No abstract

Cereal Chem. 77(1):58-63We studied the effect of amylose content on the gelatinization, retrogradation, and pasting properties of starch using wheat starches differing in amylose content. Starches were isolated from waxy and nonwaxy wheat and reciprocal F1 seeds by crossing waxy and nonwaxy wheat. Mixing waxy and nonwaxy wheat starch produced a mixed starch with the same amylose content as F1 seeds for comparison. The amylose content of F1 seeds ranged between waxy and nonwaxy wheat. Nonwaxywaxy wheat had a higher amylose content than waxy-nonwaxy wheat. Endothermic enthalpy and final gelatinization temperature measured by differential scanning calorimetry correlated negatively with amylose con-tent. Gelatinization onset and peak temperature clearly differed between F1 and mixed starches with the same amylose content as F1 starches. Enthalpy for melting recrystallized starches correlated negatively with amylose content. Rapid Visco Analyser measurement showed that F1 starches had a higher peak viscosity than waxy and nonwaxy wheat starches. Mixed starches showed characteristic profiles with two low peaks. Setback and final viscosity correlated highly with amylose content. Some of gelatinization and pasting properties differed between F1 starches and mixed starches.

No abstract

It is desirable to minimize the use of rare or toxic metals for oxidative reactions in the synthesis of pharmaceutical products. Hypervalent iodine compounds are environmentally benign alternatives, but their catalytic use, particularly for asymmetric transformations, has been quite limited. We report here an enantioselective oxidative cycloetherification of ketophenols to 2-acyl-2,3-dihydrobenzofuran derivatives, catalyzed by in situ-generated chiral quaternary ammonium (hypo)iodite salts, with hydrogen peroxide as an environmentally benign oxidant. The optically active 2-acyl 2,3-dihydrobenzofuran skeleton is a key structure in several biologically active compounds.

It′s the iodine: The intra‐ and intermolecular title reaction is catalyzed by an in situ generated ammonium (hypo)iodite species. Either H2O2 or tert‐butyl hydroperoxide (TBHP) can be used as an environmentally benign oxidant and a wide range of substrates react to give the corresponding α‐acyloxycarbonyl compounds in good to excellent yields.

No abstract

Morphological, physical, and chemical properties of grain and flour of 20 chalky rice mutants were compared with those of a translucent parental cultivar, Koshihikari. Compound starch granules were loosely packed and single starch granules were observed in chalky parts of mutant endosperm. Chalky mutant lines were classified into milky‐white and white‐core lines based on the degree of endosperm chalkiness. Physical and chemical characteristics also suggest a division of chalky mutant lines into two groups, consistent with the classification made based on morphological characteristics. Milky‐white mutant lines showed significantly lower grain weight, decreased starch content, and lower grain hardness than white‐core mutants and Koshihikari. Rice flour prepared from milky‐white mutants by dry milling showed less starch damage and finer mean particle size than white‐core mutants and the parent. These results indicated that a loosely packed structure in chalky endosperm was responsible for fragile grain and that it yielded fine flour with lower damaged starch contents. Decreased starch contents of chalky mutant lines correlated to lower RVA viscosities. Milky‐white mutant lines were expected to be useful to produce fine flour, which undergoes less starch damage during dry milling processing.

The enantioselective oxidative dearomatization of phenols and their analogues is a key reaction for the synthesis of several natural products.[1] Conventionally, enantioselective transition-metal catalysis has been used for these transformations. [1c-e] Recently, some research groups [2] have reported catalytic enantioselective oxidative dearomatization reactions using chiral hypervalent iodine compounds.[3] However, the catalytic activities and enantioselectivities are moderate, and the substrate scope of the oxidation reactions is limited to 1-naphthol derivatives. Herein, we describe the rationally designed chiral iodoarene 1, which is derived from chiral 2-aminoalcohol, as a chiral precatalyst for the first enantioselective catalytic oxidative dearomatization of phenol derivatives 3 to give the desired cyclohexadienone spirolactones 4 and the subsequent Diels-Alder adducts [4] 5 with high to excellent enantioselectivities (87-99 % ee, Scheme 1). Active iodine(III) species 2 would be generated in situ from C 2 -symmetric and conformationally flexible chiral iodoarene 1 and meta-chloroperoxybenzoic acid (m-CPBA). We envisioned that a suitable chiral environment might be constructed around the iodine(III) center via intramolecular hydrogen bonding interactions between the acidic amido protons and the iodine(III) ligands (L).A preliminary examination of 1 (10 mol %) in the oxidative dearomatization of 2,4-di-tert-butylphenol derivative 3 a with 1.2 equivalents of m-CPBA in chloroform gave cyclohexadienone 4 a in 72 % yield with 91 % ee ( Table 1, entry 1). However, the chemical yield and enantioselectivity of 4 a were significantly reduced when the reaction was performed in distilled chloroform (entry 2). The commercial chloroform that we used (Nacalai Tesque Inc., Japan) contained a small amount (ca. 1 wt %) of ethanol as a stabilizer. Thus, we serendipitously found that both the chemical yield and enantioselectivity of 4 a could be improved to the same level as in entry 1 by the addition of 10 equivalents of ethanol in distilled chloroform (entry 3). Next, alcohol additives and solvents were investigated in detail, [5] and the best result was obtained using 25 equivalents of methanol as an additive and dichloromethane as a solvent Scheme 1. Chiral organoiodine(III)-catalyzed enantioselective oxidative dearomatization of phenols and subsequent Diels-Alder reactions. m-CPBA = meta-chloroperoxybenzoic acid, L = ligand, Mes = mesityl.