Structural determination of eleven new preschisanartane-type schinortriterpenoids from two Schisandra species and structural revision of preschisanartanin J using NMR computation method

Nineteen preschisanartane-type schinortriterpenoids(SNTs),among which eleven ones were previously undescribed,were isolated from two Schisandra species,S.sphaerandra and S.rubriflora.Their structures were determined using 1 D and 2 D NMR spectroscopic analyses,NMR data comparison,quantum chemical calculation of NMR parameters,electronic circular dichroism(ECD),X-ray single crystal diffraction,and chemical derivation.Furthermore,structural re-examination of a few previously reported preschisanartane-type SNTs led to the structural revision of preschisanartanin J.Besides,it is suggested that the reported structures of arisanlactone D and schilancidilactone W should be re-checked.Finally,a few isolated SNTs were found to possess neurite outgrowthpromoting activities,and protective activities against neural injuries.

Lanostane-Type Triterpenoids from Scilla scilloides and Structure Revision of Drimiopsin D

Two hitherto unknown lanostane-type triterpenoids,namely scillascillol(1)and scillascillone(2),and a hitherto unknown norlanostane-triterpene glycoside,namely scillascilloside B-1(3),were isolated from the ethanol extract of the whole plants of Scilla scilloides.Their structures were elucidated on the basis of extensive spectroscopic studies.In addition,the structure of drimiopsin D(6a)has been revised as 2,5-dimethoxy-8-methyl-1,3,6-trihydroxyxanthone(6)by reanalysis of the spectroscopic data.

New isoflavonoids from Erythrina arborescens and structure revision of anagyroidisoflavone A

Five hitherto unknown isoflavonoids,namely erythrinins D-H(1-5),were isolated from the ethanol extract of Erythrina arborescens.Their structures were elucidated on the basis of extensive spectroscopic studies.In addition,the structure of anagyroidisoflavone A(6a)has been revised as 1″-O-methylerythrinin F(6)by re-analysis of the original spectroscopic data.

Aristolane‑type Sesquiterpenoids from Nardostachys chinensis and Revised Structure of Aristolanhydride

Four hitherto unknown aristolane-type sesquiterpenes,including one novel 8,9-secoaristolane,namely secoaristolenedioic acid(1),two aristolone derivatives,namely 1α,2β-dihydroxyaristolone(2),9-epidebilon(3),and one rare aristolane-chalcone hybrid,namely 3′-hydroxynardoaristolone A(4)were isolated from the ethanol extract of the roots and rhizomes of Nardostachys chinensis.Their structures were elucidated on the basis of extensive spectroscopic analysis.In addition,the structure of aristolanhydride,recently isolated from the same species,was corrected by reanalysis of the published NMR data.

Vibralactone Biogenesis-Associated Analogues from Submerged Cultures of the Fungus Boreostereum vibrans

A scale-up fermentation of the fungus Boreostereum vibrans facilitated the isolation of six new vibralactone biogenesis-associated analogues,namely vibralactamide A(1),vibralactone T(2),13-O-lactyl vibralactone(3),10-O-acetyl vibralactone G(4),(11R,12R)-and(11S,12R)-vibradiol(5,6).Their structures were established via extensive spectroscopic analyses,specific optical rotation comparison,and Snatzke’s method.The biosynthetic pathway for vibralactamide A was postulated.The absolute configuration of vibralactone B was revised by single crystal X-ray diffraction analysis.This work puts the divergent vibralactone biosynthesis pathway one step further and expands the structural diversity of vibralactone-associated compounds.

An attempted approach to the tricyclic core of haliclonin A：Structural elucidation of the final product by 2D NMR

We describe the design and execution of a novel synthetic route to the tricyclic core of haliclonin A,a tetracyclic marine natural product.The approach features Bachi＇s thiol-medicated free radical cyclization of alkenyl isocyanide to build the bridged ring system,and ring-closing metathesis（RCM） reaction to form the macrocycle.Execution of the synthetic plan ultimately resulted in a diazatricyclic compound.By means of 2D NMR techniques,the structure of this compound was revealed to an unexpected product 8.Analysis of the synthetic pathways allowed concluding that the unexpected product is a result of an ＂unexpected＂ migration of olefinic bond during dioxolanation of the 2-cyclohexenone derivative 7.This investigation also resulted in a concise construction of the functionalized hexahydro-1H-isoindole-1,5（4H）-dione 12 and the macrocyclic tricyclic ring system 8.

Concise,enantioselective total syntheses of both the proposed and revised structures of (-)-versiquinazoline H

The enantioselective total synthesis of the putative structure of versiquinazoline H and three diastereomers has been achieved,which allowed the revision of the stereochemistry of this natural product.This six-step total synthesis relied on the evolution of the strategy that we previously developed,which features a DMDO-triggered tandem reaction.The modification of the lactamization step resulted in a significant improvement of yield that ensured the efficient total synthesis.