Synthetic approach to pentacyclic quassinoids from communic acids, via ambracetal derivatives

Methyl (8R,13S)-8α,13:13,17-diepoxy-14,15-dinorlabdane-19-oate, easily prepared from communic acids, is a suitable intermediate for synthesizing pentacyclic quassinoids, because it enables the elaboration of the A ring and the further construction of the B-C-D ring system of these terpenoids. The cetal group is stable under the reaction conditions utilized during the elimination of the ester group and the introduction of the hydroxyl group on C-3. At the same time, it enables the regeneration of the methylketone and exocyclic double bond presented by methyl 13-oxo-14,15-dinorlabd-8(17)en-19-oate. The latter compound was previously used to construct the B-C-D-ring of these quassinoids.     

Synthetic approaches to fused heteroaromatic compounds by the condensation reactions of functional pyrroles

Condensation reactions ol the “functionalized” pyrroles which were obtained by one pot synthesis of aziridines and acetylenic dipolarophiles were discussed. On treatments of 3,4-di- and 2,3,4-tribenzoylpyrroles with hydrazine hydrate and phosphorus pentasulfide, the several pyrrolo-pyridazine derivatives and fused thiophenes, respectively, were prepared. The structure proofs for the products of the reaction of the 2,3,4-tribenzoylpyrrole ( 9a ) with hydrazine hydrate were based on the ¹³C FT-nmr spectrum of the corresponding ¹³C-enriched compounds.     

Synthetic strategies to well-defined polymers by ionic polymerization

The living cationic polymerization and sequential copolymerization of isobutylene and styrene has been achieved. Polymethylmethacrylate-g-polyisobutylene graft copolymers have been prepared by the combination of living cationic and group transfer polymerization.     

Synthetic strategies to epoxydiynes and a key synthon of the neocarzinostatin chromophore

We present herein our recent efforts towards the synthesis of epoxydiynes which represent an unusual structural feature of the neocarzinostatin chromophore. A number of different routes to these epoxydiynes have been explored with varying success. Ultimately a concise and convergent approach was developed, which involved the addition of an allenyl zinc bromide to propargylic ketones/aldehydes followed by epoxide formation. This new protocol enabled us to synthesise a fully elaborated epoxydiyne which will find application for our studies towards the total synthesis of the NCS chromophore.     

Synthetic studies on Et-743. Assembly of the pentacyclic core and a formal total synthesis

A formal total synthesis of the potent anticancer agent Et-743 is described. The tetrahydroisoquinoline core is stereoselectively constructed using a novel radical cyclization of a glyoxalimine. Further elaboration of this core rapidly accessed the pentacyclic core of Et-743, but a mixture of regiosisomers was obtained in the key Pictet-Spengler ring closure. A known advanced intermediate in the synthesis of Et-743 was intercepted, constituting a formal synthesis of the molecule.     

Synthetic strategies to alpha-trifluoromethyl and alpha-difluoromethyl substituted alpha-amino acids

The combination of the unique physical and chemical properties of fluorine with proteinogenic amino acids represents a new approach to the design of biologically active compounds including peptides with improved pharmacological parameters. Therefore, the development of routine synthetic methods which enable the effective and selective introduction of fluorine into the desired amino acids from readily available starting materials is of significant synthetic importance. The scope of this critical review is to summarize the most frequently employed strategies for the synthesis of alpha-difluoromethyl and alpha-trifluoromethyl substituted alpha-amino acids (114 references).     

Synthetic strategies to derivatizable triphenylamines displaying high two-photon absorption

A versatile synthetic strategy to access a set of highly fluorescent pi-conjugated triphenylamines bearing a functional linker at various positions on one phenyl ring is described. These compounds were designed for large two-photon absorption (2PA) and in particular for labeling of biomolecules. The monoderivatized trisformylated or trisiodinated intermediates described herein allow introduction of a large variety of electron-withdrawing groups required for large 2PA as well as a panel of chemical functions suitable for coupling to biomolecules. The monoderivatized three-branched compounds and in particular the benzothiazole (TP-3Bz) series show remarkable linear (high extinction coefficients and high quantum yield) and nonlinear (high 2-photon cross sections) optical properties. Interestingly the presence of functional side chains does not disturb the two-photon absorption. Finally, monoderivatized two-branched derivatives also appear to be valuable candidates. Altogether the good optical properties of the new derivatizable pi-conjugated TPA combined with their small size and their compatibility with bioconjugation protocols suggest that they represent a new chemical class of labels potentially applicable for the tracking of biomolecules using two-photon scanning microscopy.     

Synthetic approach to the total synthesis of fumitremorgins II synthesis of optically active pentacyclic intermediates and their dehydrogenation

Optically active pentacycles ( 13–18 ) were synthesized from L- and D-tryptophans, two of which ( 13 and 15 ) were alkylated and dehydrogenated to 21 and 22, respectively.     

Synthetic strategies to the ergoline ring system of ergot alkaloids

The synthetic strategies to the ergoline ring system (I) have been outlined, and discussed in terms of their yields and limitations. The total syntheses of ergoline, racemic and natural dihydrolysergic acid, lysergic acid, isosetoclavine, penniclavine, elymoclavine and chanoclavine-I have been described. These illustrate the synthetic problems that have been encountered in ergoline chemistry. The role of key intermediates has been emphasised. Modification to the original schemes have not given yields or procedures that can compete with the production by fermentation of ergot alkaloids. However, it is hoped that the synthetic strategies discussed in this article will provide useful information, when considering new approaches, or modification, to the unique heterocyclic ring system of ergoline.     

Synthetic studies on ecteinascidin-743: constructing a versatile pentacyclic intermediate for the synthesis of ecteinascidins and saframycins

[reaction: see text] The asymmetric synthesis of a highly functionalized pentacyclic tetrahydroisoquinoline relevant to the ecteinascidin, saframycin, safracin, and renieramycin family of antitumor alkaloids is described.     

An easy route to pentacyclic terpenylquinones

Cyclisation of terpenylnaphthohydroquinone derivatives or terpenylquinone cycloadducts, obtained from methyl myrcecommunate, was performed in the presence of HI, I₂ or BF₃·OEt₂ and provides efficient synthetic strategies for the preparation of pentacyclic terpenylquinones.     

Selectively monomodified cyclodextrins. Synthetic strategies

Monomodifications of cyclodextrins to give selectively 2-, 3-, or 6-substituted product is a challenging task because of the number of hydroxyl groups that can potentially react with the incoming reagent. The principles and the methods involved in manipulations of the differences in the chemistry of these hydroxyl groups to control the outcome of an electrophilic reaction with them to produce monoalkylated (ether-linkaged) cyclodextrin derivatives are discussed and illustrated.     

Synthetic strategies for chiral metal-organic frameworks

By direct synthesis route, chiral metal-organic frameworks are synthetized with enantiopure ligands or spontaneous resolution; by indirect method, post-synthetic method and chiral inductionare introduced to construct chiral metal-organic frameworks.     

Synthetic strategies to chiral organosulfur donors related to bis(ethylenedithio)tetrathiafulvalene

Syntheses of enantiopure organosulfur donors by three different strategies requiring only four-six steps are reported. The key step involves either double substitution of an enantiopure cyclic sulfate ester by a dithiolate, attachment of a chiral diol as a ketal, or completely diastereoselective cycloaddition of 1,3-dithiole-2,4,5-trithione to an enantiopure alkene.     

Synthetic utility of an isolable nucleoside phosphonium salt

The reaction of O6-benzyl-3',5'-bis- O-( tert-butyldimethylsilyl)-2'-deoxyxanthosine with 1H-benzotriazol-1-yloxy-tris(dimethylamino)phosphonium hexafluorophosphate (BOP) yielded the nucleoside C-2 tris(dimethylamino)phosphonium hexafluorophosphate salt as a stable, isolable species. This is in contrast to reactions of inosine nucleosides with BOP, where the in situ formed phosphonium salts undergo subsequent reaction to yield O6-(benzotriazol-1-yl)inosine derivatives. The phosphonium salt obtained from the 2'-deoxyxanthosine derivative can be effectively used to synthesize N2-modified 2'-deoxyguanosine analogues. Using this salt, a new synthesis of an acrolein-2'-deoxyguanosine adduct has also been accomplished.     

Synthesis of a novel tetrahydroisoquinoline pentacyclic framework

N-Acyliminium cyclization of 6-substituted (3R^∗,6R^∗,11aS^∗)-3-arylmethyl-pyrazino[1,2-b]isoquinoline-1,4-diones gave with very good yields a novel tetrahydroisoquinoline pentacyclic core framework (29), while this reaction failed in all-cis-isomers to give instead conjugated enamines by deprotonation. Electronic and steric factors that govern the approach to both diastereomers from 6-substituted pyrazino[1,2-b]isoquinoline-1,4-diones have been studied.