Synthesis and structure revision of litseaone A

Litseaone A, isolated from the stem barks of Litsea rubescens and Litsea pedunculata, is a chalcone derivative with a novel spiro-epoxide moiety. The structural revision of litseaone A was achieved by the racemic synthesis of the proposed structure and the asymmetric synthesis of the revised structure. The major tautomeric structure of litseaone A and the relative stereochemistry at the epoxide carbon center were also clarified.     

Versicolactones A and B: total synthesis and structure revision

To further determine absolute configurations of versicolactones A and B, total synthesis of versicolactones A and B and their six stereoisomers were reported in this Letter. The ¹H and ¹³C NMR spectra of the synthetic erythro-stereoisomers matched perfectly with those of the natural products. Combined with the comparison of the specific rotations, the absolute configuration of versicolactones A and B were revised as (4Z,6R,7S)- and (4E,6R,7S)- from the corresponding (4Z,6R,7R)- and (4E,6R,7R)-6,7-dihydroxyocta-2,4-dien-4-lactone, respectively.     

Mostueine: synthesis and structure revision

A total synthesis of mostueine (1) based upon the intramolecular alkylation of the indole nitrogen is described. A revision of the reported sterochemistry of mostueine to 3SR, 19RS as elucidated by synthesis and NOE data is disclosed.     

The cycloaddition of diethyl chlorophosphite with norbornadiene: Synthesis and crystal structure of the cycloadduct.

In the presence of Lewis acids, diethyl phosphorochloridite reacts with norbornadiene to afford the tetracyclic phosphinate ester 3 . The reaction is believed to involve formation of phosphenium ions stabilized only by alkoxy substituents. The cycloadduct of the reaction was characterized by its spectral data, by single crystal diffraction analysis of the parent acid, and ³¹P and ²⁷Al nmr experiments.     

Coniothyrione: anatomy of a structure revision

Coniothyrione is a xanthone‐derived antibiotic reported several years ago by researchers at Merck & Co. Inc. Revision of the position of the chloro substitution was recently proposed on the basis of empirical reinterpretation of the carbon chemical shift data and a hypothetical biosynthetic argument without the acquisition of any new spectral data to support the postulated change in substituent location. The originally published HMBC data lead to an equivocal assignment of the structure and do not provide a solid basis of support for either structure. Neural network ¹³C chemical shift calculations and density functional theory calculations also led to undifferentiated structures. Definitive confirmation of the structure of coniothyrione based on the acquisition and interpretation of 1,1‐ADEQUATE and inverted ¹J_CC 1,n‐ADEQUATE data is now reported. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of diversifolide and structure revision

The synthesis of diversifolide and its structural revision are reported. We synthesized the assigned structure of diversifolide via two methods, but the NMR spectra of the synthetic material did not match those of the natural material. Through careful investigation, we found that the spectra were identical with those of 11-epi-sundiversifolide.     

The crystal and molecular structure of the cycloadduct from an activated carbodiimide and methyl isothiocyanate

The crystal and molecular structures of the cycloadduct from isopropyl[α-(dimethylthio-carbamoyl)isopropyl]carbodiimide and methyl isothiocyanate were determined by single-crystal X-ray methods. The product was established to be 2-(1-isopropyl-3,5-dimethyl-4,6-dithioxo-hexahydro-1,3,5-triazine-2-ylidenamino)-N,N-dimethylthioisoburyramide, in which contrary to expectations based on hybridisation the heterocyclic ring adopts a boat conformation.     

Total synthesis and structure revision of petrobactin

The total synthesis and the revised structural assignment of petrobactin, a siderophore isolated from the marine bacterium Marinobacter hydrocarbonoclasticus, is reported. The key step in the synthesis involved condensation of N¹-(2,3-dibenzoyloxybenzoyl)-N⁴-benzylspermidine with 1,3-di-(p-nitrophenyl)-2-tert-butyl citrate. Proton NMR spectra of the synthesized product compared with those reported for the natural product revealed that the compound did not contain 2,3-dihydroxybenzoyl moieties as published; instead, the splitting pattern suggested 3,4-dihydroxybenzoyl fragments. The 3,4-dihydroxybenzoyl analogue was accessed via a similar route; the proton and carbon-13 NMR spectra of this compound were consistent with those reported for natural petrobactin.     

Total synthesis of pulverolide: revision of its structure

A flexible and practical strategy toward the synthesis of rare 2H-furo[3,2-b]benzopyran-2-one skeleton has been developed. With a microwave-assisted cyclization-dehydration as the key transformation, the first total synthesis of pulverolide has been completed in 10 steps with 9% overall yield, leading to the revision of its proposed structure.     

A total synthesis prompts the structure revision of haouamine B

A concise asymmetric approach to the indeno-tetrahydropyridine core of the unusual alkaloid haouamine B allowed for an investigation of a biomimetic oxidative phenol coupling as a proposed biosynthetic step, and ultimately provided access to the published structure of the natural product. As a consequence of our synthetic studies, the structure of haouamine B has been revised.     

Total synthesis and structure revision of deacetylravidomycin M

Total synthesis of the unnatural enantiomer of deacetylravidomycin M was accomplished. The key steps include, (1) aryl C-glycosidation of the azido-bearing fucosyl acetate 2 by using catalytic Sc(OTf)₃, (2) the [2+2] cycloaddition reaction of alkoxybenzyne bearing an azido sugar to ketene silyl acetal, and (3) the ring expansion reaction of alkoxybenzocyclobutenone. The synthesis revealed that the natural product is not the proposed amine, but the corresponding N-oxide.     

Total synthesis and structure revision of stachybotrys spirolactams

The spirolactam structure 1 reported in 1996 by Roggo et al. has been enantioselectively synthesized in 20 steps from (+)-Wieland-Miescher ketone. Spectra of this synthetic lactam differed from those of the natural spirolactam from the Roggo group, leading to the hypothesis that the natural lactam may be the regioisomer 27, a structure previously ascribed by Jarvis et al. to the natural product stachybotrylactam. This hypothesis was confirmed by the first total synthesis of (-)-stachybotrylactam (27). Double reductive amination of two molecules of aldehyde 29 with one molecule of l-lysine led by analogous chemistry to the first synthesis of the pseudosymmetric "dimer" 30, whose spectra corresponded to those of the natural "dimer" originally assigned structure 5 by the Roggo group.