Deprotection Strategy Research Articles

Thiazolidine Deprotection Using an Organic Solvent Extractable Aldehyde Scavenger for One-Pot Four-Segment Ligation.

We report a simple and convenient N-terminal thiazolidine (Thz) deprotection strategy and its application in one-pot multisegment ligation. In this strategy, O-benzylhydroxylamine (O-BHA) is used to efficiently and rapidly convert Thz into N-terminal cysteine. O-BHA can be easily separated from the ligation buffer by organic solvent extraction, avoiding the degradation of the peptide thioester by O-BHA. The utility of the O-BHA-based one-pot ligation strategy has been demonstrated in the assembly of CC chemokine ligand-2.

Dual iron- and organophotocatalyzed hydroformylation, hydroacylation and hydrocarboxylation of Michael-acceptors utilizing 1,3,5-trioxanes as C1-Synthone

A protocol based on photocatalytic cycles of both iron(III)chloride and 9,10-dicyanoanthracene (DCA) is developed for the masked hydroformylation, hydroacylation, and hydrocarboxylation of Michael-Acceptors utilizing readily available 1,3,5-trioxanes. Initiated by the LMCT of [FeCl4]– to generate chlorine radicals that promote hydrogen atom transfer (HAT) from the trioxanes, 9,10-dicyanoanthracene is used as co-photocatalyst to accelerate the formation of the desired products by facilitating the reoxidation of iron(II) to iron(III). The methodology is robust, allowing the generation of aldehydes, ketones, and carboxylic acids either by altering the trioxane and deprotection strategy or by subsequent photocatalyzed conversion of the initially obtained aldehydes.

Carboranylphosphines: B9-Substituted Derivatives with Enhanced Reactivity for the Anchoring to Dendrimers.

Several ortho-carboranes bearing a phenoxy or a phenylamino group in the B9 position were prepared employing various protection and deprotection strategies. Following established protocols, dendritic compounds were synthesized from a hexachlorocyclotriphosphazene or thiophosphoryl chloride core, and possible anchoring options for the B9-substituted ortho-carboranes were investigated experimentally and theoretically (DFT). Furthermore, 1- or 1,2-phosphanyl-substituted carborane derivatives were obtained. The resulting diethyl-, diisopropyl-, di-tert-butyl-, diphenyl- or diethoxyphosphines bearing a tunable ortho-carborane moiety are intriguing ligands for future applications in homogeneous catalysis or the medicinal sector.

Orthogonal Deprotection Strategy of Fmoc Provides Improved Synthesis of Sensitive Peptides: Application to Z-Arg-Lys-AOMK.

Protecting groups (PGs) in peptide synthesis have inspired advanced design principles that incorporate "orthogonality" for selective C- and N-terminus and side-chain deprotections. The conventionally acid-stable 9-fluorenylmethoxycarbonyl (Fmoc) group is one of the most widely used N-protection groups in solid- and solution-phase synthesis. Despite the versatility of Fmoc, deprotection by the removal of the Fmoc group to unmask primary amines requires the use of a basic secondary amine nucleophile, but this stratagem poses challenges in sensitive molecules that bear reactive electrophilic groups. An expansion of PG versatility, a tunable orthogonality, in the late-stage synthesis of peptides would add flexibility to the synthetic design and implementation. Here, we report a novel Fmoc deprotection method using hydrogenolysis under mildly acidic conditions for the synthesis of Z-Arg-Lys-acyloxymethyl ketone (Z-R-K-AOMK). This new method is not only valuable for Fmoc deprotection in the synthesis of complex peptides that contain highly reactive electrophiles, or other similar sensitive functional groups, that are incompatible with traditional Fmoc deprotection conditions but also tolerant of N-Boc groups present in the substrate.

Electrochemistry and Organic Synthesis: New Adventures with Olefin Coupling Reactions and Electrode Surfaces

Electrochemistry has long offered opportunities to explore new modes of reactivity, new approaches for introducing selectivity into synthetic reactions, and new strategies for the synthesis of everything from complex molecules to complex, addressable molecular surfaces. In the talk to be given, two aspects of our efforts along these lines will be detailed. In the first, we will take a look at recent efforts to use anodically-generated reactive intermediates to convert readily available small molecules into functionalized synthetic building blocks and natural product derivatives. Key to these efforts are oxidation reactions that generate reactive radical cation and radical intermediates. In one application, newly available chiral lactols synthesized using methodology developed by the Lin (Cornell) and Miller (Yale) groups are being transformed into C-glycoside and aza-C-glycoside derivatives. The reactions take advantage of oxidation reactions of either enol ether or vinylsulfide groups. The cyclization reactions and the subsequent deprotection strategy needed for converting the cyclization products into a useful synthetic building block will be highlighted. In a second application of an anodic cyclization, the role of thioamides in reactions targeting the chrysosoporazine family of natural products will be discussed. The reactions seek to provide an efficient method for converting lignin derived building blocks into molecules that reduce the efflux of anticancer drugs from cells. Initial cyclization attempts utilizing amide based N-radicals and anodic olefin coupling reactions were not successful. Those reactions consistently led to over-oxidation of the products that contain a highly electron-rich aryl ring. The use of thio-amide derived radicals provides a method to circumvent this problem.In the second topic to be discussed, the question of how one might begin to induce asymmetry into such electrochemical cyclizations will be highlighted. The chemistry focuses on efforts to influence the course of both electrochemical oxidation and reduction reaction and non-redox based transition metal catalyzed reactions with the surface of an electrode.

De Novo Design of Near-Infrared Fluorescent Agents Activated by Peroxynitrite and Glutathione-Responsive Imaging for Diabetic Liver Disease.

Diabetes and its complications, such as diabetes liver disease, is a major problem puzzling people's health. The detection of redox states in its pathological process can effectively help us gain a deeper understanding of the disease. The pair of oxidation-reduction substances peroxynitrite (ONOO- ) and glutathione (GSH) is considered to be closely related to their occurrence and development. Thus, direct visualization of ONOO- and GSH in diabetes liver disease is critical to evaluate the disease at the molecular level. Herein, two activatable agents NTCF-ONOO- and NTCF-GSH are prepared for selectively detecting ONOO- and GSH through protection and deprotection strategies based on hydroxyl and amino groups of near-infrared fluorophore. Fluorescence imaging of exogenous and endogenous ONOO- and GSH changes in living cells and in vivo is observed. The ONOO- and GSH level in the diabetes liver disease cellular model are visualized and the possible redox imbalance mechanism related to the oxidized (NAD+ ) and reduced (NADH) nicotinamide adenine dinucleotides is explored in this process. Moreover, these probes can sensitively recognize ONOO- and GSH in the process of oxidative stress resulting from streptozotocin and streptozotocin/acetaminophen-induced complex diabetic liver disease in vivo. In addition, they can be applied for monitoring the clinical serum sample related with diabetic patients.

A green deprotection strategy: Removing acid-labile protecting groups using lemon juice/ethanol as the solvent

Lemon juice has been studied and reported as an efficient catalyst or green medium in organic synthesis. The present digest paper shows the successful and efficient Removal of multiple acid-labile protecting groups using crude lemon juice for the first time. Several drops of lemon juice can rapidly convert some simple liquid acetals to carbonyl compounds. Also, when mixed with ethanol, lemon juice effectively removes cyclic acetals and other protection groups on primary or secondary alcohols. In addition, for the selective Removal of acetonide on diacetone-d-glucose and its derivatives, the yield can reach more than 85%. Lemon juice, combined with ethanol as a solvent, can avoid using hazardous organic or inorganic acids to remove acid-labile protecting groups while being environmentally friendly.

Incorporation of Protecting Groups in Organic Chemistry: A Mini-Review.

The approach of utilizing protecting groups (PGs) in organic chemistry has led to the successful syntheses of an array of useful organic compounds. This strategy has also addressed some of the complexities associated with many organic reactions. These PGs find useful applications in simple and complex reactions that involve the synthesis of large organic compounds such as peptides, and oligosaccharides. The fundamental role of PGs is to prevent undesired reactions that could hinder the progress or completion of such reactions. Ideal PGs must be utilized in this regard to achieve the desired objectives. This review describes the diverse protecting groups found in the literatures, the functional moieties for the protection, deprotection strategies, and their relevant applications in organic synthesis.

Utilizing Ni-Catalyzed Cross-Coupling as a Reversed Strategy for Homogeneous Deprotection of Benzyl Ethers in Batch and Flow

Utilizing Ni-Catalyzed Cross-Coupling as a Reversed Strategy for Homogeneous Deprotection of Benzyl Ethers in Batch and Flow

Incorporation of a Highly Reactive Oxalyl Thioester-Based Interacting Handle into Proteins.

Providing biomolecules with extended physicochemical, biochemical, or biological properties is a contemporary challenge motivated by impactful benefits in life or materials sciences. In this study, we show that a latent and highly reactive oxalyl thioester precursor can be efficiently introduced as a pending functionality into a fully synthetic protein domain following a protection/late-stage deprotection strategy and can serve as an on-demand reactive handle. The approach is illustrated with the production of a 10 kDa ubiquitin Lys48 conjugate.

Operationally simple enzymatic deprotection of C-3 position on 3,4,6-tri-O-acetyl-d-glucal

The new strategies to obtain selectively protected hydroxyl function on sugar derivatives are still of the high value for the progress of glycochemistry and organic synthesis. Herein, we describe an interesting enzymatic deprotection strategy that was applied to the most commonly used glycal derivative – 3,4,6-tri-O-acetyl-d-glucal. The procedure is operationally simple, easy to scale-up and the biocatalyst might be effortlessly recycled from the reaction mixture. Resulting product – 4,6-di-O-acetyl-D-glucal we then challenged to synthesize two glycal synthons armed with 3 different protecting group – a synthetic target difficult to achieve with traditional methods.

Palladium-Catalyzed Arylation of Hydantoins with Aryl Chlorides Enabled by Ylide-Functionalized Phosphines (YPhos)

The hydantoin moiety is an important structural motif present in various pharmaceuticals. Palladium complexes bearing electron-rich, bulky ylide-functionalized phosphine (YPhos) ligands were found to catalyze the arylation of N-protected hydantoins with broadly available aryl chlorides. Selective monoarylations, sequential diarylations, and arylation-alkylation sequences have been achieved. In combination with stepwise deprotection strategies, this opens up an expedient access to a wide variety of hydantoins, including derivatives of the anticonvulsant drugs phenytoin and mephenytoin.

Deconstruction of electron-deficient alkenes to carbonyl constituents by light-induced hydrogen atom transfer

Photoinduced CC bond cleavage by the HAT mechanism: photoinitiated catalyst-free CC bond cleavage for the regeneration of carbonyl compounds from electron-deficient conjugated alkenes is developed as a deprotection strategy in an aqueous medium.

Photoredox-Catalyzed Synthesis of β-Amino Alcohols: Hydroxymethylation of Imines with α-Silyl Ether as Hydroxymethyl Radical Precursor.

Carbon-carbon bond formation is an efficient approach for the synthesis of amino alcohols using two simple starting materials. Herein, we present a novel method for a divergent synthesis of β-amino ethers and β-amino alcohols in a sequential one-pot protocol under high-efficiency, mild, and metal- or metal-free conditions. Especially, TMSCH2OPMP was developed as a synthetic equivalent of α-hydroxymethyl radical in an in situ photocatalyzed oxidative PMP group deprotection strategy under air. A preliminary mechanistic investigation provides evidence for reaction mechanism involving a photoinduced α-alkoxy methyl radical and superoxide.

Tf2O- and Cu(OTf)2-Assisted Acylamination Reaction of Unactivated Alcohols with Nitriles: A One-Pot P(IV) Activation, Stereoretention in Cycloalkanols and Deprotection Approach.

Described herein is a simple, novel, one-pot acylamination reaction of unactivated alcohols. This reaction employs the combination of PCl3 and triflic anhydride (Tf2O) or copper triflate Cu(OTf)2, which serves as a source of P(IV)-activated complex for nitriles to react under the Ritter-type mechanism. The synthetic utility of Tf2O-promoted reactions was demonstrated by its effectiveness to generate different acylaminated products. By employing Cu(OTf)2, this method represents a rare example of α-selective acylamination reaction. With chiral cycloalkanols, using the Cu(OTf)2-promoted procedure, acylaminated products are formed with complete retention of configuration. The synthetic utility of the copper-assisted reaction in acetonitrile was readily demonstrated as a mild deprotection strategy.

Efficient Greener Visible‐Light‐Catalyzed Debenzylation of Benzyl Ethers and Esters: A Gateway to Wider Exploitation of Stable Benzyl Protecting Groups

AbstractA non‐hydrogenolytic mild deprotection strategy for stable benzyl protection of hydroxyl group is one of the long‐cherished goals in multistep synthesis involving carbohydrates or compounds with multiple hydroxyl groups. A greener organo‐photocatalytic method has been developed for mild and efficient visible light catalytic deprotection of benzyl group from benzyl ether and benzyl ester. The newly developed method in ambient condition with only 1 mol% of catalyst loading can efficiently remove highly stable benzyl protection from ethers and esters of wide substrate scope with excellent functional group tolerance, thus proved to be suitable for final stage deprotection. Employment of molecular oxygen as terminal oxidant and excellent yield in the multigram scale reaction signifies the eco‐friendliness, robustness and industrial applicability of the method.

A Simple and Feasible Synthetic Strategy towards Poly(4‐thiostyrene)

AbstractPoly(4‐thiostyrene), a historically challenging to synthesize polymer, is synthesized herein via a feasible three‐step protocol. Based on the newly developed protection–deprotection strategy, the precursor polymer containing thiomethyl groups is deprotected using Li/naphthalene to yield poly(4‐thiostyrene) after acidification. This newly developed procedure is crucial for preventing crosslinking of the thiol groups and therefore the resulting polymer is soluble in common organic solvents (e.g., chloroform, tetrahydrofuran) and can be stored long‐term, which has been challenging to accomplish over the past 60 years. The successful synthesis is confirmed by various characterization techniques including NMR, Fourier‐transform infrared spectroscopy (FTIR), and Raman analysis, which collectively are new and useful data that have generally been unavailable in previous reports. This work provides a robust approach for synthesizing this promising polymer and offers a new route to investigate thiol‐containing polymers.

Iterative Synthesis of Stereo‐ and Sequence‐Defined Polymers via Acid‐Orthogonal Deprotection Chemistry

AbstractAbsolute control over polymer stereo‐ and sequence structure is highly challenging in polymer chemistry. Here, an acid‐orthogonal deprotection strategy is proposed for the iterative synthesis of a family of unimolecular polymers starting with enantiopure serines, featuring precise sequence, stereoconfiguration and side‐chain functionalities that cannot be achieved using traditional polymerization techniques. Acid‐orthogonal deprotections proceed independently of one another by the selection of protecting groups that feature the respective acid‐lability. Under p‐toluenesulfonic acid, acidolysis of tert‐butyloxycarbonyl can proceed exclusively, while low‐dosage trifluoroacetic acid and low temperature only trigger the selective and quantitative cleavage of trityl. The pioneering use of this acid‐orthogonal deprotection chemistry increases the compatibility with otherwise sensitive groups and opens up pathways to facilely introduce structural and functional diversity into stereo‐ and sequence‐defined polymers, thus imparting their unique properties beyond natural biopolymers.

Iterative Synthesis of Stereo- and Sequence-Defined Polymers via Acid-Orthogonal Deprotection Chemistry.

Absolute control over polymer stereo- and sequence structure is highly challenging in polymer chemistry. Here, an acid-orthogonal deprotection strategy is proposed for the iterative synthesis of a family of unimolecular polymers starting with enantiopure serines, featuring precise sequence, stereoconfiguration and side-chain functionalities that cannot be achieved using traditional polymerization techniques. Acid-orthogonal deprotections proceed independently of one another by the selection of protecting groups that feature the respective acid-lability. Under p-toluenesulfonic acid, acidolysis of tert-butyloxycarbonyl can proceed exclusively, while low-dosage trifluoroacetic acid and low temperature only trigger the selective and quantitative cleavage of trityl. The pioneering use of this acid-orthogonal deprotection chemistry increases the compatibility with otherwise sensitive groups and opens up pathways to facilely introduce structural and functional diversity into stereo- and sequence-defined polymers, thus imparting their unique properties beyond natural biopolymers.

Designed Synthesis of Diversely Substituted Hydantoins and Hydantoin-Based Hybrid Molecules: A Personal Account

AbstractHydantoin and its analogues such as thiohydantoin and iminohydantoin have received substantial attention from both a chemical and a biological point of view. Several compounds of this class have shown useful pharmacological activities such as anticonvulsant, antitumor, antiarrhythmic, and herbicidal properties that have led, in some cases, to clinical applications. Because of these broad-spectrum activities, intensive research efforts have been dedicated in industry and academia to the synthesis and structural modifications of hydantoin and its derivatives. Realizing the importance of hydantoin in organic and medicinal chemistry, we also initiated a research program that successfully designed and developed new routes and methods for the formation of hydantoin, thiohydantoin, and iminohydantoin substituted at various positions, particularly at the N-1 position without following a protection–deprotection strategy. Because combinations of two or more pharmacophoric groups can lead to hybrid molecules that display a mixed mechanism of action on biological targets, we extended our developed strategy to the syntheses of new types of hydantoin-based hybrid molecules by combining hydantoin with a triazole, isoxazoline, or phosphate scaffold as a second pharmacophore to exploit their diverse biological functions.1 Introduction2 Chemistry and Properties2.1 Physical Properties2.2 Chemical Properties2.3 Biological Properties3 General Synthetic Methods4 Synthesis of Diversely Substituted Hydantoins5 Synthesis of Diversely Substituted Thiohydantoins6 Synthesis of Diversely Substituted Iminohydantoins7 Fused or Bicyclic (Thio)hydantoins8 Di- or Multivalent (Thio)hydantoins9 Hydantoin-Based Hybrid Molecules9.1 Hydantoin–Isooxazoline Hybrids9.2 Hydantoin–Triazole Hybrids9.3 Hydantoin–Phosphate Hybrids: Phosphorylated Hydantoins10 Summary and Outlook