O-acyl Derivatives Research Articles

An improved and practical synthesis route to antiproliferative (±)-shikonin and its O-acyl derivatives

Shikonin and its O-acyl derivatives are attracting increasing levels of attention among medicinal chemists due to their potencies as highly selective cytotoxic agents against cancer cells. However, providing a large number of shikonin-related samples by organic synthesis remains challenging. In the present study, we developed an improved and practical synthesis route to shikonin derivatives by olefin metathesis that has enabled the gram-scale preparation of a prenylated tetramethylnaphthazaline, a key intermediate in the synthesis of shikonin. In addition, a method for the selective cleavage of the acyl protecting groups at the phenolic positions of tri-O-acylated shikonins has been developed that provides concise routes to diverse O-acylshikonin derivatives.

Indole alkaloids from Vinca erecta type of sarpagine and ajmaline

The single crystal X-ray diffraction method established the absolute configuration of the Vinca erecta indole alkaloids of the akuammidine sarpagine type (3S, 5S, 15R, 16R) and its o-acyl derivative, as well as the type of ajmaline, quebrachidine (2S, 3S, 5S, 7R, 15S, 16R, 17S) and majoridine (2R, 3S, 5S, 7R, 15R, 16S, 17R). Crystal data for C21H24N2O3 (1): orthorhombic, space group P212121 (no. 19), a = 6.3949(5) Å, b = 13.5009(10) Å, c = 22.461(3) Å, Z = 4, 7694 reflections measured (7.64° ≤ 2Θ ≤ 152.294°), 3813 unique (Rint = 0.0798) which were used in all calculations. The final R1 was 0.0680 (I > 2σ(I)) and wR2 was 0.1650 (all data). Crystal data for C23H26N2O4 (2): orthorhombic, space group P212121 (no. 19), a = 9.9730(13) Å, b = 10.2090(10) Å, c = 20.409(3) Å, Z = 4, 7959 reflections measured (8.666° ≤ 2Θ ≤ 151.998°), 4212 unique (Rint = 0.0386) which were used in all calculations. The final R1 was 0.0477 (I > 2σ(I)) and wR2 was 0.1171 (all data). Crystal data for C42H48N4O6 (3): monoclinic, space group P21 (no. 4), a = 8.9320(10) Å, b = 21.515(5) Å, c = 9.5420(10) Å, β = 97.103(10)°, Z = 2, 16677 reflections measured (9.34° ≤ 2Θ ≤ 151.836°), 7393 unique (Rint = 0.0278) which were used in all calculations. The final R1 was 0.0366 (I > 2σ(I)) and wR2 was 0.1037 (all data). Crystal data for C23H28N2O3 (4): orthorhombic, space group P212121 (no. 19), a = 10.636(2) Å, b = 11.208(12) Å, c = 16.725(13) Å, Z = 4, 1650 reflections measured (9.498° ≤ 2Θ ≤ 119.97°), 1650 unique (Rint = 0.0436) which were used in all calculations. The final R1 was 0.0608 (I > 2σ(I)) and wR2 was 0.1720 (all data). In alkaloids such as sarpagine and ajmaline exo, the substituents of alkaloids do not lead to conformational changes of a stable polycyclic framework. In the series of sarpagine, alkaloids form mono-salts in the tetrahedral nitrogen N4, and in indolines of the ajmaline type, the tetrahedral hybridization of the N1 and N4 atoms favors the formation of disols. In V. erecta alkaloids, the exomethylene fragment (C18-C19=C20-C21) of the polycyclic backbone always takes on the E-state.

Synthesis, Structure, and Properties of New Lupinine O-Acyl Derivatives

Acylation of the alkaloid lupinine produced O-cinnamoyllupinine and O-lipoyllupinine. The structure of O-cinnamoyllupinine was established by an X-ray crystal structure analysis.

Ephedrines as Chiral Auxiliaries in Enantioselective Alkylation Reactions of Acyl Ephedrine Amides and Esters: A Review

Background: In modern chemistry, the asymmetric synthesis for the preparation of high purity chiral compounds to be used as pharmaceuticals or additives in foods have been of capital importance. Chiral auxiliary reagents are used to control the stereochemistry of the reaction in the generation of new chiral compounds, in this context, Ephedra compounds (ephedrines and pseudoephedrines) and some of their derivatives have been broadly used as chiral ligands in catalysis or chiral inductors in asymmetric synthesis. Objective: This review focuses on recent progress in the use of ephedra compounds and their N-substituted derivatives as chiral auxiliaries in the area of asymmetric synthesis, via the alkylation reaction of the enolates derived from their corresponding N-Acyl or O-Acyl derivatives, in the C-C bond formation. Conclusion: A vast amount of work has been done about the use of ephedra compounds in asymmetric synthesis area, in general, it was found that pseudoephedrines are much more effective than ephedrines and are preferred as chiral auxiliaries in the asymmetric alkylation of the corresponding N-acyl amides or O-Acyl esters. Alkylation with alkyl halides requires the use of more than 4 equivalents of LiCl to accelerate the alkylation rate and to complete the reaction without effecting the diastereoselectivity of the process. In contrast, the use of secondary alkyl halides was found to make the reaction very slow. Furthermore, a lot of work about the alkylation reaction in the opening of epoxides and aziridines, aldolic condensation, Manich reaction, addition of nucleophiles to α,β-unsaturated ephedrine amides and Michael additions have been demonstrated to be effective in the C-C bond formation. The aldol reaction of chiral enolates, proceeds with decreasing yields and enantioselectivities as the steric demand of the α-R of ephedrine amides and the size of carbonyl compound increase. In addition, the use of branched groups on N,N-disubstituted norephedrine esters is highly recommended in the aldol reactions of aromatic and aliphatic aldehydes.In the case of N-Acyl or O-Acyl ephedrines supported on polymers, the reaction proceed with good enantioselectivities but low yields, the enantioselectivities are goods but the yields are low. In general, the removal step of the auxiliary proceeds with low to high yields but without epimerization.

Synthesis and antibacterial activity of N- and O-acyl derivatives of primary amines and aminoalkanols

Synthesis and antibacterial activity of N- and O-acyl derivatives of primary amines and aminoalkanols

Cytotoxic Activity of Some Lupeol Derivatives

The synthesis of 3-0-acyl derivatives of lupeol is presented, as well as lupenone and the oxime of lupenone. The obtained derivatives were subjected to the MTT test in order to evaluate their cytotoxic activity toward HeLa, KB, MCF-7 and A-549 cell lines in comparison with lupeol (1). The IC₅₀ values for lupeol (1) and all of the tested derivatives (2-6) were from about 7-10 μM for lupenone (5) to about 81 μM for o-phthaloyl-lupeol (4). Acylation of the C-3 hydroxy function of compound 1 decreased the cytotoxic activity of compounds 2-4. The most active anticancer agent was lupenone (5), with IC₅₀ values 7.1-9.1 μM in comparison with 37.7-51.9 μM for lupeol (1).

Absorption and luminescence spectra of 5-aryl-3-methyl-1,2,4-oxadiazoles and their chelate complexes with Zinc(II) and copper(II)

5-(2-Hydroxyphenyl)-3-methyl-1,2,4-oxadiazole and its O-methyl and O-acyl derivatives, as well as zinc(II) and copper(II) chelates, were synthesized. All these compounds showed luminescence with the emission maxima ranging from λ = 332 to 490 nm, but only 5-(2-methoxyphenyl)- and 5-(2-acetoxyphenyl)-3-methyl-1,2,4-oxadiazoles and zinc(II) complex of 5-(2-hydroxyphenyl)-3-methyl-1,2,4-oxadiazole were characterized by high luminescence quantum yield (φ = 0.308–0.452, 0.089–0.153, and 0.115–0.334, respectively). Stable conformers of 5-(2-hydroxyphenyl)-3-methyl-1,2,4-oxadiazole with different structures of the coordination entity were identified by DFT quantum chemical calculations.

Tartaric acid and its O-acyl derivatives. Part 14: Nucleophilic ring-opening reaction of nonsymmetrically substituted tartaric acid anhydride as a tool for the synthesis of totally differentiated tartaric acid derivatives

The ring-opening reaction of nonsymmetrically substituted tartaric acid anhydride was used to synthesize monoamides and monoesters of O-benzoyltartaric acid, type I (a) and II (b) building blocks with all four functional groups differentiated. The correct structure of the regioisomers, which had earlier been misassigned, was established. The type I–type II regioisomer rearrangement, which proceeded via acyl migration, was examined. Moreover, it was shown that acyl migration induced by selective crystallization may yield one of the regioisomers quantitatively.

Regioselective Friedel–Crafts acylation of calix[4]arenes

Friedel–Crafts acylation of 25,27-dialkoxycalix[4]arenes has been studied. Direct acylation of de-tert-butylated calixarene using acyl chlorides and AlCl3 in 1,2-dichloroethane provided the corresponding diacyl derivatives regioselectively in high yields. Furthermore, ipso-substitution in the tert-butylated series under the same reaction conditions is possible, albeit in lower yields. As indicated by the unsuccessful application of this chemistry to O-acyl derivatives, the ipso-acylation reaction of calix[4]arenes proceeds by direct attack at the upper rim and not by a Fries rearrangement mechanism.

Structure-Based Design of Reactive Nucleosides for Site-Specific Modification of the A2A Adenosine Receptor

Adenosine receptors (ARs) are members of the G protein-coupled receptor (GPCR) superfamily and have shown much promise as therapeutic targets. We have used an agonist-bound A2AAR X-ray crystallographic structure to design a chemically reactive agonist for site-specific chemical modification of the receptor. To further explore and chemically engineer its binding cavity, a 2-nitrophenyl active ester was attached through an elongated chain at adenine C2 position. This general structure was designed for irreversible transfer of a terminal acyl group to a nucleophilic amino group on the A2AAR. Preincubation with several O-acyl derivatives prevented radioligand binding that was not regenerated upon extensive washing. In silico receptor docking suggested two lysine residues (second extracellular loop) as potential target sites for an O-acetyl derivative (MRS5854, 3a), and site-directed mutagenesis indicated that K153 but not K150 is essential. Similarly, a butyl azide for click reaction was incorporated in the active ester moiety (3b). These promising results indicate a stable, covalent modification of the receptor by several reactive adenosine derivatives, which could be chemical tools for future imaging, structural probing, and drug discovery. Thus, structure-based ligand design has guided the site-specific modification of a GPCR.

Piceatannol derivatives from Rheum austral D. Don and their chemotaxonomic significance

This paper reports the isolation and characterization of seven piceatannol derivatives (1–7), including two new compounds (4 and 6), along with resveratrol (8) and polydatin (9), from the underground parts of Rheum austral D. Don collected from Tibet. The structures of the isolates were identified based on analysis of their spectroscopic data and comparison with literature. Compounds 3–7, piceatannol-4′-O-glucopyranoside and its 6″-O-acylated derivatives reported in this study may be useful chemotaxonomic markers for R. austral collected from Tibet.

Formation of 3-acyloxy-γ-butyrolactones from 4-pentenols in vanadium-catalyzed oxidations

O-Acyl derivatives of 3-hydroxy-γ-butyrolactone are formed in up to 20% yield as by-products from 1-alkyl- and 1-phenyl-substituted 4-pentenols and tert-butyl hydroperoxide (TBHP) in vanadium-catalyzed synthesis of (tetrahydrofuran-2-yl)-methanols. The lactones are secondary products formed from (tetrahydrofuran-2-yl)-methanols via hydrogen atom abstraction in positions 4 and 5, as derived from experiments starting from deuterium-labeled alkenols. Stereocenters at tetrahydrofuran carbon 2 and the proximate hydroxyl carbon of the alkanol side chain retain configuration in the course of oxidative tetrahydrofuran conversion. In an atmosphere of nitrogen or argon, no γ-butyrolactone formation occurs, pointing to dioxygen as terminal oxidant for the secondary oxidation. Adding cyclohexa-1,4-diene or γ-terpinene to a solution of a 4-pentenol, TBHP, and a vanadium catalyst exposed to air inhibits formation of γ-butyrolactones. A third approach to prevent γ-butyrolactones from being formed in oxidative 4-pentenol cyclization uses cis-2,6-bis-(methanol)-piperidine instead of N-salicylidene-ortho-aminophenol as tridentate auxiliary for the vanadium catalyst.

A Synthetic Approach of D-Glucose Derivatives: Spectral Characterization and Antimicrobial Studies

A new series of methyl 4,6-O-(4-methoxyben- zylidene)-α-D-glucopyranoside derivatives was synthe- sized using the direct acylation method. Methyl-α-D- glucopyranoside was selectively converted to methyl 4,6- O-(4-methoxybenzylidene)-α-D-glucopyranoside by the reaction with 4-methoxybenzaldehyde dimethylacetal in a reasonable yield. Using a wide variety of acylating agents, a series of 2,3-di- O-acyl derivatives of this product was also prepared in order to gather additional information for structure elucidation. The structures of the newly synthesized compounds were elucidated by their spectral and elemental analysis. All synthesized compounds were screened for in vitro antimicrobial activities against ten human pathogenic bacteria and four plant pathogenic fungi. Encouragingly, a number of test compounds showed better antimicrobial activity than the standard antibiotics employed. It observed that the test compounds were more effective against fungal phytopathogens than those of the bacterial organisms.

Synthesis and biological activity of new avermectin 5-O- and 4″-O-acyl derivatives

Acylation of avermectin B1 with vicinal 1,2-dicarboxylic acid anhydrides leads only to 5-O-acyl derivatives in high yields. Avermectin 4″-O-acyl derivatives were obtained under similar conditions from avermectin B1 5-O-TBS-derivatives in good yields. The compounds obtained are of interest as antiparasitic agents.

Novel and Highly Efficient Regioselective Route to Helicid Esters by Lipozyme TLL

Highly regioselective acylation of helicid with fatty acid vinyl esters catalyzed by the lipase from Thermomyces lanuginosus has been successfully performed for the first time. For the enzymatic caproylation of helicid, under the optimal conditions, initial reaction rate was 33.2 mM/h, and substrate conversion and regioselectivity were greater than 99%. In addition, the acyl recognition of the enzyme in the regioselective acylation of helicid was investigated. The results showed that although 6’-O-acyl derivatives of helicid were exclusively obtained with all the tested acyl donors, the enzymatic reaction rate varied widely with different acyl donors, presumably owing to their different interactions with the active site of the lipase. It is also interesting that the different configuration of only one hydroxyl group at C-3 in helicid couldn’t affect the lipase-catalyzed esterification and helicid has the same regioselectivity as that of D-glucose and arbutin.

Acylation of 2-arylamino-3-chloro-5,8-dihydroxy-1,4-naphthoquinones

2-Arylamino-3-chloro-5,8-dihydroxy-1,4-naphthoquinones reacted with acetic anhydride and benzoyl chloride in pyridine to give in succession the corresponding O-acyl derivatives at both hydroxy groups. The primary acylation products were 8-acyloxy-2-arylamino-3-chloro-5-hydroxy-1,4-naphthoquinones.

Tartaric acid and its O-acyl derivatives. 7. Crystal structure of O-p-anisoyl-D-tartaric acid and its dimethylammonium salt trihydrate

Monoacylated derivatives O-p-anisoyl-d-tartaric acid and its N,N-dimethylammonium salt are synthesized by the partial hydrolysis of O,O′-di-p-anisoyl-d-tartaric acid. Crystal and molecular structures of both compounds have been determined and analyzed. In both of them, some strong and moderate strength [O-H…O] hydrogen bonds exist between the carboxylic units. The intermolecular hydrogen bonds link the adjacent fragments forming infinite one-dimensional chains parallel to the X-axis.

Preparation and characterization of O-acylated fucosylated chondroitin sulfate from sea cucumber.

Fucosylated chondroitin sulfate (FuCS), a kind of complex glycosaminoglycan from sea cucumber, has potent anticoagulant activity. In order to understand the relationship between structures and activity, the depolymerized FuCS (dFuCS) was chosen to prepare its derivates by selective substitution at OH groups. Its O-acylation was carried out in a homogeneous way using carboxylic acid anhydrides. The structures of O-acylated derivatives were characterized by NMR. The results indicated that the 4-O-sulfated fucose residues may be easier to be acylated than the other ones in the sulfated fucose branches. But the O-acylation was always accompanied by the β-elimination, and the degree of elimination was higher as that of acylation was higher. The results of clotting assay indicated that the effect of partial O-acylation of the dFuCS on their anticoagulant potency was not significant and the O-acylation of 2-OH groups of 4-O-sulfated fucose units did not affect the anticoagulant activity.

Interplay of carbonyl–carbonyl, CH⋯O and CH⋯π interactions in hierarchical supramolecular assembly of tartaric anhydrides – Tartaric acid and its O-acyl derivatives: Part 11

► Relation between conformation of acyl groups and weak intramolecular interactions. ► Hirshfeld surfaces analysis of intermolecular C=O···C=O, C–H···O, C–H···π interactions. ► Primary ribbon structure of p 2 1 symmetry directed by weak intermolecular forces. ► Pseudo-hexagonal packing of ribbons. The detailed analysis of molecular and crystal structure of the O -acyltartaric anhydrides is presented. The role of both intra- and intermolecular weak interactions is discussed. The Hirshfeld surfaces analysis in form of d norm representation and decomposed finger print plots was used to find out the types of weak but directional carbonyl–carbonyl, C H⋯O and C H⋯π interactions. The major interactions at the subsequent levels of the crystal architecture were identified. The interplay between carbonyl–carbonyl interactions and C H⋯O hydrogen bonds both at the molecular level as well as in basic supramolecular motives was analyzed. In all cases the primary supramolecular motif was found to be the ribbon showing the p 2 1 rod group symmetry. The key role of the ribbon motif is reflected in the hexagonal packing of rods.

Tartaric Acid and its O-Acyl Derivatives. Part 10. Synthesis and Applications of Tartramides, Tartrimides and O-Acyltartramides and Imides

Gawronski and Gawronska summarized 150 years of tartaric acid history in their monograph titled “Tartaric and Malic Acids in Synthesis”. 1 This is a fascinating story of a one of the most important...