A Stereoselective Total Synthesis of Xyolide,a Natural Bioactive Nonenolide

A stereoselective total synthesis of xyolide, a naturally occurring bioactive nonenolide, has been accomplished. The acid fragment of the molecule has been prepared from D ‐mannitol and the alcohol fragment from (2Z)‐but‐2‐ene‐1,4‐diol. The synthesis involves the coupling of these two fragments using the Yamaguchi esterification protocol, followed by intramolecular ring‐closing methathesis. The diastereoisomeric alcohol fragment has also been utilized in this synthesis by employing the Mitsunobu esterification.     

Separation of iron(III) and gold(III) by paper chromatography using mixed solvents containing diisopropyl ether

The separation of iron(III) and gold(III) by partition paper chromatography has been investigated employing a mixture of diisopropyl ether (IPE) and n-alcohol saturated with hydrochloric acid (initial acid concentration 5.0 M) as solvent. Methyl, ethyl, n-propyl, n-butyl, and n-pentyl alcohols were used as components of the solvent. The content of n-alcohol in the initial organic phase was varied. It was found that the R_f values for both of the metals increased with an increase in the carbon-to-oxygen ratio in the alcohol (except in the case or iron(III) and n-pentyl alcohol), and with an increase in the alcohol content in the initial organic phase (except in the case of iron(III) and n-propyl alcohol). The best separation results were obtained by using the systems: hydrochloric acid (5.0 M)-IPE-n-propyl alcohol (50:35:15) gDR_f = 0.56, hydrochloric acid (5.0 M)-IPE-ethyl alcohol (50:15:35) ΔR_f = 0.51, and hydrochloric acid (5.0 M)-IPE-n-pentyl alcohol (50:35:15) ΔR_f = 0.37.     

“In situ”13C NMR study of ethyl alcohol interaction with sulfuric acid

“In situ” NMR study of ethyl alcohol interaction with sulfuric acid of various concentrations confirmed that in accordance with chemical experience the main reaction product in an excess of concentrated acid is the mono-ethyl sulfate. Only traces of diethyl sulfate are formed in a large excess of 95% acid. In addition, ethyloxonium ions and protonated esters, which rapidly exchange protons with solvating water molecules, are detected as the reaction intermediates. The¹³C chemical shifts of methylene fragments in protonated esters and ethyl oxonium ions are more than 10 ppm higher than in neutral molecules. The study of reaction products at different sulfuric acid concentrations indicated that similarly to dissociation of concentrated sulfuric acid, hydrolysis of mono-ethyl sulfate requires at least two water molecules. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

Synthesis and Self‐Assembly of Bolaamphiphiles Based on β‐Amino Acids or an Alcohol

The synthesis of bolaamphiphiles from unusual β‐amino acids or an alcohol and C₁₂ or C₂₀ spacers is described. Unusual β‐amino acids such as a sugar amino acid, an AZT‐derived amino acid, a norbornene amino acid, and an AZT‐derived amino alcohol were coupled with spacers under standard conditions to get the novel bolaamphiphiles 5 – 8 (Scheme 1), 12 and 13 (Scheme 2), and 17 and 20 (Scheme 3). Some of these compounds, on precipitation from MeOH/H₂O, self‐assembled into organized molecular structures.     

Electron impact induced intramolecular hydrogen transfer reactions in polymethylene glycol di-p-toluenesulfonates

The mechanisms of formation of the ionized acid and the protonated acid fragments in the electron impact induced fragmentation of the title compounds were investigated. The well known mechanisms of hydrogen transfer through mono- and bicyclic transition states that occur in the molecular ions of carboxylic esters are not the main pathways giving rise to these fragments. The major component of the m/z 172 peak corresponding formally to ionized p-toluenesulfonic acid in fact has a different structure; its formation involves a complex mechanism including a double hydrogen transfer reaction.     

Notes on selectivity aspects in sorbic acid and sorbic alcohol hydrogenation

Sorbic acid and sorbic alcohol hydrogenations to the cis-hex-3-enoic acid or cis-hex-3-en-1-ol were carried out at the same conditions in three different systems—homogeneous, two-phase and heterogeneous. The complex [Cp*Ru(sorbic acid)]CF₃SO₃ was used as a catalyst. Selectivity and reactivity of both the compounds varied significantly. Using sorbic acid as a hydrogenation substrate by-products were the other izomers of hexenoic acid and hexanoic acid, with sorbic alcohol as a hydrogenation substrate by-products were aldehydes and hemiacetals.     

Synthesis of optically active polynucleotide analogs with poly(vinyl alcohol)s as backbones and adenine and 5-bromouracil derivatives as pendants

The optically active polynucleotide analogs were prepared by grafting nucleic acid base derivatives onto poly(vinyl alcohol). The (R)-ethyl 2-(5-bromouracil-1-yl)propanoate was obtained either by reaction of 5-bromouracil sodium salt with (S)-ethyl 2-[(methylsulfonyl)oxy]propanoate or reaction of 5-bromouracil with (S)-ethyl lactate in the presence of triphenyl phosphine and diethyl azodicarboxylate. Subsequent hydrolysis of the ester is aqueous acid provided the optically pure (R)-bromouracilypropanoic acid. The monomer model compounds were prepared by an esterification reaction of the pendant groups with 3-pentyl alcohol in the presence of dicyclohexylcarbodiimide and a catalytic amount of 4-pyrrolidinopyridine. Poly(vinyl alcohol) underwent reaction with the (R)-bromouracilylpropanoic acid or the (R)-adeninylpropanoic acid in the presence of dicyclohexylcarbodiimide and a catalytic amount of 4-pyrrolidinopyridine. The resulting polymers were optically active and percents grafting were almost quantitative.     

Simultaneous determination of six free fatty acids in alcohol extract of <Emphasis Type="Italic">P. japonicus</Emphasis> C. A. Mey. van <Emphasis Type="Italic">major</Emphasis> (Burk.) C. Y. Wu et K. M. Feng by gas chromatography-mass spectrometry

P. japonicus C. A. Mey. var. major (Burk.) C. Y. Wu et K. M. Feng is an important medicinal plant and has special beneficial effects on human health. Six types of free fatty acids (FFAs) were identified and quantified in the alcohol extract of P. japonicus C. A. Mey. var. major with a GC-MS method, including two fatty acids essential to the human body. All the six FFAs identified in alcohol extract were quantified using nonadecanoic acid as an internal standard. The results showed that the alcohol extract was abundant in four types of FFAs, unsaturated FFAs amounted to 47.04% of the total FFA content, and there were no trans FFAs. Palmitic acid (38.82%, 4.74 ± 0.09 mg/g) was the predominant fatty acid, followed by linoleic acid (27.92%, 2.31 ± 0.07 mg/g), stearic acid (14.14%, 1.54 ± 0.04 mg/g) and oleic acid (11.04%, 1.02 ± 0.03 mg/g).     

Photochemical substitution reactions of 4-Pyridinecarbonitrile with aliphatic alcohols in neutral and acidified medium

Chemical evidence is given that the title photo-reactions proceed via hydrogen abstraction by the photo-excited base from the alcohol in neutral medium and via electron-transfer process between the photo-excited base and the alcohol in hydrochloric acid acidified medium.     

C-ALKYLATION OF MELDRUM'S ACID USING TRIPHENYL PHOSPHINE AND N-BROMOSUCCINIMIDE

A simple and efficient method for the C-alkylation of Meldrum's acid by alcohol using triphenyl phosphine and N-bromosuccinimide is described. Primary alcohols yielded bis-alkylated Meldrum's acid whereas secondary alcohols yielded mono-alkylated Meldrum's acid.     

DPPH (= 2,2‐Diphenyl‐1‐picrylhydrazyl = 2,2‐Diphenyl‐1‐(2,4,6‐trinitrophenyl)hydrazyl) Radical‐Scavenging Reaction of Protocatechuic Acid Esters (= 3,4‐Dihydroxybenzoates) in Alcohols: Formation of Bis‐alcohol Adduct

Protocatechuic acid esters (= 3,4‐dihydroxybenzoates) scavenge ca. 5 equiv. of radical in alcoholic solvents, whereas they consume only 2 equiv. of radical in nonalcoholic solvents. While the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents as compared to that in nonalcoholic solvents is due to a nucleophilic addition of an alcohol molecule at C(2) of an intermediate o‐quinone structure, thus regenerating a catechol (= benzene‐1,2‐diol) structure, it is still unclear why protocatechuic acid esters scavenge more than 4 equiv. of radical (C(2) refers to the protocatechuic acid numbering). Therefore, to elucidate the oxidation mechanism beyond the formation of the C(2) alcohol adduct, 3,4‐dihydroxy‐2‐methoxybenzoic acid methyl ester ( 4 ), the C(2) MeOH adduct, which is an oxidation product of methyl protocatechuate ( 1 ) in MeOH, was oxidized by the DPPH radical (= 2,2‐diphenyl‐1‐picrylhydrazyl) or o‐chloranil (= 3,4,5,6‐tetrachlorocyclohexa‐3,5‐diene‐1,2‐dione) in CD₃OD/(D₆)acetone 3 : 1). The oxidation mixtures were directly analyzed by NMR. Oxidation with both the DPPH radical and o‐chloranil produced a C(2),C(6) bis‐methanol adduct ( 7 ), which could scavenge additional 2 equiv. of radical. Calculations of LUMO electron densities of o‐quinones corroborated the regioselective nucleophilic addition of alcohol molecules with o‐quinones. Our results strongly suggest that the regeneration of a catechol structure via a nucleophilic addition of an alcohol molecule with a o‐quinone is a key reaction for the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents.     

Sulfamic acid as a cost-effective and recyclable solid acid catalyst for Friedel–Crafts alkylation of indole with α,β-unsaturated carbonyl compound and benzyl alcohol

Sulfamic acid was proved to be a cost-effective and recyclable catalyst for Friedel-Crafts type reaction of indole withα,β-unsaturated carbonyl compound and benzyl alcohol.Various indoles,α,β-unsaturated carbonyl compounds and a benzyl alcohol were successfully used in this type of reaction,and the corresponding products were obtained in good to excellent yields.     

Total syntheses and absolute stereochemistry of decarestrictines C1 and C2

The total syntheses of decarestrictines C₁ and C₂ have been described. The synthetic strategy involves a practical and flexible approach using esterification and ring-closing metathesis to unite the acid and alcohol fragments. The acid fragments are enantiomers of each other and have been prepared from l-(−)-malic acid via similar transformations; in Sharpless asymmetric epoxidation, (+)-DET has been used for decarestrictine C₁ and (−)-DET for decarestrictine C₂. The alcohol fragment is identical for both decarestrictines C₁ and C₂ and has been accessed from d-(+)-mannitol. Comparison of the ¹H and ¹³C NMR data combined with the computational studies predicts the presence of two conformations without and with hydrogen bonding (conformational isomers I and II for decarestrictine C₁), respectively. The ¹H and ¹³C NMR data for decarestrictine C₂ completely agreed with the analytical data reported by Kibayashi et al.     

Systematic approach to the chemical synthesis of arabidopyrones,the unique α-pyrones of Arabidopsis metabolites

Abstract

Total synthesis of two arabidopyrones, iso-arabidopyl alcohol (1) and iso-arabidopic acid (2) isolated from Arabidopsis thaliana was achieved for the first time using Claisen condensation and Wittig reaction as the key steps. In addition, arabidopic acid (4) was synthesized from the methyl ester of arabidopyl alcohol (3). Thus, chemical synthesis of the unique natural α-pyrones 1–4 was accomplished with a short synthetic route by a systematic approach from readily available substances.     

Kinetics of esterification of the levulinic acid with n-hexanol,n-octanol,and n-decanol in the presence of dodecatungstophosphoric acid as a catalyst

Levulinic acid was esterified with n-hexanol, n-octanol, and n-decanol at 393–413 K and at molar ratios of between 3:1 and 10:1 (alcohol: acid) in the presence of the dodecatungstophosphoric acid (H₃PW₁₂O₄₀) as catalyst (0.1 wt%) to study the reaction kinetics. The results of such study are the precise form of kinetic equation, which is indispensable in design and optimization of industrial-scale chemical reactors. The authors stated that reactions were of second order and that the activation energy (E) decreased from 66 to 53 kJ/mol in the following alcohol sequence: n-hexanol > n-octanol > n-decanol.     

DPPH (= 2,2‐Diphenyl‐1‐picrylhydrazyl) Radical‐Scavenging Reaction of Protocatechuic Acid (= 3,4‐Dihydroxybenzoic Acid): Difference in Reactivity between Acids and Their Esters

Protocatechuic acid (= 3,4‐dihydroxybenzoic acid; 1 ) exhibits a significantly slow DPPH (= 2,2‐diphenyl‐1‐picrylhydrazyl) radical‐scavenging reaction compared to its esters in alcoholic solvents. The present study is aimed at the elucidation of the difference between the radical‐scavenging mechanisms of protocatechuic acid and its esters in alcohol. Both protocatechuic acid ( 1 ) and its methyl ester 2 rapidly scavenged 2 equiv. of radical and were converted to the corresponding o‐quinone structures 1a and 2a , respectively (Scheme). Then, a regeneration of catechol (= benzene‐1,2‐diol) structures occurred via a nucleophilic addition of a MeOH molecule to the o‐quinones to yield alcohol adducts 1f and 2c , respectively, which can scavenge additional 2 equiv. of radical. However, the reaction of protocatechuic acid ( 1 ) beyond the formation of the o‐quinone was much slower than that of its methyl ester 2 . The results suggest that the slower radical‐scavenging reaction of 1 compared to its esters is due to a dissociation of the electron‐withdrawing carboxylic acid function to the electron‐donating carboxylate ion, which decreases the electrophilicity of the o‐quinone, leading to a lower susceptibility towards a nucleophilic attack by an alcohol molecule.     

Esterification reactions on syndiotactic poly(2-methallyl alcohol). II. Esterification with protected (L)-aspartic and (L)-glutamic acids

The esterification of syndiotactic poly(2-methallyl alcohol) by N^α- and O^ω- protected aspartic and glutamic acids by the DCC/HOBT method is described. Depending on the extent of conversion, either homopolymers or copolymers are obtained. Both homo- and copolymers are characterized by ¹H- and ¹³C-NMR. A second route to the homopolymers has been followed, whereby the poly(2-methallyl alcohol) is first esterified by N^α-protected aspartic or glutamic acid anhydrides and, in a second step, the resulting free carboxyl group on the side chain is esterified by alcohols which are the same as the alcohol moiety of the O^ω-protecting groups. Because the homopolymers were identical to those of the first route, the formation of α-esters with the acid anhydrides is indicated.     

Formal total synthesis of enigmazole A

A stereoselective formal total synthesis of enigmazole A, a marine macrolide isolated from Cinachyrella enigmatica, is described. Lewis acid mediated intramolecular allylation of an α-acetoxy ether, prepared from alcohol and carboxylic acid fragments was carried out to construct the methylene THP ring with high stereoselectivity. The late-stage macrolactonization of the corresponding seco-acid provided a known synthetic intermediate of enigmazole A.     

Über eine Reaktion von o-Hydroxybenzylalkoholen mit Estern von Säuren des Phosphors mit der Koordinationszahl 3

Abstract

o-Hydroxybenzyl alcohol reacts with trimethyl phosphite under smooth conditions to o-hydroxyphenylmethane phosphonic acid dimethyl ester. This unusual reaction is of widest applicability. Derivatives of o-hydroxybenzyl alcohol independent of type, number or position of substituents in the ring, react with alkyl esters of phosphorous, phosphonous or phosphinous acids in an analogous process, forming the corresponding o-hydroxyphenylmethane phosphonic or phosphinic esters or phosphine oxides.     

Bioorganometallic Chemistry - Transition Metal Complexes with α-Amino Acids and Peptides

A new, interdisciplinary research area has emerged known as bioorganometallic chemistry. It focuses on the introduction of organometallic fragments into biomolecules (see, for example, structure on the right). “Classical” α-amino acid and peptide ligands have proven particularly versatile, and provide access to compounds that display interesting stereochemistry. α-Amino acids and peptides can be synthesized, labeled, stabilized, or activated by organometallic fragments.