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Many fields in chemical biology and synthetic biology require effective bioconjugation methods to achieve their desired functions and activities. Among such biomolecule conjugates, antibody–drug conjugates (ADCs) need a linker that provides a stable linkage between cytotoxic drugs and antibodies, whilst conjugating in a biologically benign, fast and selective fashion. This review focuses on how the development of novel organic synthesis can solve the problems of traditional linker technology. The review shall introduce and analyse the current developments in the modification of native amino acids on peptides or proteins and their applicability to ADC linker. Thereafter, the review shall discuss in detail each endogenous amino acid's intrinsic reactivity and selectivity aspects, and address the research effort to construct an ADC using each conjugation method., The review shall introduce and analyse the current developments in the chemical modification of native amino acids on peptides or proteins and their applicability to ADC linkers.

Searching for membrane-active synthetic analogues that are structurally simple yet functionally comparable to natural channel proteins has been of central research interest in the past four decades, yet custom design of the ion transport selectivity still remains a grand challenge. Here we report on a suite of buckyball-based molecular balls (MBs), enabling transmembrane ion transport selectivity to be custom designable. The modularly tunable MBm-Cn (m = 4-7; n = 6-12) structures consist of a C60-fullerene core, flexible alkyl linkers Cn (i.e., C6 for n-C6H12 group), and peripherally aligned benzo-3m-crown-m ethers (i.e., m = 4 for benzo-12-crown-4) as ion-transporting units. Screening a matrix of 16 such MBs, combinatorially derived from four different crown units and four different Cn linkers, intriguingly revealed that their transport selectivity well resembles the intrinsic ion binding affinity of the respective benzo-crown units present, making custom design of the transport selectivity possible. Specifically, MB4s, containing benzo-12-crown-4 units, all are Li+-selective in transmembrane ion transport, with the most active MB4-C10 exhibiting an EC50(Li+) value of 0.13 μM (corresponding to 0.13 mol % of the lipid present) while excluding all other monovalent alkali-metal ions. Likewise, the most Na+ selective MB5-C8 and K+ selective MB6-C8 demonstrate high Na+/K+ and K+/Na+ selectivity values of 13.7 and 7.8, respectively. For selectivity to Rb+ and Cs+ ions, the most active MB7-C8 displays exceptionally high transport efficiencies, with an EC50(Rb+) value of 105 nM (0.11 mol %) and an EC50(Cs+) value of 77 nM (0.079 mol %).

Reported herein is a practical method for macrolactam synthesis via a Rh(III)-catalyzed ring closing alkene-alkene cross-coupling reaction. The reaction proceeded via a Rh-catalyzed alkenyl sp2 C-H activation process, which allows access to macrocyclic molecules of different ring sizes. Macrolactams containing a conjugated diene framework could be easily prepared in high chemoselectivities and Z,E stereoselectivities. Ministry of Education (MOE) Nanyang Technological University The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (No. 21702108), the Natural Science Foundation of Jiangsu Province, China (No. BK20160977), the Six Talent Peaks Project in Jiangsu Province (No. YY-033), Tier 1 grant M4012045.110 (No. RG12/18-S) from the Ministry of Education of Singapore and Distinguished University Professor grant, Nanyang Technological University, Singapore.

A photoredox-catalyzed regio- and stereoselective trifluoroethylation reaction of enamides using commercially available 2,2,2-trifluoroethyl iodide as trifluoroethylating agents has been developed,...

This paper reports a highly site-selective alkylation of heteroarene N-oxides using hypervalent iodine(III) carboxylates to serve as an alkylating agent in the presence of a cheap copper catalyst under visible light conditions. This mild method proceeds at room temperature in an air atmosphere and can withstand various heteroarene N-oxides as well as various primary, secondary, and tertiary alkyl carboxylic acids. It also provides a practical method for enabling the rapid conversion of commercially available raw materials into medically relevant "drug-like" molecules.

2H-Azirine-2-caboxamides have been designed to perform as a new type of bifunctional thiol linker under very mild reaction conditions. The cleavage of a C-N double bond of 2H-azirine furnishes an amino amide functional group in situ through a thiol addition and ring-opening process. It works with a broad scope of thiols and 2H-azirines in the absence of any catalysts at room temperature. Cysteine-containing peptides have also been demonstrated to work efficiently in a completely water solution. We gratefully acknowledge funding from the National Natural Science Foundation of China (21971112), Jiangsu Province Funds Surface Project (BK 20161541), and the Starting Funding of Research (39837107) from Nanjing Tech University

A highly efficient Pd/Ca catalytic system for the directly dehydrative cross-coupling of allylic alcohols with terminal alkynes was developed. This calcium salt cocatalyst facilitates the oxidative addition of the palladium catalyst (1 mol %) to the C-OH bond. Then, the in situ-generated hydroxide ion deprotonates the terminal alkynes to promote the formation of the allylalkynylpalladium intermediate, liberating water as the only byproduct. This proposed mechanism is also supported by density functional theory calculations. An anticancer agent was prepared from inexpensive starting materials on a 10 g scale.

An efficient and straightforward stereoselective alkylation reaction of enamides using commercially available and easily accessible unactivated alkyl carboxylic acids as alkylating agents is described, giving rise to a diverse array of synthetically important and geometrically defined β-alkylated enamides bearing primary, secondary, or tertiary alkyl moieties. This transformation also shows excellent functional group tolerance, satisfying atom economy, and operational simplicity.

A Ba/Pd cooperative catalysis system was developed to enable the dehydrative cross-coupling of allylic alcohols with P-ylides to occur directly and promote a subsequent Wittig reaction in one pot. A variety of multisubstituted 1,4-dienes were isolated in good to excellent yields with broad P-ylides (stabilized by both ester and ketone carbonyl groups) and aldehyde (aliphatic and aromatic) substrates with excellent E selectivity.

A Pd(II)-catalyzed mild and highly regioselective 6-endo cyclization/alkylation reaction of o-(alkynyl)styrenes with simple allylic alcohols has been developed. Under mild reaction conditions, the vinyl palladium species generated in situ after cyclization could insert a C-C double bond of allylic alcohol through a cross-coupling reaction and led to the formation of (alkyl)naphthalenes. This cascade cross-coupling reaction represents a direct and atom economic method for the construction of functionalized naphthalene derivatives in moderate to good yields.

A palladium-catalyzed dialkylation of 1,3-dien-5-ynes was developed using alkenyl double bonds as the initiator and terminator for the synthesis of functionalized indene derivatives. The reactions were performed under mild reaction conditions, affording the corresponding multi-substituted indene derivatives in high efficiency via unprecedented 5- endo cyclization and alkylation processes. It was found that the substituent location at the alkenyl double bond was essential for the chemoselective synthesis of the indene and naphthalene derivatives, respectively. We gratefully acknowledge the funding support of the National Natural Science Foundation of China (21871240, 21672198), the State Key Program of National Natural Science Foundation of China (21432009), and the Fundamental Research Funds for the Central Universities (WK2060190082).

A nondirected amidation reaction of aromatic C-H bond was developed under iron(II) catalysis, using sulfonyl azides as the nitrogen source. The reaction displayed a broad substrate scope and good regioselectivities in the aspects of aromatic ring vs alkyl chain and different aromatic position of (alkyl)arenes. This method provided a new protocol for the synthesis of some aromatic amines, which were hard to achieve in a previous report. Nanyang Technological University We gratefully acknowledge Nanjing Tech University, Natural Science Foundation of Jiangsu Province (BK20171463), the State Key Program of National Natural Science Foundation of China (21432009), students’ project of Nanjing Tech University for innovation and entrepreneurship training program (2019DC0428), SICAM Fellowship and Scholarship by Jiangsu National Synergetic Innovation Center for Advanced Materials, and Nanyang Technological University for the generous financial support.

A palladium-catalyzed stereospecific alkylation of allylamines with primary and secondary alkyl iodides is described. Isoquinoline-1-carboxamide (IQA) acts as directing group to generate multisubstituted olefin products in cis configuration in moderate to good yields. Mechanistic studies suggest that alkenyl C-H bond activation is the rate-determining step. We gratefully acknowledge the funding support of the National Natural Science Foundation of China (21672198, 21871240), the State Key Program of National Natural Science Foundation of China (21432009), and the Fundamental Research Funds for the Central Universities (WK2060190082).

An efficient tertiary alkylation reaction of olefins with 1,3-dicarbonyl compounds was developed by virtue of copper catalyst without the use of expensive ligands or additives. In contrast to alkyl Heck-type reaction, alkyl halide is not required. Notably, by varying the nitrogen and air atmosphere, the reaction selectively produces alkylation and alkylation-oxygenation products, respectively. Initial investigations revealed that an α-carbonyl alkyl radical species might be involved in the process. We thank the National Natural Science Foundation of China (21702106), the Natural Science Foundation of Jiangsu Province (BK20170967), and the Start-up Grant from Nanjing Tech University (39839101 and 39837101) for financial support. The SICAM Fellowship by Jiangsu National Synergetic Innovation Center for Advanced Materials is also acknowledged.

Alkenes are ubiquitous in Nature and their functionalization continues to attract attention from the scientific community. On the other hand, activation of alkenyl sp2 C–H bonds is challenging due to their chemical properties. In this short account, we elucidate, discuss and describe the utilization of transition-metal catalysts in alkene activation and provide useful strategies to synthesize organic building blocks in an efficient and sustainable manner.1 Introduction2 Breakthrough3 Controlling E/Z, Z/E Selectivity3.1 Esters and Amides as Directing Groups3.2 The Chelation versus Non-Chelation Concept4 Other Alkene Derivatives5 Intramolecular C–H Activation6 Conclusion and Future Projects

Synthetically versatile anthranils as a bifunctional amino source have been employed for the first time to enable direct amination on unactivated C(sp3)-H bonds of thioamides under Cp*CoIII catalysis. The excellent site-selectivity on primary C(sp3)-H bonds is observed for a diverse array of thioamides with high functional group tolerance. Further applicability of the products is also highlighted through a series of interesting synthetic elaborations.

An efficient method for the synthesis of alkyl indium reagents by means of an indium(III) or lead(II) halidecatalyzed direct insertion of indium into alkyl iodides and their applications in palladium-catalyzed crosscoupling reactions with aryl halides is developed. NMR and ESI-MS analyses indicated that rather than the formation of the commonly recognized alkyl indium sesquihalide with the formulation of R3In2X3, the formed alkyl indium reagent in the present protocol should be a mixture of an alkyl indium dihalide (RInX2) and a dialkyl indium halide (R2InX) (both of them presumably exist as dimers). Nanyang Technological University We gratefully acknowledge the financial support from the Nanjing Tech University (Start-up Grant No. 39837118, 39837101, and 39837146), the SICAM Fellowship from the Jiangsu National Synergetic Innovation Center for Advanced Materials, and the Nanyang Technological University.

Stereoselective β-C(sp2)-H alkylation of enamides with redox-active N-hydroxyphthalimide esters via a photoredox-catalyzed decarboxylative cross-coupling reaction is demonstrated. This methodology features operational simplicity, broad substrate scopes, and excellent stereoselectivities and functional group tolerance, affording a diverse array of geometrically defined and synthetically valuable enamides bearing primary, secondary or tertiary alkyl groups in satisfactory yields.

Herein, we disclose a transition-metal-free reaction system that enables α-cyanation of sulfonamides through C-H bond cleavage for the preparation of α-amino nitriles, including difficult-to-access all-alkyl α-tertiary scaffolds. More than 50 substrate examples prove a wide functional group tolerance. Additionally, its synthetic practicality is highlighted by gram-scalability and the late-stage modification of natural compounds. Mechanistic experiments suggest that this process involves in situ formation of an imine intermediate via base-promoted elimination of HF.

Herein, we devised a method for stereoselective O-glycosylation using an Ir(i)-catalyst which enables both hydroalkoxylation and nucleophilic substitution of glycals with varying substituents at the C3 position. In this transformation, 2-deoxy-α-O-glycosides were acquired when glycals equipped with a notoriously poor leaving group at C3 were used; in contrast 2,3-unsaturated-α-O-glycosides were produced from glycals that bear a good leaving group at C3. Mechanistic studies indicate that both reactions proceed via the directing mechanism, through which the acceptor coordinates to the Ir(i) metal in the α-face-coordinated Ir(i)-glycal π-complex and then attacks the glycal that contains the O-glycosidic bond in a syn-addition manner. This protocol exhibits good functional group tolerance and is exemplified with the preparation of a library of oligosaccharides in moderate to high yields and with excellent stereoselectivities., Ir(i)-catalyzed α-selective O-glycosylation of glycals provided an access to both 2-deoxyglycosides and 2,3-unsaturated glycosides with a broad substrate scope. The underlying rationale of α-selectivity has been illustrated by the DFT study.

A general intermolecular reductive Heck reaction of organohalides with both terminal and internal unactivated aliphatic alkenes has been first realized in high yield with complete anti-Markovnikov selectivity. The challenging vinyl bromides, aryl chlorides, and polysubstituted internal alkenes were first applied. More than 100 remote carbofunctionalized alkyl carboxylic acid derivatives were rapidly synthesized from easily accessible starting materials. The synthesis of drug molecules has further demonstrated the wide synthetic utility of this scalable strategy. Preliminary mechanistic studies are consistent with the proposed catalytic cycle. We gratefully acknowledge funding from the National Natural Science Foundation of China (21602104), Natural Science Foundation of Jiangsu Province, China (BK 20160986), and the Starting Funding of Research (3983500176) from Nanjing Tech University.

An efficient bioinspired deamination method of both natural and unnatural amino acid derivatives has been developed. This method provides easy access to a wide variety of useful α, β‐unsaturated carbonyl compounds. The reaction is realized with two transition metal catalysts (palladium and Nickel) in‐easy handling procedure. A possible reaction pathway is also proposed and the control experiments support the involvement of the palladium‐catalyzed inert sp3 C−H activation as one of the key steps.

An environmentally benign protocol that affords propargylic sulfones containing highly congested carbon centers from easily accessible alcohols and sulfinic acids with water as the only byproduct is reported. The reaction proceeded via an in situ dehydrative cross-coupling process by taking advantage of the synergetic actions of multiple hydrogen bonds rather than relying on an external catalyst and/or additives to achieve high product distribution.

A radical-mediated oxidative cross-coupling of readily accessible α-alkylated styrenes with 1,3-dicarbonyl compounds utilizing a combination of Cu(OAc)2 and air as a catalytic system is described. Rather than requiring α-halocarbonyl compounds, this efficient approach enables direct installation of tertiary functionalized alkyl motifs to olefins with simple carbonyl derivatives. The novel protocol is characterized with high allylic selectivities via a competing β-H elimination. Both radical-clock and -trapping experiments provided clear-cut evidence for the intermediacy of an α-keto carbon-centered radical.

A general Pd-catalyzed intermolecular reductive Heck reaction of both terminal and internal unactivated aliphatic alkenes has been first developed. This method affords γ- and δ-arylated alkyl carboxylic acid derivatives in high yields with complete anti-Markovnikov selectivity. Notably, the coupling process is stereoretentive for the alkyl chain. Mechanistically, alkyl palladacycle intermediates stabilized by directing group and ligand, hydride species multigenerated from PS/TFA reductant, are two key factors that successfully promote the reaction and regioselectivity. MOE (Min. of Education, S’pore)

Copper-catalyzed conjugate protosilylation reaction of α,β-unsaturated sulfonyl ketimines has been developed. The corresponding E- and Z-stereoselective functionalized allylsilane products were obtained in good yields respectively via tuning the ligands used in the reactions. Furthermore, the highly enantioselective (E)-β-tosylamine-substituted allylsilanes were also achieved in the presence of chiral Pybox ligand. And the corresponding products could be easily transformed into other useful synthons.

Allylic sulfones, owning to their widespread distributions in biologically active molecules, received increasing attention in the past few years. However, the synthetic method under mild conditions is still a challenging task. In this paper, we report a sulfinic acids ligation with allylic alcohols via metal-free dehydrative cross-coupling. Both aliphatic and aromatic sulfinic acids react with various allylic alcohols to deliver the desired allylic sulfones in high yields with excellent selectivity. This carbon–sulfur bond formation reaction is highly efficient and practical since it works under metal-free, neutral, aqueous media and at room temperature in which the products even can be obtained by simple filtration without the need for organic extraction or column chromatography. Water is found to be essential for the success of this carbon–sulfur bond formation reaction. DFT calculations imply that water acts as promoter in this transformation via intermolecular hydrogen bonds., Despite the biological importance of sulfones, available synthetic methods usually involve toxic metals and reagents or harsh conditions. Here, the authors report an environmentally benign procedure for the metal-free carbon-sulfur bond formation of allylic sulfones in neutral aqueous medium at room temperature.

An efficient method for the preparation of alkyl indium reagents by using unactivated and cheap alkyl chlorides as substrates in the presence of indium and LiI was developed. The thus-formed alkyl indium species effectively underwent palladium-catalyzed cross-coupling reactions with aryl halides with wide functional group tolerance.

Herein we demonstrate that an alkylation of indoles could be accessed through C-H bond functionalization with α,α-difluorovinyl tosylate. The key aspect for the effective alkylation is the influence of the fluorine substituents on the reactivity of the C[double bond, length as m-dash]C double bond, allowing regioselective insertion as well as an indolyl group shift process. Furthermore, the fluorides are removed through alcoholysis to furnish the alkylation product as a traceless auxiliary.

Chemoselective functionalizations of intrinsically less reactive C(sp3)–H bonds of alkyl nitriles are of particular interest to the chemical community because these strategies provide opportunities for the introduction of important cyanoalkyl groups onto target frameworks in a step-economical fashion. In recent years, the introduction of nitrile-containing alkyl radicals in tandem radical additions and oxidative couplings has inarguably brought chemists a new radical reaction platform for the diverse synthesis of natural products and pharmaceuticals. Compared with the wide applications of various C-centered radicals adjacent to a heteroatom, however, nitrile-containing alkyl radicals remain largely unexplored. New methods for C(sp3)–H bond oxidative functionalization of alkyl nitriles and new mechanistic manifolds would result in the development of a broad range of novel reactions. Therefore, this review will give an overview of various types of radical cyanoalkylation using the key alkyl nitrile reactants, which lie beyond traditional coupling chemistry.

A synthetic method of copper-catalyzed silylperoxidation of α,β-unsaturated carbonyl compounds and conjugated enynes has been developed. The realization of silylperoxidation of the carbon–carbon double bond permits direct access to silicon-containing peroxy products in moderate to good yields. Furthermore, this protocol distinguishes itself by operational simplicity and exhibiting good tolerance of a wide scope of functional groups. This strategy provides an efficient approach to the 1,2-difunctionalization of α,β-unsaturated carbonyl compounds and conjugated enynes.

A palladium-catalyzed intramolecular amination of alkenes with retention of olefin functionalization was achieved under mild reaction conditions. In the presence of palladium catalyst, the tosyl-protected amine can directly couple with a double bond to provide versatile dihydropyrrole derivatives in moderate to excellent yields.

An efficient RhII -catalyzed synthesis of functionalized α-vinyl aldehydes with high E/Z stereoselectivity was developed. The reaction mediates the cyclopropanation of enaminones with vinyl carbenoids that are generated from cyclopropenes in situ to give the aminocyclopropane intermediates. Selective C-C bond cleavage of the cyclopropane intermediates leads to formation of α-vinyl aldehyde derivatives with high E/Z selectivity. This method proceeds at room temperature under very mild reaction conditions and works with a broad substrate scope.

A Pd(II)-catalyzed mild and highly regioselective 6- endo cyclization/allylation reaction of enynoates with simple allylic alcohols has been developed. Under mild reaction conditions, the vinyl palladium species generated in situ after cyclization could insert C-C double bond of allylic alcohol through cross-coupling reaction and lead to the formation of allyl pyrone via β-OH elimination. This cascade cross-coupling reaction represents a direct and atom economic methodology for the construction of novel allyl pyrones in moderate to good yields.

An efficient method for the synthesis of alkyl indium reagent by means of an iodine-catalyzed direct indium insertion into alkyl iodide in THF is reported. The thus-generated alkyl indium reagents effectively underwent Pd-catalyzed cross-coupling reactions with various aryl halides, exhibiting good compatibility to a variety of sensitive functional groups. By replacing THF with DMA and using 0.75 equiv of iodine, less reactive alkyl bromide could be used as substrate for indium insertion with equal ease. Nanyang Technological University We gratefully acknowledge the financial support from Nanjing Tech University (Start-up Grant No. 39837118, 39837101, and 39837146), the SICAM Fellowship from Jiangsu National Synergetic Innovation Center for Advanced Materials, and Nanyang Technological University.

An efficient iron-mediated highly diastereoselective allylation of carbonyl compounds with cyclic allylic halides is reported. The allylation reactions involving various carbonyl compounds proceeded efficiently in the presence of 20 mol% bismuth(III) chloride to give the corresponding homoallylic alcohols in moderate to good yields with excellent diastereoselectivities and wide functional group tolerance. In cases where an aldehyde and a ketone (e.g., 2-pyridinecarboxaldehyde and phenylglyoxylic acid) containing an adjacent chelating atom were used, complete reversal of product diastereoselectivities was observed which could be explained by the Cram-chelated six-membered ring transition state. Nanyang Technological University We gratefully acknowledge the financial support from Nanjing Tech University (Start-up Grant No. 39837118, 39837101, and 39837146), the SICAM Fellowship from the Jiangsu National Synergetic Innovation Center for Advanced Materials, Postgraduate Research & Practice Innovation Program of Jiangsu Province (No. KYCX18_1075), and Nanyang Technological University.

N-Alkenylated triazolinone ylides were generated through copper-catalyzed oxy-N-alkenylation of triazolopyridines. The mechanistic course of this aerobic tandem reaction has been experimentally elucidated and primary photophysical data of the ylide products are also given.

An efficient strategy which integrates visible-light-induced iminyl-radical formation with carboimination of unactivated alkenes has been developed for the easy access of densely functionalized pyrroline derivatives. With fac-[Ir(ppy)3] as photoredox catalyst, the acyl oximes were converted into iminyl radical intermediates by one electron reduction, and evolve through a cascade of intramolecular cyclization and intermolecular carbon radical trapping to give the functionalized pyrrolines. The utilization of silyl enol ethers as coupling partners not only allows the introduction of synthetically useful ketone functionalities but also renders catalyst regeneration without any external reductants. This protocol is characterized by its mild reaction conditions and the tolerance of a broad range of functionalities.

Palladium-catalyzed intermolecular alkylation of enamides with α-bromo carbonyls was developed. Under mild reaction conditions, various cyclic and acyclic enamides reacted well with α-bromo carbonyls to afford the corresponding multi-substituted alkene products in good yields. The coupling products could be converted into very useful γ-amino acid, δ-amino alcohol, 1,4-dicarbonyl and γ-lactam derivatives.

A Cu(i)-catalyzed direct intermolecular oxyamination of electron deficient alkenes is disclosed. This process is characterized by difunctionalization of a variety of α,β-unsaturated ketones with easily available N-acyloxyamine reagents as both amine and oxygen donors, which delivers ester derivatives of β-amino alcohols in good yields as well as with high regioselectivity. Control studies suggested the involvement of alkyl radical species on the way of product formation.

A practical and effective copper-catalyzed dehydrogenative Diels–Alder reaction of gem-diesters and ketone with dienes has been established. The active dienophiles were generated in situ via a radical-based dehydrogenation process, which reacted with a wide variety of dienes to afford various polysubstituted cyclohexene derivatives in good to excellent yields.

A combined Lewis acid system comprising of two or more Lewis acids occasionally exhibits augmented catalytic activity in organic transformations which are otherwise unrealizable by either of the components exclusively. On the other hand, the efficient construction of multiple new C-C bonds and polycyclic structures in minimal steps remains a subject of great interest in both academia and industry. Herein we report an efficient method to assemble aryldihydronaphthalene derivatives via a cascade reaction of diarylalkynes with acrylates under the catalysis of a combined Lewis acid derived from In(III) salt and TMSBr. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Published version

Palladium-catalyzed intermolecular oxyarylation reaction of vinylacetates with retention of the double bond in the final product is developed. Under the optimized reaction conditions, the desired products of multisubstituted vinylesters could be obtained in moderate to high yields.

Minus-one programmed ribosomal frameshifting (-1 PRF) allows the precise maintenance of the ratio between viral proteins and is involved in the regulation of the half-lives of cellular mRNAs. Minus-one ribosomal frameshifting is activated by several stimulatory elements such as a heptameric slippery sequence (X XXY YYZ) and an mRNA secondary structure (hairpin or pseudoknot) that is positioned 2-8 nucleotides downstream from the slippery site. Upon -1 RF, the ribosomal reading frame is shifted from the normal zero frame to the -1 frame with the heptameric slippery sequence decoded as XXX YYY Z instead of X XXY YYZ. Our research group has developed chemically modified peptide nucleic acid (PNA) L and Q monomers to recognize G-C and C-G Watson-Crick base pairs, respectively, through major-groove parallel PNA·RNA-RNA triplex formation. L- and Q-incorporated PNAs show selective binding to double-stranded RNAs (dsRNAs) over single-stranded RNAs (ssRNAs). The sequence specificity and structural selectivity of L- and Q-modified PNAs may allow the precise targeting of desired viral and cellular RNA structures, and thus may serve as valuable biological tools for mechanistic studies and potential therapeutics for fighting diseases. Here, for the first time, we demonstrate by cell-free in vitro translation assays using rabbit reticulocyte lysate that the dsRNA-specific chemically modified PNAs targeting model mRNA hairpins stimulate -1 RF (from 2% to 32%). An unmodified control PNA, however, shows nonspecific inhibition of translation. Our results suggest that the modified dsRNA-binding PNAs may be advantageous for targeting structured RNAs.

A RhIII -catalyzed intramolecular oxidative cross-coupling between double bonds for the synthesis of macrolides is described. Under the optimized reaction conditions, macrocycles containing a diene moiety can be formed in reasonable yields and with excellent chemo- and stereoselectivity. This method provides an efficient approach to synthesize macrocyclic compounds containing a 1,3-conjugated diene structure.

A simple and direct C–H trifluoroethylation of aromatic amides has been developed. The protocol is applicable to a variety of aromatic amides, including ones derived from amino acids. The developed method can be used for further modifications of peptides. Preliminary mechanistic studies have been done by isolating the reaction intermediate.

Using α,α-difluoromethylene alkyne as a nontraditional one-carbon reaction partner, a synthetically novel method for the construction of isoindolin-1-one derivatives via Rh(III)-catalyzed [4+1] annulation reaction is reported. The 2-fold C–F bond cleavage not only enables the generation of desired product under an overall oxidant-free condition but also results in a net migration of carbon–carbon triple bond. In addition, the present reaction protocol exhibits a tolerance of a wide spectrum of functional groups due to the mild reaction conditions employed.

A general protocol for iridium catalyzed direct C−H amidation of cyclic N‐sulfonyl ketimines using sulfonyl, acyl and aryl azides as nitrogen source is reported herein. The reaction takes place at room temperature with acyl and aryl azides, while an elevated temperature needed with sulfonyl azides to furnish aminated sultams in excellent yields with complete chemo and regioselectivity, thus providing a robust and environmentally benign process to the synthesis of aminosultams. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

A new strategy to open the 2-allyl-2H-azirines by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) promotion in metal-free conditions affording 1-azatrienes that in situ electrocyclize to the pyridines in good to excellent yields is reported. The reaction displays a broad substrate scope and good tolerance to a variety of substituents including aryl, alkyl, and heterocyclic groups. In addition, one-pot synthesis of pyridines from oximes via in situ formation of 2H-azirines was achieved.