Intramolecular 1,5- versus 1,6-hydrogen abstraction reaction promoted by alkoxy radicals in carbohydrate models

Synthesis and biological characterization of low-calorie Schisandra chinensis syrup

Schisandra chinensis (Omija) is a well-known medicinal plant in East Asia. In this study, Omija oligosaccharide syrup was prepared from sucrose with Omija fruit extract using two glucansucrases of Leuconostoc mesenteroides B-512F/KM and L. mesenteroides B-1355CF10/KM. The degree of polymerization of Omija oligosaccharide syrup was ranged from 2 - 13 by MALDI-TOF-MS analysis. Compared to the Omija syrup, the Omija oligosaccharide syrup reduced 61% calories based on the enzymatic gravimetric method. It also reduced up to 96% insoluble glucan formation from sucrose by mutansucrase of Streptococcus mutans at 500 mg/mL. Additionally, it has 1.78-fold higher oxygen radical absorbance capacity value compared to Omija syrup. Using electronic tongue sensor system, Omija oligosaccharide syrup showed decreased sourness, astringency, and saltiness compared to Omija syrup. Thus, Omija oligosaccharides can be used as functional sweetener in nutraceutical industries.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01061-8.

Construction of Nitrated Benzo[3.3.1]bicyclic Acetal/Ketal Core via Nitration of o-Carbonyl Allylbenzenes

Intramolecular annulation of o-carbonyl allylbenzenes was achieved to construct novel nitrated [6,6,6]tricycles having an acetal or ketal motif in good yields. The expeditious one-step nitration route provides 4 or 5 new bond formations, including 2 or 3 C-N bonds and 2 C-O bonds. The structural framework of benzobicycle [3.3.1] is confirmed by X-ray crystallographic analysis. A plausible mechanism is proposed.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

Aliphatic C–H azidation through a peroxydisulfate induced radical pathway

Transition-metal-free, chemo- and regioselective aliphatic tertiary C–H bond azidation with good functional group tolerance is described.

Reviews on Mechanisms of In Vitro Antioxidant Activity of Polysaccharides

It is widely acknowledged that the excessive reactive oxygen species (ROS) or reactive nitrogen species (RNS) induced oxidative stress will cause significant damage to cell structure and biomolecular function, directly or indirectly leading to a number of diseases. The overproduction of ROS/RNS will be balanced by nonenzymatic antioxidants and antioxidant enzymes. Polysaccharide or glycoconjugates derived from natural products are of considerable interest from the viewpoint of potent in vivo and in vitro antioxidant activities recently. Particularly, with regard to the in vitro antioxidant systems, polysaccharides are considered as effective free radical scavenger, reducing agent, and ferrous chelator in most of the reports. However, the underlying mechanisms of these antioxidant actions have not been illustrated systematically and sometimes controversial results appeared among various literatures. To address this issue, we summarized the latest discoveries and advancements in the study of antioxidative polysaccharides and gave a detailed description of the possible mechanisms.

Asymmetric Formal Total Synthesis of the Stemofoline Alkaloids: The Evolution, Development and Application of a Catalytic Dipolar Cycloaddition Cascade

A formal synthesis of didehydrostemofoline and isodidehydrostemofoline has been accomplished by preparing an intermediate in the Overman synthesis of these alkaloids from commercially available 2-deoxy-D-ribose. The work presented in this account chronicles the evolution of our explorations to identify the optimal steric and electronic control elements necessary to generate the tricyclic core structure of these alkaloids in a single operation from an acyclic precursor. The key step in the synthesis is a novel dipolar cycloaddition cascade sequence that is initiated by cyclization of a rhodium-derived carbene onto the nitrogen atom of a proximal imine group to generate an azomethine ylide that then undergoes spontaneous cyclization via dipolar cycloaddition. The synthesis features several other interesting reactions, including a Boord elimination to prepare a chiral allylic alcohol, a highly diastereoselective Hirama-Itô cyclization, and a useful modification of the Barton decarboxylation protocol.

Novel Entry to the Tricyclic Core of Stemofoline and Didehydrostemofoline

A novel approach to the tricyclic core of the Stemona alkaloids stemofoline and didehydrostemofoline has been discovered that features an intramolecular (3+2) dipolar cycloaddition of an unactivated carbon-carbon double bond with an azomethine ylide; the azomethine ylide was generated by an unprecedented reaction that occurred during a Swern oxidation of an α-(N-cyanomethyl)-β-hydroxy ester. In separate experiments, the efficacy of introducing the requisite oxygen functionality at C(8) and the 1-butenyl side chain at C(3) was established.

Beneficial Effect of Internal Hydrogen Bonding Interactions on the β-Fragmentation of Primary Alkoxyl Radicals. Two-Step Conversion of d-Xylo- and d-Ribofuranoses into l-Threose and d-Erythrose, Respectively

Primary alkoxyl free radicals were generated from their readily synthesized N-phthalimido derivatives under reductive conditions. Primary alkoxyl radicals derived from their corresponding xylo- and ribofuranose derivatives underwent, exclusively, an unusual beta-fragmentation affording L-threose and D-erythrose derivatives, respectively. This occurs because the alkoxyl radical is capable of achieving an internal hydrogen-bonding interaction leading to a stable six-membered ring intramolecular hydrogen-bonded structure. When the hydroxyl group is protected, the beta-fragmentation pathway is prevented and the hydrogen atom transfer (HAT) pathway occurs. Computational studies provided strong support for the experimental observations.

Atmospheric chemistry of C3-C6 cycloalkanecarbaldehydes

The rate coefficients for the gas phase reaction of NO3 and OH radicals with a series of cycloalkanecarbaldehydes have been measured in purified air at 298 +/- 2 K and 760 +/- 10 Torr by the relative rate method using a static reactor equipped with long-path Fourier transform infrared (FT-IR) detection. The values obtained for the OH radical reactions (in units of 10(-11) cm3 molecule(-1) s(-1)) were the following: cyclopropanecarbaldehyde, 2.13 +/- 0.05; cyclobutanecarbaldehyde, 2.66 +/- 0.06; cyclopentanecarbaldehyde, 3.27 +/- 0.07; cyclohexanecarbaldehyde, 3.75 +/- 0.05. The values obtained for the NO3 radical reactions (in units of 10(-14) cm3 molecule(-1) s(-1)) were the following: cyclopropanecarbaldehyde, 0.61 +/- 0.04; cyclobutanecarbaldehyde, 1.99 +/- 0.06; cyclopentanecarbaldehyde, 2.55 +/- 0.10; cyclohexanecarbaldehyde, 3.19 +/- 0.12. Furthermore, the reaction products with OH radicals have been investigated using long-path FT-IR spectroscopy and proton-transfer-reaction mass spectrometry (PTR-MS). The measured carbon balances were in the range 89-97%, and the identified products cover a wide spectrum of compounds including nitroperoxycarbonyl cycloalkanes, cycloketones, cycloalkyl nitrates, multifunctional compounds containing carbonyl, hydroxy, and nitrooxy functional groups, HCOOH, HCHO, CO, and CO2.

Efficient and selective removal of methoxy protecting groups in carbohydrates

[reaction: see text] The selective removal from carbohydrate substrates of methoxy protecting groups next to hydroxy groups is reported. On treatment with PhI(OAc)(2)-I(2), the methoxy group is transformed into an easily removable acetal. The mild conditions of this methodology are compatible with many functional groups, and good to excellent yields are usually achieved.

Intramolecular hydrogen abstraction reaction promoted by alkoxy radicals in carbohydrates. Synthesis of chiral 2,7-dioxabicyclo[2.2.1]heptane and 6,8-dioxabicyclo[3.2.1]octane ring systems

The reaction of specifically protected anhydroalditols with (diacetoxyiodo)benzene or iodosylbenzene and iodine is a mild and selective procedure for the synthesis of chiral 6,8-dioxabicyclo[3.2.1]octane and 2,7-dioxabicyclo[2.2.1]heptane ring systems under neutral conditions. This reaction can be considered to be an intramolecular glycosidation that goes through an intramolecular hydrogen abstraction promoted by an alkoxy radical followed by oxidation of the transient C-radical intermediate to an oxycarbenium ion. This methodology is useful not only for the preparation of chiral synthons but also for the selective oxidation of specific carbons of the carbohydrate skeleton, constituting a good procedure for the synthesis of protected uloses.