Tandem cycloisomerization/Suzuki coupling of arylethynyl MIDA boronates

A tandem gold-catalyzed cycloisomerization/Suzuki cross-coupling sequence involving arylethynyl-N-methyliminodiacetic acid boronates is described. Combining the mildness of homogeneous gold catalysis with the versatility of N-methyliminodiacetic acid (MIDA) boronates, this tandem two-step method enables the rapid assembly of various aryl-substituted heterocycles without having to isolate or purify any heterocyclic MIDA boronate intermediates. Another major advantage of this method is that a wide range of heterocycles bearing different aryl groups may be made from a single MIDA boronate alkyne precursor.     

One-pot reductive amination and Suzuki-Miyaura cross-coupling of formyl aryl and heteroaryl MIDA boronates in array format

Formyl-substituted aryl and heteroaryl MIDA boronates were prepared by a DMSO-free method and used in the first reported one-pot reductive amination-Suzuki-Miyaura cross-coupling sequence. This sequence was then carried out in parallel array format, using microwave-assisted in situ release cross-coupling of MIDA boronates to generate a library with diversity along two axes, affording rapid and convenient access to an array of druglike molecules.     

Direct Access to MIDA Acylboronates through Mild Oxidation of MIDA Vinylboronates

Acylboronate esters/trifluoroborates represent an elusive class of boronates that are of increasing interest for both fundamental study as well as applications at the interface of chemistry and biology. Their preparation has been limited by the use of strongly basic anions, often introduced in multistep reactions. Herein, we demonstrate the facile preparation of acylboronate N‐methyliminodiacetyl (MIDA) esters from alkenyl‐2‐boronate esters through mild dihydroxylation and meta ‐periodate cleavage. Given the well‐known functional‐group tolerance of this mild reaction sequence and the availability of alkenyl‐2‐boronates, this method should greatly increase access to acylboronate MIDA esters.     

Vinyl MIDA boronate: a readily accessible and highly versatile building block for small molecule synthesis

Iterative cross-coupling represents a potentially general approach for the simple, efficient, and flexible construction of natural products, pharmaceuticals, and materials. N-Methyliminodiacetic acid (MIDA) boronates represent a promising platform for the development of this type of synthesis strategy. This report describes the discovery that vinyl MIDA boronate (1) is an air- and chromatographically stable compound that can be conveniently prepared on a multigram scale and serve as a versatile starting material for the preparation of a range of new MIDA boronate building blocks. Analogous to tert-butylethylene, 1 is also an excellent substrate for olefin cross-metathesis, providing access to a range of trans-alkenyl MIDA boronates as single stereoisomers. An improved synthesis of the very versatile bifunctional building block trans-(2-bromovinyl) MIDA boronate (2) is also described. Collectively, these results contribute to the expanding generality of the iterative cross-coupling approach.     

Oxidative Difunctionalization of Alkenyl MIDA Boronates: A Versatile Platform for Halogenated and Trifluoromethylated α‐Boryl Ketones

The synthesis of halogenated and trifluoromethylated α‐boryl ketones via a one‐pot oxidative difunctionalization of alkenyl MIDA boronates is reported. These novel densely functionalized organoborons bearing synthetically and functionally valuable carbonyl, halogen/CF₃ and boronate moieties within the same molecule are synthetically challenging for the chemist, but have great synthetic potential, as demonstrated by their applications in a straightforward synthesis of borylated furans. The generality of this reaction was extensively investigated. This reaction is attractive since the starting materials, alkenyl MIDA boronates, are easily accessible.     

Synthesis of Aminoboronic Acid Derivatives from Amines and Amphoteric Boryl Carbonyl Compounds

Herein, we demonstrate the use of α‐boryl aldehydes and acyl boronates in the synthesis of aminoboronic acid derivatives. This work highlights the untapped potential of boron‐substituted iminium ions and offers insights into the behavior of N‐methyliminodiacetyl (MIDA) boronates during condensation and tautomerization processes. The preparative value of this contribution lies in the demonstration that various amines, including linear and cyclic peptides, can be readily conjugated with boron‐containing fragments. A mild deprotection of amino MIDA‐boronates enables access to α‐ and β‐aminoboronic acids in high chemical yields. This simple process should be applicable to the synthesis of a wide range of bioactive molecules as well as precursors for cross‐coupling reactions.     

Stereoselective Direct Chlorination of Alkenyl MIDA Boronates: Divergent Synthesis of E and Z α‐Chloroalkenyl Boronates

The individual molecules of α‐chloroalkenyl boronates include both an electrophilic C−Cl bond and a nucleophilic C−B bond, which makes them intriguing organic synthons. Reported herein is a stereodivergent synthesis of both E and Z α‐chloroalkenyl N ‐methyliminodiacetyl (MIDA) boronates through the direct chlorination of alkenyl MIDA boronates using t BuOCl and PhSeCl reagents, respectively. Both reaction processes are stereospecific and the use of sp³‐B MIDA boronate is the key contributor to the reactivity. The synthetic value of the boronate products was also demonstrated.     

Multistep synthesis of complex boronic acids from simple MIDA boronates

Due to its sensitivity to most synthetic reagents, it is typically necessary to introduce the boronic acid functional group just prior to its utilization. Overcoming this important limitation, we herein report that air- and chromatographically stable MIDA boronates are compatible with a wide range of common reagents which enables the multistep synthesis of complex boronic acid building blocks from simple B-containing starting materials. X-ray and variable temperature NMR studies link the unique stability of MIDA boronates to a kinetic inaccessibility of the potentially reactive boron p-orbital and/or nitrogen lone pair. These findings were collectively harnessed to achieve a short and modular total synthesis of (+)-crocacin C via the iterative cross-coupling of a structurally complex, MIDA-protected haloboronic acid building block.     

Visible-light-promoted alkylation of unsaturated MIDA boronates using Ru(bpy)3Cl2 as the photoredox catalyst

The development of a visible light-mediated atom transfer radical addition (ATRA) of perfluoroalkyl iodides to ethynyl-, vinyl- and allyl-MIDA boronates using the reductive and oxidative quenching of [Ru(bpy)₃]Cl₂ is described. Using an operationally simple and mild protocol, the corresponding MIDA boronates containing perfluoroalkyl groups were obtained in moderate to high yields. The structures of three products were confirmed by single crystal X-ray diffraction studies.     

Microwave-mediated synthesis of N-methyliminodiacetic acid (MIDA) boronates

A library of over 20, mainly aryl or heteroaryl, N-methyliminodiacetic acid (MIDA) boronates have been synthesised. A rapid microwave-mediated (MW) method (5–10 min) has been developed using polyethylene glycol 300 (PEG 300) as solvent. However, acetonitrile (MeCN) and dimethylformamide (DMF) were found to be alternative solvents, the latter especially for 2-substituted aryl boronic acids.     

Suzuki-Miyaura cross-coupling of alkenyl tosylates with alkenyl MIDA boronates

A practical procedure for the palladium-catalysed Suzuki-Miyaura coupling of various alkenyl tosylates with alkenyl MIDA boronates has been developed. Commercially available trans-bromo[N-succinimidyl-bis(triphenylphosphine)]palladium(II) [Pd(PPh₃)₂NBS] is an effective catalyst under the slow release conditions of MIDA boronates; with less activated alkenyl tosylates addition of the cheap, air-stable tricyclohexylphosphine tetrafluoroborate enhances reactivity.     

纤维素酶的二步分离纯化新工艺

 以普通定性滤纸为底物 ,经碱处理后 ,研究其对纤维素酶的亲和吸附作用。结果表明 ,普通定性滤纸对纤维素酶具有比较强的特异性吸附作用 ,能够从粗酶液中分离出纤维素酶 ,再经POROS 2 0HQ阴离子交换柱纯化后即可得到电泳纯的纤维素酶。该法大大简化了传统的纤维素酶纯化工艺 ,所得的纤维素酶活力极高 ,比活达 35 0U/mg以上 ,滤纸一步吸附后纤维素酶的纯化倍数为 9 5 5 ,活性回收率在 10 %左右。纯化后的纤维素酶为内切 β 葡聚糖酶 ,相对分子质量为 6 0 0 0 0 ,最佳 pH为 4 0 ,最佳温度为 70℃。     

Synthesis of Acylborons by Ozonolysis of Alkenylboronates: Preparation of an Enantioenriched Amino Acid Acylboronate

A concise synthesis of acylborons was achieved by ozonolysis of alkenyl MIDA (N ‐methyliminodiacetic acid) boronates. This reaction exhibits excellent functional‐group tolerance and is applicable to various acyl MIDA boronates and potassium acyltrifluroborates (KATs) which could not be synthesized by previous methods. In addition, α‐amino acylborons, which would be essential for peptide ligations, were prepared for the first time. The acylboron of l ‐alanine was obtained in high enantiopurity and found to be configurationally stable. Oligopeptide synthesis between the α‐amino KATs and amino acid in dilute aqueous media was studied.     

(Z)-(2-bromovinyl)-MIDA boronate: a readily accessible and highly versatile building block for small molecule synthesis

Iterative cross-coupling represents a potentially general approach for the simple, efficient, and flexible construction of a wide range of functional small molecules. In this context, (Z)-(2-bromovinyl)-N-methyliminodiacetic acid (MIDA) boronate is a very useful building block for small molecule synthesis. This compound can serve as a starting material for the preparation of a wide range of cis-alkene-containing MIDA boronates. This compound can also be used for the iterative cross-coupling-based synthesis of various cis-olefin-containing targets. Collectively, these results contribute to the expanding generality of the MIDA boronate platform.     

Site‐Differentiated Polyboron Arenes Prepared by Direct C?H Borylation and Their Highly Selective Suzuki–Miyaura Cross‐Coupling Reactions

Di‐ and polyboron (hetero)arenes, site‐differentiated with MIDA boronyl (MIDA=N‐methyliminodiacetic acid) and pinacolato boronyl (Bpin), were prepared by an iridium‐catalyzed direct C H borylation of readily available (hetero)aryl MIDA boronates. The excellent synthetic uses of these multisite nucleophiles were demonstrated by the high‐yield production of a variety of multifunctionalized poly(hetero)arenes with the highly chemoselective Suzuki–Miyaura coupling (SMC) of the Bpin moiety being an essential step.     

Site‐Differentiated Polyboron Arenes Prepared by Direct C?H Borylation and Their Highly Selective Suzuki–Miyaura Cross‐Coupling Reactions

Di‐ and polyboron (hetero)arenes, site‐differentiated with MIDA boronyl (MIDA=N‐methyliminodiacetic acid) and pinacolato boronyl (Bpin), were prepared by an iridium‐catalyzed direct C H borylation of readily available (hetero)aryl MIDA boronates. The excellent synthetic uses of these multisite nucleophiles were demonstrated by the high‐yield production of a variety of multifunctionalized poly(hetero)arenes with the highly chemoselective Suzuki–Miyaura coupling (SMC) of the Bpin moiety being an essential step.     

MIDA- and TIDA-Boronates Stabilize α-Radicals Through B−N Hyperconjugation

Multifunctional organoboron compounds increasingly enable the simple generation of complex, Csp³-rich small molecules. The ability of boron-containing functional groups to modify the reactivity of α-radicals has also enabled a myriad of chemical reactions. Boronic esters with vacant p-orbitals have a significant stabilizing effect on α-radicals due to delocalization of spin density into the empty orbital. The effect of coordinatively saturated derivatives, such as N-methyliminodiacetic acid (MIDA) boronates and counterparts, remains less clear. Herein, we demonstrate that coordinatively saturated MIDA and TIDA boronates stabilize secondary alkyl α-radicals via σ_B-N hyperconjugation in a manner that allows site-selective C−H bromination. DFT calculated radical stabilization energies and spin density maps as well as LED NMR kinetic analysis of photochemical bromination rates of different boronic esters further these findings. This work clarifies that the α-radical stabilizing effect of boronic esters does not only proceed via delocalization of radical character into vacant boron p-orbitals, but that hyperconjugation of tetrahedral boron-containing functional groups and their ligand electron delocalizing ability also play a critical role. These findings establish boron ligands as a useful dial for tuning reactivity at the α-carbon.     

外泌体分离与纯化技术研究进展

外泌体是所有真核细胞分泌到细胞外的直径介于30～150 nm的一种膜性纳米囊泡,参与细胞间生物信号的传递。大量实验证据表明,外泌体参与多种生物功能并发挥重要作用,包括蛋白质、RNA和脂质等生物分子的转移及多种疾病生理和病理过程的调节,被认为是疾病诊断、治疗和预后的重要的生物标志物和药物载体,因此发展简单、高效、经济的外泌体分离与纯化技术将有助于疾病的早期诊断和精准治疗。目前,利用外泌体的物理化学和生物化学特性已开发出多种分离外泌体的技术,但仍缺乏标准化和规模化临床级外泌体的分离方法,从而限制了其临床应用。另外,对分离出的外泌体的特征、纯度和数量的鉴定是判断外泌体分离纯化方法优劣的重要指标。本文综述了外泌体分离与纯化技术以及鉴定方法的研究进展,主要讨论分离技术的机制、性能、挑战和前景以及外泌体的鉴定方法,以期为外泌体的分离纯化提供新的思路和解决策略。     

Diversity‐Oriented Synthesis of α‐Functionalized Acylborons and Borylated Heteroarenes by Nucleophilic Ring Opening of α‐Chloroepoxyboronates

The ring‐opening reactions of N‐methyliminodiacetyl (MIDA) α‐chloroepoxyboronates with different nucleophiles allow the modular synthesis of a diverse array of organoboronates. These include seven types of α‐functionalized acylboronates and seven types of borylated heteroarenes, some of which are difficult‐to‐access products using alternative methods. The common synthons, α‐chloroepoxyboronates, could be viably synthesized by a two‐step procedure from the corresponding alkenyl MIDA boronates. Mild reaction conditions, good functional‐group tolerance, and generally good efficiency were observed. The utility of the products was also demonstrated.     

三步柱色谱法从江浙蝮蛇蛇毒中分离纯化类凝血酶

建立了一种用CM Sepharose CL-6B阳离子交换、DEAE Sepharose Fast Flow阴离子交换和Sephadex G-75凝胶排阻三步柱色谱从江浙蝮蛇蛇毒中分离纯化类凝血酶的方法。在实验室小柱分离方案的基础上,对该纯化工艺进行了放大。当上样量达实验室小柱的25倍时,所得类凝血酶的质量指标与实验室小柱基本一致。采用该法所得的蝮蛇类凝血酶经Shim-pack Diol-300高效凝胶排阻柱测得其相对分子质量约为33500,用Shim-pack VP-ODS反相色谱柱检测其纯度约为96%。从江浙粗蛇毒中提取类凝血酶时,类凝血酶的总质量收率约为0.3%,总活性收率约为64%,比活可达2000 U/mg。