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A new cyclic compound [(2S,3′S)-2-(2′-oxo-3′-methylpiperazin-1′-yl)-propanoic acid] obtained using (2S,7S)-2,7-dimethyl-3,6-diazaoctanedioic acid as a starting material was derived from N-t-butyloxycarbonyl-(2S,3′S)-2-(2′-oxo-3′-methylpiperazin-1′-yl)-propanoic acid in order to determine the molecular structure by X-ray crystal analysis. Two new macrocyclic peptides were prepared using the above cyclic compound and sarcosine as peptide units.

The insulinomimetic activity of zinc(II) complexes Zn(gln-m)2 and Zn(gln-e)2, respectively, with L-γ-glutamyl-methylamide (gln-m) and -ethylamide (theanine: gln-e), components of green tea, were co...

A new zinc(II) complex, bis(6-ethylpicolinato)zinc(II) ([Zn(6epa)2]), was prepared by introducing an electron-donating ethyl group on the pyridine ring. [Zn(6epa)2] was crystallized from an aqueous...

Zinc (Zn), an essential trace element, and its complexes have recently been known to exhibit insulinomimetic activities. However, the action mechanism of Zn(II) has yet been obscure. The purpose of the present study was to estimate the action mechanism of the Zn(II) complexes. We found first that Zn given in the chemical forms such as Zn(maltolate)2 and Zn(threoninate)2 complexes is highly uptaken in the isolated rat adipocytes compared with that of Zn(picolinate)2. Then, the action mechanism for the insulinomimetic activities was examined in terms of free fatty acid release from the adipocytes. Four Zn(II) compounds, ZnSO4, Zn(picolinate)2, Zn(maltolate)2, and Zn(threoninate)2, inhibited the free fatty acid release from the adipocytes treated with epinephrine (adrenaline). By using several inhibitors for fatty acids and glucose metabolisms in the adipocytes, the following results were obtained. (1) Zn(picolinic acid)2 complex acts on the insulin receptor and PI3-k, which relate to the glucose uptake, as indicated by the experiments using hydroxy-2-naphthalenylmethyl phosphonic acid tris acetoxy methyl ester (HNMPA-(AM)3) and wortmannin, respectively. (2) ZnSO4, and Zn(maltolate)2 and Zn(threoninate)2 complexes affect a glucose transporter 4 (GLUT 4), which is involved in the glucose uptake as indicated by the results using cytochalasin B. (3) Four Zn(II) compounds affect the activation of the phosphodiesterase as indicated by the experiments using cilostamide. These results indicate that the Zn(II) compounds promote the glucose uptake into the adipocytes by affecting at least three sites in the adipocytes, which in turn normalize the blood glucose levels in the experimental diabetic animals.

Four Zn(II) complexes with dipeptides and three new Zn(II) complexes with pseudo-tripeptides were prepared and a complex, [Zn(glythr)2]n, was revealed to have a polymeric structure by X-ray structu...

Structures, chemical properties, and in vitro insulinomimetic activities of new vanadyl [oxovanadium(IV), VO(2+)] complexes with five tripodal ligands containing an imidazole functionality were examined. The ligands, N-(carboxymethyl)- N-(4-imidazolylmethyl)amino acids, contain glycine, ( S)- and ( R)-alanine, and ( S)- and ( R)-leucine residues. The molecular structures of the latter four alanine- and leucine-containing complexes were determined by X-ray analysis. The coordination geometry around each vanadium center was octahedral, where an imino nitrogen occupied the apical site and two carboxylate oxygens, an imidazole nitrogen, and a water molecule coordinated in the equatorial plane. The spectroscopic properties of the complexes were characterized by means of IR, electronic absorption, and CD spectra. Acid dissociation constants (p K(a)) and protonation sites of the ligands were determined by a combination of potentiometric titrations and (1)H NMR spectra. The potentiometric study demonstrated that stability constants (log beta) were not so different among the present complexes (14.0-14.9) and a species of molecular complex with a 1:1 metal:ligand ratio existed predominantly at physiological pH 7.4. EPR parameters indicated that the species at pH 7.4 had an octahedral structure similar to the complex in the solid state. On the other hand, an EPR study in phosphate buffer (pH 7.4) suggested that inorganic phosphate coordinated to the vanadium center instead of the imidazole group in the presence of excess phosphate ion. Cyclic voltammograms in the phosphate buffer showed chemically reversible oxidation waves, whereas irreversible oxidation waves were observed in non-coordinating HEPES buffer. Moreover, the oxidation potential of each complex in phosphate buffer was more positive than that in HEPES buffer. Partition coefficients of the present complexes in a n-octanol/saline system were very low, probably due to hydrophilicity of the imidazole group. The in vitro insulinomimetic activities were estimated on the basis of the ability of the complexes to inhibit epinephrine-stimulated free fatty acid release from isolated rat adipocytes. The achiral glycine-derivative complex exhibited the highest insulinomimetic activity, which was higher than that of VOSO(4) as a positive control. Putting our previous observations together, it was found that the vanadyl complexes with tetradentate amino acid derivatives having no alkyl side chain tend to have high in vitro insulinomimetic activity.

Twelve new amino acid derivatives/Zn(II) complexes were prepared by the reactions of ZnSO4 and nine tetradentate ligands, Gly, Ala, Val, Leu, Ser and His derivatives and three pentadentate ligands, Asp and His derivatives. The X-ray structure analysis of [Zn3(N-pyridylmethyl-His)3(H2O)2](ClO4)3·2H2O revealed the formation of a trinuclear complex, in which three tetradentate ligands and two water molecules coordinate to three Zn(II), but the complex in an aqueous solution is present as a monomeric complex ion. Several Zn(II) complexes were found to have in vitro insulinomimetic activity which was estimated by the inhibition of free fatty acid release in isolated rat adipocytes treated with epinephrine. It was revealed that the insulinomimetic activities of Zn(II) complexes with the stability constants (log β) less than 11 were higher than that of VOSO4 and were comparable to that of ZnSO4 as positive controls except in the cases of two complexes with Gly derivatives, Zn(N,N-dipyridylmethyl-Gly)+ and Zn(N,N...

Diabetes mellitus (DM), which develops many secondary complications such as atherosclerosis, microangiopathy, renal dysfunction and failure, cardiac abnormality, diabetes retinopathy and ocular disorders, is classified as either insulin-dependent type 1 or non-insulin-dependent type 2, according to the definition of WHO. Although several types of insulin preparations for type 1 DM and those of synthetic drugs for type 2 DM have been developed and clinically used, they have several problems such as physical and mental pain due to daily insulin injections and defects involving side effects, respectively. In the 21st century, a new class of pharmaceuticals should be introduced. For this reason, metallopharmaceutical compounds containing vanadium and zinc ions are expected to treat both types of DM, by making effective use of unique characteristics of the metals. In this article, the current state of development of insulin-mimetic vanadium and zinc complexes with different coordination modes are reviewed, focusing on the preparations and coordination structures of the complexes and in vitro and in vivo evaluations as well as the possible mechanism.

A condensation reaction of glyoxal with (S)-histidine and (S)-aspartic acid yielded a new optically-active bis(amino acid) ligand, N-[(S)-1-carboxy-2-(imidazol-4-yl)ethyl]-N′-[(S)-1,2-dicarboxyethyl]ethylenediamine. Two bis(amino acid) ligands with picolyl (pyridylmethyl) groups were synthesized by condensation reactions of glyoxal with the picolyl derivative of (S)-histidine and that of (S)-aspartic acid: the obtained ligands are N,N′-bis(2-pyridylmethyl)-N-[(S)-1-carboxy-2-(imidazol-4-yl)ethyl]-N′-[(S)-1,2-dicarboxyethyl]ethylenediamine and N,N′-bis(2-pyridylmethyl)-N,N′-bis[(S)-1-carboxy-2-(imidazol-4-yl)ethyl]ethylenediamine. The protonation constants of these ligands were determined by potentiometry, and the corresponding protonation sites were located on the basis of 1H NMR spectra obtained at different pD values. The formation constants of the Gd3+ complexes were determined by potentiometric titrations, and the NMR relaxivities r1 and r2 by the measurements of the NMR relaxation times.

Following the finding of in vitro insulinominetic activities of new prepared Zn(II) complexes with amide ligands (2-picolinamide (pa-a) and 6-methyl-2-picolinmethylamide (6mpa-ma)) in isolated rat adipocytes treated with epinephrine in terms of inhibition of free fatty acid release, their blood glucose normalizing effects were observed on daily intraperitoneal injections for 14 d in a type 2 diabetes mellitus model animal, KK-Ay mice. The blood glucose levels of KK-Ay mice were maintained in a normal range during the administration of both complexes. After the administration of each complex for 14 d, the improvement of glucose metabolism was confirmed as judged by the glucose tolerance test.

Summary: In order to understand the insulinomimetic activity of zinc(II) complexes, we studied the metallokinetic features of zinc in the blood of normal rats given the zinc complexes, bis(maltolato)zinc(II) (Zn(mal) 2 ) and bis(6-methylpicolinato)zinc(II) (Zn(6mpa) 2 ) by comparing each of them with an ionic form of zinc chloride (ZnCl 2 ). The bioavailability of the zinc(II) complexes following oral administration was enhanced to 1.4-1.5-fold that of ZnCl 2 with respect to zinc level. Based on the results of a metallokinetic analysis and administration method in normal rats, we examined the antidiabetic ability of the zinc(II) complexes in GK rats, a model animal of type 2 diabetes mellitus. High blood glucose levels of GK rats were normalized following intraperitoneal injections and oral administration of the zinc(II) complexes, in which the Zn(6mpa) 2 complex was found to be more effective than Zn(mal) 2 . The present results are noteworthy, not only due to their potential relevance for clinical application, but also for the development of new zinc(II) complexes.

Three zinc(II) complexes of picolinic acid and its derivatives with a Zn(N2O2) coordination mode were prepared and evaluated for their insulinomimetic activities by in vitro and in vivo studies. By introducing an electron-donating methyl group into the picolinate ligand (pic), bis(6- or 3-methylpicolinato)zinc(II) complexes [Zn(6-mpa)2 or Zn(3-mpa)2, respectively] were prepared. The Zn(6-mpa)(2) complex was crystallized as a water adduct [Zn(6-mpa)2(H2O)].H2O, in which two carboxylate oxygens and two pyridine nitrogens of 6-mpa and a water oxygen coordinate to a zinc(II) with a trigonal bipyramidal geometry. By in vitro evaluation of the inhibition of free fatty acid (FFA) release from isolated rat adipocytes in the presence of epinephrine, the insulinomimetic activities of Zn(pic)2, Zn(6-mpa)2, and Zn(3-mpa)2 (IC50=0.64 +/- 0.13, 0.31 +/- 0.05, and 0.40 +/- 0.07 mM, respectively) were found to be higher than those of VOSO(4) (IC50=1.00 mM) and ZnSO(4) (IC50=1.58 +/- 0.05 mM) in terms of IC50 value, the 50% inhibition concentrations for the FFA release from the adipocytes. Then, Zn(6-mpa)2, which exhibited the highest in vitro insulinomimetic activity among three complexes examined, was given at a dose of 3.0 mg (45.9 micromol) Zn/kg body weight to KK-A(y) mice with type 2 diabetes mellitus by daily intraperitoneal injections for 14 days and it was found that the hereditary high blood glucose levels were lowered during the administration of the complex. The improvement of diabetes mellitus was confirmed with the oral glucose tolerance test.

Three N,N′-ethylenebis(L-amino acid) ligands have been obtained simultaneously with three α,α′-(1,4-piperazinediyl)bis[(S)-alkanoic acid] and four N,N′-ethylenedipeptide products, by reacting a mixture of L-histidine methyl ester and L-aspartic acid dimethyl ester with glyoxal in the presence of sodium cyanotrihydroborate in methanol. Europium(III) complexes with N,N′-ethylenebis(L-amino acid) ligands were useful as chiral NMR shift reagents for some unprotected natural α-amino acids as substrates in neutral aqueous solution, as characterized by large enantiomeric shift differences and unbroadened signal shapes on high-resolution NMR spectroscopy. In addition, the acid-dissociation constants of six bis(amino acid) ligands and the stability constant of the europium(III) complex with N,N′-ethylenedi(L-histidine) were obtained by potentiometric titration.

High blood glucose levels of KK-A(y) mice with type 2 diabetes mellitus were normalized by daily intraperitoneal (ip) administration of a zinc(II) complex, bis(maltolato)zinc(II) (Zn(Mal)(2)) with a Zn(O(4)) coordination mode, following the finding of strong in vitro insulinomimetic activity in isolated rat adipocytes treated with epinephrine in terms of the inhibition of free fatty acid release. The blood glucose level was maintained in the normal range during administration of the Zn(Mal)(2) complex for 14 days and improvements in the glucose tolerance were confirmed by an oral glucose tolerance test.

The oxovanadium(IV) complexes with N,N′-ethylenebis(amino acids) ([VO(XeX)(H2O)], where X=A ((S)-Ala), V ((S)-Val) and P ((S)-Pro)) are synthesized and characterized by X-ray analyses and IR spectra. The crystal structure analyses reveal that the geometry around the vanadium cation of each complex is distorted octahedral and is coordinated by a water molecule and the tetradentate N,N′-ethylenebis(amino acidate) anion with Δ-cis-α configuration, in which the water oxygen atom occupies equatorial coordination position and one of the two secondary or tertiary nitrogen atoms of each tetradendate ligand is bound trans to the vanadyl oxo moiety. The compilation of bond lengths for present and previous VO complexes containing nitrogen and oxygen donating ligands shows that the tertiary amine groups of PeP ligand elongate VN bonds. Comparison of the sum of the bond angles of three five-membered rings (one ethylenediamine ring and two amino acidate rings) indicates that the ring strain is mostly concentrated in the ethylenediamine ring and the strain of amino acidate ring lying in the equatorial plane of V(IV) ion is more pronounced than that in another amino acidate ring. The IR observations of the present complexes are well consistent with the crystallographic studies of them.

Six oxovanadium(IV) complexes with N , N ′-ethylenebis(amino acid) of general formula, [VO(XeX)(H 2 O)]· n H 2 O, where e and X represent ethylene group and ( S )-α-amino acid, respectively; and X=G (Gly) 1 , ( S )-A (Ala) 2 , ( S )-V (Val) 3 ·2H 2 O, ( S )-P (Pro) 4 , m G or G m (Sar or N -methylglycine) 5 ·H 2 O and ( S )-M (Met) 6 ) were prepared. These complexes were characterized by means of TG, DTA, and XRD, and the thermal decomposition processes of these complexes up to 650°C were investigated. The thermal studies showed that the dehydration processes for 3 and 5 having water of crystallization were endothermic, whereas decompositions of all the complexes were exothermic. Calcinations of these complexes at 650°C resulted in the formation of vanadium(V) oxide V 2 O 5 . Choosing 1 as a leading example of the oxovanadium(IV) complexes, an over all reaction scheme for the thermal decomposition was proposed on the basis of IR and MS analyses of both the solid and the volatile decomposition products at different temperatures.

Structurally constrained ethyl (2S)-3-(4-hydroxyphenyl)-2-{[(3S)-3-(imidazole-4-yl)-methyl]-2-oxo-piperazine-1-yl}propionate (N,N′-ethylene-bridged-(S)-histidyl-(S)-tyrosine ethyl ester, eHY-OEt) was obtained by a one-pot reaction from (S)-histidine methyl ester and (S)-tyrosine ethyl ester with glyoxal. Four ligands, (Boc-Gly-eHY-OEt (HL1), Boc-Gly-eHY-NH2 (HL2), Ac-eHY-OEt (HL3), and Ac-eHY-NH2 (HL4), where Boc-Gly is t-butyloxycarbonyl-glycyl and Ac is acetyl) were derived from eHY-OEt. Also, corresponding copper(II) complexes, in which only amino acid side chains coordinate to the copper(II) ion, [Cu(L1-)2(H2O)] 1, [Cu(L2-)2(H2O)] 2, [Cu(L3-)2(H2O)] 3, and [Cu(L4-)2(H2O)] 4, were prepared and characterized by elemental analyses and the FAB-MS spectra. The conformational behaviors were confirmed by the 1H NMR spectra. UV-visible-NIR, CD and ESR spectra showed that copper(II) complexes are mononuclear square-pyramidal structures in both the solid and solution states. Cyclic voltammetry of HL1 and 1 show...

We prepared zinc(II) complexes with a series of monomethyl-substituted pyridine-2-sulfonic acid derivatives to clarify the relationship between the structure and insulinomimetic activity. Towards in vitro insulinomimetic activity, bis(3-methylpyridine-2-sulfonato)zinc(II) gave the best result among the zinc(II) complexes with methylpyridine-2-sulfonates.

An attempt has been made to synthesize structurally reinforced chiral B2-18-membered hexaazamacrocyclic amine based dinuclear copper(?) complexes 2 and 2′ as models for studying the size-match selectivity of metal ions. These two dinuclear complexes have manifested a prominent difference in the electronic spin structure, although only apparent structural difference is subtle. The complex 2 is double-bridged with an oxygen and chloride atom while 2′ is single-bridged only with the oxygen atom of hydroxide ion and the fifth ligand Cl is missing. From cw ESR measurements of 2 and 2′ in polycrystalline solids a large zero-field splitting (ZFS) value has been determined for 2′ and a small ZFS value for 2, respectively. These findings have been in accordance with the results from the SQUID measurements. The ZFS values and isotropic exchange interaction have been theoretically estimated on the basis of molecular structural considerations of the complexes. The ground-state spin structures for the complex...

We have attempted to synthesize structurally reinforced chiral B2-18-membered hexaazamacrocyclic amine based dinuclear copper(II) complexes 2 and 2′ as models for studying the size-mach selectivity of metal ions. From the viewpoint of molecular based magnetism-structure relationship, these two dinuclear complexes have manifested a prominent difference in the electronic structure, although only apparent structural difference is subtle. In the dinuclear complex 2′, the fifth ligand is missing, forming slanting bi-squares with a common oxygen atom of hydroxide ion. CW ESR measurements of 2 and 2′ in polycrystalline solids have shown that a triplet fine-structure spectrum with a large zero-field splitting (ZFS) value features in 2′ and an exchange coupled copper(II) pair spectrum does in 2, respectively. These findings have been expounded in connection with the structural difference in the macrocyclic rugbyball-shaped cavity of the ligand. The ground-state spin multiplicity for the copper dinuclear c...

We have synthesized structurally reinforced chiral pentaaza-fifteen-membered polyamines 1 and 2 with a dibridge for the purposes of studying the size-match selectivity of the macrocyclic cavity. Particularly, an attempt has been made to synthesize copper(II) complexes of 1 and 2 to characterize the size-match selectivity of the polyamines in term of microscopic details of the metal-ion binding site. For this purpose the use of ESR spectroscopy has been invoked before X-ray structural analyses of the complexes are carried out. Powder-pattern ESR spectra of the copper(II) complex of 1 in crystalline solid have revealed a temperature dependence of the copper hyperfine structure. This finding suggests that a vibronic effect features in the hyperfine spectra, showing that the pentaaza-macrocycle under study accommodates copper(II) ion and the macrocycle is flexible to exert “genuine” size-match selectivity.

To design a metalloprotein and metalloenzyme model, macrocyclic pseudopeptides containing N,N′-ethylene-bridged-dipeptides were synthesized and their conformations estimated. Piperazin-2-one rings in this type of macrocyclic pseudopeptide provide a hydrophobic wall and deep cavity as shown in the structure of valinomycin. A 24-membered cyclic pseudopeptide was able to include metal cations, and a 36-membered one was able to bind organic ammonium cations enantioselectively. This offers a new type of host-guest chemistry.

The conformation of cyclo[(2S,3′S)-2-(3′-benzyl-2′-oxopiperazin-1′-yl)-3-phenyl-propanoyl-glycyl]2 crystallized with two water molecules (C44H46N6O6 2H2O) is compared with its solution structure and those of cyclo[(2S, 3′S)-2-(3′-methyl-2′-oxopiperazin-1′-yl)-propanoyl-glycyl]2.

Two structurally reinforced chiral 15-membered azamacrocycles (2S, 14S)-2,14-diisobutyl-10-methyl-1,4,7,10,13 -pentaazabicyclo[11.2.2]heptadecane and (2S,14S)-2,14-diisobutyl-7,10-dimethyl-1,4,7,10,13-pentaazabicyclo[11.2.2] heptadecane as a new type of ligand were conveniently synthesized by LiA1H4 reduction from their corresponding macrocyclic pseudopeptides cyclo[(2S,3′S)-2-(3′-isobutyl-2′-oxopiperazine-1′-yl)-4-methyl-pentanoyl-glycyl-glycyl-sarcosyl] and cyclo[(2S, 3′S)-2-(3′-isobutyl-2′-oxopiperazine -1′-yl)-4-methyl-pentanoyl-glycyl-sarcosyl-sarcosyl], respectively. Their copper(II) complexes were also prepared and characterized.

Several workers have synthesized chiral and achiral N, N'-ethylene-bridged dipeptides (piperazin-2-one derivatives), and used them mainly as units of biologically active pseudopeptides such i : as enkephalin analogs because these structurally constrained and lipophilic dipeptides afford the character resisting enzymatic hydrolysis to biologically active peptides. However, their synthetic methods have some problems (nonstereoselective, multi-steps, troublesome techniques, expensive reagents etc.) Therefore; we have developed more convenient procedures for preparing N, N'-ethylene-bridged dipeptides. This article reports four kinds of synthetic methods of chiral N, N'-ethylene-bridged dipeptides, in which various (R) or (S) -α-amino acids are used as starting materials. Moreover, a series of studies on the structures and the functionalities (enantioselective inclusion and transport of (R) - and (S) -ammonium salts, complexing of metal ions) of macrocyclic pseudopeptides and on the enkephalin- and dermorphin-like biological activities of linear pseudopeptides containing these dipeptides as their units are introduced and discussed. Also, the synthesis of a macrocyclic polyamine obtained by the BH3 reduction of macrocyclic pseudopeptide and the structure of its metal complex ion are described.

The amide and ester carbonyl groups of four piperazin-2-one derivatives (N,N'-ethylene-bridged dipeptide ethyl esters) constructed from (R)- or (S)-phenylalanine and glycine were reduced with borane-tetrahydrofuran complex to produce the corresponding piperazine derivatives in 70-80% yields. These piperazin-2-one or piperazine derivatives were used as the carboxyl-terminal residues of eight dermorphin analogues (H-tyrosyl-D-alanyl-piperazine derivatives were used as the carboxyl-terminal residues of eight dermorphin analogues (H-tyrosyl-D-alanyl-piperazin-2-one or piperazine derivatives) whose opiate activities were examined in vitro by use of the guinea pig ileum and the mouse vas deferens assays. It was found in the guinea pig ileum assay that the configuration of pheylalanine and the replacement of the piperazin-2-one ring with a piperazine ring are important for enhancing or reducing the opiate activities of these analogues.

In vitro insulinomimetic activities of Zn(II) complexes with three natural products, betaine, L-lactic acid, and D-(-)-quinic acid (qui), were found in rat adipocytes treated with epinephrine in terms of the inhibition of free fatty acid release. Based on the results, the blood glucose lowering effect in KK-A(y) mice with type 2 diabetes mellitus was observed by daily i.p. injections of a monomeric zinc(II) complex, Zn(qui)(2), for 13 d.

Stability constants of a cyclic octapseudopeptide, cyclo (Gly-eLL-Gly) 2 (eLL N , N ′-ethylene-bridged ( S )-leucyl-( S )-leucine, Gly=glycine), for eleven kinds of transition metal ions were investigated by CD spectra in acetonitrile at 25 °C. The stability constants toward bivalent ions of first transition metal are in the order of Mn 2+ > Fe 2+ > Co 2+ > Ni 2+ 2+ 2+ and those toward Group XII are Zn 2+ 2+ >Hg 2+ . This trend may be explained by the cavity size of cyclo (Gly-eLL-Gly) 2 , but not the hard and soft acids and bases principle. The titration curves obtained from CD data indicated the presence of only a PC (peptide:cation=1:1) complex for Mn 2+ , Fe 2+ , Co 2+ , Cu 2+ , Zn 2+ and Hg 2+ , both PC and P 2 C (peptide:cation=2:1) complexes for Fe 3+ , and both PC and PC 2 (peptide:cation=1:2) complexes for Fe 2+ and Cd 2+ . But ligand/metal ion interactions are considered to be very weak for Ag + and Ni 2+ because of undetectable CD spectral changes. Moreover, 13 C NMR studies revealed that six amide oxygens in cyclo (Gly-eLL-Gly) 2 coordinate to Cu 2+ and Fe 3+ in CD 3 CN.

Conformations of 24-Membered Ring Pseudopeptides Containing N,N′-Ethylene-Bridged Dipeptides Constructed from ( S )-Alanine, -Leucine, -Isoleucine, and -Phenylalanine

The interactions of the hydrobromides of (R)- and (S)-alanine-N-methylanilides (1) with 24-, 27- and 36-membered ring pseudopeptides (H-24, H-27 and H-36, respectively) derived from glycine and (2S,3′ S)-4-methyl-2-(2′-oxo-3′-isobutyl-1′-piperazinyl)pentanoic acid were studied by means of 1H and 13C NMR measurements in CDCl3. It was found from these results that H-24 and H-27 distinguished (R)- and (S)-isomers of 1, while H-36 did not entirely. Moreover, the enantioface-differentiating abilities of these cyclic peptides were investigated by means of 1H NMR measurements in CDCI3 using (R)- and (S)-1-phenylethylammonium and (R)- and (S)-p-methoxy-1-phenylethylammonium bromides as the substrates, showing that the enantio-selectivity of H-36 is superior to those of H-24 and H-27. Also, the chiral recognition ability of H-24 for the hydrochlorides of (R)- and (S)-alanine (Ala), -leucine (Leu), -methionine (Met), -phenylalanine (Phe), -proline (Pro) and -valine (Val) methyl esters were examined by 1H and 13C NMR measurements in CDCl3. Among these hydrochlorides, HCl · PheOCH3 was distinguished more effectively with H-24.

Conformationally constrained N,N′-ethylene-bridged dipeptides (eXX′) were conveniently synthesized in two steps using (R)- or (S)-phenylalanine (X = F) and -methionine (X′= M)[-leucine (X′= L)] as starting materials.These dipeptides are diastereoisomeric or enantiomeric, and were used as the carboxyl terminal residues of enkephalin analogues [H–tyrosyl–D-alanyl–glycyI–eXX′–OEt]. The opiate activities of these pentapeptides were examined preliminarily by the mouse vas deferens assay, suggesting that these enkephalin analogues possess receptor- binding affinities.

Conformationally constrained N,N′-ethylene-bridged dipeptides (eXX′) were conveniently synthesized in two steps using (R)- or (S)-phenylalanine (X = F) and -methionine (X′= M)[-leucine (X′= L)] as starting materials.These dipeptides are diastereoisomeric or enantiomeric, and were used as the carboxyl terminal residues of enkephalin analogues [H–tyrosyl–D-alanyl–glycyI–eXX′–OEt]. The opiate activities of these pentapeptides were examined preliminarily by the mouse vas deferens assay, suggesting that these enkephalin analogues possess receptor- binding affinities.

To design a metalloprotein and metalloenzyme model, macrocyclic pseudopeptides containing N,N′-ethylene-bridged-dipeptides were synthesized and their conformations estimated. Piperazin-2-one rings in this type of macrocyclic pseudopeptide provide a hydrophobic wall and deep cavity as shown in the structure of valinomycin. A 24-membered cyclic pseudopeptide was able to include metal cations, and a 36-membered one was able to bind organic ammonium cations enantioselectively. This offers a new type of host-guest chemistry.

Vanadyl and zinc(II) complexes with VO(O2S2) and Zn(O2S2) coordination mode, respectively, were synthesized. Among them, bis(1,4-dihydro-2-methyl-1-phenyl-4-thioxo-3-pyridinolato)zinc(II) complex exhibited an extremely high insulin-mimetic activity (IC50=0.04 mM when IC50 value of a positive control, VOSO4 was estimated to be 1.0 mM) compared to vanadyl and zinc(II) complexes reported previously.

Macrocyclic Peptides VI. Complex Formations and Conformations of an Ionophorous Cyclic Octapeptide Containing N , N ′-Ethylene-Bridged ( S )-Leucyl-( S )-leucine and Glycine in Acetonitrile

27- and 36-membered ring peptides were prepared using glycine, (2S, 3′ S)-4-methyl-2-(2′-oxo-3′-isobutyl-1′-piperazinyl) pentanoic acid (2) and (2S,3′ S)-3-phenyl-2-(2′-oxo-3′-benzyl-1′-piperazinyl)propanoic acid as the units of peptides. The interactions of 1-phenylethylammonium (1) and p-methoxy-1-phenylethylammonium bromides (11) with these cyclic peptides were studied by 1H and 13C NMR measurements in CDCl3. It was found from these results that the peptides distinguish the enantiomers (R- and S-isomers) of the substrates. Furthermore, it was shown that the enantioface-differentiating abilities of 36-membered ring peptides are superior to those of 27-membered rings.

Several metal ions and their complexes have been known to mimic the action of insulin in in vitro and in vivo systems. We prepared a family of Zn(II) complexes derived from amino ligands with Zn(Nn) (n=3 and 4) coordination modes, the insulinomimetic activity being estimated by an inhibitory effect of free fatty acid release from isolated rat adipocytes treated with epinephrine. In comparison with the positive controls VOSO(4) and ZnSO(4), Zn(II)-amine complexes with stability constants (log beta) lower than 11.5 exhibited higher insulinomimetic activities. Among them, a bis(2-aminomethyl pyridinato)Zn(II) (Zn(2-ampy)(2)(2+)) complex with the highest insulinomimetic activity and a higher stability constant but lower than 11.5 was selected, and subjected to in vivo evaluation in KK-A(y) mice with a genetically type 2 diabetes mellitus. The high blood glucose level of the mice was lowered by daily intraperitoneal injections of Zn(2-ampy)(2)(2+) at a dose of 2 mg Zn/kg body weight for 14 days. Based on the results, Zn(2-ampy)(2)(2+) with Zn(N(4)) coordination mode was proposed to have both a high in vitro insulinomimetic activity and an in vivo blood glucose lowering effect.

During the investigation of the development of insulin-mimetic zinc(II) complexes with a blood glucose-lowering effect in experimental diabetic animals, we found a potent bis(maltolato)zinc(II) complex, Zn(ma)(2), exhibiting significant insulin-mimetic effects in a type 2 diabetic animal model. By using this Zn(ma)(2) as the leading compound, we examined the in vitro and in vivo structure-activity relationships of Zn(ma)(2) and its related complexes. The in vitro insulin-mimetic activity of these complexes was determined by the inhibition of free fatty acid release and the enhancement of glucose uptake in isolated rat adipocytes treated with epinephrine. A new Zn(II) complex with allixin isolated from garlic, Zn(alx)(2), exhibited the highest insulin-mimetic activity among the complexes analyzed. The insulin-mimetic activity of the Zn(II) complexes examined strongly correlated (correlation coefficient=0.96) with the partition coefficient (log P) of the ligand, indicating that the activity of Zn(ma)(2)-related complexes depends on the lipophilicity of the ligand. The blood glucose-lowering effects of Zn(alx)(2) and Zn(ma)(2) were then compared, and both complexes were found to normalize hyperglycemia in KK- A(y) mice after a 14-day course of daily intraperitoneal injections. However, Zn(alx)(2) improved glucose tolerance in KK- A(y) mice much more than did Zn(ma)(2), indicating that Zn(alx)(2) possesses greater in vivo anti-diabetic activity than Zn(ma)(2). In addition, Zn(alx)(2) improved leptin resistance and suppressed the progress of obesity in type 2 diabetic KK- A(y) mice. On the basis of these observations, we conclude that the Zn(alx)(2) complex is a novel potent candidate for the treatment of type 2 diabetes mellitus.

The blood glucose lowering effects in KK-Ay mice with type 2 diabetes mellitus (DM) receiving daily an intraperitoneal (i.p.) administration of Zn(II) complexes with maltol, L-threonine, and picolinic acid for 14 days were estimated under the same conditions, and dose-dependent blood glucose lowering effects in the dose range of 0.2-3.0 mg Zn/kg body weight were found. Among them, the bis(maltolato)Zn(II) complex exhibited the highest blood sugar lowering effect at the dose of 3.0 mg Zn/kg. The improvement of DM was confirmed with oral glucose tolerance tests as well as blood HbA1c levels after the administration of the three Zn(II) complexes at the dose of 3.0 mg Zn/kg. For the purpose of the clinical trial of the complexes in the future, we examined the toxic effects of these three Zn(II) complexes in regard of the LD50 values and hepatic cytochrome P450 levels. The LD50 values of the three Zn(II) complexes exhibited high values compared with that of ZnCl2. No changes of both CYP1A1 and CYP2E1 levels in the liver of KK-Ay mice treated with the three Zn(II) complexes were observed. The obtained results will be important when the complexes are tried for clinical use.

A novel bis(6-ethylpicolinato)(H 2 O)oxovanadium(IV) complex (VO(6epa) 2 ·(H 2 O)) was prepared and its structure was revealed by X-ray analysis (space group Pc(#7), a =10.838(2), b =11.148(5), c =16.642(3) A, and Z =2). Because VO(6epa) 2 ·(H 2 O) exhibited higher in vitro insulinomimetic activity compared to that of vanadyl sulfate in terms of inhibition of free fatty acid (FFA) release from isolated rat adipocytes in the presence of epinephrine, its in vivo effect on whether the complex has a blood glucose normalizing effect was examined in KK-A y mice, a model animal of type 2 diabetes mellitus. VO(6epa) 2 ·(H 2 O) was found to normalize the high blood glucose levels of KK-A y mice when given intraperitoneally at doses of 49 μmol/kg body weight for the first 4 days and then 39 μmol/kg body weight for 10 days. In addition, VO(6epa) 2 ·(H 2 O) improved glucose tolerance ability as examined by the oral glucose test and seemed to have little toxicity in terms of serum parameters. VO(6epa) 2 ·(H 2 O) showed higher normoglycemic activity than bis(6-methylpicolinato)oxovanadium(IV) (VO(6mpa) 2 ) at the same dose. These results indicated that greater enhancement of the blood glucose normalizing effect in KK-A y mice by ethyl substitution compared to methyl substitution may be due to its being more strongly lipophilic.

Zinc(II) complexes of alpha-amino acids and their derivatives with a Zn(N2O2) coordination mode were found to have in vitro insulinomimetic activity as estimated with the inhibition of free fatty acid release in isolated rat adipocytes treated with epinephrine. It was revealed that the insulinomimetic activities of zinc(II) complexes with over-all stability constants (log beta) less than 10.5 are higher than those of ZnSO4 and VOSO4. The high blood glucose level of KK-Ay mice with type 2 diabetes mellitus was lowered by daily intraperitoneal injections of a zinc(II) complex, cis-[Zn(L-Thr)2(H2O)2], for 14 d. The improvement of diabetes mellitus was confirmed with the oral glucose tolerance test.

A europium(III) complex with a new chiral ligand, N,N-bis[2-{N-methyl((1S)-1-carboxy-3-methyl)butylamino}ethyl]glycine, is described as a new chiral shift reagent for α-amino acids and N-acyl-oligopeptides in aqueous solutions without signal broadening on high resolution NMR spectroscopy. In addition, the molecular structure of lanthanum(III) complex with this ligand is revealed by X-ray crystallography.