Ruthenium‐Catalyzed C7 Amidation of Indoline CH Bonds with Sulfonyl Azides

A ruthenium‐catalyzed direct C7 amidation of indoline C?H bonds with sulfonyl azides was developed. This procedure allows the synthesis of a variety of 7‐amino‐substituted indolines, which are useful in pharmaceutical. The good functional tolerances, as well as the mild conditions, are prominent feature of this method.     

Highly Curved Bowl‐Shaped Fragments of Fullerenes: Synthesis,Structural Analysis,and Physical Properties

Highly curved buckybowls 3 , 4 , and 5 were synthesized from planar precursors, fluoranthenes 8 , benzo[k]fluoranthenes 10 and naphtho[1,2‐k]‐cyclopenta[cd]fluoranthenes 12 , respectively, using straightforward palladium‐catalyzed cyclization reactions. These fluoranthene‐based starting materials were easily prepared from 1,8‐bis(arylethynyl)naphthalenes 6 . Both buckybowls 3 and 4 are fragments of C₆₀, whereas 5 is a unique subunit of C₇₀. The curved structures were identified by X‐ray crystallography, and they are deep bowls. The maximum π‐orbital axis vector (POAV) pyramidalization angle in both 3 and 4 is 12.8°. Such a high curvature is very rarely obtained. Buckybowls 5 are less curved than the others because they have a lower density of five‐membered rings, analogous to the tube portion of C₇₀. Cyclopentaannulation increases the bowl depths of 3 and 4 , but not the maximum POAV pyramidalization angle. Among the eight buckybowls studied herein, five form polar crystals. The bowl‐to‐bowl inversion dynamics of these buckybowls can be classified into two types; one has a planar transition structure, whereas the other has an S‐shaped transition structure. A larger longitudinal length of these buckybowls corresponds to a stronger preference for the latter. The photophysical properties of these buckybowls were examined and compared with those of C₆₀ and C₇₀. Buckybowls 5 have absorption bands at wavelengths greater than 450 nm, which are similar to those of C₇₀. The chiral resolution of the mono‐substituted buckybowl 4 ac was also studied by using HPLC with a chiral column.     

Dissolution of cellulose in aqueous NaOH/urea solution: role of urea

Urea can improve the solubility and stability of cellulose in aqueous alkali solution, while its role has not come to a conclusion. To reveal the role of urea in solution, NMR was introduced to investigate the interaction between urea and the other components in solution. Results from chemical shifts and longitudinal relaxation times show that: (1) urea has no strong direct interaction with cellulose as well as NaOH; (2) urea does not have much influence on the structural dynamics of water. Urea may play its role through van der Waals force. It may accumulate on the cellulose hydrophobic region to prevent dissolved cellulose molecules from re-gathering. The driving force for the self-assembly of cellulose and urea molecules might be hydrophobic interaction. In the process of cellulose dissolution, OH^? breaks the hydrogen bonds, Na⁺ hydrations stabilize the hydrophilic hydroxyl groups and urea stabilizes the hydrophobic part of cellulose.     

人全血中锶元素的分布及血浆中锶元素的形态分析

建立了基于液相色谱-电感耦合等离子体质谱(LC-ICP-MS)联用定量分析血浆中锶元素形态的方法,方法检出限为0.3 ng/mL,无机锶加标回收率为88%~97%,利用LC-ICP-MS分析,无机锶质量浓度在1.0~50.0μg/L之间时,线性回归系数r大于0.999。通过湿法消解,对73份人血和血浆用电感耦合等离子体质谱(ICP-MS)测定得出全血锶平均含量为38.1 ng/mL,血浆平均锶含量为35.8 ng/mL,说明全血中绝大部分锶存在于血浆中。通过LC-ICP-MS对血浆锶进行形态分析得出无机锶平均含量为10.2%,随色谱流出的有机锶平均含量为18.7%,而未随色谱流出的有机锶平均含量为71.1%,因此可推断摄入人体的锶主要以有机锶的形式发挥其生理作用。     

A Borinic Acid Polymer with Fluoride Ion‐ and Thermo‐responsive Properties that are Tunable over a Wide Temperature Range

A new type of smart borinic acid polymer with luminescence and multiple stimuli‐responsive properties is reported. In DMSO with small amounts of water, the homopolymer PBA shows a tunable upper critical solution temperature (UCST). As the amount of water increases from 0 to 2.5 % (v/v), the UCST rises linearly from 20 °C to 100 °C (boiling point of water). Thus, the thermal responsive behavior can be tuned over a wide temperature range. Furthermore, polymer solutions in DMSO show a reversible response to fluoride ions, which can be correlated to the presence of the Lewis acidic borinic acid groups. Upon addition of fluoride, the polymer becomes soluble because the functional R₂BOH groups are converted into ionic [R₂BF₂]^? groups, but turns insoluble again upon addition of H₂O, which reverses this process.     

Highly Enantioselective Kinetic Resolution of Axially Chiral BINAM Derivatives Catalyzed by a Brønsted Acid

A highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid‐catalyzed imine formation and transfer hydrogenation cascade process was developed. The kinetic resolution provides a convenient route to chiral BINAM derivatives in high yields with excellent enantioselectivities.     

An Unusual Dehydratase Acting on Glycerate and a Ketoreducatse Stereoselectively Reducing α‐Ketone in Polyketide Starter Unit Biosynthesis

Polyketide synthases (PKSs) usually employ a ketoreductase (KR) to catalyze the reduction of a β‐keto group, followed by a dehydratase (DH) that drives the dehydration to form a double bond between the α‐ and β‐carbon atoms. Herein, a DH*‐KR* involved in FR901464 biosynthesis was characterized: DH* acts on glyceryl‐S‐acyl carrier protein (ACP) to yield ACP‐linked pyruvate; subsequently KR* reduces α‐ketone that yields L ‐lactyl‐S‐ACP as starter unit for polyketide biosynthesis. Genetic and biochemical evidence was found to support a similar pathway that is involved in the biosynthesis of lankacidins. These results not only identified new PKS domains acting on different substrates, but also provided additional options for engineering the PKS starter pathway or biocatalysis.     

Crowning Proteins: Modulating the Protein Surface Properties using Crown Ethers

Crown ethers are small, cyclic polyethers that have found wide‐spread use in phase‐transfer catalysis and, to a certain degree, in protein chemistry. Crown ethers readily bind metallic and organic cations, including positively charged amino acid side chains. We elucidated the crystal structures of several protein‐crown ether co‐crystals grown in the presence of 18‐crown‐6. We then employed biophysical methods and molecular dynamics simulations to compare these complexes with the corresponding apoproteins and with similar complexes with ring‐shaped low‐molecular‐weight polyethylene glycols. Our studies show that crown ethers can modify protein surface behavior dramatically by stabilizing either intra‐ or intermolecular interactions. Consequently, we propose that crown ethers can be used to modulate a wide variety of protein surface behaviors, such as oligomerization, domain–domain interactions, stabilization in organic solvents, and crystallization.     

Cyclic‐Disulfide‐Based Prodrugs for Cytosol‐Specific Drug Delivery

The cytosolic conversion of therapeutically relevant nucleosides into bioactive triphosphates is often hampered by the inefficiency of the first kinase‐mediated step. Nucleoside monophosphate prodrugs can be used to bypass this limitation. Herein we describe a novel cyclic‐disulfide class of nucleoside monophosphate prodrugs with a cytosol‐specific, reductive release trigger. The key event, a charge‐dissipating reduction‐triggered cyclodeesterification leads to robust cytosolic production of the cyclic 3′,5′‐monophosphate for downstream enzymatic processing. The antiviral competence of the platform was demonstrated with an O‐benzyl‐1,2‐dithiane‐4,5‐diol ester of 2′‐C‐methyluridine‐3′,5′‐phosphate. Both in vitro and in vivo comparison with the clinically efficacious ProTide prodrug of 2′‐deoxy‐2′‐α‐fluoro‐β‐C‐methyluridine is provided. The cytosolic specificity of the release allows for a wide range of potential applications, from tissue‐targeted drug delivery to intracellular imaging.