A Protecting-Group-Free Synthesis of (−)-Salvinorin A

A concise enantioselective total synthesis of the neoclerodane diterpene (−)-salvinorin A is reported. The stereogenic center at C-12 was installed by catalytic asymmetric propargylation with excellent enantioselectivity, and the remaining six stereogenic centers were set up highly diastereoselectively under substrate control. As for our previous synthesis of racemic salvinorin A, two intramolecular Diels-Alder reactions were applied to generate the tricyclic core. A chemoselective Mitsunobu inversion of a syn 1,2-diol allowed for further streamlining of the original reaction sequence by two steps. Overall, (−)-salvinorin A was synthesized in only 16 steps starting from 3-furaldehyde with 1.4 % total yield. Furthermore, an alternative intramolecular Diels-Alder strategy employing a 2-bromo-1,3-diene moiety was investigated.     

Total Synthesis of Illisimonin A and Merrilactone A

Illicium sesquiterpenes are a large family of biologically active secondary metabolites isolated from Illicium species of plants and are well-known for their activity of neurite outgrowth in cultured neurons. Herein, we propose a comprehensive biosynthetic pathway for illicium sesquiterpenes and report a synthetic route to illisimonin A and merrilactone A based on it. We think that the carbon scaffolds of most of the illicium sesquiterpenes could be synthesized from a dicarbonyl derivative of allo-cedrane through retro-Dieckmann condensation, oxidative cleavage and aldol reaction at suitable oxidation states in Nature. The common intermediate for illisimonin A and merrilactone A similar to the dicarbonyl derivative of allo-cedrane was assembled with up to 82 % ee by an asymmetric intramolecular desymmetrizing reductive Heck reaction by the use of a new type of chiral phosphine ligand. The syntheses of illisimonin A and merrilactone A supported the key transformations of the proposed biosynthetic pathway.     

A Taxatetraene from Microbial Transformation of Sinenxan A

Sinenxan A [2α, 5α, 10β, 14β-tetraacetoxytaxa-4(20), ll-diene, 1] was biotransformed by a filamentous fungus, Aspergillus niger JCM 5546, and an unusual taxatetraene [2α,5α-acetoxytaxa-4(20), 10(11), 12(18), 13(14)-tetraene, 2], together with two known products,10β-deacetyl sinenxan A (3) and 10β, 14β-dideacetyl sinenxan A (4) were produced.     

Total Synthesis of Przewaquinone A

PrzetvaquinolleA,anaturalortloquinoneisoIatedfromSalviaPrzewakiiMtalmvarmandarinorunIShb.['J.hasbeenshowedanhtumorachvityinaVariety'oftumormodels,sucha5Let`dsIungcarcil1oma,Il1e1anolnaBl6,sarcomal8Oandleuke1niaPss8,bothinvitroandvivo.Inthepresentpaper,h1efirsttota19'11tl1esisofprzett2q[linoneAisdescribed.Targetmoleculeunpreparedtliroughareactionsequence(asshoxvnil1scheme.).Con1pound5ttasobtalnedbycyclizahonof4in56.l%}jeld.Dicarbox})licacid5washeatedwithcoPperPOwderinquinolinetoaffordmo…     

Total Synthesis of Homodimericin A

We report the concise total synthesis of homodimericin A ( 1 ), a recently identified fungal metabolite bearing an unprecedented molecular architecture. The success of the approach hinges on a series of rationally designed and bioinspired transformations, including a Moore rearrangement to assemble the monomeric hydroquinone precursor, homodimerization through double Michael addition to construct the planar A/B/C tricyclic framework, and a tandem Diels–Alder reaction/carbonyl–ene cyclization to forge the congested D/E/F tricyclic cage motif. Unequivocal evidence for the elucidated structure of homodimericin A was also provided by this study.     

Total Synthesis of N-Methylsansalvamide A

Sansalvamide A is a cyclic depsipeptide, isolated from a marine fungus of the genus Fusarium by Belofsky in 19991. The depsipeptide displays cytotoxic and antiviral activities, and also possesses inhibitor of MCV topoisomerase2. The corresponding amide de…     

Crystal Structure of Taxinine A

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Synthesis of 7-Epi-howiinol A

InprcviousPaPCI'],wellaverePortcd1l1etotalSyntl1csisofhowiinolA(1).anovellactoneisolaledfromh1erootandStembarkofGonioIhamushowiiMerr.(Annoaceae)inourl3bobory,whichwasshowntoPossesssignincanlc}1otoxicactiviticsto~sevendhumantllIIlrCellsinl'ilroandin.i.oI=1.Aspartofourworkondevelopingnewthebortrigs,weparellthereinthCs}nll1csisofitS7-ePimcr,7-ePi-llot'iinolA(2).Theroutelo2isilthetedinSchemel.CommerciallyavailableQ-D-glucohCPtonicy-lactone3wastransformedintothetetraol4inayieldof28%by4st…     

A novel synthesis of perfluoroalkylglycine

Perfluoroalkylglycine was obtained through perfluoroalkylation of 2-phenyl-5-etho-xyoxazole using RFI-Na2S2O4 reagent system, followed by acid hydrolysis of the intermediates, 2-phenyl-4-perfluoroalkyl-5-ethoxyoxazole and 2-phenyl-4-perfluoroalkyl-2-oxazolin-5-one.     

Synthesis of A New Kind of Acetylenic Polysilazane

A new kind of conjugated polymer, acetylenic polysilazane was prepared by ammonolysis of acetylenic dimethylchlorosilane. The polymer was characterized by ^29Si、 ^13C NMR and elemental analysis.     

A Convenient Method of Synthesis of Ferrocenylethynyl Ketones

It is well known that molecules possessing extensive conjugated π-electron systems exhibit large non-linear optical properties,[1,2] but the compounds of ferrocenylethynyl ketones have not been reported so far. We now reported preparation of some ferrocenylethyl ketones. These new ethynylketones containing ferrocenyl were prepared conveniently via coupling reaction catalyzed by PdCl2(PPh3)2/PdBzCl(PPh3)2-CuI from ferrocenylethyne and acyl chlorides. This coupling reaction proceeded smoothly in argon and free-water atmosphere at room temperature and gave coupling products in satisfactory yields. All products were characterized by 1H NMR, MS, IR and UV spectra.     

A new structural model of Aβ40 fibrils

The amyloid fibrils of beta-amyloid (Aβ) peptides play important roles in the pathology of Alzheimer's disease. Comprehensive solid-state NMR (SSNMR) structural studies on uniformly isotope-labeled Aβ assemblies have been hampered for a long time by sample heterogeneity and low spectral resolution. In this work, SSNMR studies on well-ordered fibril samples of Aβ(40) with an additional N-terminal methionine provide high-resolution spectra which lead to an accurate structural model. The fibrils studied here carry distinct structural features compared to previous reports. The inter-β-strand contacts within the U-shaped β-strand-turn-β-strand motif are shifted, the N-terminal region adopts a β-conformation, and new inter-monomer contacts occur at the protofilament interface. The revealed structural diversity in Aβ fibrils points to a complex picture of Aβ fibrillation.     

A theoretical form of the Martin-Hou equation of state

A new equation of state is derived from the Barker-Henderson hard-sphere perturbation theory. It has the form similar to the Martin-Hou equation of state. The numerical values of the characteristic constants in the equation can be calculated by the method of Martin and Hou. The equation can be used to predict P-V-T properties accurately for fluids when the critical parameters (T_c, P_c and V_c) and one point on the vapor pressure cure are given. By using the functional relationships between the characteristic constants and the microscopic parameters, the molecular microscopic parameters of the substance can be obtained.     

Asymmetric Total Synthesis of a Diastereisomer A of Tuxpanolide

α-Alkylidene-β-hydroxy butyrolactones have been attractive and challenging targets for organic synthesis in various laboratories because that not only they are rich in skeletal diversity and stereochemistry complexity but also many of them possess quite intriguing and wide biological activities.[1] A novel class of the phytane-type diterpenoid named Tuxpanolide, bearing α-alkylidene-β-hydroxy-γ-butyrolactone skeleton, was isolated from Perymenium hintonii in Central Mexico by Maldonado and co-wokers in 1998.[2] Now we firstly report the efficient strategy of the stereocontrolled total synthesis of a diastereisomer A of Tuxpanolide.     

A stereocontrolled total synthesis of (±)-saframycin A

A thirteen-step total synthesis of (±)-saframycin A from a tricyclic lactam intermediate is described. The key step of this total synthesis is the stereocontrolled construction of a pentacyclic saframycin framework via a modified Pictet-Spengler type cyclization generating a bis-carboxylic acid ester derivative, followed by decarboxylation. The cytotoxicity profiles are also presented.     

A convenient synthesis of 6-demethoxycapillarisin

A convenient and effective method for the synthesis of 6-demethoxycapillarisin was described.The highlight was involved in asimple access to the key intermediate 2-ethylthio-5,7-dimethoxy-4H-chromen-4-one from the inexpensive 2,4,6-trihydroxyacetophenone,using AlCl3 as the demethylation reagent.     

A Novel Synthesis of Difloxacin Hydrochloride

Difloxacin, the third generation of new quinolone antibiotics, has broad-spectrum in vitro activity and excellent potency in vivo and has been found to be against gram-positive cocci, gram-negative bacteria, anaerobe, mycoplasm, chlamydia1,2. As described previously, high reaction temperature and hazardous reagents are the defects of the methods for preparation of difloxacin3,4. We have developed a new synthetic method as shown in the Scheme. 2,4-Dichloro-5-fluoro-acetophenone 1 was used as …     

A Convenient Synthesis of β-Ketosulfoxides

β-Ketosulfoxideshaveattractedmanyorganicchemistsbecauseoftheirwideuseinsynthesisofketones,a-ketols,glyoxals,a-ketoacids,glycols,a-hydroxyacidsandsoculGenerally,6-ketosulfoxidescanbepreparedbythereactionofesterwithsulfoxidel',acylchloridewithsulfoxi...     

Bioinspired Asymmetric Synthesis of Hispidanin A

The first enantiospecific synthesis of hispidanin A ( 4 ), a dimeric diterpenoid from the rhizomes of Isodon hispida, was achieved with a longest linear sequence of 12 steps in 6.5 % overall yield. A key component is the use of the abundant and naturally occurring diterpenoids (+)-sclareolide and (+)-sclareol as starting materials, which enables the gram-scale preparation of the key intermediates totarane ( 1 ) and s-trans-12E,14-labdadien-20,8β-olide ( 2 ). Subsequently a thermal or an erbium-catalyzed intermolecular Diels–Alder reaction of totarane ( 1 ) with labdadienolide ( 2 ) provide convergent and rapid access to the natural product hispidanin A ( 4 ). The synthetic studies have offered significant impetus for the efficient construction of these architecturally complex natural products.