Discovery of LYS006, a Potent and Highly Selective Inhibitor of Leukotriene A4 Hydrolase

The cytosolic metalloenzyme leukotriene A4 hydrolase (LTA4H) is the final and rate-limiting enzyme in the biosynthesis of pro-inflammatory leukotriene B4 (LTB4). Preclinical studies have validated this enzyme as an attractive drug target in chronic inflammatory diseases. Despite several attempts, no LTA4H inhibitor has reached the market, yet. Herein, we disclose the discovery and preclinical profile of LYS006, a highly potent and selective LTA4H inhibitor. A focused fragment screen identified hits that could be cocrystallized with LTA4H and inspired a fragment merging. Further optimization led to chiral amino acids and ultimately to LYS006, a picomolar LTA4H inhibitor with exquisite whole blood potency and long-lasting pharmacodynamic effects. Due to its high selectivity and its ability to fully suppress LTB4 generation at low exposures in vivo, LYS006 has the potential for a best-in-class LTA4H inhibitor and is currently investigated in phase II clinical trials in inflammatory acne, hidradenitis suppurativa, ulcerative colitis, and NASH.

Identification of a 3-β-homoalanine conjugate of brusatol with reduced toxicity in mice

Brusatol, a quassinoid natural product, is effective against multiple diseases including hematologic malignancies, as we reported recently by targeting the PI3Kγ isoform, but toxicity limits its further development. Herein, we report the synthesis of a series of conjugates of brusatol with amino acids and short peptides at its enolic hydroxyl at C-3. A number of conjugates with smaller amino acids and peptides demonstrated activities comparable to brusatol. Through in vitro and in vivo evaluations, we identified UPB-26, a conjugate of brusatol with a L- β-homoalanine, which exhibits good chemical stability at physiological pH's (SGF and SIF), moderate rate of conversion to brusatol in both human and rat plasmas, improved mouse liver microsomal stability, and most encouragingly, enhanced safety compared to brusatol in mice upon IP administration.

Synthesis and Inhibitory Studies of Phosphonic Acid Analogues of Homophenylalanine and Phenylalanine towards Alanyl Aminopeptidases

A library of novel phosphonic acid analogues of homophenylalanine and phenylalanine, containing fluorine and bromine atoms in the phenyl ring, have been synthesized. Their inhibitory properties against two important alanine aminopeptidases, of human (hAPN, CD13) and porcine (pAPN) origin, were evaluated. Enzymatic studies and comparison with literature data indicated the higher inhibitory potential of the homophenylalanine over phenylalanine derivatives towards both enzymes. Their inhibition constants were in the submicromolar range for hAPN and the micromolar range for pAPN, with 1-amino-3-(3-fluorophenyl) propylphosphonic acid (compound 15c) being one of the best low-molecular inhibitors of both enzymes. To the best of our knowledge, P1 homophenylalanine analogues are the most active inhibitors of the APN among phosphonic and phosphinic derivatives described in the literature. Therefore, they constitute interesting building blocks for the further design of chemically more complex inhibitors. Based on molecular modeling simulations and SAR (structure-activity relationship) analysis, the optimal architecture of enzyme-inhibitor complexes for hAPN and pAPN were determined.

Preparation of Optically Active 2-Aminobutanoic AcidviaOptical Resolution by Replacing Crystallization

An attempt was made to use a simple procedure to obtain (R)- and (S)-2-aminobutanoic acids [(R)- and (S)-1] which are non-proteinogenic alpha-amino acids and are useful as chiral reagents in asymmetric syntheses. Compound (RS)-1 p-toluenesulfonate [(RS)-2], which is known to exist as a conglomerate, was optically resolved by replacing crystallization with (R)- and (S)-methionine p-toluenesulfonate [(R)- and (S)-3] as optically active co-solutes. When (S)-3 was employed as the co-solute, (R)-2 was preferentially crystallized from a supersaturated solution of (RS)-2 in 1-propanol, as was (S)-2 in the presence of (R)-3. (R)- and (S)-2 recrystallized from 1-propanol were treated with triethylamine in methanol to give (R)- and (S)-1 in optically pure forms.

Asymmetrical Synthesis of l-Homophenylalanine Using Engineered Escherichia coli Aspartate Aminotransferase

Site-directed mutagenesis was performed to change the substrate specificity of Escherichia coli aspartate aminotransferase (AAT). A double mutant, R292E/L18H, with a 12.9-fold increase in the specific activity toward L-lysine and 2-oxo-4-phenylbutanoic acid (OPBA) was identified. E. coli cells expressing this mutant enzyme could convert OPBA to L-homophenylalanine (L-HPA) with 97% yield and more than 99.9% ee using L-lysine as amino donor. The transamination product of L-lysine, 2-keto-6-aminocaproate, was cyclized nonenzymatically to form Delta(1)-piperideine 2-carboxylic acid in the reaction mixture. The low solubility of L-HPA and spontaneous cyclization of 2-keto-6-aminocaproate drove the reaction completely toward L-HPA production. This is the first aminotransferase process using L-lysine as inexpensive amino donor for the L-HPA production to be reported.

l-(+)-2-Amino-4-thiophosphonobutyric Acid (l-thioAP4), a New Potent Agonist of Group III Metabotropic Glutamate Receptors: Increased Distal Acidity Affords Enhanced Potency

L-2-Amino-4-phosphonobutyric acid (l-AP4), l-2-amino-4-thiophosphonobutyric acid (l-thioAP4), and l-2-amino-4-(hydroxy)phosphinylbutyric acid (desmethylphosphinothricin, DMPT) were synthesized from protected vinylglycine. They were tested as agonists at group III metabotropic glutamate receptors (mGluR) along with phosphinothricin (PT). DMPT and PT display a much lower potency at mGlu4 receptor (EC50 = 4.0 and 1100 microM, respectively) in comparison to l-AP4 (EC50 = 0.08 microM), whereas l-thioAP4 has a 2-fold higher potency (EC50 = 0.039 microM). Similar rank orders of potency were observed at mGlu6,7 and mGlu8 receptors. The higher potency of l-thioAP4 is due to its stronger second acidity compared to l-AP4. These pKa values of 5.56 and 6.88, respectively, were determined using 31P NMR chemical shift variations. The second distal negative charge of l-AP4/l-thioAP4 probably provides stronger binding to specific basic residues of the binding sites of group III mGluRs, which stabilizes the active conformation of the receptor.

Diastereoselective synthesis of 2-amino-4-phosphonobutanoic acids by electrophilic substitution and tin-Peterson olefination of bis-lactim ethers derived from cyclo-[L-AP4-D-Val]

Electrophilic substitutions on lithiated Schöllkopf's bis-lactim ethers derived from cyclo-[L-AP4-D-Val] take place regio- and stereoselectively at the alpha-position of the phosphonate ester. Subsequent olefination of alpha-silyl-, alpha-phosphoryl-, and alpha-stannyl-stabilized phosphonate carbanions give rise exclusively to vinylphosphonates. Both processes allow a direct and stereoselective access to a variety of 4-substituted and 3,4-disubstituted 2-amino-4-phosphonobutanoic acids (AP4 derivatives) in enantiomerically pure form that may be useful tools for characterizing the molecular pharmacology of metabotropic glutamate receptors (mGluRs) of group III. The relative stereochemistry was assigned from X-ray diffraction analyses or NMR studies of 1,2-oxaphosphorinane and other cyclic derivatives. In accordance to density functional theory (DFT) calculations, the syn-selectivity in the electrophilic substitutions may originate from the intervention of seven- and eight-membered chelate structures in which the bis-lactim ether moiety shields one of the faces of the phosphonate carbanion. DFT calculations for the tin-Peterson olefination of alpha-stannyl stabilized phosphonate carbanions indicate that rate and selectivity are determined in the initial carbon-carbon bond formation step where the unlike transition structures leading to (Z)-vinylphosphonates are favored both in the gas phase and in THF solution.

Stereocontrolled Route to Vicinal Diamines by [3.3] Sigmatropic Rearrangement of Allyl Cyanate: Asymmetric Synthesis of anti-(2R,3R)- and syn-(2R,3S)-2,3-Diaminobutanoic Acids

A stereocontrolled route via allyl 1,2-diols to vicinal diamines based on the [3.3] sigmatropic rearrangement of allyl cyanate has been developed. Our approach consists of two consecutive steps: stereoselective construction of allyl anti- and syn-1,2-diols followed by [1,3]-chirality transfer by sigmatropic rearrangement, which allow an access to anti-(2R,3R)- and syn-(2R,3S)-2,3-diaminobutanoic acids. [reaction: see text]

Discovery of a potent, nonpolyglutamatable inhibitor of glycinamide ribonucleotide transformylase

Glycinamide ribonucleotide transformylase (GAR Tfase) catalyzes the first of two formyl transfer steps in the de novo purine biosynthetic pathway that require folate cofactors. Herein we report the discovery of a potent, nonpolyglutamatable, and selective inhibitor of GAR Tfase. Compound 12, which possesses a tetrazole in place of the gamma-carboxylic acid in the l-glutamate subunit of the potent GAR Tfase inhibitor 1, was active in cellular-based functional assays exhibiting purine-sensitive cytotoxic activity (IC(50) = 40 nM, CCRF-CEM) and was selective for inhibition of rhGAR Tfase (K(i) = 130 nM). Notably, 12 was only 2.5-fold less potent than 1 in cellular assays and 4-fold less potent against rhGAR Tfase. Like 1, this functional activity of 12 in the cell-based assay benefits from and requires transport into the cell by the reduced folate carrier but, unlike 1, is independent of folyl polyglutamate synthase (FPGS) expression levels and polyglutamation.

Design, Synthesis, and Activity of Analogues of Phosphinothricin as Inhibitors of Glutamine Synthetase

A new group of potent inhibitors of glutamine synthetase was designed and synthesized. The X-ray structure of bacterial glutamine synthetase complexed with phosphinothricin was used for computer-aided structure-based design of the inhibitors, in which the methyl group of phosphinothricin was chosen as the modification site. Amino and hydroxyl moieties were introduced into the phosphinic acid portion of the lead molecule to interact with ammonium binding site in the active cleft of the enzyme. Designed compounds were synthesized in enantiomerically pure form analogous to l-glutamic acid. In vitro kinetic studies with Escherichia coli glutamine synthetase confirmed the biological activity of the designed inhibitors, which with K(i) values in the micromolar range (K(i) = 0.59 microM for the most potent compound 2) appear to be slightly weaker inhibitors or equipotent to phosphinothricin.

Preparation and properties of 99mTc(CO)3+-labeled N,N-bis(2-pyridylmethyl)-4-aminobutyric acid

Labeling biomolecules with (99m)Tc(CO)(3)(+) ((99m)Tc tricarbonyl) is attracting increasing attention. Although histidine is often considered an ideal bifunctional chelator for (99m)Tc (or (188)Re) tricarbonyl, the family of dipicolylamine carboxylate chelators may be a useful alternative because of the expected ease of synthesis and because the structure provides a pendent carboxylate for potential conjugation to biomolecules. The dipicolylamine chelator N,N-bis(2-pyridylmethyl)-4-aminobutyric acid (BPABA) was synthesized using 4-aminobutyric acid in place of glycine or aminopropionic acid in the literature, to avoid possible involvement of the carboxylate in the complex formation process by forming five- or six-membered chelation rings. Using a commercial tricarbonyl kit (Mallinckrodt), the complex formation properties of both BPABA and commercial histidine with (99m)Tc tricarbonyl were investigated, and the in vitro complex stabilities in saline and in serum were compared. Stability in vivo was also examined following i.v. administration to normal mice. BPABA was synthesized simply and quantitatively by reacting picolyl chloride with aminobutyric acid in one step. On RP HPLC, the product eluted essentially in one peak and the structure was confirmed by ESI-MS. After labeling, both BPABA and histidine were shown by RP HPLC to form tricarbonyl complexes. In both cases, after incubation at 100 degrees C for 20 min, only one predominant peak of (99m)Tc(CO)(3)(+)-histidine or (99m)Tc(CO)(3)(+)-BPABA was apparent, and both complexes were stable at room temperature in saline for at least 24 h. After incubation for 24 h in 37 degrees C serum, by SE HPLC, 20% of the (99m)Tc(CO)(3)(+)-histidine was bound to serum protein compared to less than 10% for (99m)Tc(CO)(3)(+)-BPABA. A 5000 molar excess of histidine at 100 degrees C for 6 h was unable to dissociate (99m)Tc(CO)(3)(+)-BPABA. By contrast, BPABA easily dissociated (99m)Tc(CO)(3)(+)-histidine under the same conditions. Both complexes were stable in vivo in mice, and (99m)Tc(CO)(3)(+)-BPABA showed rapid and specific hepatobiliary clearance while (99m)Tc(CO)(3)(+)-histidine was cleared through the kidneys. In conclusion, BPABA was easily synthesized and was shown to possess properties comparable to histidine for labeling of biomolecules with (99m)Tc tricarbonyl. However, it was found that the chelator concentration required for quantitative (99m)Tc tricarbonyl labeling with both BPABA and histidine were 2 orders higher than that required with more conventional labeling using MAG(3). Finally, the complex (99m)Tc(CO)(3)(+)-BPABA itself was found to clear exclusively via the hepatobiliary pathway and may have value as a potential hepatobiliary imaging agent.

Asymmetric Synthesis and Translational Competence of l-α-(1-Cyclobutenyl)glycine

[reaction: see text] L-alpha-(1-Cyclobutenyl)glycine (1-Cbg) was targeted as a potentially translatable analogue of isoleucine and valine and as a useful building block for peptides. An enantioselective synthesis was executed in which the key step was diastereoselective addition of 1-cyclobutenylmagnesium bromide to the sulfinimine 2b derived from (S)-t-butanesulfinimide and tert-butyl glyoxylate. 1-Cbg was found to substitute efficiently for isoleucine and valine, but not leucine, in the translation of green fluorescent protein in vitro.

Discovery of potent and selective β-homophenylalanine based dipeptidyl peptidase IV inhibitors

Modification of in-house screening lead beta-aminoacyl proline 8 gave an equipotent thiazolidide 9. Extensive SAR studies on the phenyl ring of 9 led to the discovery of a novel series of potent and selective DP-IV inhibitors. Introduction of a fluorine at the 2-position proved to be crucial for the potency of this series. The 2,5-difluoro (22q) and 2,4,5-trifluoro (22t) analogues were potent inhibitors of DP-IV (IC(50)=270, 119nM, respectively).

Enniatins of Fusarium sp. strain F31 and their inhibition of Botrytis cinerea spore germination

A spectrum of enniatins was isolated from Fusarium sp. strain F31 by bioassay-guided isolation directed against Botrytis cinerea. Two new enniatins, J(2) (7) and J(3) (8), were co-isolated and both contained, in addition to three hydroxyisovaleric acid units, N-methylated l-alanine, l-valine, and l-isoleucine units, differing only in their primary sequence. Two other enniatins, named enniatin J(1) (1) and enniatin K(1) (6), each containing two N-Me-l-Val units and one N-Me-l-Ala or alpha-N-Me-l-butyric acid unit, respectively, were isolated for the first time without directed biosynthesis. The enniatin structures were elucidated by spectroscopic and chemical methods, and the absolute configuration of the amino acids (l) and hydroxyisovaleric acid (d) was consistent with all previously isolated enniatins. The known enniatins B (2), B(1) (4), B(2) (5), and B(4) (3) were also isolated. The minimum inhibitory concentration of pure enniatins against Botrytis cinerea was 75 microg/mL.

Synthesis of All Four Stereoisomers of 3-Amino-2-hydroxybutanoic Acids

All four stereoisomers of 3-amino-2-hydroxybutanoic acids were been obtained as single enantiomers via stereospecific reactions from D-gulonic acid gamma-lactone and D-glucono-delta-lactone.

Diastereoselective synthesis of 2-amino-4-phosphonobutanoic acids by conjugate addition of lithiated Schöllkopf's bislactim ethers to vinylphosphonates

Conjugate additions of lithiated bislactim ethers derived from cyclo-[Gly-Val] and cyclo-[Ala-Val] to alpha-, beta-, or alpha,beta-substituted vinylphosphonates allow direct and stereoselective access to a variety of 3- or 4-monosubstituted and 2,3-, 2,4-, or 3,4-disubstituted 2-amino-4-phosphonobutanoic acids (AP4 derivatives) in enantiomerically pure form. The relative stereochemistry was assigned by X-ray diffraction analysis or NMR study of 1,2-oxaphosphorinane derivatives. Competitive eight-membered "compact" and "relaxed" transition-state structures are invoked to rationalize the stereochemical outcome of the conjugate additions.

Enantioselective synthesis of (S)-2-amino-4-phenylbutanoic acid by the hydantoinase method

Biosynthesis of (S)-(+)-2-amino-4-phenylbutanoic acid (1) was performed by nonenantioselective hydantoinase and L-N-carbamoylase using racemic 5-[2-phenylethyl]-imidazolidine-2,4-dione (rac-2) as a substrate. The compounds involved in this biocatalysis process could be simultaneously resolved by high-performance liquid chromatography using Chirobiotic T column with a mobile phase of EtOH/H(2)O = 10/90 at pH 4.2-4.5. To our knowledge, this is the first report of the successful production of 1 by the combination of recombinant hydantoinase and L-N-carbamoylase.

Asymmetric synthesis of L-homophenylalanine by equilibrium-shift using recombinant aromatic L-amino acid transaminase

L-Homophenylalanine (L-HPA) was asymmetrically synthesized from 2-oxo-4-phenylbutyric acid (2-OPBA) and L-aspartate using a recombinant aromatic amino acid transaminase (AroAT). To screen microorganisms having such an L-specific AroAT with a relaxed substrate inhibition in the asymmetric synthesis of unnatural amino acids, enrichment cultures were performed in a minimal media containing 50 mM L-HPA as a sole nitrogen source. To reduce the intracellular background synthetic activity by amino acid pools in the cells, a two-step screening method was used. The putative AroAT (i.e., AroATEs) from the screened Enterobacter sp. BK2K-1 was cloned, sequenced, and overexpressed in E. coli cells. The activity of the overexpressed AroATEs was 314-fold higher than that of the wild-type cell. The substrate specificities of the enzyme and homology search revealed that the cloned transaminase is true AroAT. The AroATEs showed a substrate inhibition by 2-OPBA from 40 mM in the asymmetric synthesis, which made it difficult to perform batch asymmetric synthesis of L-HPA at high concentrations of 2-OPBA. To avoid the substrate inhibition by 2-OPBA, intermittent addition of the solid-state substrate was attempted to obtain a high concentration of L-HPA. By using the cell extract (75 U) obtained from the recombinant E. coli harboring the AroATEs gene, the asymmetric synthesis of L-HPA at 840 mM of 2-OPBA resulted in >94% of conversion yield and >99% ee of L-HPA of optical purity. Due to the low solubility (<2 mM) of L-HPA in the reaction buffer, synthesized L-HPA was continuously precipitated in the reaction media, which drives the reaction equilibrium towards the product formation. After full completion of the reaction, L-HPA of high purity (>99% ee) was easily recovered by simple pH shift of the reaction media. This method can permit very efficient asymmetric synthesis of other unnatural amino acids using a single transaminase reaction.

Synthesis and evaluation of 2-amino-4-[(18)F]fluoro-2-methylbutanoic acid (FAMB): relationship of amino acid transport to tumor imaging properties of branched fluorinated amino acids

Radiolabeled amino acids represent a promising class of tumor imaging agents, and the determination of the optimal characteristics of these tracers remains an area of active investigation. A new (18)F-labeled branched amino acid, 2-amino-4-[(18)F]fluoro-2-methylbutanoic acid (FAMB), has been prepared in 36% decay-corrected yield using no-carrier-added [(18)F]fluoride. In vitro uptake assays with rat 9L gliosarcoma cells suggest that [(18)F]FAMB was transported primarily via the L type amino acid transport system. In vivo studies with [(18)F]FAMB demonstrated tumor to normal brain ratios of 14:1 in rats with intracranial 9L gliosarcoma tumors at 60 minutes after injection. Comparison of [(18)F]FAMB with structurally related (18)F-labeled branched amino acids demonstrated that A type transport in vitro was positively correlated with the tumor to brain ratios observed in vivo.

Analogues of dealanylalahopcin are inhibitors of human HIF prolyl hydroxylases

Analogues of the naturally occurring cyclic hydroxamate dealanylalahopcin, which is an inhibitor of procollagen prolyl-4-hydroxylase, were synthesised and shown to be inhibitors of the human hypoxia-inducible factor prolyl hydroxylases.

Synthesis of (R)-3,4-diaminobutanoic acid by desymmetrization of dimethyl 3-(benzylamino)glutarate through enzymatic ammonolysis

Lipase B from Candida antarctica is shown to be a highly efficient catalyst for the desymmetrization of dimethyl 3-(benzylamino)glutarate (1) through aminolysis and ammonolysis reactions. Using this procedure, enantiopure monoamides are obtained in high yield. The synthetic value of these compounds is demonstrated by the preparation of an enantiopure nonnatural amino acid, i.e. (R)-3,4-diaminobutanoic acid [(+)-12].

[Innovative molecular transformation using optically active alpha-amino acids]

Some methods for innovative molecular transformations using optically active alpha-amino acids have been exploited. 1) The non-Kolbe reaction of the N-benzoyloxazoline derivative 1 derived from L-serine gave the optically active N,O-acetal 2 when graphite was used an anode material. This reaction represents the first example of "memory of chirality" in the carbenium ion chemistry. 2) The optically active pipecolic acid derivative 13, prepared from L-lysine by using electrochemical oxidation, was cyclopropanated with high diastereoselectivity (96.6%de), and the product 14 was transformed into (2S,3R)-metanopipecolic acid (7). 3) An enantiomerically pure 1,2-dihydropyridine 23 was prepared from L-lysine using electrochemical oxidation as a key step and was utilized as a chiral diene synthon in the Diels-Alder reaction. That is, in the presence of AlCl3, the Diels-Alder reaction between 23 and N-acryloyloxazolidinone 24 gave a cycloadduct with high stereoselectivity, which was converted to an optically active isoquinuclidine derivative 26 (96.8% ee). 4) The Hofmann rearrangement of the L-glutamine derivative 27 to the enantiomerically pure 2-aminobutyric acid derivative 28 was successfully achieved with an electrochemical method using a trifluoroethanol-MeCN solvent system. 5) Some types of N-formyl cyclic amine derivatives were found to be effective activators of trichlorosilane to reduce ketones and imines. Namely, the reduction of ketones and imines by trichlorosilane with a catalytic amount of L-proline derivatives 30 and 32 gave enantiomerically enriched sec-alcohols and amines, respectively, to some extent of optical yields.

Total synthesis of amiclenomycin, an inhibitor of biotin biosynthesis

We describe the first synthesis of amiclenomycin, a natural product that has been found to inhibit biotin biosynthesis and, as a consequence, to exhibit antibiotic properties. Structure 1, with a trans relationship between the ring substituents. had previously been proposed for amiclenomycin on the basis of its 1H NMR spectrum. We have prepared the trans and cis isomers 1 and 2 by unequivocal routes and we conclude that the natural product is in fact the cis isomer 2. The properly substituted cyclohexadienyl rings were constructed first. A cycloaddition reaction between 1,2-di(phenylsulfonyl)ethylene and the N-allyloxycarbonyl diene 13, followed by reductive elimination of the phenylsulfinyl groups, gave the cis isomer 15. To obtain the trans isomer, the O-trimethylsilyl diene was used to give the cis hydroxylated Diels-Alder adduct 33, which was transformed into the corresponding trans amino derivative by means of a Mitsunobu reaction. The L-alpha-amino acid functionality was introduced by means of a Strecker reaction on the aldehydes 16 and 42, followed by enzymatic hydrolysis with immobilised pronase.

Backbone modifications of aromatic peptide nucleic acid (APNA ) monomers and their hybridization properties with DNA and RNA

Aromatic peptide nucleic acid (APNA) monomers containing N-(2-aminobenzyl)-glycine, N-(2-aminobenzyl)-(R)- or -(S)-alanine, and N-(2-aminobenzyl)-beta-alanine moieties as part of their backbone were synthesized. These novel analogues were incorporated as a single "point mutation" in PNA hexamers, and their physicochemical properties were investigated by UV thermal denaturation and CD experiments. Destabilization in triplex formation between the PNA-APNA chimeras and complementary DNA or RNA oligomers was observed, as compared to the PNA control. The APNA monomer composed of the N-(2-aminobenzyl)-glycine backbone led to the smallest decrease in the thermal stability of the triplexes formed with DNA and RNA, while maintaining selectivity for base-pairing recognition. Since the PNA-APNA chimeras are more lipophilic than the corresponding PNA homopolymers, these oligomers may also exhibit better cell membrane permeability properties.

Conjugate additions of 1-propenylphosphonates to metalated Schöllkopf's bis-lactim ether: stereocontrolled access to 2-amino-3-methyl-4-phosphonobutanoic acids

Diastereoselectivity in the conjugate addition of metalated Schöllkopf's bis-lactim ethers 5a-e to (E)- and (Z)-1-propenylphosphonates 4a,b was studied experimentally and theoretically and utilized to achieve a direct and stereocontrolled synthesis of all four diastereoisomers of 2-amino-3-methyl-4-phosphonobutanoic acid, 6a,b and their enantiomers. The relative stereochemistry was assigned from an NMR study of cyclic derivatives 13a,b. According to semiempirical calculations, both in vacuo (PM3) or a dielectric continuum (PM3/COSMO), initial lithium-phosphoryl coordination, without an energy barrier, to form a solvated chelate complex is followed by the rate-determining reorganization to the 1,4-addition product through an eight-membered transition state. The translation of the Z,E geometry into a syn, anti configuration at the adducts originates from an orientational preference in the transition state for a compact disposition of the reaction partners.

Synthesis and characterization of gamma-N-(2-furoylmethyl)aminobutyric acid

The product of acid hydrolysis of the Amadori compound gamma-N-(1-deoxy-D-fructosyl)aminobutyric acid was isolated and identified by (1)H NMR and (13)C NMR as gamma-N-(2-furoylmethyl)aminobutyric acid. This compound is an analogue to furosine, formed during acid hydrolysis of the corresponding Amadori compound. The retention time of the isolated compound was the same as that of the main peak observed in acid hydrolysates of stored orange juice powder. gamma-N-(2-Furoylmethyl)aminobutyric acid can be a useful indicator of the early stages of Maillard reaction in foods containing free gamma-aminobutyric acid.

Isomers of substituted 3-benzo[b]furyl and 3-thienylaminobutyric acids as potent ligands of the GABA-B receptor: synthesis and preparative liquid chromatographic separation

Baclofen (4-amino-3-(4-chlorophenyl)butyric acid) is the only selective agonist for GABA-B receptors. Its R-(-)-enantiomer is about 100 times more active than the S-(+)-enantiomer. In the search for new compounds that bind to GABA-B receptors, it is very important to clarify the structural requirements. The authors report the synthesis and separation of isomers of various 3-heteroaromatic (benzo[b]furan and thiophen) aminobutyric acids. The 4-amino-3-(7-methylbenzo[b]furan-2-yl)butanoic acid is a potent and specific ligand for GABA-B receptors, with an IC50 value of 5.4 microM for the displacement of [3H] GABA.

Synthesis, physicochemical properties, anticonvulsant activities and voltage-sensitive calcium channels affinity of N-substituted amides of alpha-(4-phenylpiperazino)-GABA. Part 3: Search for new anticonvulsant compounds

This paper describes the synthesis and preliminary anticonvulsant evaluation of some GABA analogues i.e. derivatives of 2-(4-phenylpiperazino)- or 2-(4-benzylpiperidino)-GABA (5, 6), N-substituted amides of 2-(4-phenylpiperazino)-4-phthalimidobutyric acid and N-substituted amides of 2-(4-phenylpiperazino)-GABA. N-Substituted amides of 2-(4-phenylpiperazino)-4-phthalimidobutyric acid (7-11) were prepared by condensation of the acid with the corresponding derivatives of benzylamine in the presence of different coupling reagents (2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and carbonyldiimidazole (CDI). N-Substituted benzylamides of 2-(4-phenylpiperazino)-4-aminobutyric acid (12-14) were prepared by hydrazinolysis of amides 9-11. Anticonvulsant activities were determined in mice (for all compounds) and in rats using the subcutaneous metrazol (scMet) and maximal electroshock (MES) screens. The amides (12-14) showed protection against MES and/or scMet seizures in mice. N-(4-Methoxybenzyl)-2-(4-phenylpiperazin-1-yl)-4-aminobutyric amide (13) was the most effective and displayed anticonvulsant activity in both tests at doses of 100-300 mg/kg in mice and at 30 mg/kg in the MES screen in rats. The active compounds (12-14) were tested for their ability to displace [3H]nitrendipine binding sites (voltage-sensitive calcium channel receptors) from rat cortex. Amide 13 was the most active both in pharmacological and biochemical tests. These preliminary results suggest that the anticonvulsant activity of compounds 12-14 may be related to their influence on voltage-sensitive calcium channel receptors.

Conformational analysis of the dipeptide taste ligand L-aspartyl-D-2-aminobutyric acid-(S)-alpha-ethylbenzylamide and its analogues by NMR spectroscopy, computer simulations and X-ray diffraction studies

A dipeptide taste ligand L-aspartyl-D-2-aminobutyric acid-(S)-alpha-ethylbenzylamide was found to be about 2000 times more potent than sucrose. To investigate the molecular basis of its potent sweet taste, we carried out conformational analysis of this molecular and several related analogues by NMR spectroscopy, computer simulations and X-ray crystallographic studies. The results of the studies support our earlier model that an L-shape molecular array is essential for eliciting sweet taste. In addition, we have identified an aromatic group located between the stem and the base of the L-shape, which is responsible for enhancement of sweetness potency. In this study, we also assessed the optimal size of the essential hydrophobic group (X) and the effects of the chirality of the second residue toward taste.

N-acyl-(alpha, gamma diaminobutyric acid)n hydrazide as an efficient gene transfer vector in mammalian cells in culture

PURPOSE

This study investigates the structure/activity relationship of a series of N-acyl-peptides (lipopeptides) for the transfection of mammalian cells.

METHODS

Lipopeptides comprising 1 to 3 basic amino-acids and a single fatty acid chain were synthesized. Transfecting complexes between lipopeptide, plasmid DNA and dioleoyl phosphatidylethanolamine were prepared and applied on cells in culture. Transfection efficiency was evaluated by measuring beta-galactosidase activity 48 h post-transfection. Lipopeptide-DNA binding was also investigated by physical means and molecular modelling.

RESULTS

Besides the length of the fatty acid chain, the nature of the basic amino-acid and the C-terminal group were crucial parameters for high transfection efficiency. The N-acyl-(diaminobutyric acid)n derivatives were the most potent transfecting agents among those tested and induced a beta-galactosidase activity 2 to 20 times higher than the N-acyl-lysine, -ornithine or -diaminopropionic acid derivatives. Furthermore, a hydrazide C-terminal modification greatly enhanced transfection efficiency for all compounds tested. The reason why alpha, gamma-diaminobutyric acid hydrazide-based lipopeptides were the most potent in transfection is not fully understood but could be related to their high DNA binding.

CONCLUSIONS

Poly- or oligo-diaminobutyric acid containing or not a hydrazide C-terminus could advantageously be used in peptide-based gene delivery systems.

Feasibility of labeled alpha-acetamido-aminoisobutyric acid as new tracer compound for kinetic labeling of neutral amino acid transport: preparation of alpha-(N-[1-11C]acetyl)- and alpha-(N-[1-14C]acetyl)-aminoisobutyric acid

The nonphysiological, nonracemic, branched-chain alpha-acetamido-aminoisobutyric acid was labeled with the carbon isotope 11C with the intention to use it in conjunction with positron emission tomography (PET) to measure the kinetics of amino acid transport in vivo. It was produced by the reaction of the novel 11C-precursor N-[1-11C]acetylpyridinium chloride with alpha-aminoisobutyric acid. Typically, 2 GBq of alpha-(N-[1-11C]acetyl)-aminoisobutyric acid were isolated with a specific activity of 12 to 20 GBq. mumol-1 at the time of application, and with a radiochemical purity of > 98%. The chemical identity of alpha-(N-[1-11C]acetyl)-aminoisobutyric acid was confirmed by comparison with alpha-(N-[1-14C]acetyl)-aminoisobutyric acid that was independently prepared by a standard acetylation procedure of alpha-aminoisobutyric acid using [1-14C]acetic anhydride. In vivo, both labeled substrates were not metabolized. In cell-culture experiments, 84% of the substrate entered the cells by the sodium-dependent amino acid transport system A, whereas 16% was taken up by the sodium-independent system. The uptake of the radiotracer was measured 20 min and 40 min postinjection in tumor-bearing male Copenhagen rats for assessment of its in vivo biodistribution.

Synthesis and structure-activity relationships of a novel antifungal agent, azoxybacilin

A new antifungal substance, azoxybacilin (an unusual amino acid with an azoxy moiety) and its derivatives have been synthesized from Boc-L-Asp-OtBu utilizing the Moss procedure for the preparation of the azoxy moiety. The ester derivative, Ro 09-1824, showed more potent antifungal activity and a broader antifungal spectrum than azoxybacilin did.

The absolute configuration of an intermediate in the asymmetric synthesis of unusual amino acids

(4R)-3-[(2'R,3'R)-2'-Bromo-3'-(phenylbutanoyl)]-4-(phenylmethyl)-2 - oxazolidinone, C20H20Br-NO3, M(r) = 402.30, monoclinic, P2(1), a = 11.542 (2), b = 7.625 (1), c = 11.667 (1) A, beta = 113.97 (1) degrees, V = 938.2 (2) A3, Z = 2, Dx = 1.42 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 21.8 cm-1, F(000) = 412, T = 296 +/- 1 K, final R = 0.028 for 2369 observed reflections. Since a D-chiral auxiliary was used the configuration at the alpha-carbon was R as expected. The two carbonyls are aligned in opposite directions to each other to overcome van der Waals repulsions.

Synthesis and binding properties to GABA receptors of 3-hydroxypyridinyl- and 3-hydroxypiperidinyl-analogues of baclofen

The synthesis of 3-(3-hydroxy-2-pyridinyl)propanoic acid, 3-(3-hydroxy-2-pyridinyl)-4-aminobutanoic acid, their corresponding piperidine compounds, and of some cyclized derivatives is described. In in vitro assays none of the new compounds shows any noteworthy affinity for GABAA or GABAB receptors; only (R,S)-3-(3-hydroxy-2-pyridinyl)-4-aminobutanoic acid and its lactam inhibited in some degree [3H]GABA binding, at 10(-4) M concentration, with low specificity as regards the two receptors.

Characterization of retinal and hippocampal L-AP4 receptors using conformationally constrained AP4 analogues

In the past, the absence of useful 2-amino-4-phosphonobutanoic acid (AP4) analogues has hampered the pharmacological study and comparison of different systems which are sensitive to L-AP4. Several conformationally constrained AP4 analogues have now been synthesized: (E)- and (Z)-1-amino-3-phosphonocyclopentanecarboxylic acid [(E)- and (Z)-cyclopentyl AP4], and (E)- and (Z)-1-amino-3-phosphonocyclohexanecarboxylic acid [(E)- and (Z)-cyclohexyl AP4], and the recently synthesized cyclopropyl analogues (E)- and (Z)-2-amino-2,3-methano-4-phosphonobutanoic acid [(E)- and (Z)-cyclopropyl AP4]. Therefore, we have examined and report here the pharmacology of two retinal and two hippocampal L-AP4 sensitive systems using these analogues. In addition, the pharmacology of two kainic acid/alpha-amino-3-hydroxy-5-methylisoxazole-4- propionic acid (KAIN/AMPA) pathways and one N-methyl-D-aspartate (NMDA) hippocampal pathway was examined. We found that the rank order potency of the L-AP4 sensitive systems were similar though not identical. The KAIN/AMPA and NMDA systems had a quite different rank order of potencies than the L-AP4 systems. These data suggest that the L-AP4 receptors in these different systems are structurally similar to each other and differ from both KAIN/AMPA and NMDA receptors.

Synthesis of the 2-amino-4-phosphonobutanoic acid analogues (E)- and (Z)-2-amino-2,3-methano-4-phosphonobutanoic acid and their evaluation as inhibitors of hippocampal excitatory neurotransmission

The cyclopropyl compounds (Z)- and (E)-2-amino-2,3-methano-4-phosphonobutanoic acid, 5 and 6, respectively, were prepared as constrained analogues of 2-amino-4-phosphonobutanoic acid (AP4), a selective glutamate receptor ligand. A Horner-Emmons reaction of trimethyl N-(benzyloxycarbonyl)phosphonoglycinate with 2-(diethoxyphosphinyl)acetaldehyde gave the protected dehydroamino acids 9 and 10, which were individually subjected to the following sequence of reactions: cycloaddition of diazomethane, photoelimination of N2, and acid hydrolysis, to give 5 and 6, respectively. Extracellular recording techniques were used to evaluate the abilities of 5 and 6 to block evoked synaptic transmission in specific neuronal pathways of the rat hippocampal slice. In the lateral perforant path (LPP) 5 and 6 were equipotent and possessed IC50 values of 18 and 17 microM, respectively. In the medial perforant path (MPP), 6 (IC50 = 81 microM) was much more potent than 5 (IC50 = 1580 microM). In paired pulse experiments which differentiate presynaptic and postsynaptic inhibition, 5 and 6 enhanced the second response to the same extent as L-AP4, suggesting a presynaptic site of action for these compounds. In contrast, the cyclopentyl AP4 analogues 3 and 4 enhanced the second response to a lesser extent. It was concluded that the biologically active conformation of AP4 in the LPP is different than in the MPP. In order to explain the same potency of 5 and 6 in the LPP, it was postulated that the two analogues assume a conformation that allows their functional groups to occupy the same relative place in space. Molecular modeling showed that the best overlap was achieved when the alpha C-beta C-gamma C-P dihedral angle for 5 was in the range of 130 degrees to 180 degrees and that of 6 was in the range of -130 degrees to -180 degrees. The results suggest that the bioactive conformation of AP4 in the LPP is an extended one.

4-Amino-3-alkylbutanoic acids as substrates for gamma-aminobutyric acid aminotransferase

A variety of alkyl-substituted 4-aminobutanoic acid derivatives, including a homologous series of 3-alkyl-4-aminobutanoic acid analogues, 4-methyl isomer analogues, the 3,3-dimethyl analogue, and (E)-4-amino-3-methyl-2-butenoic acid, were synthesized and tested as alternate substrates for purified gamma-aminobutyric acid aminotransferase from pig brain. All of the compounds were substrates, but their activities diminished as the size and bulk of the 3-alkyl substituent increased. Several differences were observed between the alkyl-substituted analogues and the corresponding aryl-substituted compounds previously reported (Silverman, R. B., Invergo, B. J., and Levy, M. A. (1987) J. Biol. Chem. 262, 3192-3195). These findings will be important in future designs of inhibitors of gamma-aminobutyric acid aminotransferase.

Orally potent human renin inhibitors derived from angiotensinogen transition state: design, synthesis, and mode of interaction

A three-dimensional structure of the complex of human renin and the scissile site P4 Pro to P1' Val of angiotensinogen was deduced in order to design potent human renin inhibitors rationally. On the basis of this structure, an orally potent human renin inhibitor (1a) was designed from the angiotensinogen transition state and synthesized. The inhibitor 1a contains a (2R)-3-(morpholinocarbonyl)-2-(1-naphthylmethyl)propionyl residue (P4-P3) with a retro-inverso amide bond, L-histidine, and a novel amino acid, (2R,3S)-3-amino-4-cyclohexyl-2-hydroxybutyric acid, named cyclohexylnorstatine (2a). The optically pure cyclohexylnorstatine was efficiently prepared from Boc-L-cyclohexylalaninol (3), and the stereochemistry of 1a was established by X-ray crystal analysis. The analyses of interaction between 1a and human renin using modeling techniques indicated that (1) the cyclohexyl group of P1 and the naphthyl group of P3 were accommodated in large hydrophobic subsites S1 and S3, respectively; (2) the imidazole of P2 His was hydrogen bonded to the side chain OH of Ser-233 to contribute to the selectivity of renin inhibition; (3) cyclohexylnorstatine isopropyl ester residue was accommodated in S1-S1'. The importance of the stereochemistry in the potent and specific inhibitor was clearly shown. Oral administration to monkeys of this inhibitor resulted in a drop of 10-20 mmHg in mean blood pressure and a reduction of plasma renin activity for a 5-h period.

[Synthesis of 4-[(4-chlorophenyl) (5-fluoro-2-hydroxyphenyl) methylene amino]butyrates and its anticonvulsant activity]

It is known that gamma-aminobutyric acid (GABA) plays an important role in the pathophysiology of epilepsy. Under physiological conditions it is very difficult for GABA to cross the blood-brain barrier. It is likely that the esters of GABA, Which easily enter the brain, will have useful therapeutic properties. With this in mind, we have designed and synthesized 8 derivatives (IVa to IVh) of gamma-aminobutyric acid with an imine to link a lipophilic carrier in order to facilitate the passage of gamma-aminobutyric acid to cross the blood-brain barrier. All the eight synthesized title compounds were evaluated as anticonvulsants in mice via the Antiepileptic Drug Development Program of NIH. The compounds IVb and IVf showed anticonvulsant activity.

Polymerization of amino acids containing nucleotide bases

We have prepared the nucleoamino acids 1-(3'-amino,3'-carboxypropyl)uracil (3) and 9-(3'-amino,3'-carboxypropyl)adenine (4) as (L)-enantiomers and as racemic mixtures. When 3 or 4 is suspended in water and treated with N,N'-carbonyldiimidazole, peptides are formed in good yield. The products formed from the (L)-enantiomers are hydrolyzed to the monomeric amino acids by pronase. Attempts to improve the efficiency of these oligomerizations by including a polyuridylate template in the reaction mixture were not successful. Similarly, oligomers derived from the (L)-enantiomer of 3 did not act as templates to facilitate the oligomerization of 4.

Substrate variability as a factor in enzyme inhibitor design: inhibition of ovine brain glutamine synthetase by alpha- and gamma-substituted phosphinothricins

Ovine brain glutamine synthetase (GS) utilizes various substituted glutamic acids as substrates. We have used this information to design alpha- and gamma-substituted analogues of phosphinothricin [L-2-amino-4-(hydroxymethylphosphinyl)butanoic acid], a naturally occurring inhibitor of GS. These compounds display competitive inhibition of GS, and a correlation between the inhibitor Ki values and the Km/Vmax values of the analogously substituted glutamates supports the hypothesis that the phosphinothricins participate in transition-state analogue inhibition of GS. At concentrations greater than Ki these inhibitors caused biphasic time-dependent loss of enzyme activity, with initial pseudo-first-order behavior; k'inact parameters were determined for several compounds and were similar to the 2.1 X 10(-2)s-1 value measured for PPT. Dilution after GS inactivation caused a non-first-order recovery of activity. Reactivation kinetics were insensitive to inhibitor and ADP concentrations over wide ranges, although very high postdilution concentrations of inhibitor suppressed reactivation. The burst activity level, beta, as well as the concentration of inhibitor required to suppress reactivation to this level, mu, expressed as a multiple of the Ki value, was characteristic for each compound in the phosphinothricin series. Increasing substitution of the phosphinothricin parent structure caused an increase in Ki values as well as in the inactivation/reactivation parameters. The kinetic behavior of these inhibitors is consistent with a mechanistic scheme involving initial phosphorylation and rapid partial inhibitor dissociation, followed by slow release of remaining bound inhibitor.

4-N-hydroxy-L-2,4-diaminobutyric acid. A strong inhibitor of glutamine synthetase

Analogues of glutamic acid were synthesized and evaluated for their inhibitory activity toward glutamine synthetase (EC 6.3.1.2; GS). The title compound, 4-N-hydroxy-L-2,4-diaminobutyric acid (NH-DABA), showed a potent inhibitory activity against GS from both sheep brain and soybean. The inhibition is competitive with respect to glutamic acid and the Ki values of sheep brain GS and soybean GS for NH-DABA are 0.007 mmol and 0.021 mmol, respectively. The activity of inhibition is comparable to those of L-methionine sulfoximine and 2-amino-4-(hydroxymethyl-phosphinyl)butyric acid (phosphinothricin).

Asymmetric synthesis of L-2-amino[3-11C]butyric acid, L-[3-11C]norvaline and L-[3-11C]valine

The short-lived radionuclide 11C (t1/2 = 20.4 min) has been used in the asymmetric synthesis of L-2-amino[3-11C]butyric acid, L-[3-11C]-norvaline and L-[3-11C]valine. The syntheses were performed by alkylation of [(+)-2-hydroxypinanyl-3-idene]-glycine tert-butyl ester under anhydrous conditions in tetrahydrofuran/1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone with lithiated 2,2,6,6-tetramethylpiperidine as base, using the appropriate 11C-alkyl iodides prepared in a one-pot reactor from [11C]carbon dioxide. Following removal of the protecting groups, the -[3-11C]amino acids were obtained in 80-82% enantiomeric excess and in 9-25% radiochemical yields, decay corrected and calculated on the basis of the amount of [11C]carbon dioxide at the start of the syntheses within 50-55 min.

Cyclic analogues of 2-amino-4-phosphonobutanoic acid (APB) and their inhibition of hippocampal excitatory transmission and displacement of [3H]APB binding

Conformationally restricted analogues of 2-amino-4-phosphonobutanoic acid (APB,2) were prepared where the structure of APB was incorporated into cyclopentane (3) or cyclohexane (4) rings. Hydrophosphinylation of the appropriate cycloalkenones followed by Strecker amino acid syntheses provided the desired analogues. Assignments of the relative configurations for 3a (trans), 3b (cis), 4a (cis), and 4b (trans) were determined through 13C NMR studies. Compounds 3b, 4a, and 4b possessed low activity as inhibitors of excitatory synaptic field potentials in the rat hippocampal perforant path. Analogues 4a and 4b also showed little activity in displacing [3H]APB from synaptic plasma membranes. The cyclopentyl APB analogue 36, on the other hand, was extremely potent in inhibiting the binding of [3H]APB, possessing an IC50 = 4.7 microM, thus giving further credence to the idea that the APB binding site in the rat brain synaptosomal membrane preparation is not the same as the receptor mediating APB-induced inhibition of the lateral perforant path. Of the four cyclic APB analogues, 3a most resembled APB in its spectrum of biological activity. It showed significant potency (IC50 = 130 microM) in inhibiting lateral entorhinal projections to hippocampal granule cells. Analogous to APB, 3a also showed selectivity for the lateral perforant path over the medial perforant path. Its activity in the radioligand binding assay paralleled its activity in inhibiting the lateral perforant path. It thus appears that 3a comes closest to mimicking the active conformation of APB and suggests that a folded conformation wherein the amino and phosphonate moieties are in a cis relationship to one another may approximate the active conformation of APB.

Radiochemical synthesis of DL-canaline and the colorimetric assay of canaline

A procedure is available for the production of DL-[carboxy-14C]canaline from [14C]cyanide by reaction of ethyl N-hydroxyacetimidate and acrolein to form ethyl N-[3-oxopropoxy]acetimidate. The reaction product is converted to the nitrile and then to the hydantoin derivative of DL-canaline; alkaline hydrolysis produces the free amino acid (2-amino-4-aminooxypropionic acid). This procedure can be extended to the production of DL-[carboxy-14C]canavanine by guanidination of C-1-labeled DL-canaline with O-methylisourea. A markedly improved colorimetric assay for canaline has been achieved by a procedure involving carbamylation of canaline with cyanate to form O-ureidohomoserine (2-amino-4-ureidooxybutyric acid). Colorimetric analysis of the latter amino acid markedly enhances the sensitivity, reproducibility, and accuracy of the analysis of L-canaline from biological materials.

Substituted 4-aminobutanoic acids. Substrates for gamma-aminobutyric acid alpha-ketoglutaric acid aminotransferase

Substituted 4-aminobutanoic acids were studied as potential irreversible inactivators of purified pig brain gamma-aminobutyric acid aminotransferase, the enzyme responsible for the degradation of the inhibitory neurotransmitter, gamma-aminobutyric acid. It was found that unlike the related 4-amino-5-halopentanoic acids (Silverman, R. B., and Levy, M. A. (1981) Biochemistry 20, 1197), the 4-amino-3-halobutanoic acids were substrates for this enzyme, undergoing exclusive elimination to succinic semialdehyde and producing no inactivation. The hydroxy analogue, however, underwent exclusive transamination and no succinic semialdehyde was detected. These results are discussed in terms of the nature of the substituents, the structure of the active site of gamma-aminobutyric acid aminotransferase, and the design of mechanism-based inactivators.

Potential pancreatic imaging agents. Tellurium-123m labeled DL-alpha-amino-gamma-(phenyltelluro)butyric acid

This report describes the first successful preparation of a 123mTe-labeled alpha-amino acid as a potential pancreatic imaging agent. Tellurium-123m labeled DL-alpha-amino-gamma-(phenyltelluro)butyric acid was prepared by basic hydrolysis of the radiolabeled 5-[beta-(phenyltelluro)ethyl]hydantoin. The hydantoin was prepared by the reacitron of 123mTe-labeled phenyltellurol, generated by sodium borohydride reduction of diphenyl ditelluride, with 5-(beta-bromoethyl)hydantoin. Tissue distribution studies in rats with the 123mTe-labeled amino acid for periods varying from 30 min to 24 h demonstrated only marginal pancreatic accumulation of radioactivity. The significant result of these studies is that a general synthetic method has been developed for the preparation of 123mTe-labeled amino acids.

Synthesis of alpha-[7-methyl-9-methoxy-5-oxo-furo-[3,2-g] [1]-benzopyranoxy-4]-butyric and valeric acids and their aminoesters

In the reaction of 4-desmethylkhelline with ethyl alpha-bromobutyrate or alpha-bromovalerate we obtained alpha-[7-methyl-9-methoxy-5-oxo-furo[3,2-g] [1] benzopyranoxy-4]-butyric 2 and valeric 3 acids and later their dialkylaminoethylesters as hydrochlorides (2b--2, 3b--3e). Compounds 2c, 2e, 2f (Table 1) and 3e (Table 2) show a weak hypotensic activity. Moreover compound 2f possesses an antriarrhythmic activity.

Cyclic GABA-GABOB analogues. II - Synthesis of new 2-oxo and 2,5-dioxo-delta3-pyrroline derivatives

Within the framework of a research program on new compounds potentially active on learning and memory processes, some esters and amides of 2-oxo- and 2,5-dioxo-delta3-pyrroline-1-acetic acids were synthesized. Such compounds can be regarded either as dehydration products of the corresponding 4-hydroxy-2-pyrrolidinones or as cyclic derivatives of 4-aminoisocrotonic acid. Two approaches were used in an attempt to synthesize pyrrolinone derivatives. One method involved the direct alkylation with ethyl bromoacetate of 1,5-dihydro-2H-pyrrol-2-one (III b), obtained for the first time in pure form by cyclization of 4-amino-3-hydroxybutyric acid (GABOB). Another approach involved the preparation of the ethyl 3-bromo-2-oxo-1-pyrrolidineacetate (VI), by cyclization of N-(2,4-dibromobutyryl)glycine ethyl ester (V), and its 4-bromo isomer (X b) by bromination of ethyl 4-hydroxy-2-oxo-1-pyrrolidineacetate (X a). While the dehydrobromination of (VI) was unsuccessful, heating of (X b) with TEA afforded ethyl 2,5-dihydro-2-oxo-1H-pyrrole-1-acetate (IV a). Alternatively, (X a) was treated with methanesulfonyl chloride, then with TEA to give (IV a). Final ammonolysis of (IV a) provided the corresponding amide (IV b). For the synthesis of the maleimide analogue (XIII b), the N-(carboxymethyl)maleamic acid (XII a) was treated with PCl5 and then with anhydrous ammonia.