Total synthesis of (±)-manzacidin D

We report herein the first total synthesis of the alkaloid manzacidin D, in 11 steps and 16% overall yield from commercially available glycine tert-butyl ester hydrochloride. Our synthesis demonstrates for the first time in a total synthesis the utility of two different methodologies. A highly diastereoselective iodocyclization of an olefinic isothiourea is used to induce stereocontrol at the quaternary centre, and to form the heterocyclic core. Conversion of a thiourea to the requisite formamidine is achieved in good yield using our modified procedure.     

Stereocontrolled synthesis of 8,11-dideoxytetrodotoxin,unnatural analogue of puffer fish toxin

[structure: see text] 8,11-Dideoxytetrodotoxin, an unnatural tetrodotoxin analogue, was synthesized in a highly stereoselective manner from a common intermediate in our synthetic studies on tetrodotoxin. The synthesis features neighboring group participation of trichloroacetamide for stereoselective hydroxylation, protection of ortho ester, and guanidine installation with Boc-protected isothiourea.     

A second-generation synthesis of the C1-C28 portion of the altohyrtins (spongistatins)

A practical second-generation synthesis of an advanced intermediate in our total synthesis of altohyrtin C (spongistatin 2) has been developed. A new approach to the C1-C15 (AB) portion features a vinyllithium addition to an aldehyde followed by a palladium-catalyzed allylic reduction to install the troublesome C13-C15 segment. Our general approach to the C16-C28 (CD) spiroketal has been retained, but some improvements have been made. Most notably, the kinetically controlled CD-spiroketalization reaction now proceeds in high yield with excellent diastereoselection. This new strategy uses the anti-aldol coupling used in our first-generation synthesis to join AB and CD fragments. A total of 9.6 g of intermediate 57 has been produced using this improved route.     

Stereocontrolled synthesis of 8,11-dideoxytetrodotoxin, an unnatural analogue of puffer fish toxin

8,11-Dideoxytetrodotoxin, an unnatural tetrodotoxin analogue, was synthesized in a highly stereoselective manner from a common intermediate from our synthetic studies on tetrodotoxin. The key features in the synthesis were as follows: neighboring group participation of a trichloroacetamide to allow regioselective and stereoselective hydroxylation, protection of a delta-hydroxylactone as an ortho ester, and guanidine installation through the use of Boc-protected isothiourea. Global deprotection of the fully protected intermediate under acidic conditions gave 8,11-dideoxytetrodotoxin, which exhibited very weak biological activities.     

Progress toward the syntheses of (+)-GB 13, (+)-himgaline, and himandridine. new insights into intramolecular imine/enamine aldol cyclizations

A full account of our total synthesis of the galbulimima alkaloids GB 13 and himgaline is provided. Using a strategy adapted from the proposed biosynthesis of the GB alkaloid family, a linear precursor underwent successive intramolecular Diels-Alder, Michael, and imine aldol cyclizations to form the polycyclic alkaloid core. We now show that modification of this strategy can also deliver an advanced intermediate en route to the related alkaloid himandridine. The success of the key imine aldol cyclization is acutely sensitive to substrate structure and solvent, including a case in which cyclization was spontaneous in protic solvents. A detailed computational investigation of the course of the reaction closely correlates with, and suggests a rationale for, the observed patterns of imine aldol reactivity.     

Enantioselective synthesis of the bromopyrrole alkaloids manzacidin A and C by stereospecific C-h bond oxidation

The manzacidins represent a small family of structurally unique secondary metabolites found only sparingly in nature. Efforts to probe the pharmacological profile of these intriguing bromopyrrole alkaloids have been precluded by a deficiency of available material. Access to substantive quantities of both manzacidins A and C is now made possible through a rapid, enantioselective, and highly efficient synthesis that is described herein. The path to these targets showcases for the first time the distinct power of our catalytic C-H bond amination methodology for simplifying problems in alkaloid total synthesis. Application of this chemistry enables the facile and enantiospecific installation of tetrasubstituted carbinolamine stereocenters, functionality common to all of the manzacidins. The requisite materials for implementing our plan are assembled using modern tools for catalytic asymmetric synthesis that include both carbonyl-ene and directed hydrogenation reactions. In addition, a new protocol for tetrahydropyrimidine synthesis is established. The synthesis of each manzacidin comprises a 10-step sequence that proceeds in an overall yield of approximately 30%.     

The catalytic asymmetric total synthesis of elatol

Described in this report is the first total synthesis of elatol, a halogenated sesquiterpene in the chamigrene natural product family. The key disconnections in our synthetic approach include an enantioselective decarboxylative allylation to form the all-carbon quaternary stereocenter and a ring-closing olefin metathesis to concomitantly form the spirocyclic core as well as the fully substituted chlorinated olefin. This strategy represents a general platform for accessing the chamigrene natural product family, as demonstrated by the synthesis of (+)-laurencenone B as an intermediate in our route.     

An original traceless linker strategy for solid-phase synthesis of N,N',N'-substituted guanidines

An original sequence for solution- and solid-phase synthesis of N,N',N"-trisubstituted guanidines is described. The sequence involves as key intermediate a bis-electrophilic chlorothioformamidine that is stable, easy to prepare and also easy to handle. Supported chlorothioformamidine, prepared in two steps from Merrifield resin, undergoes smooth nucleophilic addition of a primary amine to afford the corresponding supported isothiourea. The guanidine is obtained in satisfactory yield and good purity through a functionalizing-release process by heating the supported isothiourea in the presence of a primary amine in toluene at 100 degrees C. Compatibility of this sequence with several functional groups is demonstrated.     

Diastereoselective phenol para-alkylation: access to a cross-conjugated cyclohexadienone en route to resiniferatoxin

We document a route for the synthesis of a densely functionalized spiro-fused 2,5-cyclohexadienone as an intermediate for the synthesis of resineferatoxin. The strategy is based on an unprecedented diastereoselective, intramolecular phenol para-alkylation to a cross-conjugated cyclohexadienone. In the course of these synthetic studies we developed rapid access to a chiral nitrile possessing a quaternary stereocenter and disclose an unusual acetal rearrangement from a dioxane, which favors the corresponding dioxepane.     

An improved cyclization protocol for the synthesis of diazabicyclo[4.3.0]alkanes

We have recently described the synthesis of diazabicyclo[4.X.0]alkanes and their use as ligands for the prostate specific membrane antigene (PSMA). The key step of our synthetic route toward these diazabicycloalkanes is an oxidative cleavage of a bicyclic diol moiety followed by the attack of a nitrogen nucleophile to the resulting intermediate bisaldehyde. We herein describe the mechanism of this ring closure and its stereochemical consequences. In addition, we report a convenient method for trapping intermediate bisaldehydes by Wittig reagents. This trapping allows the synthesis of 3,5-disubstituted proline derivatives, which are shown to be versatile precursors for functionalized diazabicycloalkane dipeptide mimetics.     

New synthesis of (±)-cis-trikentrin A via tandem indole aryne cycloaddition/Negishi reaction. Applications to library development

We describe herein an efficient new route to the trikentrins and their related structures using a tandem 6,7-indolyne cycloaddition/Negishi cross-coupling reaction starting from a 4,6,7-tribromoindole (obtained in good yield via the Bartoli indole synthesis). The key step of this second generation route to the trikentrins is based on our observation that the 7-bromo substituent appears to undergo selective metal-halogen exchange and elimination to give the 6,7-indolyne, which is trapped in the presence of excess cyclopentadiene. Subsequent Negishi cross-coupling at the 4-bromoindole position with Et₂Zn gave directly the same intermediate obtained from our previous work. Application of this chemistry to the construction of trikentrin-related libraries using this general cycloaddition/cross-coupling tactic will also be described.     

Synthesis and absolute structure of manzacidin B

[reaction: see text] Four possible stereoisomers of manzacidin B were synthesized using stereochemically defined synthetic routes via the azide 7 and oxazoline 11 starting with the (R)-alpha-methyl Garner aldehyde 5. Comparisons of the spectroscopic data of the synthetic isomers 4a-d with those of the natural manzacidin B revised the proposed structure 3 to (4S,5S,6R)-4d.     

Total Synthesis of the Polyoxygenated Sesquiterpenes Guignarderemophilanes C and D

The total syntheses of the neural anti‐inflammatory agents guignarderemophilanes C and D have been accomplished for the first time starting from γ‐hydroxy carvone in 15 and 14 steps, respectively. The presented synthetic route proceeds via a known intermediate, whose synthesis has been elaborated in our group in the course of the total synthesis of the sesquiterpenoid periconianone A. Key for the successful conversion of this intermediate into both targets was finding a suitable strategy to install the 1,2,3‐trihydroxylated A‐ring scaffold. For this purpose, we effectively employed a Mitsunobu inversion, epoxidation, and regioselective epoxide opening sequence, before the bicyclic ring system was constructed by an aldol condensation reaction on a sterically demanding substrate. Our reported synthesis set the stage for SAR studies to prepare even more potent compounds by modification and derivatization of the natural product's scaffold.     

Racemic synthesis of an intermediate for the formal synthesis of madindoline A and B

On the basis of the application of the Darzens/ring-expansion process of cyclobutenedione developed previously by our group, a new strategy for the multisubstituted cyclopentene units of madindoline A and madindoline B has been reported in this paper. In light of the strategy, the synthesis of racemic Omura’s intermediate was finished in four steps and 34% overall yield, which furnished a new formal synthetic route to madindolines A and B.     

Combining two-directional synthesis and tandem reactions: a short formal synthesis of halichlorine

A short and efficient synthesis of an advanced intermediate (1) in the Clive route to halichlorine has been achieved in 12 steps and 13.2% yield by a combined two-directional synthesis/tandem reaction strategy.     

4-苯胺喹唑啉类化合物合成研究进展

4-苯胺喹唑啉类化合物是一类具有广泛药理活性的喹唑啉类生物碱,在酪氨酸激酶受体(EGFR)抑制剂的研发中具有重要的作用。已经上市的此类药物有吉非替尼(gefitinib)和厄洛替尼(erlotinib)等。此类化合物的合成都是经过喹唑啉酮中间体或直接环合成4-苯胺喹唑啉。苯甲醛及其衍生物被用作反应原料,两种合成路线都要经历对苯甲醛的硝化及硝基的还原两步反应。笔者经查阅资料,设计并验证了以苯胺为原料、经靛红中间体得到4-苯胺喹唑啉类化合物的新的合成路线。本文依据这两种合成策略综述了4-苯胺喹唑啉类化合物的合成方法,并对各种方法的优缺点进行了总结,为进一步研究4-苯胺喹唑啉合成及设计具有药理活性的新化合物提供参考。     

SYNTHESIS OF 3-BENZYL-GLYCERIC ACID:A KEY INTERMEDIATE OF A NOVEL CYCLIC ESTER MONOMER

A route was proposed to synthesize 3-benryl-glyceric acid (3-BGA) as an important intermediate for the synthesis ofa novel six-membered cyclic ester monomer - 3-benzyloxymethyl-1,4-dioxane-2,5-dione (3-BMG). According to this route,3-BGA was obtained from ring-opening reaction of benzyl alcohol with methyl glycidate, which was prepared from theepoxidation of methyl acrylate using sodium hypochlorite as the oxidant.     

An improved asymmetric synthetic route to a novel triple uptake inhibitor antidepressant (2S,4R,5R)-2-benzhydryl-5-((4-methoxybenzyl)amino)tetrahydro-2H-pyran-4-ol (D-142)

Triple monoamine reuptake inhibitors have been implicated in the development of a new generation of antidepressants with higher efficacy than the currently existing therapies. In this paper, we have developed an alternative efficient synthetic route for triple monoamine reuptake inhibitor D-142 in 18.5% overall yield in 11 steps starting from diphenylmethane. D-142 was developed by us recently. The key step of the present synthetic strategy is the preferential formation of a bromohydrin from olefin via a cis-bromoinum intermediate, which introduced significant efficiency in the overall synthesis. Furthermore, we have developed an efficient way to recycle the optically active intermediate diol back to the desired chiral epoxide.     

Leucascandrolide a: synthesis and related studies

The total synthesis of the biologically active marine natural product leucascandrolide A is reported. A convergent strategy is employed, allowing for the rapid assembly of the macrolide moiety. Key steps of our approach include the diastereoselective addition of a zinc alkynilide to (R)-isopropylidene glyceraldehyde, the enantioselective copper(I) fluoride catalyzed aldol addition of a TMS-dienolate to crotonaldehyde, and the formation of a 2,6-trans-substituted tetrahydropyran by selenium-mediated intramolecular cyclization. Moreover, dramatic solvent effects observed in the macrolactonization reaction suggest that hydrogen-bonding effects play a critical role. An improved route to a key intermediate of our synthesis is documented.     

Toward the total synthesis of FR901483: concise synthesis of the azatricyclic skeleton

A concise synthesis of the azatricyclic core of FR901483 has been accomplished using a novel strategy that involves a nucleophilic addition to an N-acyl iminium ion, a ring-closing metathesis, a diastereoselective hydroboration, and a lactone-lactam rearrangement that worked well in a preliminary model study. Extension of this approach to the synthesis of a more highly functionalized intermediate that could be transformed into (-)-FR901483 first required the development of a new protecting group, the 1-ethylallyloxycarbamate group, for amines that may be removed under mild conditions. However, because the stereoselectivity in a key step in which a functionalized allyl zinc reagent was added to an intermediate hydroxy-substituted imine was low, this route to (-)-FR901483 is no longer being pursued.