Anti and syn glycolate aldol reactions with a readily displaced thiol auxiliary

The TBDPS protected glycolate derivative of thiol auxiliary 1 is readily prepared (3 steps, 80% overall yield) and has been shown to give excellent anti:syn selectivity (>97:3) and high facial selectivity (88:12 to 97:3) in glycolate aldol reactions with a range of aldehydes (75-87% isolated yield major diastereomer). In contrast, its benzyl protected counterpart displays more versatility with respect to the generation of either anti or syn glycolate aldol adducts, but only modest facial selectivity. The thiol auxiliary has been shown to be readily displaced under mild conditions to give alcohol and ester derivatives of the glycolate aldol adducts.     

Subtiligase as a hydrothiolase for the synthesis of peptide thioacids

Subtiligase catalyzes the hydrolysis or the aminolysis of a peptide glycolate ester substrate via an acyl-enzyme thioester intermediate. We show that this intermediate can be intercepted by a hydrosulfide ion to generate a peptide thioacid as the hydrothiolysis product. Also shown is the use of the so-prepared peptide thioacids in mini thiol capture ligation.     

Constant-rate titrations in studies of chemical kinetics: Part 5. Thermometric Titrations of Ethyl Glycolate with Sodium Hydroxide,and Simultaneous Determination of Glycolic Acid and Evaluation of the Rate Constant for Alkaline Hydrolysis

The data obtained in a constant-rate thermometric titration of an aqueous solution of ethyl glycolate with standard sodium hydroxide can be used to evaluate the rate constant and change of enthalpy for the reaction and also to determine the percentage of glycolic acid present as an impurity in the ester.     

Stereoselective synthesis of (+)-blastmycinone

(+)-Blastmycinone has been synthesized based on diastereoselective synthesis of (2R,3S)-2-hydroxy-3-(1-propenyl)heptanoic acid by the ester enolate Claisen rearrangement of (R)-(E)-1-methyl-2-heptenyl glycolate and stereoselective reduction of α-hydroxy ketone with Zn(BH₄)₂.     

Studies directed toward the synthesis of the massileunicellins

An approach to the massileunicellins is described that employs a cycloaldol reaction to assemble the isobenzofuran bicyclic core. A stereoselective rearrangement-epoxidation-oxidation cascade and a chelation controlled addition to a hindered acyl furan are used to install the C3, C11, C12, and C13 oxygens. The synthesis establishes eight of the nine stereocenters present in the isobenzofuran core of the massileunicellins.     

Stereoselective construction of an anti-β-alkoxy ether by Ireland-Claisen rearrangement for medium-ring ether synthesis

The asymmetric synthesis of an acyclic anti-β-alkoxy ether was achieved by the Ireland-Claisen rearrangement of Z-3-alkoxy-2-propenyl glycolate ester, prepared from Garner’s aldehyde, a glycolic acid derivative, and ethynyl N,N-diisopropylcarbamate. The resulting acyclic ether was facilely converted to seven- and eight-membered cyclic ethers via processes involving ring-closing olefin metatheses.     

Biodegradable Poly(ester hydrazide)s via Enzymatic Polymerization

Summary: The reaction of hydrazine with ethyl glycolate results in 1,2‐bisglycoylhydrazine, a monomer that was used for the lipase‐catalyzed synthesis of biodegradable poly(ester hydrazide)s. The polymers derived from the hydrazide‐containing monomer and vinyl‐activated adipic, suberic, and sebacic acid, respectively, showed low melting temperatures of 136 to 141 °C and are thermally stable up to 300 °C. The aliphatic poly(ester hydrazide)s (PEHs) are highly crystalline, as proven by polarization microscopy and atomic force microscopy. Further, the PEHs represent the first described biodegradable poly(hydrazide)s. They degrade in the presence of lipase at 37 °C within a few weeks.

Synthetic route to poly(ester hydrazide)s.     

Asymmetric phase-transfer catalyzed glycolate alkylation, investigation of the scope, and application to the synthesis of (-)-ragaglitazar

[Reaction: see text]. Asymmetric glycolate alkylation using a protected acetophenone surrogate under solid-liquid phase-transfer conditions is a new approach to the synthesis of 2-hydroxy esters and acids. Diphenylmethyloxy-2,5-dimethoxyacetophenone 1 with a trifluorobenzyl cinchonidinium bromide catalyst 9 (10 mol %) and cesium hydroxide provided S-alkylation products 2 at -35 degrees C in high yield (80-99%) and with excellent enantioselectivities using a wide range of electrophiles (80-90% ee). Alkylated products were elaborated to useful alpha-hydroxy intermediates 3 using bis-TMS peroxide Baeyer-Villiger conditions and selective transesterification reactions. The ester products have been enantioenriched by simple recrystallization from ether to give a single isomer (99% ee). A tight ion-pair model is proposed for the observed S-stereoinduction that includes van der Waals contacts between the extended enolate and the isoquinoline of the catalyst. To demonstrate the utility of the new methodology, the anti-diabetes drug (-)-ragaglitazar 24 was synthesized in six steps from a key 2-alkoxy-3-p-phenoxypropionic acid 26 that was made using PTC glycolate alkylation.     

Asymmetric glycolate aldol reactions using cinchonium phase-transfer catalysts

Cinchona phase-transfer catalysts (PTC) were developed for glycolate aldol reactions to give differentially protected 1,2-diol products. Silyl enol ether 9 reacted to generate benzhydryl-protected products. O-Allyl trifluorobenzyl cinchonium hydrofluoride CN-4 (20 mol %) catalyzed the addition of 9 to benzaldehyde to give 8 as a single syn-product in 76% yield and 80% ee. Recrystallization enriched the product to 95% ee, and a Baeyer-Villiger reaction transformed the product into useful ester intermediates. [reaction: see text]     

高异三尖杉酯碱的合成及其立体异构体的分离鉴定

2-氧代-6-甲基庚酰基三尖杉碱(3)与0-(1-甲氧基异丙基)羟基乙酸甲酯(4)在强碱性试剂二异丙胺锂(LDA)存在下,起亲核加成反应,反应中间体5在室温用酸性丙酮水解,得到一种新的三尖杉酯类生物碱一一高异三尖杉酯碱(6c)及其立体异构体(6a、6b、6d)的混合物,产率56%、通过制备薄层层析分得这四个立体异构体,它们的1H NMR和异三尖杉酯碱及其立体异构体的1H NMR类似,推定了它们的绝对构型。初步药理试验表明,高异三尖杉酯碱及其立体异构体的混合物对白血病L7712的DNA合成有明显的抑制作用。     

Rhodium-Catalyzed Asymmetric Arylation-Induced Glycolate Aldol Additions of Silyl Glyoxylates

(Diene)Rh(I) complexes catalyze the stereoselective three-component coupling of silyl glyoxylates, arylboronic acids, and aldehydes to give glycolate aldol products. The participation of Rh-alkoxides in the requisite Brook rearrangement was established through two component Rh-catalyzed couplings of silyl glyoxylates with ArB(OH)₂ to give silyl-protected mandelate derivatives. The intermediacy of a chiral Rh-enolate was inferred through enantioselective protonation using a chiral Rh-catalyst. Diastereoselective three-component couplings with aldehydes as terminating electrophiles to give racemic products were best achieved with a bulky aryl ester on the silyl glyoxylate reagent. Optimal enantioselective couplings were carried out with the tert-butyl ester variant using an anisole-derived enantiopure tricyclo[3.2.2.0^2,4]nonadiene ligand.     

Phase-transfer-catalyzed asymmetric glycolate alkylation

[reaction: see text] Asymmetric surrogate glycolate alkylation has been performed under phase-transfer conditions. Diphenylmethyloxy-2,5-dimethoxyacetophenone with trifluorobenzyl cinchonidinium catalyst and cesium hydroxide provided alkylation products at -35 degrees C in high yield (80-99%) and with excellent enantioselectivities (90:10 to 95:5). Useful alpha-hydroxy products were obtained using bis-TMS peroxide Baeyer-Villiger conditions and selective transesterification. The intermediate aryl ester can be obtained with >99% ee after a single recrystallization. A tight ion-pair model for the observed (S)-stereoinduction is proposed.     

Derivatization and high-performance liquid chromatographic determination of urinary glycolic acid

A high-performance liquid chromatographic method for the determination of urinary glycolic acid is proposed, based on pre-column derivatization with phenylhydrazine coupled with the enzymatic oxidation of glycolate to glyoxylate. The phenylhydrazone formed is separated by liquid chromatography and detected at 324 nm. The minimum detectable concentration of glycolate was 10.0 mumol/l. The recovery of glycolate added to urine averaged 96.1%. The day-to-day coefficients of variation calculated by analysis of two urine samples with normal and high glycolate contents were 4.6 and 7.5%, respectively. Results of analyses of urine samples from healthy persons, idiopathic calcium stone formers and Type I primary hyperoxaluria patients are reported.     

Hexagonal‐Shaped Tin Glycolate Particles: A Preliminary Study of Their Suitability as Li‐Ion Insertion Electrodes

Tin glycolate particles were prepared by a simple, one‐step, polyol‐mediated synthesis in air in which tin oxalate precursor was added to ethylene glycol and heated at reflux. Hexagonal‐shaped, micron‐sized tin glycolate particles were formed when the solution had cooled. A series of tin oxides was produced by calcination of the synthesized tin glycolate at 600–800 °C. It was revealed that the micron‐sized, hexagonal‐shaped tin glycolate now consisted of nanosized tin‐based particles (80–120 nm), encapsulated within a tin glycolate shell. XRD, TGA, and FT‐IR measurements were conducted to account for the three‐dimensional growth of the tin glycolate particles. When applied as an anode material for Li‐ion batteries, the synthesized tin glycolate particles showed good electrochemical reactivity in Li‐ion insertion/deinsertion, retaining a specific capacity of 416 mAh g^?1 beyond 50 cycles. This performance was significantly better than those of all the other tin oxides nanoparticles (<160 mAh g^?1) obtained after heat treatment in air. We strongly believe that the buffering of the volume expansion by the glycolate upon Li–Sn alloying is the main factor for the improved cycling of the electrode.     

Preparation of functionalized, conformationally constrained DTPA analogues from L- or D-serine and trans-4-hydroxy-L-proline. Hydroxymethyl substituents on the central acetic acid and on the backbone

The enantio- and diastereospecific syntheses of conformationally constrained diethylenetriaminepentaacetic acid (DTPA) analogues that are functionalized with a hydroxymethyl linker substituent on the central acetic acid or on the backbone are described. Key synthetic steps include (i) displacement of the 4-hydroxyl group of N-BOC-trans-4-hydroxy-L-proline benzyl ester, via activation as the triflate, with suitable amines derived from L- or D-serine, (ii) the low-temperature alkylation of diethylenetriamines with the triflate of benzyl glycolate, thereby minimizing competitive lactamization, to give DTPA pentabenzyl esters, and (iii) deprotection to afford the corresponding DTPA analogues under very mild hydrogenolysis conditions.     

Enolate generation under hydrogenation conditions: catalytic aldol cycloreduction of keto-enones

[reaction: see text] Formal heterolytic activation of elemental hydrogen under Rh catalysis enables the reductive generation of enolates from enones under hydrogenation conditions. Enolates generated in this fashion participate in catalytic C-C bond formation via carbonyl addition to aldehyde and, as demonstrated in this account, ketone partners. Notably, the use of appendant dione partners enables diastereoselective formation of cycloaldol products possessing 3-stereogenic centers, including 2-contiguous quaternary centers.     

Concise stereoselective synthesis of cis-3-alkoxy-2-carbomethoxy medium-ring oxacycles from (R)-3-(3-butenyl)-4-propynoyloxazolidin-2-one

A concise process for the stereoselective synthesis of chiral cis-3-alkoxy-2-carbomethoxy medium-ring oxacycles from (R)-3-(3-butenyl)-4-propynoyloxazolidin-2-one (1) was developed. The process includes five major steps: (i) hetero-Michael reaction between an alcohol and 1, (ii) stereoselective reduction of the resulting ketone, featuring stereochemical assistance of the neighboring oxazolidin-2-one group, (iii) esterification with an alkoxy acetic acid, (iv) chirality-transferring Ireland-Claisen rearrangement of the resulting 3-alkoxyallyl glycolate ester to provide a syn-2,3-dialkoxy carboxylate ester, and (v) relay ring-closing olefin metathesis to form a medium-ring ether along with the simultaneous removal of the oxazolidin-2-one moiety.     

Binary vapor–liquid equilibrium of methyl glycolate and ethylene glycol

Vapor pressure of methyl glycolate and the binary isothermal vapor–liquid equilibrium of ethylene glycol and methyl glycolate were measured by using static method. The experimental data was correlated with the Wilson and NRTL activity coefficient models. Good agreement between the experimental data and model is achieved.     

Effects of temperature and concentration factors on the conformational state and reactivity of potassium poly(oxyethylene glycolate)

With the use of pulsed magnetic-field gradient NMR, self-diffusion coefficients of potassium poly(oxyethylene glycolate) macromolecules and solvent molecules (acetone) and the variation in the dimensions of supramolecular structures of potassium poly(oxyethylene glycolate) with temperature and its concentration in acetone are measured. It is discovered that the temperature dependences of change in the rate constants of reactions that proceed during the interaction of potassium poly(oxyethylene glycolate) with 2,4-toluylene diisocyanate do not fit Arrhenius coordinates.     

The stability of some lanthanide complexes with methylethyl glycolate and with methylpropyl glycolate

The 4 successive stability constants have been determined for the methyIethyl glycolate and methylpropyl glycolate complexes of some lanthanide elements by potentiometric titration For all the metal ions, except lanthanum, the average ligand number exceeds a value of 3 indicating the formation of uninegative tetra-ligand complexes, ML₄^-, The stability constants are close to the values of the corresponding α-hydroxyisobutyrate complex systems