Total synthesis of apoptolidin: completion of the synthesis and analogue synthesis and evaluation

The total synthesis of apoptolidin (1) is reported together with the design, synthesis, and biological evaluation of a number of analogues. The assembly of key fragments 6 and 7 to vinyl iodide 3 via dithiane coupling technology was supplemented by a second generation route to this advanced intermediate involving a Horner-Wadsworth-Emmons coupling of fragments 22 and 25. The final stages of the synthesis featured a Stille coupling between vinyl iodide 3 and vinylstannane 2, a Yamaguchi lactonization, a number of glycosidations, and final deprotection. The developed synthetic technology was applied to the construction of several analogues including 74, 75, and 77 which exhibit significant bioactivity against tumor cells.     

Total synthesis of pyridovericin: studies toward the biomimetic synthesis of pyridomacrolidin

[reaction: see text] The total synthesis of the novel metabolite pyridovericin 1 is reported. The synthesis of this key intermediate in our proposed biomimetic synthesis of pyridomacrolidin 2 has been accomplished in good yield from readily available 2,4-dihydroxypyridine.     

Computational modelling of the YAG synthesis

Mathematical and numerical models of the yttrium aluminium garnet (YAG) synthesis are presented in the article. The models allow the effective computer simulation of the YAG synthesis. The synthesis by sol–gel and solid-state reaction methods is considered in the article. The question concerning the reasons for the observed changes in the preparation temperature by changing synthesis method is answered. The inverse modelling problem is solved: using known experimental data (synthesis time, dimensions of reactants) the unknown input parameters of the model (diffusion and reaction rate coefficients) are calculated.     

New synthesis of vaulted biaryl ligands via the Snieckus phenol synthesis

[reaction: see text] In an effort to develop a synthesis of the VAPOL ligand that avoids the use of a chromium carbene complex, a route was examined that involved the annulation of a naphthalene carboxamide via the method of Snieckus. The latter derivatives could be converted in a two-step sequence to 2-phenyl-4-phenanthrols in 60-72% overall yields. The utility of this method for the synthesis of VAPOL derivatives is demonstrated in the synthesis of (S)-7,7'-dimethyl-VAPOL.     

The total synthesis of (+)-16-hydroxydihydrocleav-amine and the partial synthesis of demethoxy-carbonyldeoxyvinblastine

The total synthesis of (+)-16-hydroxydihydrocleavamine and the partial synthesis of demethoxycarbonyldeoxyvinblastine are described.     

Benzothiazines in synthesis: studies directed toward the synthesis of erogorgiaene

The use of benzothiazenes for the formal total synthesis of erogorgiaene and stereoselective total syntheses of two diastereomers of this natural product is described. In particular, the stereochemical course of a radical cyclization anticipated to give the correct relative stereochemistry for the synthesis of erogorgiaene is discussed utilizing both experimental and computational data.     

Studies towards the synthesis of trocheliophorolides

Total synthesis of trocheliophorolide C epimer is reported. The synthetic strategy involves generation of lactone skeleton and preparation of unsaturated side chain followed by cross-metathesis. The Eglinton oxidative coupling, Cadiot-Chodkiewicz cross-coupling and cross-metathesis are the key reactions used in the synthesis. We also attempted the synthesis of trocheliophorolide D epimer, which includes Cu catalyzed various cross-coupling reactions.     

Studies towards the total synthesis of Sch 56036; isoquinolinone synthesis and the synthesis of phenanthrenes

The isoquinolinone hemisphere of Sch 56036 has been prepared using a modified Pomeranz-Fritsch reaction and the synthesis of the phenanthrene core has been modelled via a Suzuki coupling and subsequent ring closing metathesis.     

Ionic-liquid-supported peptide synthesis demonstrated by the synthesis of Leu(5)-enkephalin

A new strategy for the synthesis of oligopeptides was developed using an ionic liquid as a soluble support. The efficiency of this ionic liquid-phase approach was demonstrated by the synthesis of a bioactive pentapeptide, Leu(5)-enkephalin, in good yield and reasonable purity. The structures and purities of the reaction intermediates in each step were verified easily by routine spectroscopic analysis, and no chromatographic procedures were needed during the synthesis.     

Biomimetic synthesis of the shimalactones

A biomimetic synthesis of shimalactone A and B is described. Its key features are an unprecedented acid-catalyzed cyclization of a dienyl beta-ketolactone and a Stille coupling/8pi-6pi electrocyclization cascade to create the oxabicyclo[2.2.1]heptane and bicyclo[4.2.0]octadiene, respectively. The synthesis is convergent and void of protecting groups.     

New convenient synthesis of iridol. An approach to the synthesis of ubiquinones

A strategy for the synthesis of ubiquinones, in which iridol is the key intermediate, has been developed, together with a new convenient synthesis of iridol (2,3-dimethoxy-5-methylphenol) starting from the easily available 4-methylphenol and using mild conditions and friendly and high-yielding reactions.     

Toward the synthesis of thapsigargin: enantioselective synthesis of 7,11-dihydroxyguaianolides

[reaction: see text] The enantioselective synthesis of a 7,11-dihydroxyguaianolide bearing the stereochemistry present in thapsigargin, a potent and selective inhibitor of the Ca(2+) SERCA-ATPase pumps, is described. Starting from (+)-dihydrocarvone, the synthesis presents two key steps. The first one involves the photochemical rearrangement of a gamma,delta-unsaturated ketone eudesmane into the corresponding guaiane. The second step consists of the regioselective oxidation of an unprotected tetrahydroxylated ketone to provide a dihydroxylactone with the required stereochemistry.     

Serendipitous synthesis of a cyclic formamidine. Application to the synthesis of polyazamacrocycles

An unexpected synthesis of 4,5,6,7,8,9-hexahydro-1,3-diazonine, using hexamethylenediamine and dimethylformamide, is presented. The cyclization process was explained as a two-step process involving formylation and subsequent intramolecular condensation. The scope of this process was demonstrated through the synthesis of two other nitrogen-containing macroheterocycles.     

Organic synthesis using chemical tags: the third Leg of parallel synthesis

Increasing emphasis has recently been placed on the development of synthetic methods which effectively couple chemical synthesis and purification. For example, new formats for parallel synthesis are being developed which involve attachment of chemical tags to both reagents, reactants, and substrates to permit their chemoselective removal from reaction mixtures. The driving force for the development of tagged organic reagents is the ability to use standard solution-phase chemistry methods and reaction monitoring techniques (e.g. TLC and HPLC). In this mini-review, we will outline recent developments on the growing class of chemically tagged reagents, reactants, and substrates and highlight examples of their use in multistep synthesis.     

Studies on the total synthesis of lactonamycin: synthesis of the CDEF ring system

A concise and efficient synthesis of the tetracyclic CDEF ring system of lactonamycin (1) is described. The key step involved the Lewis acid mediated, intramolecular Friedel-Crafts acylation of carboxylic acid 6 to produce the tetracyclic CDEF core structure of target 1. The synthesis of 6 was carried out using a high-yielding Negishi coupling of benzyl bromide 7 with triflate 8, which was accessible in 11 steps and 31% overall yield on a multigram scale starting from trihydroxy acid 9.     

Kinetics of the carnallite synthesis

The kinetics of the carnallite synthesis from crystalline KCl and a MgCl₂ solution at temperatures from 20 up to 100°C was studied. The temperature dependence of the conversion degree was determined. The activation energy and the rate constant of the carnallite synthesis in the temperature range of 30–60°C were determined.     

A concise synthesis of the cortistatin core

We describe a concise and convergent route to the core matrix of the cortistatin steroidal alkaloids. The salient features of the synthesis are the Snieckus cascade methodology and the Masamune alkylative dearomatization. This chemistry lends itself to a total synthesis of the cortistatins and to the development of a SAR program based on diverted total synthesis.     

An improved synthesis of the scyphostatin side-chain

A formal synthesis of the lipophilic side-chain of scyphostatin has been achieved using a convergent synthesis, in 16% yield over six steps. This synthesis involves enzymatic desymmetrisation of a meso-diol, resolution of 2-methylbutan-1-ol, stereoselective hydrozirconation of a volatile acetylene and a Negishi-style cross coupling.     

Enantioselective synthesis of the bottom-half of chlorothricolide

The first enantioselective synthesis of a chlorothricolide intermediate is described. The synthesis features the intramolecular Diels-Alder reaction of tetraene 3.     

Total synthesis of bryostatins: the development of methodology for the atom-economic and stereoselective synthesis of the ring C subunit

Bryostatins, a family of structurally complicated macrolides, exhibit an exceptional range of biological activities. The limited availability and structural complexity of these molecules makes development of an efficient total synthesis particularly important. This article describes our initial efforts towards the total synthesis of bryostatins, in which chemoselective and atom-economical methods for the stereoselective assembly of the ring C subunit were developed. A Pd-catalyzed tandem alkyne-alkyne coupling/6-endo-dig cyclization sequence was explored and successfully pursued in the synthesis of a dihydropyran ring system. Elaboration of this methodology ultimately led to a concise synthesis of the ring C subunit of bryostatins.