Protection Of Hydroxyl Groups Research Articles

Synthesis and structure-activity relationship of theasapogenol galactosides against Magnaporthe oryzae

Camellia oleifera is expected to provide alternative aglycone to synthesize some saponins similar to that from Schima superba with inhibitory activity against Magnaporthe oryzae. Eight theasapogenol galactosides were synthesized via protection of adjacent hydroxyl groups by a benzylidene for regioselective glycosylation in the multi-hydroxyl sapogenin. Water soluble galactose chain connected far from liposoluble end was a key group in inhibiting the growth of M. oryzea unless theasapogenol was modified by two galactosyl groups or by one galactosyl group and one benzylidene group. The amphoteric characteristics of saponin such as saccharide group number, distance between bipolar groups play an important role in inhibiting mycelium growth of M. oryzae.

The role of water on the selective decarbonylation of 5-hydroxymethylfurfural over Pd/Al2O3 catalyst: Experimental and DFT studies

Highly selective decarbonylation of 5-hydroxymethylfurfural (HMF) to furfuryl alcohol (FOL) was originally realized by adding water to organic solvent. Side reactions such as hydrogenolysis, dehydrogenation and etherification could be effectively suppressed by introducing appropriate amount of water in pure organic solvent. Based on DFT calculations, hydrogen bonds between hydroxymethyl groups and water hinder the dehydrogenation of FOL to furfural (FAL) and furan. On the other hand, in situ water-pyridine-FTIR measurements revealed that the hydrogen bonding interaction between water and the hydroxyl groups on γ-Al2O3 surface decrease the acidity of Pd/Al2O3 and suppresses side reactions such as hydrogenolysis and etherification. Therefore, adding water to organic solvent could be a strategy for the protection of hydroxyl groups.

Tetrahydropyranyl: A Non-aromatic, Mild-Acid-Labile Group for Hydroxyl Protection in Solid-Phase Peptide Synthesis.

The use of the tetrahydropyranyl (Thp) group for the protection of serine and threonine side‐chain hydroxyl groups in solid‐phase peptide synthesis has not been widely investigated. Ser/Thr side‐chain hydroxyl protection with this acid‐labile and non‐aromatic moiety is presented here. Although Thp reacts with free carboxylic acids, it can be concluded that to introduce Thp ethers at the hydroxyl groups of N‐protected Ser and Thr, protection of the C‐terminal carboxyl group is unnecessary due to the lability of Thp esters. Thp‐protected Ser/Thr‐containing tripeptides are synthesized and the removal of Thp studied in low concentrations of trifluoroacetic acid in the presence of cation scavengers. Given its general stability to most non‐acidic reagents, improved solubility of its conjugates and ease with which it can be removed, Thp emerges as an effective protecting group for the hydroxyl groups of Ser and Thr in solid‐phase peptide synthesis.

2-Pyridinyl Thermolabile Groups as General Protectants for Hydroxyl, Phosphate, and Carboxyl Functions.

Application of 2-pyridinyl thermolabile protecting groups (2-PyTPGs) for protection of hydroxyl, phosphate, and carboxyl functions is presented in this unit. Their characteristic feature is a unique removal process following the intramolecular cyclization mechanism and induced only by temperature rise. Deprotection rate of 2-PyTPGs is dependent on certain parameters, such as solvent (aqueous or non-aqueous medium), pH values, and electron distribution in a pyridine ring. The presented approach pertains not only to protecting groups but also to an advanced system of controlling certain properties of 2-pyridinyl derivatives. We improved the "chemical switch" method, allowing us to regulate the protecting group stability by inversing the electron distribution in 2-PyTPG. Together with pH values manipulation, this allows us to regulate the protecting group stability. Moreover, phosphite cyclization to oxazaphospholidine provides a very stable but easily reversible tool for phosphate protection/modifications. For all TPGs we confirmed their utility in a system of protecting groups. This concept can contribute to designing the general protecting group that could be useful in bioorganic chemistry. © 2017 by John Wiley & Sons, Inc.

Rapid access to 6″-functionalized α-galactosyl ceramides by using 2-naphthylmethyl ether as the permanent protecting group

A versatile strategy for the synthesis of 6″-functionalized α-GalCers by using NAP ether group for permanent hydroxyl protection was developed, which provide the flexibility necessary for the incorporation of a wide range of functional groups in target molecules including alkyne, azide, thiol that are intolerant to Pd-catalyzed hydrogenolysis as well as other functionalities like carboxylic acid and amine. This strategy is also adaptable to other glycoconjugate synthesis especially those containing clickable tags and unsaturated functionalities.

Bioinspired Syntheses of Partially Methylated Flavonoids – Untapped Source of Bioactivities

Alkylation of hydroxyl groups of flavonoids is known to increase their bioavailability, metabolic stability and also impart new bioactivities. Though partially alkylated flavonoids and related compounds occupy substantial chemical space, there is scant information on their biological activities. They are comparatively less accessible, therefore development of their general syntheses are desirable. Chalcones play key role in the biosynthesis of array of flavonoids. Taking cues from nature, bioinspired, ecofriendly syntheses of polyhydroxy- and partially alkylated flavonoids have been developed. Compared to conventional protection groups, methoxymethylation was found to be more useful for the protection of hydroxyl groups. A library of flavones, flavonols, isoflavones and biflavones has been prepared. A brief account of our ongoing effort towards syntheses of small molecules is summarized here. Biological screening of the synthesized compounds led to recognition of several hitherto unreported inhibitors of biomarkers for MMP’s, NFkB, carbonic anhydrase etc.

A Synthetic Strategy for Conjugation of Paromomycin to Cell-Penetrating Tat(48-60) for Delivery and Visualization into Leishmania Parasites.

A successful approach to deliver paromomycin, a poorly absorbed aminoglycoside antibiotic, to parasite cells is reported, based on selective protection of amino and hydroxyl groups followed by conjugation to a fluorolabeled, PEG-functionalized cell-penetrating Tat(48-60) peptide. The resulting construct is efficiently internalized into Leishmania cells, evidencing the fitness of cell-penetrating peptides as vectors for efficiently transporting low-bioavailability drugs into cells.

The 3-nitro-2-pyridinesulfenyl group: synthesis and applications to peptide chemistry.

The 3-nitro-2-pyridinesulfenyl chloride, commonly abbreviated as Npys-Cl, was among the first stable heterocyclic sulfenyl halides to be isolated. After its discovery, the Npys group was widely used as a protecting group for the amines, alcohols and thiols. Herein, we have reviewed some of the aspects of the Npys-Cl moiety, and its most promising recent uses are summarized, from the stability of the Npys protection of amines, hydroxyls and thiols and removal conditions for potential applications in peptide synthesis, to one of its most successful applications for the formation of mixed disulfides. Indeed, Npys protects thiols and acts as an activator for disulfide bond formation, thereby facilitating thiol/disulfide exchange to the corresponding disulfides. The selectivity and mild reaction conditions opened up a wide range of applications in chemical biology as well. Finally, some of the most recent developments regarding the synthesis and applications of solid-phase Npys derivatives are discussed. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Magnetic Fe3O4@silica sulfuric acid nanoparticles promoted regioselective protection/deprotection of alcohols with dihydropyran under solvent-free conditions

Protection (and deprotection) of hydroxyl groups via tetrahydropyranylation was carried out effectively using a catalytic amount of Fe3O4 supported silica sulphuric acid nanoparticles (Fe3O4@SiO2@SO3H) under solvent-free conditions.

Nano Fe3O4@ZrO2/SO42−: A highly efficient catalyst for the protection and deprotection of hydroxyl groups using HMDS under solvent-free condition

GRAPHICAL ABSTRACT

Highly regioselective homoallyl alcohol protection through ring opening of p-methoxybenzylidene acetal

A highly regioselective homoallylic alcohol protection was achieved in the reductive cleavage of anisylidene acetal with DIBAL-H during the selective protection of hydroxyl group in terminal unsaturated diols which was unlikely compare to the diols present adjacent to internal and cyclic double bond. Reductive cleavage of terminal olefenic diols protected as its acetals gave exclusively allyl alcohol product in good to excellent yield. Though the actual reason of such observation is not quite clear, the current reductive protocol can be applied as an efficient solution for indirect protection of less reactive hydroxy group in preference to that of more reactive allylic one as PMB-mono ether.

1,3-Dipolar cycloaddition of a cyclic nitrone derived from 2-deoxy-D-ribose to α,β-unsaturated lactones: An entry to carbapenem antibiotics

1,3-Dipolar cycloadditions of 2-deoxy-D-ribose-derived L-threo five-membered cyclic nitrone to α,β-unsaturated γ- and δ-lactones were investigated. Cycloadducts obtained from δ-lactones, after NO bond cleavage, opening of the lactone ring, and protection of hydroxyl groups were subjected to β-lactam ring formation by using Mukaiyama's salt. Cycloadducts from γ-lactones subjected to the same reaction sequence undergo β-elimination of a water molecule to provide pyrrolidine-substituted unsaturated γ-lactones.

Solvent- and catalyst-free, quantitative protection of hydroxyl, thiol, carboxylic acid, amide and heterocyclic amino functional groups

Various substrates are quantitatively protected by 3,4-dihydro-2H-pyran at 125 °C in the absence of any additional chemicals, without generating any waste materials.

Efficient Synthesis of Chloromethyl Methyl Ether and One-Pot Hydroxyl Protection

Efficient Synthesis of Chloromethyl Methyl Ether and One-Pot Hydroxyl Protection

Acyclic analogs of nucleosides based on tris(hydroxymethyl)phosphine oxide: synthesis and incorporation into short DNA oligomers

Abstract Tris-(hydroxymethyl)phosphine oxide (THPO) to a certain extent resembles a part of 2′-deoxyribofuranose, although it exists in an acyclic form only and the oxygen atom at the THPO phosphorus center provides additional hydration site or acceptor of hydrogen bonds. After proper protection of hydroxyl groups, THPO was functionalized with nucleobases and converted into phosphoramidite monomers suitable for incorporation into growing oligonucleotide chains within the solid phase synthesis protocol. The resultant THPO-DNA analogs show reduced affinity to complementary DNA strands, and are resistant towards snake venom and calf spleen exonucleases.

A Concise Synthesis of Azoxystrobin using a Suzuki Cross-Coupling Reaction

A simple, efficient and eco-friendly process for the synthesis in good yield of azoxystrobin from 2-bromophenol has been developed using phenolic hydroxyl protection, Grignard reaction, Suzuki cross-coupling, hydrogenation and a nucleophilic reaction on a 2-chloropyrimidine.

Silica sulfuric acid-coated Fe3O4 nanoparticles as high reusable nanocatalyst for the oxidation of sulfides into sulfoxides, protection and deprotection of hydroxyl groups using HMDS and Ac2O

Oxidation of sulfides, acetylation of alcohols and phenols and selective trimethylsilylation of primary and secondary benzyl alcohols are carried out using silica sulfuric acid-coated Fe3O4 magnetic nanoparticles (SSA@MNPs) as a stable, efficient and magnetically recoverable nanocatalyst. Also, deprotection of silyl ethers was reported in ethanol at room temperature in the presence of SSA@MNPs as a magnetic nanocatalyst. The magnetic nanocatalyst was characterized by FT-IR spectroscopy, TGA, XRD and SEM techniques. The catalyst was easily separated with the assistance of an external magnetic field from the reaction mixture and reused for several consecutive runs without significant loss of its catalytic efficiency.

Allylic oxidation of steroidal olefins by vanadyl acetylacetonate and tert-butyl hydroperoxide

Readily available vanadyl acetylacetonate was found to oxidize the allylic sites of Δ5 steroidal alcohols without protection of hydroxyl groups. Cholesterol, dehydroepiandrosterone, cholesterol benzoate, cholesterol acetate, pregnenolone, and 5-pregnen-3,20-diene were oxidized to 7-keto products using vanadyl acetylacetonate in one pot reactions at room temperature in the presence of oxygen and water.

1,4-Polybutadienes with Pendant Hydroxyl Functionalities by ROMP: Synthetic and Mechanistic Insights

The reactivity of cis-3,4-bis(hydroxymethyl)cyclobutene derivatives bearing free and protected hydroxyl groups during ring-opening metathesis polymerization (ROMP) was investigated using ruthenium-based initiators. It was found that the ROMP of cis-4-benzyloxymethyl-3-hydroxymethylcyclobutene (1) using highly reactive initiators containing N-heterocyclic carbenes as nonlabile ligands leads to well-defined polymers while cis-3,4-bis(hydroxymethyl)cyclobutene (2) was reluctant to polymerize under the same conditions. Kinetic studies were performed to assess a number of critical reaction parameters: initiator structure, solvent, and temperature. The results demonstrate that Grubbs’ second- and third-generation catalysts are the best initiators to prepare well-defined 1,4-polybutadienes containing simultaneously free and protected hydroxyl side groups with predictable molecular weights (up to 40 000 g mol–1) and narrow molecular weight distributions. Besides, low values of kp/ki (the ratio of the rate constan...

Carbocatalysis: reduced graphene oxide-catalyzed Boc protection of hydroxyls and graphite oxide-catalyzed deprotection

A new metal-free method for O-Boc protection of alcohols and phenols was achieved with reduced graphene oxide (RGO) as an efficient and recyclable catalyst. Graphite oxide (GO) served as the catalyst for the deprotection of Boc group with methanol. The plausible mechanisms were proposed, in which RGO acted as a solid base catalyst and GO as a solid acid catalyst.