Synthesis of the C12-C24 fragment of peloruside A by silyl-tethered diastereomer-discriminating RCM

The C12-C24 fragment of peloruside A has been synthesized using, as a key step, a silyl-tethered ring closing metathesis reaction to form the C16-C17 (Z)-alkene. The metathesis reaction discriminates between diastereoisomers of the starting material. A diphenylsilyl bis-ether provides simultaneous protection for the C15 and C24 hydroxyl groups, and is expected to lead to high 1,5-anti selectivity in subsequent aldol reactions of the methyl ketone, allowing for a convergent stereoselective synthesis of peloruside A.     

Carbohydrate‐Based Studies Toward the Synthesis of Hamigeromycin E: A Stereoselective Total Synthesis of an Isomer of Zeaenol

A stereoselective synthesis of 14‐membered macrolide hamigeromycin E ( 6 ) has been studied by employing ortho‐lithiated formylation, Barbier allylation, Julia–Kocienski olefination, Mitsunobu esterification, and ring‐closing metathesis (RCM) reactions. The final RCM reaction did not provide the target molecule. This study has prompted us to synthesize a stereoisomer of zeaenol and accomplish the total synthesis with the above protocols.     

Synthesis of the structures proposed for natural butanolides piliferolides A and C

The structures proposed for natural butanolides piliferolides A and C have been synthesized. The allylic and lactone stereogenic centers in the target structures were derived from d-mannitol, while that near the side-chain terminal was taken from (R)-propylene oxide. The synthetic samples helped to reveal that a signal at around δ 2.0 ppm was missing in the ¹H NMR data listing for the structures proposed for natural piliferolides, whereas the δ 29.7 ppm signal in the ¹³C NMR reported for the structure proposed for natural piliferolide C most likely stemmed from the impurities in the chromatography solvent.     

Synthesis of a vinylchlorine-containing 1,3-diol from a marine cyanophyte

Using epoxy chiral building blocks readily derived from d-gluconolactone as the source of the stereogenic centers, both (6R,8R)- and (6R,8S)-isomers of (E)-1-chlorotridec-1-ene-6,8-diol were synthesized. The vinylchloro unit was installed onto the substrate carbon chain in an approximately 9:1 (E)/(Z) ratio via a condensation of CrCl₂/CHCl₃ with a terminal aldehyde. A tosylation protocol featuring addition of H₂O was also developed for a highly polar tetraol. The synthetic products allowed for re-acquisition of the NMR spectra of better quality and revealed some delicate yet unignorable discrepancies in the ¹³C NMR for the natural isomer obtained by synthesis and that isolated some 30 years ago from the marine cyanophyte. The puzzling discrepancies were eventually shown to be caused by deuteration of the hydroxyl groups.     

Chemistry of renieramycins. Part 9: Stereocontrolled total synthesis of (±)-renieramycin G

A 25-step stereocontrolled total synthesis of (±)-renieramycin G (1g) from readily available 2-hydroxy-3-methyl-4,5-dimethoxybenzaldehyde (3) is described. This synthesis features the concise construction of the pentacyclic framework using the stereoselective Pictet-Spengler type cyclization reaction of lactam (14) with ethyl diethoxyacetate, followed by the base-catalyzed isomerization of the C-1 stereo center.     

Ruthenium‐Catalyzed Metathesis Cascade Reactions in Natural Products Synthesis

In this account, we provide a brief summary of recent developments in ruthenium‐catalyzed metathesis cascade reactions towards the total synthesis of natural products. We also highlight recent progress from our own laboratory regarding the synthesis of securinega alkaloids and humulanolides, which has resulted in the development of novel ruthenium‐catalyzed metathesis cascade reactions. Inspired and guided by the pioneering and elegant research conducted in this area, we developed a regio‐controlled relay dienyne metathesis cascade reaction and a cyclobutene‐promoted RCM/ROM/RCM cascade reaction for the synthesis of securinega alkaloids and humulanolides, respectively.     

Macrolide Analogues of the Novel Immunosuppressant Sanglifehrin: New Application of the Ring-Closing Metathesis Reaction

Macrocycles containing a conjugated 1,3-diene moiety have been synthesized for the first time in good yields by the ring-closing metathesis reaction [Eq. (1)]. The new compounds represent cyclophilin-binding, simplified analogues of the macrocyclic core of sanglifehrin A, an immunosuppressant which binds with high affinity to cyclophilin.     

Synthesis and biological evaluation of novel imidazole-containing macrocycles

A new family of compounds made of a 5-aryl-1H-imidazole motif included in a macrocycle has been designed and synthesized. The synthesis of the imidazole core makes use of our previously developed method for the regioselective preparation of 1,2,5-trisubstituted imidazoles while the construction of the macrocycle is based on a three steps sequence: S_NAr, Suzuki coupling, and RCM reaction. Biological evaluation of synthesized imidazole-containing macrocycles revealed that they display actual binding activity toward A₃ adenosine (h) receptor, dopamine D₁ (h) receptor, chloride channel (GABA-gated), and choline transporter (h) CHT1.     

Synthesis of extended spacer-linked neooligodeoxysaccharides by metathesis olefination and evaluation of their RNA-binding properties

The preparation of linear 1,4-butanediol-linked oligodeoxysugars 50-53, 58 and 60 is described which are potential binders to polynucleotides. Various aminodeoxymonosaccharides 9, 13-18, 30, 31 and 40-42 which are either allylated at the anomeric center or at C4 were subjected to the metathesis olefination protocol. Depending on the position of allylation E/Z-mixtures of C₂-symmetric head-to-head or tail-to-tail homodimers were formed. Among them, saccharides 13, 30, 31 and 40 were transformed into the corresponding 1,4-butanediol linked disaccharides 50-53 by catalytic hydrogenation of the central olefinic double bond and exhaustive deprotection. In order to target extended spacer-linked neooligosaccharides homodimeric aminoglycoside 37 was bisallylated and subjected to cross metathesis conditions using methyl 4-O-allyl daunosamide 40 as reaction partner which yielded two desired trimeric and tetrameric linearly spacer-linked daunosamine derivatives. After hydrogenation and deprotection two additional probes 58 and 60 for nucleic acid binding studies were at hand.     

Asymmetric total synthesis of (+)-gabosine C and (+)-4-epi-gabosine J using acetate migration and RCM reaction

A concise, unified and stereoselective total synthesis of (+)-gabosine C and (+)-4-epi-gabosine J from a common polyhydroxylated cyclohexenol intermediate which was synthesized from readily available D-ribose has been described. The synthetic avenue includes stereoselective Grignard reaction, silyl ether deprotection followed by acetate migration, RCM reaction, oxidative diol cleavage, hydroxymethylation and oxidative rearrangement as key steps.     

Synthesis and anti-tumor activity evaluation of novel podophyllotoxin derivatives

In order to investigate the effects on the cytotoxicity of indole-3-oxalylamino podophyllotoxin analogs, seven novel podophyllotoxin derivatives were synthesized.The compounds were tested against Hela, K562 or K562/A02 cancer cells in vitro,four of which showed significant cytotoxicity.Among them 9a,9b and 9c were superior to the positive control VP-16.     

Synthesis and study of the antimalarial cardamom peroxide

A full account of our previously disclosed synthesis of the monoterpene dimer cardamom peroxide is reported. Inspired by hypotheses regarding the potential biosynthetic origins of this natural product, several unproductive routes are also reported. The chemical reactivity of this structurally unique metabolite in the presence of iron (II) sources is also reported as is its antimalarial activity against Plasmodium falciparum clinical isolates from several Cambodian provinces.     

Synthesis,characterization and biological evaluation of purine nucleoside analogues

We present a convenient route for the synthesis of C6-amino-C5′-N-cyclopropyl carboxamido-C2-alkynylated purine nucleoside analogues 11a–g via Sonogashira coupling reaction. The nine step synthesis is easy to perform, employing commercially available reagents. Compound 9 is used as key intermediate for the synthesis of analogues 11a–g. Synthetic intermediates and final products are appropriately characterized by IR, ¹H NMR, ¹³C NMR and Mass. The modified nucleoside analogues 11a–g is evaluated for in vitro anticancer activity against MDA-MB-231 and Caco-2 cell lines. Screening data reveals that compounds 11b and 11e displayed potent IC₅₀ value of 7.9, 6.8 µg/mL respectively against MDA-MB-231 and of 7.5, 8.3 µg/mL respectively against Caco-2 than the standard drug doxorubicin, thus establishing the potential anti-cancer properties of these newer derivatives.     

天然产物goodyeroside A的全合成研究

以5-(S)-(d-盖氧基)-2(5H)-呋喃酮为起始原料．对具有肝保护活性的天然产物goodyeroside A进行了全合成研究。将合成所得目标产物的比旋光值及光谱数据与天然产物的数值相比较，两者一致，证明两者的结构与构型相同。     

Synthesis of diversifolide and structure revision

The synthesis of diversifolide and its structural revision are reported. We synthesized the assigned structure of diversifolide via two methods, but the NMR spectra of the synthetic material did not match those of the natural material. Through careful investigation, we found that the spectra were identical with those of 11-epi-sundiversifolide.     

Synthesis and evaluation of nitrate derivatives of colchicine as anticancer agents

To search for more potent antitumor agent,a series of novel nitric oxide-donating colchicine(Col) derivatives(6a-f,8a and b) were synthesized by coupling nitrates with N-methyl colchiceinamide.Their cytotoxicity against four human cancer cell lines in vitro were evaluated by MTT assay.It was found that many of the derivatives displayed significant activity,particularly,compounds 6c,8a and 8b showed more potent cytotoxic activities than Col.     

Synthesis and cation complexation properties of new macrolides

The cis-2-alkyl-3-oxy-tetrahydropyran unit as a novel structure for the design and synthesis of a new type of ionophores with C₂-symmetry is reported. The synthesis of seven different macrolides and a crown ether and their cation complexation properties were investigated. The X-ray crystal structure of some of the receptors provides valuable information on the preferred conformation of tetrahydropyrans in the solid state that can be related to the cation complexation properties in solution. The kinetic template effect has been proved to be a useful tool to improve the yield and selectivity in the synthesis of macrodiolide 3.     

Synthesis of the DE-ring of goniodomin A and prediction of its natural relative stereochemistry

Goniodomin A (1) was first isolated from Alexandrium hiranoi as a stereochemically unidentified antifungal agent in 1987 by Murakami. In this study, two stereoisomeric series of non-macrocyclic and macrocyclic DE-ring model compounds of 1 were synthesized, and the natural relative stereochemistry of the DE-ring was predicted by NMR comparison of 1 with these model compounds.     

Synthesis of (thia)calix[4]arene oligomers: towards calixarene-based dendrimers

Thiacalix[4]arenes bearing two or four carboxylic functions on the lower rim served as starting compounds for the synthesis of novel calixarene oligomers connected by amidic functions. The cone conformers react smoothly with four molecules of 5-amino-calix[4]arene to yield the corresponding pentakis-calixarenes. On the other hand, because steric hindrance, the 1,3-alternate condenses only with two molecules leading thus to tris-calixarene, possessing a novel type of inherent chirality based on the 25,26-substitution pattern. The title compounds, which connect together ‘classical’ calixarene and thiacalixarene building blocks, represent a first step towards calixarene-based dendritic structures.