Proposed Extension to the Natta Projection Notation System for Enabling an Indication of Relative Stereochemistry and the Stereochemical State

A system of structure depiction, as an extension of the wedge and hashed wedge bonds (Natta projection), and text notation is herein suggested that embodies more explicit information—or reduced over-statement as circumstances warrant—on the stereochemical nature of the system at hand, in particular, for those cases where only the relative stereochemistry of a compound is known.

Stereochemistry of Acetone Condensation on Solid Base Catalysts

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STEREOCHEMISTRY IN CYCLOPHOSPHORYLATION OF NUCLEOSIDES

In the presence of tetrazole,2'-substituted nucleosidesreacted ster■os■ifi■ally with n-BuOPIN■_2H_5■_2I_2 to nucleoside 3',5'-■lopnosphites with avial n-Buo group.The stereochemistry of oxidation of■y■lophosphite was investigated.

The Stereochemistry of the Migrating Groups in the Pyrolysis of Stable Steroidal Ozonides

Diacholest-13(17)-ene ozonide(1a andlb) and 4, 4-dimethyldiacholest-13 (17)-eneozonides(2a and 2b) underwent pyrolysis to afford the coressponding 17-oxo-13,14;13,17- dis14-lactones (3a and 3b)and 4.4-dimethyl-17-oxo-13,14; 13,17-disecodiacholestano-13,14-lactones(4 and 4b), respectively. The stereochemi-stry of the migratingpoups was Proven to be conserved by comparison with the Baeyer-Villiger oxidation of the corresponding 13,17-secodiacholesta-13,17-diones (5) and 4,4-dimethyl-13, 17-secodiacholesta13, 17-diones(6).

STEREOCHEMISTRY OF THE BENZILIC ACID-TYPE REARRANGEMENT IN BASE-CATALYZED AUTOXIDATION OF 3α,5-CYCLO-5α-CHOLESTANE-6-ONE

The configuration of the hydroxy acid 2, a product from base-catalyzed autoxidation of 3α,5-cyclo-5α-cholestane-6-one,was established on the basis of NMR techniques and the mechanism of the formation of 2 was discussed.

Stereochemistry Control in Direct 1α-Hydroxylation of 5,6-trans-Vitamin D_(3) by Solid Support

A solid-phase synthesis of 1α-hydroxylation of 5,6-trans-vitamin D3 8 is described.The solid phase resin acts as a special protecting group, which gives a higher stereoselectivity in oxidation step than classical protecting groups. The stereochemistry control is favored by using high crosslinkage polymer support in a poor solvent. This work may be of benefit to the synthesis of vitamin D system.

Studies on the Total Synthesis of Hainanolide(Ⅳ)-Revising the Stereochemistry of C_(2α)-H and Introducing the Two Hydroxy Groups at C_(3β),C_(4α) Positions

Tricyclic compound 6 was synthesized form compound 1 through sis steps, thus preblem of the stereochemistry of C2α-H being solved. The stereochemistry for introducing hydroxy groups at C3β and C4α positions in compound 1 was also described.

Super Antibiotics, Part IV. Hyperforin, Relative and Absolute Stereochemistry Elucidated by Gas-Chromatography Mass-Spectrometry with Supersonic Molecular Beams

Relative and absolute stereochemistry for hyperforin has been proposed by Brondz et al. was supported and new isomer of hyperforin-perforatrin has been discovered. Relative and absolute stereochemistry for perforatrin was proposed and elucidated by using gas-chromatography mass-spectrometry with supersonic molecular beams (SMB). The possibility of the existence of ambiguities in chirality as a hypothesis for the existence, and a new understanding, of chiral substances with shifting chirality is presented.

Super Antibiotics, Part VI: Hyperforin, Revision of Stereochemistry. Short Communications

This short communication is an overview and revision of previous published papers about the relative and absolute stereochemistry of hyperforin and discovery of a new isomer of hyperforin that has been named perforatrin.

Minimizing interfacial energy losses in inverted perovskite solar cells by a dipolar stereochemical 2D perovskite interface

Inverted perovskite solar cells(PSCs) have attracted broad research and industrial interest owing to their suppressed hysteresis,cost-effectiveness,and easy-fabrication.However,the issue of non-radiative recombination losses at the n-type interface between the perovskite and fullerene has impeded further improvement of photovoltaic performance.Here,we modify the n-type interface of FAPbI_(3) perovskite films by constructing a stereochemical two-dimensional(2D) perovskite interlayer,in which the organic cations comprise both pyridine and ammonium groups.The pyridine N donor can create stable bonding with the surface-uncoordinated Pb on the perovskite,thereby passivating the shallow-level defects and enhancing the air stability of the film.Furthermore,the pyridine N donor also offers a positive polar interface to decrease the surface work function of the perovskite film,enabling n-type modification.Ultimately,we employ a p-i-n photovoltaic(PV) device with the positive dipole interlayer at perovskite/fullerene contact and achieve remarkable photoelectric conversion efficiency(PCE) of 22.0%.

Nitrogenous Sesquiterpenoids from the South China Sea Nudibranch Hexabranchus sanguineus and Its Possible Sponge-Prey Acanthella cavernosa: Chiral Separation, Stereochemistry and Chemical Ecology

A detailed chemical investigation of the South China Sea nudibranch Hexabranchus sanguineus,as well as its possible sponge-prey Acanthella cavernosa,led to the isolation of fifteen new nitrogenous sesquiterpenoids,namely ximaocavernosins A-0,including seven cadinanes(1-7),seven spiroaxanes(12-18)and one aromadendrane(19),together with thirteen known related compounds(8-11 and 20-28).

Ring-opening Polymerization of 2-Oxabicyclo[2.2.2]octan-3-one and the Influence of Stereochemistry on the Thermal Properties of the Polyesters

Polyesters with cyclic structures in the main chain typically possess superior mechanical and thermal properties together with chemical recyclability.Ring-opening polymerization(ROP)of bridged or fused bicyclic lactones is a simple,and in most cases controlled method to synthesize polyesters with alicyclic moieties in the polymer backbone.The stereochemistry of the alicyclic structures has a great effect on the polymer properties,which can be regulated by varying the polymerization conditions.Here,we report a systematic investigation on the ROP of 2-oxabicyclo[2.2.2]octan-3-one([2.2.2]VL)under different conditions.When initiated byn-butyl lithium(n-BuLi)or catalyzed by trifluoromethanesulfonic acid(TfOH)in the presence of benzyl alcohol,P[2.2.2]VLs containing all cis^(-1),4 disubstituted cyclohexane ring were obtained.However,P[2.2.2]VLs initiated by sodium methoxide(MeONa)or catalyzed by organic superbase contained both cis and trans isomeric structural units.The cis to trans transformation mechanism under these conditions was manifested,and the effect of stereochemical variations on the properties ofP[2.2.2]VLwas revealed.The stereoregularP[2.2.2]VLs,bothcisandtrans,exhibited higher crystallinity and melting temperatures(Tm)than those of the stereoirregular isomers.Finally,the degradation of P[2.2.2]VL with acid at high temperature could recover 3-cyclohexenecarboxylic acid.

Polyoxygenated anti-inflammatory biscembranoids from the soft coral Sarcophyton tortuosum and their stereochemistry

Five novel biscembranoids,ximaolides H-L(1-5),along with four known related compounds(6-9) were isolated from the Hainan soft coral Sarcophyton tortuosum.The structures of the new compounds were determined by extensive spectroscopic analysis,quantum chemical calculations,and/or by comparing their CD spectra with those of the known compounds.Compounds 1 and 2 are the first examples of biscembranoids bearing a 1,35-bridged lactone moiety,4 is the first biscembranoid comprising an uncommon oxetane ring,and 5 represents the first 36-peroxyl biscembranoid.Ximaolides Ⅰ(2),K(4) and F(9) exhibited interesting anti-inflammatory activity by the inhibition of LPS-induced TNF-α protein release in RAW264.7 macrophages.

STUDIES ON 2D NMR SPECTRA OF SUBEROGO RGIN AND ITS STEREOCHEMISTRY

Suberogorgin（S）, a new reversible anticholinesterase agent, is a tricyclopentapentalane sesquiterpene acid with a rare novel structure. It is important for the exploration of the relationships between its structure and bioactivities and for the development of terpene chemistry to study its structural characteristics. This note is on using 2D NMR techniques to analyse the 1H and 13C NMR spectra and the stereochemistry of it.

Total synthesis and stereochemistry establishmentof tumescenamide A

Tumescenamide A (1), isolated from Streptomyces tumescens YM23-20, consists of a cyclic depsipeptideand a side-chain 2,4-dimethylheptanoate (Dmh). Herein, we report the first total synthesis of tumescenamide A (1) and establish its stereochemistry. The configuration of Dmh is 2S,4S and, notably, the configuration of Val is revised as D. In addition, a mild and practical method for the β-elimination of derivatives ofserine and threonine by using nano-K_(2)CO_(3) as a base was established. A highly stereoselective synthesis ofthe Dmh substructure was also developed.

Stereochemistry of the coupling step in photo-S_(RN) 1 reaction

The photo-S_(RN) 1 reaction of (+)-camphor and aryl halides was investigated in order to estimate the stereochemistry of the coupling step of aryl radicals with a nucleophile. The ratio of endo to exo products determined by ~1H NMR and CD spectra was found to be 99:1. MNDO calculations of the orbital parameters showed a favorable one-sided overlap of the enolate ion with the SOMO of aryl radical. In addition, fragmentation of (ArX)^- was found to be related to the energy of SOMO of (ArX)^-.

Plant-Derived Enzymes Producing Chiral Aroma Compounds and Potential Application

Aroma(volatile)compounds play important ecological functions in plants,and also contribute to the quality of plant-derived foods.Moreover,chiral aroma compounds affect their functions in plants and lead to different flavor quality properties.Formations of chiral aroma compounds are due to the presence of enzymes producing these compounds in plants,which are generally involved in the final biosynthetic step of the aroma compounds.Here,we review recent progress in research on the plant-derived enzymes producing chiral aroma compounds,and their changes in response to environmental factors.The chiral aroma enzymes that have been reported produce(R)-linalool,(S)-linalool,(R)-limonene,and(S)-limonene,etc.,and these enzymes are found in various plant species.We also discuss the origins of enantioselectivity in the plant-derived enzymes producing chiral aroma compounds and summarize the potential use of plants containing enzymes producing chiral aroma compounds for producing chiral flavors/fragrances.

Structural analysis of tumor-relatedsingle amino acid mutations in human MxA protein

Background:Human myxovirus resistant protein A(MxA),encoded by the myxovirus resistance 1(Mx1) gene,is an interferon(IFN)-triggered dynamin-like multi-domain GTPase involved in innate immune responses against viral infections.Recent studies suggest that MxA is associated with several human cancers and may be a tumor suppressor and a promising biomarker for IFN therapy.Mxl gene mutations in the coding region for MxA have been discovered in many types of cancer,suggesting potential biological associations between mutations in MxA protein and corresponding cancers.In this study,we performed a systematic analysis based on the crystal structures of MxA and elucidated how these mutations specifically affect the structure and therefore the function of MxA protein.Methods:Cancer-associated Mxl mutations were collected and screened from the COSMIC database.Twenty-two unique mutations that cause single amino acid alterations in the MxA protein were chosen for the analysis.Amino acid sequence alignment was performed using Clustal W to check the conservation level of mutation sites in Mx proteins and dynamins.Structural analysis of the mutants was carried out with Coot.Structural models of selected mutants were generated by the SWISS-MODEL server for comparison with the corresponding non-mutated structures.All structural figures were generated using PyMOL.Results:We analyzed the conservation level of the single-point mutation sites and mapped them on different domains of MxA.Through individual structural analysis,we found that some mutations severely affect the stability and function of MxA either by disrupting the intraVinter-molecular interactions supported by the original residues or by incurring unfavorable configuration alterations,whereas other mutations lead to gentle or no interference to the protein stability and function because of positions or polarity features.The potential clinical value of the mutations that lead to drastic influence on MxA protein is also assessed.Conclusions:Among all of the reported tumor-associated single-point mutations,seven of them notably affect the structure and function of MxA and therefore deserve more attention with respect to potential clinical applications.Our research provides an example for systematic analysis and consequence evaluation of single-point mutations on a given cancer-related protein.