A study of ADMET polyethylene with 21-carbon branches on every 15th compared to every 19th carbon: What a difference four extra backbone methylenes make

Precision polyethylenes with 21-carbon alkyl branches precisely spaced on every either 15th or 19th carbon along the polymer backbone lead to the formation of two kinds of lamellae, yielding different thicknesses during the crystallization process. Thinner lamellae originate from side-chain crystallization, whereas thicker lamellae are formed by cocrystallization of the branch and the main chain. Side-chain crystallization (separate from main chain crystallization) is favored when the branch is placed on every 15th carbon. Cocrystallization (side chain with main chain) is favored with the branch on every 19th carbon. Both form stable hexagonal crystal units. A branch spacing separation of just four carbons along the main chain makes a remarkable difference in crystallization behavior. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3090–3096     

Chemical Synthesis of O‐Glycosylated Human Interleukin‐2 by the Reverse Polarity Protection Strategy

The chemical synthesis of human interleukin‐2 (IL‐2) , having a core 1 sugar, by a ligation method is reported. Although IL‐2 is a globular glycoprotein, its C‐terminal region, in particular (99‐133), is extremely insoluble when synthesized by solid‐phase method. To overcome this problem, the side‐chain carboxylic acid of the Glu residues was protected by a picolyl ester, thus reversing its polarity from negative to positive. This reverse polarity protection significantly increased the isoelectric point of the peptide segment and made it positive under acidic conditions and facilitated the purification. An efficient method to prepare the prolyl peptide thioester required for the synthesis of the (28‐65) segment was also developed. These efforts resulted in the total synthesis of the glycosylated IL‐2 having full biological activity.     

High-Frequency ESR Measurements of <Emphasis Type="Italic">S</Emphasis> = 1/2 1-D Heisenberg Antiferromagnetic Zig-Zag Chain (VO)(SO<Subscript>4</Subscript>)(2,2-bpy)

High-frequency electron spin resonance (ESR) measurements of S = 1/2 one-dimensional Heisenberg antiferromagnetic zig-zag chain substance (VO)(SO₄)(2,2-bpy) were performed in the temperature region from 1.8 to 265 K. ESR measurements at 265 K show typical powder pattern spectra of the V⁴⁺ ion and g _|| = 1.925 ± 0.001 and g _⊥ = 1.976 ± 0.001 were obtained. Although the magnetic susceptibility shows a maximum at 3.1 K suggesting the existence of a short-range order, no g-shift and line width broadening were observed down to 1.8 K. We suggest that these temperature-independent features of ESR can be attributed to the result of frustration in (VO)(SO₄)(2,2-bpy).     

Dioxygen activation and substrate oxygenation by a p-nitrothiophenolatonickel complex: unique effects of an acetonitrile solvent and the p-nitro group of the ligand

The nickel(II) complex [Ni(Tp(Me2)) (SC(6)H(4)NO(2))] [1a; Tp(Me2) = hydrotris(3,5-dimethylpyrazol-1-yl)borate] reacts with O(2) to form the ligand oxygenation product ArSO(2)(-) in MeCN, and also 1a catalyzes the oxygenation of external substrates such as triphenylphosphine. The reactivity may correlate to the unique quinoid-like resonance structure of the thiophenolate ligand. The structure is stabilized by a p-nitro group and induced by coordination of MeCN.     

Synthesis of biantennary complex-type nonasaccharyl asn building blocks for solid-phase glycopeptide synthesis

The biantennary complex-type N-glycans bearing LacNAc and LacdiNAc as the nonreducing end motif were synthesized in a protected form suitable to use in the Fmoc solid-phase peptide synthesis studies. Two approaches for the nonasaccharide synthesis were examined by taking advantage of the highly β-selective glycosylation with GlcNTCA (N-phenyl)trifluoroacetimidate. An earlier approach, which involved the reaction of the trisaccharide donor (Gal-GlcNTCA-Man) and trisaccharide acceptor (Man-GlcNPhth(2)-N(3)), produced a mixture of nonasaccharide isomers. On the other hand, mannosylation of the trisaccharide acceptor (Man-GlcNPhth(2)-N(3)) stereoselectively afforded the known pentasaccharide (Man(3)-GlcNPhth(2)-N(3)), which was reacted with the disaccharyl glycosyl donor (Gal-GlcNTCA or GalNTCA-GlcNTCA) to produce the desired nonasaccharide as a single stereoisomer. Selective dephthaloylation followed by N-acetylation furnished the GlcNAc(2) functionality. The resulting nonasaccharyl azides were condensed with Fmoc-Asp(OPfp)-OBu(t) or Fmoc-Asp(OPfp)-OPac in the presence of Ph(CH(3))(2)P and HOOBt. Finally, the Zn reduction and cleavage of the tert-butyl ester or Zn reduction alone produced the targeted nonasaccharyl Asn building blocks.     

Organocatalytic asymmetric direct aldol reactions of trifluoroacetaldehyde ethyl hemiacetal with aromatic methyl ketones

The organocatalytic asymmetric direct aldol reaction of trifluoroacetaldehyde ethyl hemiacetal with aromatic methyl ketones in the presence of a catalytic amount of (S)-5-(pyrrolidin-2-yl)-1H-tetrazole in dichloroethane at 40 °C proceeds smoothly to produce (R)-4,4,4-trifluoro-1-aryl-3-hydroxy-1-butanones in high yields with up to 90% ee.     

Double 1,4-rhodium migration cascade in rhodium-catalysed arylative ring-opening/spirocyclisation of (3-arylcyclobutylidene)acetates

1,4-Rhodium migration occurs twice during the course of the rhodium-catalysed arylative ring-opening/spirocyclisation reaction of (3-arylcyclobutylidene)acetates with sodium tetraarylborates to afford ketones possessing a 1,1'-spirobiindane skeleton.     

Charge-based and charge-free molecular assemblies comprising π-extended derivatives of anion-responsive acyclic oligopyrroles

Assemblies comprising anion complexes of π-extended oligopyrrole derivatives and counter cations, as well as those of anion-free receptor molecules, exhibited the formation of mesophases based on columnar structures using electrostatic and π-π interactions.     

New type of azacyclization: thermal preparation of 4,6-disubstituted 2-piperidinone from N-sulfonyldienamide and its substituent effect

The thermal 6-endo cyclization of N-sulfonyl-2,4-dienamide compounds to produce 4,6-disubstituted 2-piperidinone is described. The observed remarkable substituent effect due to the N-sulfonyl and C3 ethoxycarbonyl groups for acceleration of this 6-endo cyclization strongly suggests that the reaction would proceed via the 6π-azaelectrocyclization of the intermediary imidic acid. On the contrary, the corresponding 5-formyl and 5-acetyl derivatives rapidly cyclized at room temperature to produce the 5-exo cyclized products.     

Chemical Modification of Proteins at Cysteine: Opportunities in Chemistry and Biology

Cys‐tematic modification : Cysteine is a versatile amino acid for selective chemical modification of proteins. Both chemical and biological innovations made possible by cysteine modification are highlighted in this Focus Review.