A synthesis of the aromatic segment of rifamycin s

The aromatic segment $\text{15}$ of rifamycin S ($\text{1}$) was synthesized from the cyclohexadienone $\text{2}$ or $\text{ii}$ in high overall yield.     

Synthetic studies on palytoxin. Stereocontrolled,practical synthesis of the C.101–C.115 segment

A stereocontrolled and practical synthetic route to the acetal $\text{2a}$, a degradation product of palytoxin, in optically active form is described.     

Synthetic studies of incednine: synthesis of C1-C13 pentaenoic acid segment

Stereoselective synthesis of the C1-C13 pentaenoic acid segment (4) of the novel antibiotic incednine (1) is described.     

Synthetic studies on (+)-aplasmomycin. 1. Stereoselective synthesis of the C-12˜C-17 segment

The C-12˜C-17 segment of (+)-aplasmomycin ( ) was synthesized stereoselectively starting from (−)-malic acid based on the stereoselective ketone reduction.     

Thiazo rifamycins II: Mechanism of the reaction between rifamycin S and 2-amino ethanethiol derivatives

A mechanism for the reaction between rifamycin S and HS-CH₂-CH(NH₂)-R derivatives, leading to the formation of thiazole and thiazin-2-one rifamycin derivatives is proposed. It is shown that the ringcontraction thiazine thiazole occurs with extrusion of the CH₂ group to the S atom, while the formation of the thiazole and the thiazin-2-one rifamycins depends on the nature of the R group.     

Synthetic studies on amphidinolides C and F: synthesis of the C18-C29 segment of amphidinolide F

The C18-C29 segment of amphidinolide F is synthesised in 12 steps from 1,4-butanediol. Key steps include a mono-Sharpless dihydroxylation of a dienoate, iodocyclisation to construct the trans-THF ring and an E-selective Wittig reaction to introduce the C25-C26 olefin.     

Synthetic studies of tedanolide, a marine macrolide displaying potent antitumor activity. Stereoselective synthesis of the C13-C23 segment

[structure: see text] A highly stereoselective synthesis of the C13-C23 segment of tedanolide (1), an 18-membered macrolide isolated from the Caribbean sponge Tedania ignis, displaying significant cytotoxicity against KB and PS tumor cell lines, is described which involves two stereoselective epoxidations of regioisomeric trisubstituted double bonds and a stereospecific S(N)2' methylation reaction of a trans-gamma,delta-epoxy-cis-alpha,beta-unsaturated ester as the key steps.     

Computational studies on the cyclization of polycyclic aromatic hydrocarbons in the synthesis of curved aromatic derivatives.

Computational studies on the cyclization reactions of some polycyclic aromatic hydrocarbons (PAHs) were performed at the DFT level. Compounds C26H14 and C24H14, which show the connectivity of C60 fullerene fragments, were chosen as suitable models to study the formation of curved derivatives by six- or five-membered ring formation, upon oxidation to their radical cations. Four possible pathways for the cyclization process were considered: a) initial C-C bond formation to afford a curved derivative, followed by dehydrogenation; b) homolytic C-H cleavage prior to cyclization; c) initial concerted H2 elimination and subsequent cyclization; and d) deprotonation of the radical cations prior to cyclization. Computed reaction and activation energies for these reactions show that direct cyclization from radical cations (pathway a) is the lowest-energy mechanism. The formation of five-membered rings is somewhat more favourable than benzannulation. After new cycle formation, homolytic C-H dissociation to afford the corresponding cations is the most favourable process. These cations react with H* without barrier to give H2* Intermediate deprotonations are strongly disfavoured. The relatively low activation energies compared with carbon cage rearrangements suggest that ionization of PAHs can be used for the tailored preparation of nonplanar derivatives from suitable precursors.     

Synthetic studies toward diazonamide A. A novel approach for polyoxazole synthesis

[Reaction in text]The indole-bisoxazole fragment of diazonamide A was prepared by a Chan-type rearrangement of a tertiary amide. This approach represents a remarkably direct strategy for polyoxazole synthesis.     

Synthetic studies on maitotoxin. 2. Stereoselective synthesis of the WXYZA'-ring system

The stereoselective synthesis of the WXYZA'-ring system of maitotoxin has been accomplished via a linear synthetic approach, in which key reactions were SmI 2-induced cyclization of beta-alkoxyacrylate for the construction of the A'-, Y-, and X-rings and 6- endo cyclization of hydroxy vinylepoxide for that of the Z- and W-rings.     

Synthetic studies on maitotoxin. 3. Stereoselective synthesis of the BCDE-ring system

The stereoselective synthesis of the BCDE-ring system of maitotoxin has been accomplished through a two-directional strategy for the construction of polycyclic ether. The key reactions involve SmI 2-induced double cyclization of a beta-alkoxyacrylate and a double dihydroxylation for construction of the B- and E-rings.     

Synthetic studies on thiostrepton family of peptide antibiotics: synthesis of the pentapeptide segment containing dihydroxyisoleucine, thiazoline and dehydroamino acid

The dihydroxyisoleucine-, thiazoline- and dehydroamino acid-containing pentapeptide of the thiostrepton family of peptide antibiotics was synthesized, which featured the β-lactone opening by phenylselenylation, the vinylzinc addition to the chiral sulfinimine, the Wipf oxazoline-thiazoline conversion method and the oxidative syn-elimination of the phenylseleno group.     

A model study for the biomimetic-type synthesis of rifamycin S

Acid treatment of the hydroperoxide $\text{5}$ yielded the enol ether $\text{9}$. Hydrogenation of $\text{9}$ gave the dihydro derivative, the structure of which was established by comparison with the substance synthesized by a different route.     

Synthetic studies directed toward the total synthesis of dolabriferol

Herein we report our results towards the total synthesis of (−)-dolabriferol, describing the synthesis of fragments C1-C9 and C10-C21. This convergent asymmetric approach relies on the use of a common Weinreb amide precursor for the preparation of both fragments, an efficient anti-aldol reaction followed by Zn(BH₄)₂ reduction to give a 1,3-syn diol, a selective oxidation of a triol under Swern conditions with concomitant lactol formation, and a diastereoselective epoxidation of an allylic alcohol with m-CPBA followed by an efficient epoxide opening with Me₂CuCNLi₂.     

Synthetic studies towards furanocembrane diterpenes. A total synthesis of bis-deoxylophotoxin

Synthetic approaches to the furanocembrane family of natural products, e.g. lophotoxins, pukalides, bipinnatins, based on: i) an intramolecular cyclisation of an alpha,beta-unsaturated acyl radical intermediate into a conjugated enone, and ii) an intramolecular Stille coupling reaction involving a 2-stannylfuran and a vinyl iodide, are described. A total synthesis of bis-deoxylophotoxin , the probable biological precursor to the neurotoxin lophotoxin, isolated from species of the Pacific sea whip Lophogorgia, is then presented.