Total Synthesis of Sanguiin H-5

Sanguiins-Promising Molecules with Broad Biological Potential

Compounds of natural origin, an infinite treasure of bioactive chemical entities, persist as an inexhaustible resource for discovering new medicines. In this review, we summarize the naturally occurring ellagitannins, sanguiins, which are bioactive constituents of various traditional medicinal plants, especially from the Rosaceae family. In-depth studies of sanguiin H-6 as an antimicrobial, antiviral, anticancer, anti-inflammatory, and osteoclastogenesis inhibitory agent have led to potent drug candidates. In addition, recently, virtual screening studies have suggested that sanguiin H-6 might increase resistance toward SARS-CoV-2 in the early stages of infection. Further experimental investigations on ADMET (absorption, distribution, metabolism, excretion, and toxicity) supplemented with molecular docking and molecular dynamics simulation are still needed to fully understand sanguiins' mechanism of action. In sum, sanguiins appear to be promising compounds for additional studies, especially for their application in therapies for a multitude of common and debilitating ailments.

Reversing Reactivity: Stereoselective Desulfurative 1,2-trans-O-Glycosylation of Anomeric Thiosugars with Carboxylic Acids under Copper or Cobalt Catalysis

We have discovered a new mode of reactivity of 1-thiosugars in the presence of Cu(II) or Co(II) for a stereoselective O-glycosylation reaction. The process involves the use of a catalytic amount of Cu(acac)₂ or Co(acac)₂ and Ag₂CO₃ as an oxidant in α,α,α-trifluorotoluene. Moreover, this protocol turned out to have a broad scope, allowing the preparation of a wide range of complex substituted O-glycoside esters in good to excellent yields with an exclusive 1,2-trans-selectivity. The late-stage modification of pharmaceuticals by this method was also demonstrated. To obtain a closer insight into the reaction mechanism, cyclic voltammetry was performed.

Total Synthesis of Phyllanemblinin B

A total synthesis was developed of phyllanemblinin B, a natural ellagitannin containing 1-O-galloyl and 2,4-O-hexahydroxydiphenoyl groups on a d-glucose scaffold. The use of a μ-hydroxo copper(II) complex resulted in a completely stereoselective oxidative coupling of the galloyl groups on the open-chain glucose moiety and facilitated the first total synthesis of phyllanemblinin B.

Fundamental Methods in Ellagitannin Synthesis

This account describes methods for synthesizing natural ellagitannins. The ellagitannins, a class of polyphenols, has a wide variety of chemical structures and biological activities. Here, we focus on three topics, which are the synthesis of the hexahydroxydiphenoyl group, construction of the hexahydroxydiphenoyl bridge, and synthesis of C–O digallates. The hexahydroxydiphenoyl group and the C–O digallates are C–C and C–O coupled galloyl groups, respectively, both group of which are the two major components of ellagitannins. By combining methods described in this account, many ellagitannins might be synthesized.

Copper porphyrin catalyzed esterification of C(sp3)–H via a cross-dehydrogenative coupling reaction

Copper porphyrin was an efficient catalyst for the direct esterification of C(sp³)–H bonds using DTBP as an oxidant.

Diversity-oriented synthesis and cytotoxic activity evaluation of biaryl-containing macrocycles

Synthesis of biaryl-containing macrocycles has been carried out through a four-step approach comprising two Ugi four component reactions and a Suzuki–Miyaura macrocyclization.

Stereospecific, High-Yielding, and Green Synthesis of β-Glycosyl Esters

A new method of synthesizing β-glycosyl esters stereospecifically has been developed by treating O-benzyl-protected glycosyl chlorides with Cs2CO3, tetrabutylammomium bromide (TBAB), a carboxylic acid, water, and granular polytetrafluoroethylene (PTFE) at 80 °C under mechanical agitation. D-Glucosyl, D-xylosyl, and D-galactosyl chlorides and 20 carboxylic acids were used to demonstrate the scope of the reaction. Control experiments showed that the water and granular PTFE had indispensable roles. Water-soluble TBAB has been found to be as efficient as N-methyl-N,N,N-trioctyloctan-1-ammonium chloride (Aliquat 336) in the reactions. After scaling up to 5-12 g, all of the products were obtained quantitatively via simple filtration and no organic solvents or chromatography was needed for the entire process.

A NCS mediated oxidative C-H bond functionalization: direct esterification between a C(sp(3))-H bond and carboxylic acids

A transition metal free oxidative C-H bond functionalization/esterification of α-alkoxy alkanes with acids is described in this report. This method is effectively mediated by NCS instead of traditional oxidants, like TBHP or its derivatives, and directly generates the esterification products in moderate to high yield under mild conditions. This tranformation constitutes a practical and general approach toward various α-acyloxy ethers with broad substrate generality; alkyl-, aryl-, alkenyl- and alkynyl-carboxylic acids are all well tolerated.

Copper catalyzed C-O bond formation via oxidative cross-coupling reaction of aldehydes and ethers

A practical and efficient construction of C-O bonds via oxidative cross-coupling reaction of aldehydes and ethers has been realized under open air. When 2 mol% copper was used as the catalyst, various α-acyloxy ethers were obtained with up to 93% isolated yield.

Structure-activity relationships for vitamin D3-based aromatic a-ring analogues as hedgehog pathway inhibitors

A structure-activity relationship study for a series of vitamin D3-based (VD3) analogues that incorporate aromatic A-ring mimics with varying functionality has provided key insight into scaffold features that result in potent, selective Hedgehog (Hh) pathway inhibition. Three analogue subclasses containing (1) a single substitution at the ortho or para position of the aromatic A-ring, (2) a heteroaryl or biaryl moiety, or (3) multiple substituents on the aromatic A-ring were prepared and evaluated. Aromatic A-ring mimics incorporating either single or multiple hydrophilic moieties on a six-membered ring inhibited the Hh pathway in both Hh-dependent mouse embryonic fibroblasts and cultured cancer cells (IC50 values 0.74-10 μM). Preliminary studies were conducted to probe the cellular mechanisms through which VD3 and 5, the most active analogue, inhibit Hh signaling. These studies suggested that the anti-Hh activity of VD3 is primarily attributed to the vitamin D receptor, whereas 5 affects Hh inhibition through a separate mechanism.

Synthesis and biological profiling of tellimagrandin I and analogues reveals that the medium ring can significantly modulate biological activity

A novel synthesis of the ellagitannin natural product tellimagrandin I and a series of medium ring analogues is described. These compounds were all subsequently screened for redox activity, ability to precipitate protein and cellular phenotype in HeLa cells. From this we have shown that all properties can be modulated independently by varying ring size and by moving the ester out of conjugation with the biaryl ring system. Increasing ring size increased redox activity and cytotoxicity, leading to the identification of a compound (10) which was significantly more cytotoxic. In addition compounds identified with a redox active scaffold and low cytotoxicity may be employed as a new class of redox probes.

Plant polyphenols: chemical properties, biological activities, and synthesis

Eating five servings of fruits and vegetables per day! This is what is highly recommended and heavily advertised nowadays to the general public to stay fit and healthy! Drinking green tea on a regular basis, eating chocolate from time to time, as well as savoring a couple of glasses of red wine per day have been claimed to increase life expectancy even further! Why? The answer is in fact still under scientific scrutiny, but a particular class of compounds naturally occurring in fruits and vegetables is considered to be crucial for the expression of such human health benefits: the polyphenols! What are these plant products really? What are their physicochemical properties? How do they express their biological activity? Are they really valuable for disease prevention? Can they be used to develop new pharmaceutical drugs? What recent progress has been made toward their preparation by organic synthesis? This Review gives answers from a chemical perspective, summarizes the state of the art, and highlights the most significant advances in the field of polyphenol research.

Intramolecular Suzuki-Miyaura reaction for the total synthesis of signal peptidase inhibitors, arylomycins A(2) and B(2)

Development of the total syntheses of arylomycins A(1) and B(2) is detailed. Key features of our approach include 1) formation of 14-membered meta,meta-cyclophane by an intramolecular Suzuki-Miyaura reaction; 2) incorporation of N-Me-4-hydroxyphenylglycine into the cyclization precursor, which avoids the late-stage low-yielding N-methylation step; 3) segment coupling of a fully elaborated peptide side chain to the macrocycle, which makes the synthesis highly convergent. Overall, arylomycin A(2) was obtained in 13 steps from L-Tyr for the longest linear sequence, in 13 % overall yield. Arylomycin B(2) was synthesized in 10 steps from L-3-nitro-Tyr, in 10 % overall yield.