First Synthesis of （＋）-2,14-Deoxyalatol from α-Santonin

A novel and general approach for synthesis of the multi-oxygenated dihydrofuran sesquiterpenes has been developed starting from santonin. The key steps involve: the strategic acid-catalyzed double-bond shifting affording 4, the novel base-promoted epoxide rearrangement of 5 generating two key functionals (the C5-OH and the Δ^7,11 double bond), and the stereoselective cyclization of tetrahydrofuran ring without pre-controlling the stereochemistry of C-7. As an example of this approach, synthesis of ( )-2,14-deoxyalatol was described in detail.     

An Efficient Cationic Cyclization Approach for the Construction of Labdane Diterpenoid Decalin Ring Skeleton

An effective approach for the construction of the decalin ring skeleton of labdane diterpenoids was developed based on a key biomimetic cationic polyene cyclization of an epoxy allylsilane precursor. The synthetic approach demonstrated here would be useful in the enantioselective and diastereoselective total synthesis of natural labdane diterpenoids in general.     

First total synthesis of(±)-sepicanin A

<正>A facile approach for the first total synthesis of naturally occurring geranylated flavanoids sepicanin A has been obtained with total yield 16%starting from 2,4,6-trihydroxyacetophenone after four steps.The key step was the protic acids(HCl or p-TsOH)-catalyzed benzopyrone formation in a protic polar solvent by deprotection and cycUzation of chalcone in one step.     

First total synthesis of 10α-hydroxy-4-muurolen-3-one and its C10-isomer

An efficient synthetic route to muurolane type sesquiterpenes starting from （R）-carvone, employing allylic diazene rearrangement and the ring closing methesis （RCM） reaction as key steps, is described. The first asymmetric total synthesis of （-）-10α- hydroxy-4-muurolen-3-one 11 and （-）-10β-hydroxy-4-muurolen-3-one C was accomplished. Through the total synthesis, the absolute configurations of the natural products A, B and C were established.     

Insight of unresolved complex mixtures of saturated hydrocarbons in heavy oil via GC×GC-TOFMS analysis

The saturated hydrocarbon fraction of a heavily biodegraded crude oil from Liaohe oilfield was analyzed by using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS). The "humps", which was termed as unresolved complex mixtures (UCMs) in conventional gas chromatographic analysis, was separated for identification of the individual compound. Main compounds of UCMs were identified according to the combined information of characteristics of GC×GC chromatogram and time-of-flight mass spectra. It’s found that UCMs are mainly composed of great number of ring compounds with extremely low concentration. The ring compounds are separated according to their boiling point diversity in the first dimension column, then to their polarity or ring number variety in the second dimension column. In the sample there are two groups of UCMs, i.e., the first group compounds with boiling point lower that of C24 and the second group compounds with boiling point higher than that of C24. The first group of UCMs mainly consists of monocyclic, bicyclic and tricyclic ring compounds. The first group of UCMs is mainly composed of saturated hydrocarbons, in which the percentage of ring compounds with signal-to-noise ratio above 100 is about 75% of the total quantity of saturated hydrocarbon, while its mass is over 80% of the total saturated hydrocarbon. The second group of UCMs is mainly composed of tetracyclic and pentacyclic ring compounds, in which the percentage of UCM compounds with signal-to-noise ratio over 100 is about 17% of the total quantity of saturated hydrocarbon, and its mass is about 0.5% of the total saturated hydrocarbon. The results of this study are helpful for heavy oil developing and genesis mechanism understanding.     

Synthetic studies towards(-)-deserpidine:Total synthesis of the stereoisomer and derivative of (-)-deserpidine

The asymmetric synthesis of 16,17,20-epi-deserpidine and a derivative of(-)-deserpidine has been achieved.Key feature s in the assembly of the pentacyclic framework include a visible-light photocatalytic intra-/inter-/intramolecular radical cascade reaction to construct the tetracyclic ABCD ring system in one-pot and an intramolecularaldol reaction to forge the cyclohexane E ring.     

Studies on the Total Synthesis of Hainanolide (VI)-The First Access to the Lactone Functionality

The intramolecular Diels-Alder reaction (IMDA) stands as the t'undamental strategy inour total synthesis of hainanolide l, to assemble the tricyclic skeleton. ring B. C and D.as it was reported 1. Cyclization of triene 2 afforded a mixture of endt,-IMDA-additive3 and exo-IMDA-additive 4, the ratio of which varied with reaction conditions. Yetneither 3, with the C2. hydrogen at a position, nor 4, with the C, methyl at a position.fits the configuration of that in the natural product. The…     

Asymmetric synthesis of emericellamide B

Asymmetric total synthesis of emericellamide B(9.4%, 17 longest linear steps) is detailed in this report. In this synthetic route, the highly methylated(2R,3R,4S,6S)-3-hydroxy-2,4,6-trimethyldodecanoic acid(HTMD) unit was effectively prepared through the asymmetric methylation, Wittig and Horner–Wadsworth–Emmons reaction. Moreover, pentafluorophenyl diphenylphophinate(FDPP) proved to be an effective condensation reagent for the macrolactamization between C14 and C18.     

Entry into Major Groups Retaining Taxol via Sinenxan A

Compound 1 as a key intermediate of 1,7,9-trideoxytaxol was synthesized in ten steps from a biosynthetically available taxane,Sinenxan A. The key steps in the synthesis were deoxygenation at C-14,allylic oxidation at C-13 and construction of the oxetane ring.     

Using factor analysis scales of generalized amino acid information for prediction and characteristic analysis of β-turns in proteins based on a support vector machine model

This paper offers a new combined approach to predict and characterize β-turns in proteins.The approach includes two key steps,i.e.,how to represent the features of β-turns and how to develop a predictor.The first step is to use factor analysis scales of generalized amino acid information(FASGAI),involving hydrophobicity,alpha and turn propensities,bulky properties,compositional characteristics,local flexibility and electronic properties,to represent the features of β-turns in proteins.The second step is to ...     

Toward Total Synthesis of Yohimbine and Reserpine Alkaloids;Part 1.An Improved Synthesis of cis-5,8-Dihydroxy-1,4,5,8,9,10-hexahydronaphthalene-1,8-lactone via Selective Reduction of the Conjugated Ketone with Zn(BH_4)_2

cis-5, 8-Dihydroxy-1, 4, 5, 8, 9, 10-hexahydronaphthalene-1, 8-lactone 7 is the key intermediate to build E ring 2 possessing five chiral centers in total synthesis of (-)-reserpine 11, 2. In 1958, Woodward firstly reported an artful route to the synthesis of (-)-reserpine from the acid 4. One major drawback of this promising approach is the low yield obtained in the synthesis of the required lactone 7. Herein, we described an efficient and improved method for the synthesis of 7 as shown …     

Asymmetric Synthesis of the C（17）——C（28） Subunit of Didemnaketal B

The stereocontrolled synthesis of the C（17）--C（28） fragment 3 of didemnaketal B was accomplished in 21 steps from the natural （R）-（＋）-pulegone and （S）-（--）-citronellal. The key steps involved diastereoselective construction of two chiral carbon centers through the intramolecular chiral induction and uncommon Julia olefination of ketone forming the E-trisubstituted C（22）--C（23） double bound.     

The first enantioselective total synthesis of(+)-preussin B and an improved synthesis of(+)-preussin by step-economical methods

The first enantioselective total synthesis of(+)-preussin B and an improved synthesis of the antifungal alkaloid(+)-preussin are described. Our approach relied on the four step-economical synthetic methods developed in our laboratory:(1) the cis-diastereoselective reductive dehydroxylation of hemiaminals;(2) the direct amide/lactam reductive alkylation;(3) the one-pot N,O-bisdebenzylation-N-methylation; and(4) the one-step synthesis of malimide from malic acid. Both total syntheses are quite concise, which have been achieved in six steps, and gave overall yields of 25.7% and 27.6%, respectively.     

A Mild and Efficient Procedure for the Preparation of Chromone-2-carboxylates

Chromone-2-carboxylates are widely used for the pharmacological activity of several of its derivatives1. The general synthesis of such chromone derivates includes two steps (Scheme 1): a Claison condensation of dialkyl oxalate with 2-hydroxyacetophenones to achieve alkyl 3-(2-hydroxyphenyl)-3-oxopropanoates in the presence of NaH, NaOEt, or NaOMe; cyclodehydration of the alkyl 3-(2-hydroxyaryl)-3-oxopropanoates to obtain chromones under acid condition. The total yield of the two steps is q…     

A Convenient Synthesis of Octahydro-pyrazino [ 1,2- a ] pyrazine

The recent research results suggest that a series of octahydro-pyrazino[ 1,2-a ]pyrazines are useful as antiallergic agents.[1] Gubert et al. [2] developed a route from 1,4-dibenzyl-2-ethoxycarbonylpiperazine for the synthesis of this ring system. Under their conditions, this ring system was obtained with a low overall yield in six steps. Optimization of synthetic route to this ring system is still desirable. In this paper, we presented an efficient synthesis of octahydropyrazino[1,2-a]pyrazine by a new and efficient method starting from 1,3-dichloro-2-propanol and N-tosylated diethylenetriamine. The structure of title compound was determined by spectroscopy and X-ray diffraction technique.     

Two Chiral Building Blocks for the Stereocontrolled Synthesis of Anti-and Syn-1,3-Diols

During the last decade, chiral building blocks for 1, 3-diols of various configurations have been synthesized and applied widely in the total synthesis of natural polyene macrolide antibiotics1 and 1(, 25-dihydroxyvitamin D3 analogues2,3. The synthesis of the building block has attracted much interest in recent years. Herein, we report the synthesis of two chiral building blocks 1 and 2 in 8 steps and 7 steps respectively, starting from the readily available and inexpensive D (+)-xylose 3 as o…     

Microwave-assisted synthesis of α-hydroxy aromatic ketones from α-bromo aromatic ketones in water

A reaction ofα-bromo aromatic ketones in water with microwave irradiation gave the correspondingα-hydroxy aromatic ketones in good yields.The use of microwaves was found to significantly improve yields and shorten the reaction time.This reaction afforded a very clean,convenient method for the synthesis ofα-hydroxy aromatic ketones.     

Characterization and catalytic performance of CeO2-Co/SiO2 catalyst for Fischer-Tropsch synthesis using nitrogen-diluted synthesis gas over a laboratory scale fixed-bed reactor

The surface species of CO hydrogenation on CeO2-Co/SiO2 catalyst were investigated using the techniques of temperature programmed reaction and transient response method. The results indicated that the formation of H2O and CO2 was the competitive reaction for the surface oxygen species, CH4 was produced via the hydrogenation of carbon species step by step, and C2 products were formed by the polymerization of surface-active carbon species （-CH2-）. Hydrogen assisted the dissociation of CO. The hydrogenation of surface carbon species was the rate-limiting step in the hydrogenation of CO over CeO2-Co/SiO2 catalyst. The investigation of total pressure, gas hourly space velocity （GHSV）, and product distribution using nitrogen-rich synthesis gas as feedstock over a laboratory scale fixed-bed reactor indicated that total pressure and GHSV had a significant effect on the catalytic performance of CeO2-Co/SiO2 catalyst. The removal of heat and control of the reaction temperature were extremely critical steps, which required lower GHSV and appropriate CO conversion to avoid the deactivation of the catalyst. The feedstock of nitrogen-rich synthesis gas was favorable to increase the conversion of CO, but there was a shift of product distribution toward the light hydrocarbon. The nitrogen-rich synthesis gas was feasible for F-T synthesis for the utilization of remote natural gas.     

Racemic and enantioselective total synthesis of heliespirones A&C

An account of the total synthesis of(±)-,(+)-heliespirone A and(±)-,(-)-heliespirone C is presented.In the first-generation total synthesis,we found rac-24a could be easily transformed to rac-heliespirones A&C in a biomimic way.Taking the disappointing diastereoselectivity of prenylation from 3 to 4,the nonselective dihydroxylation from 4 to 5 and the lenthy route in strategy A into account,we designed a different synthetic plan targeting a highly enantioselective,concise and protective-group free synthesis...     

First total synthesis of isoquinolinone alkaloid marinamide and its methyl ester

The first total synthesis of isoquinolinone alkaloid marinamide 1 and its methyl ester 2 was described. The key steps involved a regioselective Frieclel-Crafts reaction of 1-benzyl-1H-pyrrole to form the intermediate 8.