1,7,8‐Tri‐O‐acetyl‐6‐O‐benzoyl­castanospermine

The title compound (alternatively 1,7,8‐tri­acetoxy­per­hydro­indolizin‐6‐yl benzoate), C₂₁H₂₅NO₈, was obtained during studies of castanospermine derivatives. The crystal structure consists of independent mol­ecules with only van der Waals contacts. The fused six‐ and five‐membered rings adopt chair and twist conformations, respectively.     

Synthesis and fungicidal activity of O‐alkyl O‐aryl O‐2‐(stearamido)ethyl phosphates

N‐stearoylethanolamine (NAE18:0) was reacted with O‐alkyl O‐aryl chlorophosphate and a series of O‐alkyl O‐aryl O‐2‐(stearamido)ethyl phosphates were synthesized to explore their antifungal activity. Compared with parent NAE18:0, title compounds without substitution or with methyl substitution on a benzene ring exhibited improved antifungal activity. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:602–608, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20485     

Synthesis and Structure/Property Relationships of Regioselective 2‐O‐, 3‐O‐ and 6‐O‐Ethyl Celluloses

Regioselectively ethylated celluloses, 2‐O‐ ( 1 ), 3‐O‐ ( 2 ), and 6‐O‐ethyl‐ ( 3 ) celluloses were synthesized via ring‐opening polymerization of glucopyranose orthopivalate derivatives. The number‐average degrees of polymerization (DP_ns) of compounds 1 and 2 were calculated to be 10.6 and 49.4, respectively. Three kinds of compound 3 with different DP_ns were prepared: DP_ns = 12.9 ( 3‐1 ), 60.3 ( 3‐2 ), and 36.1 ( 3‐3 ). The 2‐O‐, 3‐O‐, and 6‐O‐ethylcelluloses were soluble in water, confirmed by NMR analysis. Furthermore, the 3‐O‐ ( 2 ), and 6‐O‐ethyl‐ ( 3‐2 ) celluloses showed thermo‐responsive aggregation behavior and had a lower critical solution temperature (LCST) at about 40 °C and 70 °C, respectively, based on the results from turbidity tests and DSC measurements. The 6‐O‐ethyl‐cellulose ( 3‐3 ) with DP_n = 36.1 and DP_w = 54.6 showed gelation behavior over approx 70 °C, whereas the 6‐O‐ethyl‐celluloses 3‐1 and 3‐2 with lower and higher molecular weight, such as DP_ns 12.9 and 60.3, did not show gelation behavior at this temperature. It was revealed that the position of ethyl group affected the phase transition temperature. According to our experiments, the 3‐O‐ethyl and 6‐O‐ethyl groups along the cellulose chains caused the thermo‐responsive property of their aqueous solutions. The appropriate DP of the regioselective 6‐O‐ethyl‐cellulose existed for gelation of the aqueous solution.

     

O‐Ethyl and O‐methyl N‐(2,3,4,6‐tetra‐O‐acetyl‐β‐d‐glucopyranosyl)thiocarbamate

In both the title structures, O‐ethyl N‐(2,3,4,6‐tetra‐O‐acetyl‐β‐d ‐gluco­pyran­osyl)­thio­carbam­ate, C₁₇H₂₅NO₁₀S, and O‐methyl N‐(2,3,4,6‐tetra‐O‐acetyl‐β‐d ‐gluco­pyran­osyl)­thiocar­bam­ate, C₁₆H₂₃NO₁₀S, the hexo­pyran­osyl ring adopts the ⁴C₁ conformation. All the ring substituents are in equatorial positions. The acetoxy­methyl group is in a gauche–gauche conformation. The S atom is in a synperi­planar conformation, while the C—N—C—O linkage is antiperiplanar. N—H?O intermolecular hydrogen bonds link the mol­ecules into infinite chains and these are connected by C—H?O interactions.     

Polyisobutylene‐based polyurethanes. VIII. Polyurethanes with ‐O‐S‐PIB‐S‐O‐ soft segments

We describe the synthesis, characterization, and select properties of a novel polyurethane (PU) prepared using a new polyisobutylene diol, HO‐CH₂CH₂‐S‐PIB‐S‐CH₂CH₂‐OH, soft segment and conventional hard segments. The diol is synthesized by terminal functionalization of ally‐telechelic PIB followed by low‐cost thiol‐ene click chemistry. Properties of ‐S‐ containing PU (PIB_S‐PU) containing 72.5% PIB were investigated and compared to similar PUs made with HO‐PIB‐OH (PIB_O‐PU). Hydrolytic resistance was studied by contact with phosphate‐buffered saline, oxidative resistance by immersing in concentrated HNO₃, and metal ion oxidation resistance by exposure to CoCl₂/H₂O₂. Hydrolytic and oxidative resistances of PIB_S‐PU and PIB_O‐PU are similar and superior to a commercial PDMS‐based PU, Elast‐Eon? E2A. According to ¹H NMR spectroscopy the ‐S‐ in PIB_S‐PUs remained unchanged upon treatment with HNO₃, however, oxidized mainly to ‐SO₂‐ by CoCl₂/H₂O_2. Static mechanical properties of PIB_S‐PU and PIB_O‐PU are similar, except creep resistance of PIB_S‐PU is surprisingly superior. The thermal stability of PIB_S‐PUs is ～15 °C higher than that of PIB_O‐PU. FTIR spectroscopy indicates H bonded S atoms (N‐H…S) between soft and hard segments, which noticeably affect properties. DSC and XRD studies suggest random low‐periodicity crystals dispersed within a soft matrix. Energy dispersive X‐ray spectroscopy–scanning electron microscopy indicates homogeneous distribution of S atoms on PIB_S‐PU surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1119–1131     

1,2,7,8‐Tetra‐O‐acetyl­australine

The title compound, C₁₆H₂₃NO₈, was obtained during studies of australine derivatives. The molecular stereochemistry is similar to that reported for other australine derivatives even though there is no intermolecular hydrogen bonding in this case.     

Two modes of O—H...O hydrogen bonding utilized in dimorphs of racemic 6‐O‐acryloyl‐2‐O‐benzoyl‐myo‐inositol 1,3,5‐orthoformate

The title compound, C₁₇H₁₆O₈, yields conformational dimorphs [forms (I) and (II)] at room temperature, separately or concomitantly, depending on the solvent of crystallization. The yield of crystals of form (I) is always much more than that of crystals of form (II). The molecule has one donor –OH group that can make intermolecular O—H...O hydrogen bonds with one of the two acceptor C=O groups, as well as with the hydroxyl O atom; interestingly, each of the options is utilized separately in the dimorphs. The crystal structure of form (I) contains one molecule in the asymmetric unit and is organized as a planar sheet of centrosymmetric dimers via O—H...O hydrogen bonds involving the OH group and the carbonyl O atom of the acryloyl group. In the crystal structure of form (II), which contains two independent molecules in the asymmetric unit, two different O—H...O hydrogen bonds, viz. hydroxyl–hydroxyl and hydroxyl–carbonyl (benzoyl), connect the molecules in a layered arrangement. Another notable feature is the transformation of form (II) to form (I) via melt crystallization upon heating to 411 K. The higher yield of form (I) during crystallization and the thermal transition of form (II) to form (I) suggest that the association in form (I) is more highly favoured than that in form (II), which is valuable in understanding the priorities of molecular aggregation during nucleation of various polymorphs.     

First Synthesis of 3‐O‐Functionalized Cellulose Ethers via 2,6‐Di‐O‐Protected Silyl Cellulose

The present paper describes the synthesis of 2,6‐di‐O‐thexyldimethylsilyl cellulose as a novel 2,6‐di‐O‐protected cellulose derivative. This material was obtained by reacting cellulose in N,N‐dimethylacetamide/LiCl solution with thexyldimethylchlorosilane and imidazole for 24 h at 100°C. In a typical subsequent reaction the residual OH‐group in position 3 could be completely etherified without loss of any protecting groups. Treatment with tetrabutylammonium fluoride leads to the novel compounds 3‐O‐allyl and 3‐O‐methyl cellulose. The structures of all polymers are revealed by means of one‐ (¹H and ¹³C) and two‐dimensional (COSY and HMQC) NMR techniques.     

Site‐Selective O‐Arylation of Glycosides

Direct and site‐selective O‐arylation of carbohydrates has been a challenge in synthesis. Herein we report a method based on copper‐catalyzed O‐arylation to address this challenge. Proper choice of the ancillary ligand on copper is critical for the efficiency and site selectivity of this transformation. This method features mild conditions, tolerates various functional groups, and demonstrates broad substrate scope.     

Chiral crystals from an achiral molecule: 4,6‐di‐O‐benzyl‐1,3‐O‐benzylidene‐2‐O‐(4‐methoxybenzyl)‐myo‐5‐inosose

The title achiral compound, C₃₅H₃₄O₇, crystallizes in the chiral monoclinic space group P2₁. The molecules are densely packed to form a helical assembly along the crystallographic twofold screw axis via C—H...O and C—H...π interactions. Interestingly, the unit‐translated helical chains are loosely connected via a rather uncommon edge‐to‐edge Ph—H...H—Ph short contact (H...H = 2.33 Å).     

O-氯丙基和O-氰丙基间苯二酚杯芳烃的合成，晶体结构和电化学性质

四烃基和四二茂铁基间苯二酚杯芳烃在丙酮回流条件和碳酸钾存在下用1-溴-3-氯丙烷或4-氯丁腈进行烃基化反应分别生成全取代的O-氯丙基和O-氰丙基间苯二酚杯芳烃,晶体结构测定表明烷基间苯二酚杯芳烃倾向于以全顺式构型存在,而芳基间苯二酚杯芳烃倾向于以顺-反-反式构型存在。本文还已经了四二茂铁基间苯二酚杯芳烃的电化学性质。     

Retention Prediction System of O‐Aryl,O‐(1‐methylthioethylidene‐amino)phosphates on RP‐HPLC

Using factor analysis and stepwise linear regression methods, two parameters – CMR and ECCR – were selected from eight solute‐related structure parameters as the most retention‐influencing parameters. The relationships between the retention data (k ´) and the two structure parameters were established for 13 O‐aryl,O‐(1‐methylthioethylideneamino)phosphate compounds under a wide range of experimental conditions. The retention data (k ´) of another seven compounds with similar structures were predicted using these QSRR equations. Good agreement was obtained between the experimental k ´ values and predicted ones.     

Electrooxidative Ruthenium‐Catalyzed C−H/O−H Annulation by Weak O‐Coordination

Electrocatalysis has been identified as a powerful strategy for organometallic catalysis, and yet electrocatalytic C?H activation is restricted to strongly N‐coordinating directing groups. The first example of electrocatalytic C?H activation by weak O‐coordination is presented, in which a versatile ruthenium(II) carboxylate catalyst enables electrooxidative C?H/O?H functionalization for alkyne annulations in the absence of metal oxidants; thereby exploiting sustainable electricity as the sole oxidant. Mechanistic insights provide strong support for a facile organometallic C?H ruthenation and an effective electrochemical reoxidation of the key ruthenium(0) intermediate.     

Synthesis of O‐Acyl Isopeptides

O‐Acyl isopeptides, in which the N‐acyl linkage on the hydroxyamino acid residue (e.g., Ser and Thr) is replaced with an O‐acyl linkage, generally possess superior water‐solubility to their corresponding native peptides, as well as other distinct physicochemical properties. In addition, O‐acyl isopeptides can be rapidly converted into their corresponding native peptide under neutral aqueous conditions through an O‐to‐N acyl migration. By exploiting these characteristics, researchers have applied the O‐acyl isopeptide method to various peptide‐synthesis fields, such as the synthesis of aggregative peptides and convergent peptide synthesis. This O‐acyl‐isopeptide approach also serves as a means to control the biological function of the peptide in question. Herein, we report the synthesis of O‐acyl isopeptides and some of their applications.     

Acid/base‐catalyzed cyclization of O‐alkynylphenylphosphonic acid monoesters and (O‐hydroxyphenyl)ethynylphosphinates

In this work, we found that acids (i.e., HCl and NaHSO₃) rather than bases could catalyze the cyclization of o‐alkynylphenylphosphonic acid monoesters at slow rates and give phosphaisocoumarins in low to medium yields, whereas the cyclization of (o‐hydroxyphenyl)ethynylphosphinates proceeded very smoothly under basic conditions rather than acidic conditions, and a series of phosphachromones could be prepared in excellent yields at room temperature using K₂CO₃ as catalyst. This is the first example of the synthesis of phosphorus heterocycles via acid/base‐catalyzed intramolecular cyclization of alkynes. Possible mechanisms were discussed. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:649–652, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20728