Intramolecular Hydrolysis Research Articles

Autohydrolysis of Diglycine‐Activated Succinic Esters Boosts Cellular Uptake

AbstractRapid cellular uptake of synthetic molecules remains a challenge, and the motif frequently employed to generate prodrugs, succinic ester, unfortunately lowers the efficacy of the desired drugs due to their slow ester hydrolysis and low cell entry. Here we show that succinic ester‐containing diglycine drastically boosts the cellular uptake of supramolecular assemblies or prodrugs. Specifically, autohydrolysis of the diglycine‐activated succinic esters turns the nanofibers of the conjugates of succinic ester and self‐assembling motif into nanoparticles for fast cellular uptake. The autohydrolysis of diglycine‐activated succinic esters and drug conjugates also restores the efficacy of the drugs. 2D nuclear magnetic resonance (NMR) suggests that a “U‐turn” of diglycine favors intramolecular hydrolysis of diglycine‐activated succinic esters to promote autohydrolysis. As an example of rapid autohydrolysis of diglycine‐activated succinic esters for instant cellular uptake, this work illustrates a nonenzymatic bond cleavage approach to develop effective therapeutics for intracellular targeting.

Autohydrolysis of Diglycine-Activated Succinic Esters Boosts Cellular Uptake.

Rapid cellular uptake of synthetic molecules remains a challenge, and the motif frequently employed to generate prodrugs, succinic ester, unfortunately lowers the efficacy of the desired drugs due to their slow ester hydrolysis and low cell entry. Here we show that succinic ester-containing diglycine drastically boosts the cellular uptake of supramolecular assemblies or prodrugs. Specifically, autohydrolysis of the diglycine-activated succinic esters turns the nanofibers of the conjugates of succinic ester and self-assembling motif into nanoparticles for fast cellular uptake. The autohydrolysis of diglycine-activated succinic esters and drug conjugates also restores the efficacy of the drugs. 2D nuclear magnetic resonance (NMR) suggests that a "U-turn" of diglycine favors intramolecular hydrolysis of diglycine-activated succinic esters to promote autohydrolysis. As an example of rapid autohydrolysis of diglycine-activated succinic esters for instant cellular uptake, this work illustrates a nonenzymatic bond cleavage approach to develop effective therapeutics for intracellular targeting.

Histone Deacetylase‐Triggered Self‐Immolative Peptide‐Cytotoxins for Cancer‐Selective Drug Delivery

AbstractPrecise delivery and release of therapeutics in the subcellular targets are critical for tumor‐selective chemotherapy. Self‐immolative structures are sophisticatedly designed to achieve stimuli‐responsive drug delivery. Herein, the facile fabrication of self‐immolative peptide‐camptothecin (CPT) nanoassemblies is reported for cancer‐selective drug delivery by utilizing the dual‐mode peptide targeting design and amine‐catalyzed intramolecular hydrolysis. The dual‐mode peptide targeting design is realized by co‐assembly of tumor targeting and nuclei‐localizing peptide‐CPT prodrugs, rendering the nanoassemblies with efficient cancer cell‐selective capability. When the nanoassemblies enter cancer cell, the overexpressed endonuclear histone deacetylases (HDACs) cleave the acetyl group to generate primary amines, triggers amine‐catalyzed intramolecular hydrolysis, and fast‐release drug in the cell nuclei. The peptide‐CPT prodrugs release up to 68% CPT in 1 h in the presence of HDACs, while no detectable CPT release is observed in the absence of HDACs at the same time. The peptide‐CPT prodrugs selectively kill cancer cells with high HDACs levels. The dual targeting peptide‐CPT nanoassemblies exhibit extended blood circulation, excellent tumor accumulation, and potent antitumor activity by inhibiting tumor progression and metastasis in mice bearing 4T1 aggressive breast tumors. Overall, the HDAC‐triggered self‐immolative strategy is promising for developing cancer‐selective drug delivery systems.

Unimolecular, Bimolecular, and Intramolecular Hydrolysis Mechanisms of 4-Nitrophenyl β-d-Glucopyranoside.

1,2-trans-Glycosides hydrolyze through different mechanisms at different pH values, but systematic studies are lacking. Here, we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect of k(H3O+)/k(D3O+) = 0.65 in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with the heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibit general catalysis with a single proton in flight, a normal solvent isotope effect of kH/kD = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect of k(H2O)/k(D2O) = 1.1, consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in 18O-labeled water and H2O/MeOH mixtures allowed the detection of bimolecular hydrolysis and neighboring group participation, with a minor contribution of nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular concerted mechanism is implicated through an inverse solvent isotope effect of k(HO-)/k(DO-) = 0.5 and a strongly negative entropy of activation (ΔS‡ = -13.6 cal mol-1 K-1). Finally, at high pH, an inverse solvent isotope effect of k(HO-)/k(DO-) = 0.5 indicates that the formation of 1,2-anhydrosugar is the rate-determining step.

Dinuclear neodymium and lanthanum bis(2,6-diisopropylphenyl) phosphate complexes bearing a hydroxide ligand: catalytic activity of the Nd complex in 1,3-diene polymerization.

The reactions of K[(2,6-iPr2C6H3-O)2POO] either with LaCl3(H2O)7 or with Nd(NO3)3(H2O)6 in a 3:1 molar ratio, followed by vacuum drying and recrystallization from alkanes, have led to the formation of diaquapentakis[bis(2,6-diisopropylphenyl) phosphato]-μ-hydroxido-dilanthanum hexane disolvate, [La2(C24H34O4P)5(OH)(H2O)2]·2C6H14, (1)·2(hexane), and tetraaquatetrakis[bis(2,6-diisopropylphenyl) phosphato]-μ-hydroxido-dineodymium bis(2,6-diisopropylphenyl) phosphate heptane disolvate, [Nd2(C24H34O4P)4(OH)(H2O)4]·2C6H14, (2)·2(heptane). The compounds crystalize in the P21/n and P-1 space groups, respectively. The diaryl-substituted organophosphate ligand exhibits three different coordination modes, viz. κ2O,O'-terminal [in (1) and (2)], κO-terminal [in (1)] and μ2-κ1O:κ1O'-bridging [in (1) and (2)]. Binuclear structures (1) and (2) are similar and have the same unique Ln2(μ-OH)(μ-OPO)2 core. The structure of (2) consists of an [Nd2{(2,6-iPr2C6H3-O)2POO}4(OH)(H2O)4]+ cation and a [(2,6-iPr2C6H3-O)2POO]- anion, which are bound via four intermolecular O-H...O hydrogen bonds. The molecular structure of (1) displays two O-H...O hydrogen bonds between OH/H2O ligands and a κ1O-terminal organophosphate ligand, which resembles, to some extent, the `free' [(2,6-iPr2C6H3-O)2POO]- anion in (2). NMR studies have shown that the formation of (1) undoubtedly occurs due to intramolecular hydrolysis during vacuum drying of the aqueous La tris(phosphate) complex. Catalytic experiments have demonstrated that the presence of the coordinated hydroxide anion and water molecules in precatalyst (2) substantially lowered the catalytic activity of the system prepared from (2) in butadiene and isoprene polymerization compared to the catalytic system based on the neodymium tris[bis(2,6-diisopropylphenyl) phosphate] complex, which contains neither OH nor H2O ligands.

Synthesis and Biological Evaluation of Paclitaxel and Camptothecin Prodrugs on the Basis of 2-Nitroimidazole.

Due to the low esterase activity in human plasma, many ester and carbonate prodrugs tested in humans may be less effective than that in preclinical animals. In this letter, PTX and SN-38 were attached to the N-1 position of 2-nitroimidazole via a carbonate linker. Presumably, 2-aminoimidazole may help promote the intramolecular hydrolysis of the carbonate bond. The prodrugs exhibited a considerable stability in buffers at different pH values as well as in human plasma. Furthermore, a rapid reduction was exhibited in the presence of nitroreductase. An in vitro cytotoxicity assay demonstrated that hypoxic conditions could increase the toxicity of prodrugs. Potentially, the compound species may form a new class of promising antitumor agents.

Synthesis and Self-Assembly of Amphiphilic Hybrid Nano Building Blocks via Self-Collapse of Polymer Single Chains

Nano building blocks (NBBs) decorated with well-defined polymer tethers have emerged as a promising type of building blocks for constructing hierarchical materials through programmable self-assembly. We present a general and facile strategy for preparing hybrid NBBs composed of silica-like heads decorated with well-defined polymer tethers by the self-collapse of polymer single chains. Using amphiphilic block copolymers (BCPs) of poly(ethylene oxide)-block-[poly(methyl methacrylate)-co-poly(3-(trimethoxysilyl)propyl methacrylate)] (PEO-b-P(MMA-co-TMSPMA)), the intramolecular hydrolysis and polycondensation of silane moieties led to the formation of hybrid NBBs with silica-like heads and PEO tethers. The formation of hybrid NBBs was carefully characterized by gel permeation chromatography, nuclear magnetic resonance spectroscopy, transmission electron microscopy, and static/dynamic light scattering. In a mixed solvent of THF/water, amphiphilic NBBs could assemble into spherical micelles, vesicles, and large...

Intramolecular acyl migration and enzymatic hydrolysis of 2-O-α-d-glucopyranosyl-6-O-(2-pentylheptanoyl)-l-ascorbic acid

2-O-α-D-Glucopyranosyl-6-O-(2-pentylheptanoyl)-L-ascorbic acid (6-bDode-AA-2G) underwent an intramolecular acyl migration to yield approximately 12% of 2-O-α-D-glucopyranosyl-5-O-(2-pentylheptanoyl)-L-ascorbic acid (5-bDode-AA-2G) in neutral solutions for 3 days. In small intestine homogenate from guinea pigs for 12h, 6-bDode-AA-2G, which hardly underwent acyl migration to give 5-bDode-AA-2G, was predominantly hydrolyzed with α-glucosidase and then with esterase to ascorbic acid.

SOLVENT AND SUBSTITUENT EFFECTS ON THE INTRAMOLECULAR AMIDE HYDROLYSIS OF N-METHYLMALEAMIC ACID

Intramolecular amide hydrolysis of N-methylmaleamic acid is revisited at the B3LYP/6-311G(2df, p)//B3LYP/6-31G(d, p) + ZVPE level, including solvent effects at the CPCM-B3LYP/6-311G(2df, p)//Onsager-B3LYP/6-31G(d, p) + ZPVE level. The concerted reaction mechanism is energetically favorable over stepwise reaction mechanisms in both the gas phase and solution. The calculated reaction barriers are significantly lower in solution than in the gas phase. In addition, it is concluded that the substituents of the four N-methylmaleamic acid derivatives considered herein have a significant effect on the gas-phase reaction barriers but a smaller, or little, effect on the barriers in solution.

Kinetics and Mechanism of the Hydrolytic Degradation of Indinavir: Intramolecular Catalysis

The pH-rate profile of first-order rate constants for the lactonization of Indinavir in aqueous solutions with ionic strength I = 1 (KCl) at 40 degrees C is reported. The lactonization reaction is a subject of strong buffer catalysis with a nonlinear dependence of the first-order rate constants on the concentration of the buffer. The pH-rate profile is more complex than the pH-rate profiles for the hydrolysis of simple peptides and for the intramolecular OH-catalyzed hydrolysis of gamma-hydroxyamides. This complexity appears unique to Indinavir and is a result of the cis-aminoindanol leaving group. The mechanistic pathways for the lactonization are discussed. The buffer catalysis data are consistent with kinetic general acid catalysis. The second-order rate constant for the specific-acid catalyzed hydrolysis of Indinavir at 40 degrees C (k(H) = 2.2 x 10(-4) M(-1) min(-1)) is similar to that for a simple peptide indicating similar interactions in the rate limiting transition state for both reactions.

The Mechanism of Autocatalytic Activation of Plant-type L-Asparaginases

Plant l-asparaginases and their bacterial homologs, such as EcAIII found in Escherichia coli, form a subgroup of the N-terminal nucleophile (Ntn)-hydrolase family. In common with all Ntn-hydrolases, they are expressed as inactive precursors that undergo activation in an autocatalytic manner. The maturation process involves intramolecular hydrolysis of a single peptide bond, leading to the formation of two subunits (alpha and beta) folded as one structural domain, with the nucleophilic Thr residue located at the freed N terminus of subunit beta. The mechanism of the autocleavage reaction remains obscure. We have determined the crystal structure of an active site mutant of EcAIII, with the catalytic Thr residue substituted by Ala (T179A). The modification has led to a correctly folded but unprocessed molecule, revealing the geometry and molecular environment of the scissile peptide bond. The autocatalytic reaction is analyzed from the point of view of the Thr(179) side chain rotation, identification of a potential general base residue, and the architecture of the oxyanion hole.

Reaction of 2-chloro-6-hydroxy-5,5-dimethyl-5,6-dihydro-1H-pyridine-3,4,4-tricarbonitriles with methanol

We previously reported [1] that tetracyanoethylene reacts with aldehydes in the presence of excess hydrohalic acid to give 5,5-dialkyl-2-halo-6-hydroxy-5,6-dihydro-1H-pyridine-3,4,4-tricarbonitriles like I. Molecules of the products contain a hemiaminal moiety and spatially close axial hydroxy and cyano groups. We believe that such structure should favor mild intramolecular hydrolysis of the cyano group by nucleophiles (by analogy with structurally related compounds [2, 3]), as well as replacement of the hydroxy group.

Reduction of activated carbonyl groups by alkyl phosphines: formation of α-hydroxy esters and ketones

Reduction of activated carbonyl groups such as alpha-keto esters, benzils, 1,2-cyclohexanedione, and alpha-ketophosphonates by alkyl phosphines afforded the corresponding alpha-hydroxy esters or ketones in good to excellent yields in THF at room temperature. The mechanism of the proton transfer and intramolecular hydrolysis has been studied on the basis of deuterium and 18O labeling experiments.

Direct monitoring of enzymatic glucan hydrolysis on a 27-MHz quartz-crystal microbalance.

By using a highly sensitive 27-MHz glucan-immobilized quartz-crystal microbalance, we could follow kinetically all processes (enzyme binding and release, kon and koff, and intramolecular hydrolysis rates, kcat) of glucan hydrolysis by glucoamylase by detecting directly the formation and decay of the enzyme-substrate complex as mass changes.

Investigation of IrO2/SnO2thin film evolution by thermoanalytical and spectroscopic methods

The formation mechanism of thermally prepared IrO2/SnO2 thin films has been investigated under in situ conditions by thermogravimetry combined with mass spectrometry (TG-MS) and infrared emission spectroscopy (IRES). Mixtures of varying composition of the precursor salts (SnCl2·2H2O dissolved in ethanol and IrCl3·3H2O dissolved in isopropanol) were prepared onto titanium metal supports. Then the solvent was evaporated and the gel-like films were heated in an atmosphere containing 20% O2 and 80% Ar to 600°C. The thermogravimetric curves showed that the evolution of the oxide phases take place in several decomposition stages and the final mixed oxide film is formed between 490 and 550°C, depending on the noble metal content. Mass spectrometric ion intensity curves revealed that below 200°C crystallization water, residual solvent, and hydrogen-chloride (formed as a result of an intramolecular hydrolysis) are liberated. The decomposition of surface species (surface carbonates, carbonyls and carboxylates) formed via the interaction of the residual solvent with the precursor salts takes place up to 450°C as evidenced by emission Fourier transform infrared spectrometry.

Studies on Synthesis and Intramolecular Catalyzed Hydrolysis of Thiophosphoramidate Derivatives of Nucleoside

AbstractNovel thiophosphoramidate derivatives of nucleoside analogue as membrane‐soluble prodrugs of the bioactive free nucleotides have been prepared by thiophosphorylation reaction. 2′,3′‐O, O′‐Isopropylidene uridine‐5′‐yl N‐thiophosphoryl serine and threonine methyl esters underwent the intramolecular catalyzed hydrolysis reaction.

The hydrolysis of 4-nitrophenylphosphate promoted by [(N) 4Co(OH/H)(OH/H)] +/2+/3+ species ((N) 4=abap, tren); use of 31P NMR to uncover mechanistic complexity

Rate studies of the reaction of [(N) 4Co(OH/H)(OH/H)] +/2+/3+ species ((N) 4=abap ( 5- and 6-isomers), tren) with sodium 4-nitrophenylphosphate (Na 2NPP) in aqueous solution (15, 25 or 40 °C, I=0.50 M, NaClO 4) have been carried out using UV–Vis spectrophotometry and 31P NMR spectroscopy. Under weakly acidic conditions (pH ca. 5, excess Co(III) reagent) anation is faster than hydrolysis, and the first formed [(N) 4Co(OH 2)(NPP/H)] 1+/2+ complex reacts largely with [(N) 4Co(OH 2)OH] 2+ to produce a host of dimeric Co(III) products plus 4-nitrophenol. Under less acidic conditions (pH 6) rates of anation approach those of hydrolysis, and 4-nitrophenol production increasingly occurs via the intramolecular reaction of [(N) 4Co(OH)NPP]. For [Co] T=0.040 M (abap system) this pathway account for 4% of the observed products at pH 5, 47% at pH 7 and 96% at pH 9. Rate laws for the processes are described. Under no pH condition does the pseudo first-order rate constant (or apparent pseudo first-order rate constant) determined from spectrophotometry directly relate to that for intramolecular hydrolysis in [(N) 4Co(OH)NPP]. The X-ray crystal structure of 6-[(abap)Co(O 2PO 2)]·6H 2O is reported, and confirms the presence of chelated phosphate in this species.

Reactivity studies of ethyl(Z)-N-(2-amino-1,2-dicyanovinyl) formimidate with carbonyl compounds in the presence of base

The reaction of ethyl(Z)-N-(2-amino-1,2-dicyanovinyl)formimidate 6 with carbonyl compounds in the presence of triethyl amine occurs with formation of the Schiff s base and intramolecular hydrolysis of the adjacent cyano group to give the alkylideneamino derivatives 8a-f. When the α-carbon of the ketone has at least one proton, the prolonged contact of 8a-f with triethylamine causes intramolecular cyclization between this carbon and the imidate carbon atom to form a seven membered ring. This is followed by cyclization of the cyano and amido groups, leading to the pyrrolo[4,3-b][1,4]diazepines 9. If a strong base is used the first ring to be formed is the pyrrole ring as evidenced in the reaction of 8a with 1,8-diazabicyclo[5.4.0]undec-7-ene leading to 14. The subsequent addition of methyl amine to the reaction mixture, caused cleavage of the alkylideneamino unit and formation of the amidine function from the imi date (15). The addition of acid to the imidates 8a and 8f led to the diazepine compounds 10a and 10f respectively. A suspension of compound 8e in ethanol and triethylamine evolved to a pyrazinone structure 12 under kinetic conditions (4 hours, room temperature) and to the pyrrolo[4,3-b][1,4]diazepine 9e under thermodynamic conditions (48 hours, room temperature).

Novel Syntheses of 5-Acetyl-2,3-dihydro-1,4-thiazine, a Very Intense Roasty, Popcornlike Odorant

Two new synthetic pathways toward the new Maillard flavor compound 5-acetyl-2,3-dihydro-1,4-thiazine are disclosed. 1-Bromo-3,3-dimethoxy-2-butanone and N-protected 2-mercaptoethylamine are the key components in both synthetic routes. The first approach involves a one-step synthesis via nucleophilic substitution, followed by cyclization and hydrolysis. The second route entails a nucleophilic substitution, followed by TFA-deprotection of the primary amino function, which led to a spontaneous intramolecular transimination and hydrolysis of the acetal moiety to afford the desired flavor compound in very good yield. Keywords: Popcorn flavor; roasty flavor; 5-acetyl-2,3-dihydro-1,4-thiazine; Maillard; flavor compound

Development and applications of a chemical method for sequential analysis of reducing oligosaccharides

A new method based on the chemical reaction has been devised for the sequential analysis of reducing oligosaccharides using 8-amino-2-naphthalenesulfonic acid (ANS), a fluorescent precolumn derivatization reagent for reducing saccharides. The procedure established includes 1) the derivatization of a reducing oligosaccharide to produce a Schiff base, 2) the reduction of the base with sodium cyanoborohydride (NaBH(3)CN), 3) the methoxycarbonylation of the resultant secondary amino group, 4) the cleavage of the glycoside bond next to the reducing end, based on the intramolecular acid hydrolysis by the action of a sulfonic acid group of the ANS derivative, 5) the identification of the liberated reducing end by high-per-formance liquid chromatography (HPLC), and finally 6) the recovery of the resultant oligosaccharide fragment from the cleavage reaction mixture. The extensive examination of the conditions for the sequential analysis of reducing oligosaccharides resulted in the procedure of simplicity, high selectivity and high recovery. This procedure was found to be useful for the sequential analysis of di-, tri- and tetrasaccharides.