Structural analogues of diosgenyl saponins: Synthesis and anticancer activity

Saponins display various biological activities including anti-tumor activity. Recently intensive research has been focused on developing saponins for tumor therapies. The diosgenyl saponin dioscin is one of the most common steroidal saponins and exhibits potent anticancer activity in several human cancer cells through apoptosis-inducing pathways. In this paper, we describe the synthesis of several diosgenyl saponin analogues containing either a 2-amino-2-deoxy-β-d-glucopyranosyl residue or an α-l-rhamnopyranosyl-(1→4)-2-amino-2-deoxy-β-d-glucopyranosyl residue with different acyl substituents on the amino group. The cytotoxic activity of these compounds was evaluated in MCF-7 breast cancer cells and HeLa cervical cancer cells. Structure–activity relationship studies show that the disaccharide saponin analogues are in general less active than their corresponding monosaccharide analogues. The incorporation of an aromatic nitro functionality into these saponin analogues does not exhibit significant effect on their cytotoxic activity.     

Affinity electrophoretic detection of primary amino groups in nucleic acids: application to modified bases of tRNA and to aminoacylation.

Thiolation of primary amino groups in tRNA with the heterobifunctional reagent N-succinimidyl 3-(2-pyridyldithio)propionate gives rise to species which are retarded during electrophoresis in organomercury-containing polyacrylamide gels. Since such amino groups occur, as far as is known, only as part of the modified bases 3-(3-amino-3-carboxypropyl)uridine and N-2-(5-amino-5-carboxypentyl)cytidine or as the alpha-amino group of aminoacylated tRNAs, this extension of the principle of affinity electrophoresis can be used for the detection and analysis of a specific functional group in both single tRNA species and in a mixed population. The strength of the interaction may be quantified and provides information on the chemical environment/conformation of the derivatized bases.     

Stereoselective synthesis of 2-amino-1-hydroxy-3-phenylpropylphosphonic acid

A highly stereoselective synthesis of 2-amino-1-hydroxy-3-phenylpropylphosphonic acid was achieved by simple addition of diethyl phosphite to enantiomeric N-blocked phenylalaninals. These compouds exhibit significant herbicidal activity.     

Stereoselective Synthesis of 2-Amino-2-deoxy-d-arabinose and 2-Deoxy-d-ribose

An efficient method for the stereoselective synthesis of 2-amino-2-deoxy-d-arabinose and 2-deoxy-d-ribose is described.

The key step in this method was accomplished by the nucleophilic addition of methyl isocyanoacetate to 2,3-O-isopropylidene-d-glyceraldehyde with high erythro-selectivity (nearly 100%).

Subsequent intermolecular cyclization predominantly gave the desired oxazoline derivative (trans-form), in which two new chiral centers were formed. The oxazoline derivative was efficiently converted to both 2-amino-2-deoxy-d-arabinose and 2-deoxy-d-ribose.     

Synthesis, in vitro pharmacology, and pharmacokinetic profiles of 2-[1-amino-1-carboxy-2-(9H-xanthen-9-yl)-ethyl]-1-fluorocyclopropanecarboxylic acid and its 6-heptyl ester, a potent mGluR2 antagonist

In this paper, we describe the synthesis of (+)-(1R( *),2R( *))-2-[(1S( *))-1-amino-1-carboxy-2-(9H-xanthen-9-yl)-ethyl]-1-fluorocyclopropanecarboxylic acid (+)-16a, a compound, that is, fluorinated at the alpha position of the carboxylic acid in the cyclopropane ring of a group II mGluRs antagonist, 1 (LY341495), using a previously reported stereoselective cyclopropanation reaction. The fluorinated compound (+)-16a exhibited almost the same affinity (IC(50)=3.49 nM) for mGluR2 as 1 but had a superior pharmacokinetic profile. Furthermore, a marked elevation of the plasma levels of (+)-16a was observed following the administration of a prodrug, (+)-17.     

Design and synthesis of new secretory phospholipase A2 inhibitor of a phospholipid analog

All stereoisomers of N-acyl-4,5-disubstituted oxazolidinone phospholipid analogs were synthesized by regio and stereoselective epoxide ring opening accompanied by introduction of an amino group. The (4R,5S)-derivative showed stronger inhibitory activity toward type II phospholipase A₂ than the 4-substituted oxazolidinone phospholipid analog previously reported.     

Comparison of inhibitory activity of isomeric triazolopyridine derivatives towards adenosine receptor subtypes or do similar structures reveal similar bioactivities?

The synthesis of an array of 8-amino-2-aryl-[1,2,4]triazolo[1,5-a]pyridine-6-carboxyl amide derivatives is described for the first time. A subset of 20 derivatives were compared to their isomeric 5-amino-2-aryl-[1,2,4]triazolo[1,5-a]pyridine-7-carboxyl amide counterparts with regard to their potential to inhibit the human adenosine 2a (hA2a) receptor and their selectivity against the human adenosine 1 (hA1) receptor. Based on the analysis of H-bond donor/acceptor capabilities of the isomeric triazolopyridine pairs it can be concluded that the H-bond donor strength of the free amino functionality is the main determinant for hA2a inhibitory activity and hA1 selectivity.     

The effect of amino groups on the stability of DNA duplexes and triplexes based on purines derived from inosine

The effect of amino groups attached at positions 2 and 8 of the hypoxanthine moiety in the structure, reactivity and stability of DNA duplexes and triplexes is studied by means of quantum mechanical calculations, as well as extended molecular dynamics (MD) and thermodynamic integration (MD/TI) simulations. Theoretical estimates of the change in stability related to 2′-deoxyguanosine (G) → 2′-deoxyinosine (I) → 8-amino-2′-deoxyinosine (8AI) mutations have been experimentally verified, after synthesis of the corresponding compounds. An amino group placed at position 2 stabilizes the duplex, as expected, and surprisingly also the triplex. The presence of an amino group at position 8 of the hypoxanthine moiety stabilizes the triplex but, surprisingly, destabilizes the duplex. The subtle electronic redistribution occurring upon the introduction of an amino group on the purine seems to be responsible for this surprising behavior. Interesting ‘universal base’ properties are found for 8AI.     

Stereoselective synthesis of 2-amino-3-fluoro bicyclo[3.1.0]hexane-2,6-dicarboxylic acid.

(+)-2-Aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (LY354740) is a conformationally restricted glutamate analogue that is a potent, selective and orally active group 2 metabotropic glutamate receptor agonist possessing anticonvulsant and anxiolytic properties. Herein, we describe a stereoselective and highly efficient synthesis of its 3-beta fluoro derivative using the Corey-Link methodology to create the amino acid stereogenic center.     

Utilization of a common pathway for the synthesis of high affinity macrocyclic Grb2 SH2 domain-binding peptide mimetics that differ in the configuration at one ring junction

As typified by 2-{(9S,10S,14R,18S)-18-(2-amino-2-oxoethyl)-14-[(5-methyl-1H-indol-1-yl)methyl]-8,17,20-trioxo-10-[4-(phosphonomethyl)phenyl]-7,16,19-triazaspiro[5.14]icos-11-en-9-yl}acetic acid ((14R)-1b), ring-closing methathesis-derived macrocyclic tetrapeptide mimetics have recently been reported that bind with high affinity to Grb2 SH2 domains in both extracellular and whole-cell assays. The synthetic complexity of this class of agents limits further therapeutic development. Although a significant component of this synthetic complexity arises from the presence of three stereogenic centers, C(9) (S), C(10) (S), and C(14) (R), it is unclear whether stereoselective introduction of defined configuration at C(14) is required for high-affinity binding. Reported herein is a synthetic route to these macrocycles lacking stereoselectivity in the formation of the C(14) ring junction, which is four synthetic steps shorter than the original stereoselective synthesis. Separation of C(14)-epimers obtained by this approach was achieved by preparative HPLC. Molecular-dynamics studies of ligands bound to the Grb2 SH2 domain protein indicated that the (14R)-configuration should display more-favorable interactions with the protein relative to the (14S)-epimer. Indeed, although surface-plasmon-resonance-derived binding constants to Grb2 SH2 domain protein indicated that the affinity of the (14R)-epimer (KD = 4.8 nM) is greater than that of the (14S)-epimer (KD = 11 nM), it is only marginally so. Therefore, little affinity would be lost through a non-stereoselective synthesis of the C(14)-center. Further studies are in progress to explore reduced structural complexity at the C(14)-center.     

Synthesis of bisaminoacylated pdCpAs and tandemly activated transfer RNAs

Described herein is the preparation of new bisacylated tRNAs and their participation in protein synthesis. It has been reported that Thermus thermophilus phenylalanyl-tRNA synthetase can introduce two phenylalanine moieties onto the 3'-terminal adenosine of its cognate tRNA. It is also possible to prepare bisactivated tRNAs in vitro; these participate in protein synthesis [Wang, B.; Zhou, J.; Lodder, M.; Anderson, R. D.; Hecht, S. M. J. Biol. Chem.2006, 281, 13865]. Presently, the chemical strategy used for the synthesis of the key intermediate bisacylated pdCpAs is described. Bis-S-alanyl- and bis-S-methionyl-pdCpAs were prepared initially. Further, S-threonine, S-allo-threonine, S-homoserine, and (S)-(+)-2-amino-3-hydroxy-3-methylbutyric acid were coupled with the dinucleotide to define preparative methods applicable to more complex amino acids bearing additional functionality in the form of an OH group.     

Synthesis of a coumarin based fluorescent amino acid

L-2-amino-3-(6,7-dimethoxy-4-coumaryl)-propionic acid (L-Adp), as a non-proteinogenic fluorescent amino acid has been synthesized by a highly stereoselective routine (>99.5%). This fluorescent amino acid, as fluorophore-quencher pair, may be used to study peptide assays. For enantiomeric excess determination, the racemic D-Adp (D-2-amino-3-(6,7-dimethoxy-4-coumaryl)-propionic acid) has also been synthesized.     

Preparation of 2S-(—)-4-Amino-2-Hydroxybutanoic Acid via Yeast-Catalyzed Stereoselective Reduction

The unusual amino acid S2-(—)-4-amino-2-hydroxybutanoic acid (S-AHBA) (1), a structural component of the antibiotic Amikacin, has been prepared via yeast-catalyzed stereoselective reduction of methyl-4-benzyloxycarbonyloxyamino-2-oxobutanoate (5). The most suitable yeast was found to be Saccharomyces carlsbergensis ATCC2345 and Saccharomyces sp. Edme, which gave 40% and 54% yield, respectively, of (S)-(+)-6 (88% ee).     

Metabolism of l-Canavanine and l-Canaline in Leguminous Plants

Massive accumulation of l-canavanine, the 2-amino-4-(guanidinooxy)butyric acid structural analog of l-arginine, occurs in many legumes. Accumulation of large amounts of this nonprotein amino acid results in large part from canavanine's protective efficacy; it forms an effective chemical barrier to predation, disease, and even competition with other plants. Diversion of metabolic resources for the synthesis and storage of appreciable canavanine does not place an inordinate burden on the plant. Catabolism of this nonprotein amino acid provides respiratory carbon, generates essential primary metabolites, and ammoniacal nitrogen for the developing plant.     

The application of the intermediate 2-methyl-glyco-[2,1-d]-2-oxazolines for glycoside synthesis

The synthesis of 2-acylamino-2-deoxysugars 1,2-trans-glycosides is described via the oxazolinium salt generated from an O,N-acetylated 1,2-cis-glycosyl halide of 2-amino-2-deoxysugar under the conditions of halide-anion catalysis. This salt was then interacted with alcohol to form the corresponding 1,2-trans-glycoside. A method for removing the generated hydrogen chloride is described. The conditions of this synthesis allow glycosides with acid-labile functional groups to be obtained. Suppression of the anomerisation of 1,2-trans-glycosides was achieved by the introduction of N,N'-dicyclohexyl urea into the reaction medium.     

Synthesis of new sugar amino acid derivatives of D-glucosamine

The synthesis of several new sugar amino acid derivatives of 2-acetamido-2-deoxy-D-glucose, bearing a C-glycosyl functionality as building blocks for the design and synthesis of natural glycoconjugates mimetics, is described. These compounds were prepared from the readily accessible per-benzylated amino C-allyl glucopyranosyl compounds, with TMSOTf/Ac(2)O-mediated selective acetolysis of the 6-O-benzyl group as the key step.     

Synthesis of oligonucleotides containing 2''-deoxy-6-thioguanosine at a predetermined site.

A new approach has been devised for the synthesis of oligonucleotides containing 2'-deoxy-6-thioguanosine [d(s6G)]. The synthesis of oligonucleotides containing d(s6G) requires special protection and deprotection strategies to prevent the thione functionality from undergoing oxidation and hydrolysis. Previous attempted syntheses have neglected to address this problem. By using the cyanoethyl protecting group for the thione and phenoxyacetyl for the exocyclic amino group, it was possible to deprotect oligonucleotides with a mixture of sodium hydroxide and sodium hydrogen sulfide without any significant conversion of d(s6G) to deoxyguanosine. Application of this strategy will allow investigation of the structural as well as biological activity of d(s6G)-containing oligonucleotides.     

Engineering of enzymes using non-natural amino acids

In enzyme engineering, the main targets for enhancing properties are enzyme activity, stereoselective specificity, stability, substrate range, and the development of unique functions. With the advent of genetic code extension technology, non-natural amino acids (nnAAs) are able to be incorporated into proteins in a site-specific or residue-specific manner, which breaks the limit of 20 natural amino acids for protein engineering. Benefitting from this approach, numerous enzymes have been engineered with nnAAs for improved properties or extended functionality. In the present review, we focus on applications and strategies for using nnAAs in enzyme engineering. Notably, approaches to computational modelling of enzymes with nnAAs are also addressed. Finally, we discuss the bottlenecks that currently need to be addressed in order to realise the broader prospects of this genetic code extension technique.     

Synthesis and biological evaluation of constrained analogues of the opioid peptide H-Tyr-D-Ala-Phe-Gly-NH2 using the 4-amino-2-benzazepin-3-one scaffold.

The synthesis of conformationally restricted dipeptidic moieties 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one (Aba)-Gly ([(4S)-amino-3-oxo-1,2,4,5-tetrahydro-1H-2-benzazepin-2-yl]-acetic acid) and 8-hydroxy-4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one (Hba)-D-Ala ([(4S)-amino-8-hydroxy-3-oxo-1,2,4,5-tetrahydro-benzo[c]azepin-2-yl]-propionic acid) was based on a synthetic strategy that uses an oxazolidinone as an N-acyliminium precursor. Introducing these Aba scaffolds into the N-terminal tetrapeptide of dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2)-induced remarkable shifts in affinity and selectivity towards the opioid mu- and delta-receptors. This paper provides the synthesis and biological in vitro and in vivo evaluation of constricted analogues of the N-terminal tetrapeptide H-Tyr-D-Ala-Phe-Gly-NH2, which is the minimal subunit of dermorphin needed for dermorphin-like opiate activity.     

First total synthesis of 1,2-dipalmitoyl-3-(N-palmitoyl-6′-amino-6′-deoxy-α-d-glucosyl)-sn-glycerol—a glycoglycerolipid of a marine alga with a high inhibitor activity against human Myt1-kinase

The first total synthesis of 1,2-dipalmitoyl-3-(N-palmitoyl-6′-amino-6′-deoxy-α-d-glucosyl)-sn-glycerol, a glycoglycerolipid isolated from a marine alga extract, is described. Starting from α-methylglucopyranoside the multistep strategy allows the stereoselective synthesis of the final compound using various protective group procedures as well as derivatization of partial molecule domains. The latter offers the development of lead structures for inhibitors of human Myt1-kinase.