characterized as an irreversible ligand for the phencyclidine (PCP)-binding site. It is the first chiral electrophilic affinity ligand for this site to have been described. This affinity ligand is based upon etoxadrol, a 1,3-dioxolane known to have PCP-like effects in vivo and in vitro. Etoxadrol-meta-isothiocyanate was found to be four-five times more potent in vitro than metaphit (1-[1-(3- isothiocyanatophenyl)cyclohexyl]piperidine), the only previously known electrophilic affinity ligand for the PCP-binding site. The binding was shown to be highly enantioselective for etoxadrol-meta-isothiocyanate (4a). The 2R,4R,6R-enantiomer of 4a was essentially inactive. The ability of the 2S,4S,6S-enantiomer (4a) to interact with the benzodiazepine, muscarinic, and mu opioid receptor systems was also examined, and it was found not to interact with these receptor systems. It seems likely that 4a will prove to be a valuable tool in the study of structure and function of the PCP-binding site.     

Comparisons of the conformational biases imposed by trans-2,3-methanomethionine and α-methylmethionine

A comparative study of four peptidomimetics of the sequence Phe-Met-Arg-Phe-amide (FMRFa) was performed to compare the conformational bias caused by trans-2,3-methanomethionine and α-methylmethionine stereoisomers. The specific compounds studied were F[(2S,3S)-cyclo-M] RFa, F[(2R,3R)-cyclo-M]RFa, F[(S)-α-MeM]RFa, and F[(R)-α-MeM]RFa. Molecular simulations based on CHARMm 22 indicate that γ-turn, inverse γ-turn, and α-helical conformations about the cyclo-M residue are accessible to the two F[cyclo-M]RFa stereoisomers. Similar calculations for F[(S)-α-MeM]RFa, and F[(R)-α-MeM]RFa indicate that the α-methylamino acids tend to favor α-helical conformations. The nmr data is presented for the four peptidomimetics. Most informative were the rotating frame nuclear Overhauser effect cross peaks between the NH protons proximal to the methionine surrogates, and the C_β hydrogens. Overall, these nmr data indicate F[(2S,3S)-cyclo-M]RFa and F[(2R,3R)-cyclo-M]RFa preferentially adopt inverse γ-turn and γ-turn conformations, respectively, whereas F[(S)-α-MeM]RFa and F[(R)-α-MeM]RFa tend to form partial left- and right-handed helical structures (although energy differences between the two turn structures, and between the two helical structures are likely to be small). It is suggested that the wider NH-C_α-CO angle of cyclopropane amino acids and their more severe steric requirements around the C_β carbons force the peptidomimetic N- and C-termini into the same region of conformational space. This favors C⁷ turns in the cyclopropane amino acid series relative to the less constrained α-methyl derivatives. © 1997 John Wiley & Sons, Inc. Biopoly 42: 439–453, 1997     

New bulky chiral Lewis acid catalyst: 3,3'-di(2-mesitylethynyl)binaphthol-titanium(IV) complex

A new chiral Lewis acid catalyst 9 was prepared in situ from a 1:2 molar mixture of (R)-3,3'-di(2-mesitylethynyl)binaphthol (6) and titanium(IV) isopropoxide at ambient temperature. The 3- and 3'-substituents on 6 were effective for preventing undesired aggregation between Ti(IV) complexes and increasing the enantioselectivity (up to 82% ee) in the Diels-Alder reaction of methacrolein with cyclopentadiene.     

Isomer abundance of bis(beta-diketonato) complexes of titanium(IV). Crystal structures of the antitumor compound budotitane [Ti(IV)(bzac)(2)(OEt)(2)] and of its dichloro-derivative [Ti(IV)(bzac)(2)Cl(2)] (bzac=1-phenylbutane-1,3-dionate)

The molecular tumor inhibiting titanium compound budotitane [Ti(IV)(bzac)(2)(OEt)(2)] (1) and its dichloro-derivative [Ti(IV)(bzac)(2)Cl(2)] (2) (bzac=1-phenylbutane-1,3-dionate) have been crystallized and characterized by X-ray crystallography and further physical methods. Budotitane (1) crystallizes in the tetragonal, non-centrosymmetric space group P4(1) with two molecules in the asymmetric unit. Both molecules adopt the cis-cis-trans configuration with the acetyl ends of the benzoylacetonate ligands in the trans position. The dichloro-derivative of budotitane, [Ti(IV)(bzac)(2)Cl(2)] (2) crystallizes in the monoclinic, centrosymmetric space group P2(1)/n with one molecule only in the asymmetric unit. In contrast to budotitane (1), (2) shows a cis-trans-cis arrangement with the benzoyl groups in the trans position. In both complexes there are equal numbers of Delta and Lambda enantiomers within the unit cell. The phenyl groups in (1) as well as in (2) are in approximately coplanar conjugation to the metal enolate rings. The thermal degradation of budotitane (1) was investigated in the temperature range from 25 degrees C up to 800 degrees C and reveals the formation of Ti(IV)O(bzac(2-)) as an intermediate and of the rutile phase of TiO(2) as a final product. It may be worthwhile to introduce budotitane in the form of isomerically pure crystals in the preparation of the drug used for future tests.     

Characterization and Immunotherapeutic Implications for a Novel Antibody Targeting Interleukin (IL)-13 Receptor α2

The high affinity interleukin-13 receptor α2 (IL13Rα2) is selectively expressed at a high frequency by glioblastoma multiforme (GBM) as well as several other tumor types. One approach for targeting this tumor-specific receptor utilizes the cognate ligand, IL-13, conjugated to cytotoxic molecules. However, this approach lacks specificity because the lower affinity receptor for IL-13, IL13Rα1, is widely expressed by normal tissues. Here, we aimed to develop and characterize a novel monoclonal antibody (mAb) specific to IL13Rα2 for the therapeutic purpose of targeting IL13Rα2-expressing tumors. Hybridoma cell lines were generated and compared for binding affinities to recombinant human IL13Rα2 (rhIL13Rα2). Clone 47 demonstrated binding to the native conformation of IL13Rα2 and was therefore chosen for further studies. Clone 47 bound specifically and with high affinity (K(D) = 1.39 × 10(-9) m) to rhIL13Rα2 but not to rhIL13Rα1 or murine IL13Rα2. Furthermore, clone 47 specifically recognized wild-type IL13Rα2 expressed on the surface of CHO and HEK cells as well as several glioma cell lines. Competitive binding assays revealed that clone 47 also significantly inhibited the interaction between human soluble IL-13 and IL13Rα2 receptor. Moreover, we found that N-linked glycosylation of IL13Rα2 contributes in part to the interaction of the antibody to IL13Rα2. In vivo, the IL13Rα2 mAb improved the survival of nude mice intracranially implanted with a human U251 glioma xenograft. Collectively, these data warrant further investigation of this novel IL13Rα2 mAb with an emphasis on translational implications for therapeutic use.     

Cyclic analogs of alpha-melanocyte-stimulating hormone (alphaMSH) with high agonist potency and selectivity at human melanocortin receptor 1b

Alpha-melanotropin (alphaMSH), Ac-Ser1-Tyr2-Ser3-Met4-Glu5-His6-Phe7-Arg8-Trp9-Gly10-Lys11-Pro12-Val13-NH2,(1) has been long recognized as an important physiological regulator of skin and hair pigmentation in mammals. Binding of this peptide to the melanocortin receptor 1 (MC1R) leads to activation of tyrosinase, the key enzyme of the melanin biosynthesis pathway. In this study, interactions of the human MC1bR (an isoform of the receptor 1a) with the synthetic cyclic analogs of alphaMSH were studied. These ligands were analogs of MTII, Ac-Nle4-cyclo-(Asp5-His6-D-Phe7-Arg8-Trp9-Lys10)-NH2, a potent pan-agonist at the human melanocortin receptors (hMC1,3-5R). In the structure of MTII, the His6-D-Phe7-Arg8-Trp9 segment has been recognized as "essential" for molecular recognition at the human melanocortin receptors (hMC1,3-5R). Herein, the role of the Trp9 in the ligand interactions with the hMC1b,3-5R has been reevaluated. Analogs with various amino acids in place of Trp9 were synthesized and tested in vitro in receptor affinity binding and cAMP functional assays at human melanocortin receptors 1b, 3, 4 and 5 (hMC1b,3-5R). Several of the new peptides were high potency agonists (partial) at hMC1bR (EC50 from 0.5 to 20 nM) and largely inactive at hMC3-5R. The bulky aromatic side chain in position 9, such as that in Trp, was found not to be essential to agonism (partial) of the studied peptides at hMC1bR.     

Characterization of diorganotin(IV) complexes with captopril. The first crystallographically authenticated metal complex of this anti-hypertensive agent

Diorganotin(IV) complexes R(2)Sn(cap) (capH(2)=N-[(S)-3-mercapto-2-methylpropionyl]-L-proline; R=Me, Et, n-Bu and t-Bu) were prepared and characterised. The FTIR and Raman spectra demonstrated that the organotin(IV) moieties interact with the [S] atom of the ligand, while the other coordination sites are the carboxylate and the amide -CO groups. M?ssbauer Delta data showed that the diorganotin(IV) compounds adopt slightly distorted trigonal-bipyramidal (tbp) geometry. A single-crystal X-ray study was performed on the compound Me(2)Sn(cap): the Sn atom is five-coordinated in a distorted tbp environment, with two [O] atoms in the axial positions and the [S] and two [C] atoms in the equatorial (eq) plane. Each cap ligand coordinates to two different Sn atoms, and infinite zigzag chains are formed, directed parallel to each other and to the b axis of the unit cell. NMR (CDCl(3)) of the Me(2)Sn(IV) and n-Bu(2)Sn(IV) complexes indicated the presence of different oligomeric species.     

Histamine differentially regulates the production of Th1 and Th2 chemokines by keratinocytes through histamine H1 receptor

Histamine is a biological amine that plays an important role in allergic responses. However, the involvement of histamine signaling in late allergic responses in the skin is poorly understood. Therefore, we attempted to investigate the involvement of histamine signaling in late allergic responses, especially in keratinocytes (KCs). HaCaT KCs and normal human KCs (NHKs) predominantly expressed histamine H1 receptor (H1R) and H2 receptor (H2R). Histamine suppressed tumor necrosis factor α (TNF-α)- and interferon-γ (IFN-γ)-induced production of CC chemokine ligand 17(CCL17), a type 2 T-helper (Th2) chemokine, by HaCaT KCs. It suppressed the phosphorylation of p38 mitogen-activated protein (MAP) kinase, but not that of extracellular signal-regulated kinases (ERKs), and TNF-α- and IFN-γ-induced nuclear factor κB (NFκB) activity. In contrast, histamine enhanced the production of CXC chemokine ligand 10 (CXCL10), a Th1 chemokine, by TNF-α- and IFN-γ-stimulated HaCaT KCs and NHKs. TNF-α- and IFN-γ-induced CXCL10 production was upregulated by suppression of p38 MAP kinase or NF-κB activity, which could explain histamine involvement. We concluded that histamine suppresses CCL17 production by KCs by suppressing p38 MAP kinase and NF-κB activity through H1R and may act as a negative-feedback signal for existing Th2-dominant inflammation by suppressing CCL17 and enhancing CXCL10 production.     

Synthesis and characterization of new chromium(III), vanadium(IV), and titanium(III) complexes with biologically active isonicotinic acid hydrazide

New complexes of the type [Cr(INH)2Cl2]Cl.2H2O, VO(INH)2Cl2 and TiO(INH)2Cl, where INH = isonicotinic acid hydrazide, have been prepared. The complexes were characterized by infrared and UV-vis spectroscopy, proton nuclear magnetic resonance (NMR) and elemental analyses, molar conductivity and x-ray powder diffraction measurements. For the Cr(III)-complex, the ligand was coordinated through its carbonyl group and amino nitrogen atom; for V(IV)-complex and Ti(III)-complex, the ligand was coordinated through its carbonyl oxygen and heterocyclic nitrogen, respectively. Octahedral geometry has been proposed for all the complexes. The complexes of Cr(III) and Ti(III) showed significant tuberculostatic activity.     

Photogeneration of titanium(III) from titanium(IV) citrate in aqueous solution

Current interest in the biochemistry of Ti(IV) arises from its widespread use in white pigments and its potential in therapeutic agents. Citrate is known to form strong complexes with Ti(IV). We show here that Ti(III) citrate is generated in a facile manner and in good yield by the action of UV radiation on Ti(IV) citrate in aqueous solution. The Ti(III)-citrate species formed was isolated and characterised by UV-Visible spectroscopy, showing an absorption at 547 nm (epsilon=100 M(-1)cm(-1)), and by electron paramagnetic resonance (EPR) spectroscopy giving a resonance at g=1.949 (linewidth=60G) . An X-ray structure of the parent Ti(IV) complex in the form [TiNa(3)(C(6)H(6)O(7))(2)(C(6)H(5)O(7))(H(2)O)(6.8)].2H(2)O is reported along with a study of the reaction of Ti(IV)-citrate with N,N-ethylenebis(o-hydroxytoluene)glycine (EHTG), which was more rapid than those of other related Ti(IV) complexes.     

Synthese von O-(3-desoxy-α-d-manno-2-octulopyranosylonsäure)-(2→4)-O-(3-desoxy-α-d-manno-2-octulopyranosylonsäure)- (2→6)-O-(2-amino-2-desoxy-β-d-glucopyranosyl)-(1→6)-2-amino-2-desoxy-d-glucopyranose

Benzyl-3-O-benzyl-2-benzyloxycarbonylamino-6-O-[2-benzyloxycarbonyl-amino-2-deoxy-3,4-O-(tetraisopropyldisiloxane-1,3-diyl)- β-d-glucopyranosyl]-2-deoxy-α-d-glucopyranoside was coupled with methyl (4,5,7,8-tetra-O-acetyl-3-deoxy-α-d-manno-2-octulopyranosyl bromide)onate (13) to yield the α-glycosidically linked trisaccharide. After deacetylation and selective introduction of a second 7′,8′-O-tetraisopropyldisiloxane group, a further glycosidation reaction with 13 led regioselectively to the tetrasaccharide benzyl O-[methyl (4,5,7,8-tetra-O-acetyl-3-deoxy-α-d-manno-2-octulopyranosyl)onate]-(2→4)-O-{methyl [3-deoxy-7,8-O-(tetraisopropyldisiloxane-1,3-diyl)-α-d-manno-2-octulopyranosyl]-onate}-(2→6)-O- [2-benzyloxycarbonylamino-2-deoxy-3,4-O-(tetraisopropyldisiloxane-1,3-diyl)-β-d-glucopyranosyl]- (1→6)-3-O-benzyl-2-benzyloxycarbonyl-amino-2-deoxy-α-d-glucopyranoside. A series of deblocking steps gave O-(3-deoxy-α-d-manno-2-octulopyranosylonic acid)-(2→4)-O-(3-deoxy-α-d-manno-2-octulopyranosylonic acid)- (2→6)-O-(2-amino-2-deoxy-β-d-glucopyranosyl)-(1→6)-2-amino-2-deoxy-d-glucopyranose which was identical with a tetrasaccharide that had been isolated by hydrazinolysis of the lipopolysaccharide from Salmonella minnesota R 595. Hence, synthetic proof is provided for the linkages in this part of the inner core region of lipopolysaccharides.     

Two New Norlignans and a New Lignanamide from Peperomia tetraphylla

Two new cyclobutane-type norlignans, methyl rel-(1R,2S,3S)-2-(7-methoxy-1,3-benzodioxol-5-yl)-3-(2,4,5-trimethoxyphenyl)cyclobutanecarboxylate (1), and methyl rel-(1R,2R,3S)-2-(7-methoxy-1,3-benzodioxol-5-yl)-3-(2,4,5-trimethoxyphenyl)cyclobutanecarboxylate (2), and a new lignanamide, 3-hydroxy-N-[2-(4-hydroxyphenyl)ethyl]-α-[4-(2-{N-[2-(4-hydroxyphenyl)ethyl]carbamoyl}ethenyl)-3-methoxyphenoxy]-4-methoxycinnamamide 4,8″-ether (3), along with five known amides, 4-8, were obtained from the whole plant of Peperomia tetraphylla. Their structures were elucidated mainly by the analysis of NMR and MS data. The new compounds 1-3 and the known compound 4 were tested for their cytotoxic activities against the HepG2 (human hepatocarcinoma), A549 (human lung cancer), and HeLa (human cervical cancer) cell lines. Compound 4 showed significant cytotoxicity against HepG2 cell lines with an IC(50) value of 9.4 ± 1.0?μM.     

牛心朴子须根的化学成分研究

从采自宁夏的萝摩科鹅绒藤属植物牛心朴子 (CynanchumkomaroviiAl.Iljinski.)须根的乙醇提取物中分离鉴定了十个非C2 1 甾体类化合物 :β D 呋喃果糖基 (2→ 1) α D [6 O 芥子酰基 ] 吡喃葡萄糖甙 (1) ,β D (3 O 芥子酰基 ) 呋喃果糖基 (2→ 1) α D [6 O 芥子酰基 ] 吡喃葡萄糖甙 (2 ) ,[6 O β D 吡喃葡萄糖基 (1→ 6 ) β D 吡喃葡萄糖基 1,2 双氧 (4 羟基 3,5 二甲氧基肉桂酰 ) (3) ,7 脱甲氧基娃儿藤碱 (4) ,9 羟基 芳樟醇 3 O β D 吡喃木糖基 (1→ 6 ) β D 吡喃葡萄糖甙 (5 ) ,(2E ,6R) 2 ,6 二甲基 2 ,7 辛二烯 1,6 二醇 (6 ) ,[(+) 丁香素 ](7) ,4′ O demethylepiyangambin(8) ,4′ 羟基 2′ 甲氧基苯乙酮 (9) ,(2S ,3S ,4R ,12E) N [2′ (R) 羟基二十二碳烷基 ] 1,3,4 三羟基 2 酰胺 二十碳烷基 12 烯 (10 )。除化合物 4和 9外 ,其余化合物均为首次从该植物中分离得到。     

Jack bean α-mannosidase digestion profile of hybrid-type N-glycans: effect of reaction pH on substrate preference

Jack bean α-mannosidase (JBM) is a well-studied plant vacuolar α-mannosidase, and is widely used as a tool for the enzymatic analysis of sugar chains of glycoproteins. In this study, the JBM digestion profile of hybrid-type N-glycans was examined using pyridylamino (PA-) sugar chains. The digestion efficiencies of the PA-labeled hybrid-type N-glycans Manα1,6(Manα1,3)Manα1,6(GlcNAcβ1,2Manα1,3)Manβ1,4GlcNAcβ1,4GlcNAc-PA (GNM5-PA) and Manα1,6(Manα1,3)Manα1,6(Galβ1,4GlcNAcβ1,2Manα1,3)Manβ1,4GlcNAcβ1,4GlcNAc-PA (GalGNM5-PA) were significantly lower than that of the oligomannose-type N-glycan Manα1,6(Manα1,3)Manα1,6Manβ1,4GlcNAcβ1,4GlcNAc-PA (M4-PA), and the trimming pathways of GNM5-PA and GalGNM5-PA were different from that of M4-PA, suggesting a steric hindrance to the JBM activity caused by GlcNAcβ1-2Man(α) residues of the hybrid-type N-glycans. We also found that the substrate preference of JBM for the terminal Manα1-6Man(α) and Manα1-3Man(α) linkages in the hybrid-type N-glycans was altered by the change in reaction pH, suggesting a pH-dependent change in the enzyme-substrate interaction.     

Bile acid amides derived from chiral amino alcohols: novel antimicrobials and antifungals

Cholic and deoxycholic acid amides 10-17 have been synthesised from (1R,2R)-1-phenyl-2-amino-1,3-propanediol 2, (1S,2S)-1-phenyl-2-amino-1,3-propanediol 4, (1R,2R)-1-para-nitrophenyl-2-amino-1,3-propanediol 3, (1S,2S)-1-para-nitrophenyl-2-amino-1,3-propanediol 5. Amide 12 derived from N-succinimidyl ester 9 of deoxycholic acid and (1R,2R)-1-phenyl-2-amino-1,3-propanediol 2, found to be active against Cryptococcus neoformans and the amide 17 obtained from N-succinimidyl ester 9 of deoxycholic acid and (1S,2S)-1-para-nitrophenyl-2-amino-1,3-propanediol 5, is found to be potent against various gram-positive bacteria.     

Stereoselective effects of chiral clofibric acid analogs on rat peroxisome proliferator-activated receptor α (rPPARα) activation and peroxisomal fatty acid β-oxidation

Enantiomers of a series of substituted analogs of 2-(4-chloronhenoxy)-acetic acid (CPAA) were synthesized and used to examine the influence of steric and structural parameters on peroxisome proliferation. The effects of these compounds were studied on the activation of the peroxisome proliferator-activated receptor α (PPARα) in CV-1 cells using an in vitro co-transfection assay. Selected sets of isomers were tested for their ability to increase peroxisomal fatty acyl-CoA oxidase (ACO) activity in H4IIEC3 (rat Reuber hepatoma) cells. Of the series of 2-substituted analogs studied, the isomers of the n-propyl and phenyl derivatives of CPAA showed a high degree of stereoselectivity [(S)-isomer ≫ (R)-isomer]. In general, the potency of the compound to activate the receptor increased with the size of the 2-alkyl substituent. Among the 4-chlorobenzyloxy- and 4-(4′-chlorophenyl)benzyloxy- analogs studied, 2-[4-(4′-chlorophenyl)-benzyloxy]-propanoic acid exhibited a high degree of stereoselectivity in both the biological systems studied [(R) ≫ (S)]. The congeners of 2-methyl substituted CPAA showed a reverse stereoselectivity [(R) > (S)] as compared to the other 2-substituted analogs [(S) > (R)]. Our results indicate that (1) both structural and steric characteristics of CPAA analogs play an important role in the activation of rPPARα and on stimulation of peroxisomal ACO activities, and (2) clofibric acid and analogs exert their peroxisome proliferative effects by interaction with a specific site on a protein. The enantiomers of the 2-n-propyl and the 2-phenyl CPAA analogs may be useful as mechanistic probes in elucidating the nature of this binding site. Chirality 9:37–47, 1997. © 1997 Wiley-Liss, Inc.     

Role of Group III Metabotropic Glutamate Receptors in Excitotoxin-Induced Cerebellar Granule Cell Death

Abstract: The neuronal effects of the metabotropic glutamate receptor agonist (1 S ,3 R )-aminocyclopentane-1,3-dicarboxylic acid have been studied in cultured rat cerebellar granule cells, and compared with those of the endogenous excitotoxin glutamate, and the dietary excitotoxin β- N -methylamino- l -alanine. Glutamate, β- N -methylamino- l -alanine, and (1 S ,3 R )-aminocyclopentane-1,3-dicarboxylic acid all caused concentration-dependent cerebellar granule cell death over a 24-h exposure period. The metabotropic antagonist ( RS )-α-methyl-4-carboxyphenylglycine reduced glutamate-, β- N -methylamino- l -alanine-, and (1 S ,3 R )-aminocyclopentane-1,3-dicarboxylic acid-induced death by 50, 37, and 90%, respectively. (1 S ,3 R )-Aminocyclopentane-1,3-dicarboxylic acid-induced death was unaffected by the group I antagonist ( RS )-1-aminoindan-1,5-dicarboxylic acid, increased by the group II antagonist ethylglutamic acid, and markedly decreased by the group III antagonist ( RS )-α-methylserine- O -phosphate. Neither (1 S ,3 R )-aminocyclopentane-1,3-dicarboxylic acid nor the group I agonist ( RS )-3,5-dihydroxyphenylglycine caused an increase in intracellular free calcium levels. The group III agonist l -(+)-2-amino-4-phosphonobutyric acid also induced concentration-dependent cerebellar granule cell death, and so it was suggested that the group III metabotropic glutamate receptors were responsible for (1 S ,3 R )-aminocyclopentane-1,3-dicarboxylic acid-induced death. Blocking these receptors with ( RS )-α-methylserine- O -phosphate also prevented a proportion of glutamate- and β- N -methylamino- l -alanine-induced death.