The stereoselective preparation of fullerene bis-adducts through nontethered methods remains difficult due to the significant amount of regioisomers produced. The trans-4 aziridinofullerenes, C60(NC6H4R)n (n = 1 or 2, R = OMe, OEt, OBu), were selectively synthesized even without a catalyst by reacting octabromofullerene with the corresponding aniline. Nuclear magnetic resonance spectroscopy, UV-vis spectroscopy, and X-ray structural analysis provided convincing characterization of the compounds. A possible reaction process was proposed to clarify the synthesis of highly regioselective trans-4-bisaziridinofullerenes. The possible use of these aziridinofullerene derivatives as propellant stabilizers was also explored.
Chemically, N1 nitrogen of piperazic acid is more nucleophilic than N2 nitrogen, but amide bonds predominantly formed at N2 nitrogen are prevalent in piperazic acid-containing natural products, with only one exception of sanglifehrin. Thus two orthogonal protecting groups of nitrogen are often employed to realize selective coupling of N2 nitrogen, resulting in increased synthetic steps and low synthetic efficiency. However, we developed selective deprotection of N2-Cbz from the N1,N2-diCbz piperazic acid-containing peptide to form the N2 amide exclusively, avoiding the tedious orthogonal protection strategy commonly applied to the easily-accessible N1,N2-diCbz piperazic acid as the building block. We employ this method to achieve an efficient synthesis of piperazic acid-containing cyclodepsipeptide core of verucopeptin with an overall yield of 21%. The key steps include late stage coupling of piperazic acid with 3-hydroxyleucine derivatives, and HATU-mediated macrolactamization of 19-membered macrocycle at N9 and C10. The selective deprotection of N2-Cbz from the N1,N2-diCbz-piperazic acid at late-stage would greatly facilitate the total syntheses of piperazic acid-containing cyclodepsipeptides of biological interest.
C-Glycosides are critical, naturally occurring products and medicinal candidates, and extensive efforts have been made to explore efficient approaches for creating C-glycosidic bonds. Transition-metal-catalysis, particularly nickel-catalyzed C-glycosylation reactions constitute a promising strategy. However, achieving a stereoselective synthesis of α- and β-C-glycosides has been a long-standing challenge. To address this problem, a variety of nickel-mediated strategies have been developed. This review highlights recent developments in the nickel-catalyzed diastereoselective C-glycosylation reactions and briefly summarizes the mechanistic understandings of these methods.
Radiotherapy is a mainstay treatment for malignant tumors in clinical. However, enhancing radiation damage to tumor cells meanwhile sparing normal tissues is still a great challenge in radiotherapy. Nanomaterials with high atomic number (Z) values are promising radiosensitizers by promoting the radiation energy deposition in irradiated tumor cells, thus enhancing the therapeutic ratio of radiotherapy. In this review, we described the mechanisms of high-Z element radiosensitizers and systematically summarized the recent progress on metal-based nanomaterials, including high-Z metal nanoparticles, metal-organic frameworks (MOFs) and other high-Z-containing nanomaterials. Finally, further potential and challenges in this field were discussed.
Organic luminogens with persistent room temperature phosphorescence (RTP) have drawn tremendous attentions due to their prom-ising potentials in optoelectronic devices, information storage, biological imaging, and anti-counterfeiting. In this work, six triazatrux-ene-based lumiogens with different peripheral substituents and configurations are synthesized and systematically studied. The results show that their fluorescence quantum yields in solid states range from 15.73% to 37.58%. Dispersing the luminogens as guest into the host (PPh3) could turn on the persistent RTP, where PPh3 acts as not only a rigid matrix to suppress the non-radiative transitions of the guest, but also provides energy transfer channels to the guest. The maximum phosphorescence efficiency and the longest lifetime could reach 29.35% and 0.99 s in co-crystal films of 6-TAT-CN/PPh3 and 5-TAT-H/PPh3, respectively. Moreover, these host-guest co-crystalline films exhibit great potentials in advanced dynamic data encryption and anti-counterfeiting. This work deepens the insight for low cost, halogen-free, and facile fabrication of all-organic persistent RTP materials.
Isochromanone is the core structure of many bioactive compounds. Direct oxidation of isochromans is one of leading methods for the construction of isochromanones, while most established processes remain suffering from the use of environmental unfriendly metal oxidants, harsh reaction conditions, and the difficulty in catalyst recycling and production separation. Herein, we report a convenient, cost-effective, and green method for the synthesis of high-value added isochromanones via isochroman oxidations with O2 by a novel heterogeneous vanadium cluster catalyst (Cat.1) under mild conditions. This reaction protocol demonstrates high catalytic activity with good catalyst recyclability and reusability for a wide scope of substrates.
Carbon dots (CDs) are an emerging class of nanomaterials with intriguing photophysical properties. Recently, achieving room-temperature phosphores-cence (RTP) for CDs have attracted considerable attention for biomedical and information applications. However, the CDs based RTP materials generally require the use of polymeric and inorganic matrix to provide the rigid environments, which remains a great challenge to obtain matrix-free CDs with RTP. Herein, a novel supramolecular strategy based on strong interparticle interactions has been developed to attain this objective, by covalent decoration of ureido-pyrimidinone (UPy, a multiple hydrogen bonding unit) on the surface of CDs. Structural characterizations validated the core-shell structure of the as-prepared CDs (EDTA-CDs) and demonstrated the successful attachment of UPy via post-modification (UPy-CDs). The presence of UPy recognition units render the strong hydrogen bonding between UPy-CDs, which stabilizes the triplet state via rigidifying effect. As a result, UPy-CDs exhibit matrix-free efficient RTP (λem = 534 nm) with high brightness and long lifetime (33.6 ms) in the solid state. Owing to the dual-emission character, we further explored the application potential of UPy-CDs in information encryption and anti-counterfeiting. Overall, this work provides a new and facile strategy for achieving matrix-free phosphorescent CDs with elegant incorporation of supramolecular chemistry.
Pd-catalyzed asymmetric allylic C−H functionalization has emerged as a powerful tool to access chiral, densely functionalized molecules from easily ac-cessible alkenes, enabling the increase of the step- or atom-economy by minimizing functional group manipulations for preparing allylating reagents. Due to the inadequacy of stereoselection strategies, the asymmetric allylic C-H functionalization is still in the early stage. In this essay, we will describe our journey to identification of asymmetric catalytic systems, mechanism of allylic C−H activation, control of stereo- and regioselectivity, and applica-tions in asymmetric synthesis.
Protein glycosylation is the most complex and diverse form of post-translational modification in human body. Meanwhile, glycosylation of peptides and proteins emerges as a promising strategy to improve the pharmacokinetic profile of peptide- and protein-based therapeutics. Owing to the importance of protein glycosylation, rigorous evaluation of the relationship between the precise structure and biological function of glycoproteins has to be per-formed. Recently, chemical synthesis, chemoenzymatic synthesis and semisynthesis strategy have attracted extensive attentions towards the prepara-tion of structurally defined glycopeptides and glycoproteins; the obtained synthetic glycoforms thus enable the thorough investigation of specific effects of protein glycosylation. This review highlights the recent progress in the development of novel strategies, preparation of homogeneous glycoproteins and exploration of structure-activity relationships. On this basis, the challenges and prospects are discussed.
Herein, we have developed a strategy of Rh(III)-catalyzed C–H activation of N-nitrosoanilines and iodonium ylides to construct novel tetralydrocarbzol-4-one scaffolds, which provided valuable templates for sequential C-H functionalization such as alkylation, alkenyla-tion, amidation and (hetero)arylation at C5-position of tetralydrocarbzol-4-one with different coupling partners. Gram-scale synthesis and further transformation of tetralydrocarbzol-4-one derivatives to Ondansetron and its analogues demonstrated the utility of this protocol, which enabled the concise and diverse construction of biologically active molecules.
Currently, solid-state fluorescent carbonized polymer dots (CPDs) have attracted attention increasingly due to their applications for op-toelectronic display. However, designing CPDs possessing solid-state fluorescence and clarifying the fluorescence mechanism still remain challenging. Herein, we initially synthesized a novel type of polythiophene derivatives CPDs, poly-4,4’-(thiophene-3,4-diyl)dibenzoic acid carbonized polymer dots (PDBA-CPDs) with solid-state fluorescence. Subsequently, the structural and optical characterization re-vealed that solid-state fluorescence originating from the aggregation induced emission of the CPDs. In brief, in aggregation state, the remaining polymer structure groups on the surface of the CPDs overlapped and weakened the non-radiative transition, enhancing sol-id-state fluorescence emission. Thirdly, three polythiophene-derived CPDs were designed to further demonstrate the aggregation in-duced solid-state fluorescence mechanism. Finally, owing to their unique properties of solid-state fluorescence, the white LEDs (light emitting diodes) were fabricated with high color rendering index (CRI) of 82.7 and CIE coordinates of (0.37, 0.39) using commercial 460 nm chip. This work facilitates the development of CPDs’ solid-state fluorescence mechanisms and advances the application of CPDs in the field of optoelectronics.
By employing thiazole and 4-chlorothiazole as the A′ units, two A-D-A′-D-A type nonfused-ring electron acceptors (NFREAs) Tz-H and Tz-Cl were designed and synthesized. Replacing thiazole in Tz-H with 4-chlorothiazole can not only remarkably shorten the synthetic route through C-H direct arylation but also enhance molecular planarity with the simultaneous incorporation of S···N and S···Cl non-covalently conformational locks (NoCLs). The photovoltaic devices based on PM6:Tz-Cl exhibited a power conversion efficiency as high as 11.10%, much higher than that of PM6:Tz-H (6.41%), mainly due to more efficient exciton dissociation, better and more balanced carrier mobility, less charge recombination, and more favorable morphology. These findings demonstrate the great potential of NoCLs in achieving low-cost and high-performance NFREAs.
The utilization of cyclobutanones as the synthon in transition metal catalysis has been made great success. Because C(carbonyl)−C bond of cyclobutanones can be cleaved through strain release. Despite those advancements, the main catalysts in literature are Rh catalysts or Ni catalysts and the reaction with C–H bond is still underdeveloped. Herein, we realized the first palladium-catalyzed skeletal reorganisation of cyclobutanones invoving successive cleavage of C(carbonyl)−C bonds and C−H bond cleavage, which con-stitutes an rapid access to diverse indanones.
Lobophorins (LOBs) belong to a large family of spirotetronate antibiotics with antibacterial and antitumor activities. In this study, we demonstrated the function of LobP1, a P450 monooxygenase encoded in the LOB biosynthetic gene cluster, by in vivo deletion and in vitro biochemical assays. The disruption of lobP1 led to the isolation of three new LOBs derivatives (3‒5) and three known ones (6‒8) without the hydroxyl group at C-32. LobP1 was shown to have relatively broad substrate scope. Determing the kinetic parameters of LobP1 towards different substrates revealed that LobP1 preferred substrate with a nitrosugar. The major product LOB E (6) from the ∆lobP1 mutant displayed better cytotoxic activities against several cancer cell lines than LOB B, the C-32 hydroxlated counterpart.
Usually, the aniline-based late-transition-metal catalysts often require bulky steric substituents on both sides of the ortho-aryl position to achieve efficient suppression of chain transfer in ethylene polymerization. In this contribution, we demonstrated that α-diimine catalysts based on naphthylamine with only one bulky ortho-aryl substituent also demonstrated excellent capabilities to suppress the chain transfer. Firstly, a class of α-diimine nickel and palladium complexes with only one o-aryl-dibenzhydryl or o-aryl-dibenzosuberyl substituent were synthesized and characterized. Secondly, the as-prepared naphthylamine-based nickel catalysts demonstrated outstanding activities and yielded lightly branched (16-40/1000C) polyethylenes with very high molecular weights (445.8-854.3 kg/mol) in ethylene polymerization. In comparison, the corresponding palladium catalysts showed moderate activities, generating moderately branched polyethylenes with moderate molecular weights (21.6-82.0 kg/mol). Moreover, the palladium catalysts could also copolymerize ethylene and methyl acrylate (MA), albeit in low activity (level of 103 g·mol-1·h-1)，providing E-MA copolymers with low to moderate molecular weight (1.4-16.3 kg/mol) and a moderate level of incorporation ratio (2.4-7.4 mol%) and branching density. As compared with aniline-based nickel and palladium catalysts, the naphthylamine-based catalysts displayed a superior ability to suppress the chain transfer reactions and could give access to (co)polymers with orders of magnitude higher molecular weight in ethylene (co)polymerization.