Complex peptidyl nucleoside antibiotics: efficient syntheses of the glycosyl nucleoside amino acid cores

Employing an amino acid chiral template strategy, the present research describes a general and highly efficient protocol for the rapid construction of enantiopure furanosyl and pyranosyl nucleoside amino acid cores as present in various complex peptidyl nucleoside antibiotics. Starting from easily available d-serine, the strategy and the approach involve rapid and efficient stereoselective synthesis of five- or six-membered lactone amino alcohols, followed by incorporation of the required functionalities of the target molecules on these strategically functionalized chiral templates.     

Wallichanol类天然产物ABC环系合成研究

Wallichanol是一类具有独特桥环结构的二萜天然产物.以2-甲基-1,3-环己二酮作为起始原料,通过高立体选择性的Diels-Alder反应和金催化的炔烃碳环化反应构建Wallichanol的ABC三环核心骨架,共七步路线,总收率为42%.该合成工作为Wallichanol类天然产物全合成奠定了研究基础.     

Total synthesis of the tricyclic marine alkaloids (-)-lepadiformine, (+)-cylindricine c, and (-)-fasicularin via a common intermediate formed by formic acid-induced intramolecular conjugate azaspirocyclization

A very short and efficient enantioselective total synthesis of the tricyclic marine alkaloids (-)-lepadiformine (3), (+)-cylindricine C (1c), and (-)-fasicularin (4) has been developed utilizing the formyloxy 1-azaspiro[4.5]decane 5 as a common intermediate. The key strategic element for the synthesis was the formic acid-induced intramolecular conjugate azaspirocyclization, which proved to be a highly efficient and stereoselective way to rapid construction of the 1-azaspirocyclic substructure of these natural products in a single operation. Thus, the common intermediate 5, synthesized in two steps with 70% overall yield starting from the known (S)-N-Boc-2-pyrrolidinone 7 via the conjugate spirocyclization using an acyclic ketoamide 6, was utilized for the concise and stereoselective total synthesis of (-)-lepadiformine (3), which was accomplished in seven steps with 45% overall yield from 5 (31% yield from 7). The developed strategy based on the conjugate spirocyclization was also applied to the stereoselective total synthesis of (+)-cylindricine C (1c), which was achieved in 10 steps from 5 in 18% overall yield (12% yield from 7). Further application of this approach using 5 led to the synthesis of (-)-fasicularin (4), wherein an extremely efficient method for the introduction of the thiocyanato group via an aziridinium intermediate at the last step was developed. Thus, the highly efficient first enantioselective total synthesis of (-)-fasicularin was accomplished in nine steps with an overall yield of 41% from 5 (28% yield from 7).     

Pharmacophore mapping in the laulimalide series: total synthesis of a vinylogue for a late-stage metathesis diversification strategy

An efficient synthesis of the macrocyclic core of laulimalide with a pendant vinyl group at C20 is described, allowing for late-stage introduction of various side chains through a selective and efficient cross metathesis diversification step. Representative analogues reported herein are the first to contain modifications to only the side chain dihydropyran of laulimalide and des-epoxy laulimalide. This step-economical strategy enables the rapid synthesis of new analogues using alkenes as an inexpensive, abundantly available diversification feedstock.     

A concise synthesis of the pentacyclic framework of cortistatins

An efficient synthesis of the pentacyclic framework of cortistatins has been developed. The key strategy comprises assembly of the A- and the CD-ring fragments by Knoevenagel reaction, facile formation of the pyran ring via electrocyclization, and construction of the seven-membered B-ring by radical addition to an alpha,beta-unsaturated ketone.     

Stereoselective Mukaiyama-Michael/Michael/Aldol Domino Cyclization as the Key Step in the Synthesis of Pentasubstituted Arenes: An Efficient Access to Highly Active Inhibitors of Cholesteryl Ester Transfer Protein (CETP)

Seemingly heartbreaking for a stereochemist, the one-step selective construction of a stereopentad and its prompt destruction by aromatization has been proven to be an efficient strategy for the synthesis of fivefold substituted, pharmacologically highly active arenes (see scheme).     

Dramatic influence of the substitution of alkylidene-5H-furan-2-ones in Diels-Alder cycloadditions with o-quinonedimethide as diene partner: en route to the CDEF polycyclic ring system of lactonamycin

An efficient and rapid synthesis of the CDEF ring system of lactonamycinone is reported via a highly chemo- and diastereoselective intermolecular Diels-Alder cycloaddition between trans-1,2-disilyloxybenzocyclobutene and the appropriate γ-alkylidenebutenolide. The feasibility and the total chemoselectivity of the [4 + 2] cycloaddition for the construction of a spirolactone moiety via an intramolecular approach (IMDA) using both partners is also described demonstrating the versatility of the γ-alkylidenebutenolide building block.     

Application of the Helquist annulation in Lycopodium alkaloid synthesis: unified total syntheses of (-)-8-deoxyserratinine, (+)-fawcettimine, and (+)-lycoflexine

A unified strategy for total synthesis of the Lycopodium alkaloids (-)-8-deoxyserratinine (7), (+)-fawcettimine (1), and (+)-lycoflexine (4) is detailed. The key features include a highly efficient Helquist annulation to assemble the cis-fused 6/5 bicycle, facile construction of the aza nine-membered ring system employing double N-alkylation strategy, providing access to the common tricyclic skeleton, asymmetric Shi epoxidation, delivering the desired β-epoxide stereospecifically to furnish (-)-8-deoxyserratinine (7), SmI(2) reduction of dihydroxylation derivative 35 to enable formation of (+)-fawcettimine (1), and a rapid biomimetic transformation of (+)-fawcettimine (1) into (+)-lycoflexine (4) via an intramolecular Mannich cyclization.     

Efficient and straightforward preparation of a building block for (−)-teubrevin G synthesis via chemically diversed oriented synthesis

A rapid and efficient methodology to highly functionalised molecular units well suited as scaffolds for diversity-oriented molecular construction in the synthesis of natural products is reported herein. A key macrocyclic intermediate in the synthesis of the neo-clerodane diterpene (−)-teubrevin G was successfully synthesized in a 5-step sequence in a 70% overall yield using a novel intramolecular coupling between an allylborating agent and a 1,5-dialdehyde moiety.     

Total synthesis of (-)-brevenal: a concise synthetic entry to the pentacyclic polyether core

Total synthesis of (-)-brevenal, a novel marine polycyclic ether natural product, is described. Highly efficient and scalable entries to the AB-ring exo-olefin and the DE-ring enol phosphate and a rapid construction of the C-ring by means of our Suzuki-Miyaura coupling-based strategy realized a concise synthesis of the pentacyclic skeleton of (-)-brevenal. The present synthesis is considerably more efficient than our previous synthesis (longest linear sequence: 50 steps from 2-deoxy-d-ribose).     

A synthesis of the tetracyclic carboskeleton of isaindigotidione

An efficient synthesis of the unique indolizino[7,6-c]quinoline carboskeleton of isaindigotidione has been achieved. This strategy employed l-proline and isatin as the main building blocks in the construction of the framework. Four transformations occurred in a one-pot operation to furnish the tetracyclic nucleus.     

Brønsted Acid Catalyzed Asymmetric Hydroamination of Alkenes: Synthesis of Pyrrolidines Bearing a Tetrasubstituted Carbon Stereocenter

The first highly enantioselective Brønsted acid catalyzed intramolecular hydroamination of alkenes enables the efficient construction of a series of chiral (spirocyclic) pyrrolidines with an α‐tetrasubstituted carbon stereocenter with excellent functional group tolerance. A unique feature of this strategy is the use of a thiourea group acting as both the activating and the directing group through cooperative multiple hydrogen bonding with a Brønsted acid and the double bond. The utility of this method is highlighted by the facile construction of chiral synthetic intermediates and important structural motifs that are widely found in organic synthesis.     

Synthesis of bistramide A

We have developed an efficient and highly stereocontrolled synthesis of bistramide A, a selective activator of protein kinase C isotype delta. Our synthetic strategy featured a novel bidirectional approach for spiroketal construction based on the ring-opening/cross-metathesis sequence employing a highly strained cyclopropenone acetal. The synthesis afforded the final target with the longest linear sequence of 15 steps and provided unambiguous structural determination of bistramide A, including assignment of the previously unknown C(37) stereochemistry.     

RhIII‐Catalyzed Synthesis of Highly Substituted 2‐Pyridones using Fluorinated Diazomalonate

A Rh^III‐catalyzed strategy was developed for the rapid construction of highly substituted 2‐pyridone scaffolds using α,β‐unsaturated oximes and fluorinated diazomalonate. The reaction proceeds through direct, site‐selective alkylation based on migratory insertion and subsequent cyclocondensation. A wide substrate scope with different functional groups was explored. The requirement of fluorinated diazomalonate was explored for this transformation. The developed methodology was further extended with the synthesis of the bioactive compound.     

Suzuki cross-coupling/reductive debenzyloxycarbonylation sequence for the syntheses of [c]annulated isoquinolines: application for the syntheses of pancratistatin-like isoquinolines

A two-step strategy involving Suzuki cross-coupling of boronic acids with a diverse array of alpha-iodoenones followed by hydrogenation is developed for the construction of [c]annulated isoquinolines. This mild and efficient procedure is also applied to the synthesis of highly oxygenated isoquinolines.     

Stereodivergent and Protecting‐Group‐Free Synthesis of the Helicascolide Family: A Rhodium‐Catalyzed Atom‐Economical Lactonization Strategy

Natural products of polyketide origin, in particular small‐sized lactones often possess a very broad range of impressive biological activities. An efficient way to demonstrate the concise access to six‐membered lactones was emphasized as part of a stereodivergent and protecting‐group‐free synthesis of all three representatives of the helicascolide family. This strategy features an atom‐economical and highly diastereoselective rhodium‐catalyzed “head‐to‐tail” lactonization by an intramolecular addition of ω‐allenyl‐substituted carboxylic acids to terminal allenes, including the selective construction of a new stereocenter in the newly formed core structures. The excellent selectivities with which the helicascolide precursors were obtained are remarkable, thus resulting in an expeditious and highly efficient natural product synthesis.     

Divergent Biomimetic Total Syntheses of Ganocins A–C,Ganocochlearins C and D,and Cochlearol T

A divergent synthetic approach to six Ganoderma meroterpenoids, namely ganocins A–C, ganocochlearins C and D, and cochlearol T, has been developed for the first time. This synthetic route features a two-phase strategy which includes early-stage rapid construction of a common planar tricyclic intermediate followed by highly selective late-stage transformations into various Ganoderma meroterpenoids. Key to the strategy are a bioinspired intramolecular hetero-Diels–Alder reaction and Stahl-type oxidative aromatization, allowing efficient formation of the common tricyclic phenol intermediate. A nucleophilic dearomatization of the phenol unit, combined with a regioselective 1,4-reduction of the resulting dienone, enabled rapid access to ganocins B and C. Additionally, site-selective Mukaiyama hydration, followed by an intramolecular oxa-Michael addition/triflation cascade, served as a key strategic element in the chemical synthesis of ganocin A.     

Formal Synthesis of (−)-Englerin A and Cytotoxicity Studies of Truncated Englerins

An efficient formal synthesis of (−)-englerin A ( 1 ) is reported. The target molecule is a recently isolated guaiane sesquiterpene that possesses highly potent and selective activity against renal cancer cell-lines. Our enantioselective strategy involved the construction of the BC ring system of compound 1 through a Rh^II-catalyzed [4+3] cycloaddition reaction followed by subsequent attachment of the A ring through an intramolecular aldol condensation reaction. As such, this strategy allows the synthesis of truncated englerins. Evaluation of these analogues with the A498 renal cancer cell-line suggested that the A ring of englerin is crucial to its antiproliferative activity. Moreover, evaluation of these analogues led to the identification of potent growth-inhibitors of CEM cells with GI₅₀ values in the range 1–3 μM .     

Divergent Biomimetic Total Syntheses of Ganocins A–C,Ganocochlearins C and D,and Cochlearol T

A divergent synthetic approach to six Ganoderma meroterpenoids, namely ganocins A–C, ganocochlearins C and D, and cochlearol T, has been developed for the first time. This synthetic route features a two‐phase strategy which includes early‐stage rapid construction of a common planar tricyclic intermediate followed by highly selective late‐stage transformations into various Ganoderma meroterpenoids. Key to the strategy are a bioinspired intramolecular hetero‐Diels–Alder reaction and Stahl‐type oxidative aromatization, allowing efficient formation of the common tricyclic phenol intermediate. A nucleophilic dearomatization of the phenol unit, combined with a regioselective 1,4‐reduction of the resulting dienone, enabled rapid access to ganocins B and C. Additionally, site‐selective Mukaiyama hydration, followed by an intramolecular oxa‐Michael addition/triflation cascade, served as a key strategic element in the chemical synthesis of ganocin A.     

Cyclopropane ring-opening of tricyclo[3.3.0.0]octan-3-ones: a quick access to bicyclo[3.2.1]octanones from 2-methoxyphenols

We herein report an efficient and rapid strategy for the synthesis of highly functionalized bicyclo[3.2.1]octanones via sequential reactions: Diels-Alder reaction of MOB—ODPM rearrangement—reductive cleavage of cyclopropane, and its application to synthesize the core structure of drechslerine D.