Synthesis of Nucleosides and Deoxynucleosides via Gold(I)-Catalyzed N-Glycosylation of Glycosyl (Z)-Ynenoates

Nucleoside analogues are widely used as anticancer and antiviral drugs. Here, we develop a highly efficient gold(I)-catalyzed N-glycosylation approach for versatile synthesis of various types of nucleosides and deoxynucleosides with glycosyl (Z)-ynenoates as donors. The wide scope of the N-glycosylation approach was demonstrated by the synthesis of 31 pyrimidine nucleosides and 8 purine nucleosides. Remarkably, the gold(I)-catalyzed N-glycosylation of pyranosyl (Z)-ynenoates with purines was found to be very effective for regioselective synthesis of pyranosyl N9 purine nucleosides. Based on the catalytic N-glycosylation approach, convenient synthesis of two 5'-deoxynucleosides drugs (capecitabine and galocitabine), four 2'-deoxynucleoside drugs (floxuridine, trifluridine, decitabine and cladribine), four 3',5'-dideoxynucleoside analogues, and four 2',5'-dideoxynucleoside analogues was achieved in a collective manner.

Exploiting photoredox catalysis for carbohydrate modification through C–H and C–C bond activation

Photoredox catalysis has recently emerged as a powerful synthetic platform for accessing complex chemical structures through non-traditional bond disconnection strategies that proceed through free-radical intermediates. Such synthetic strategies have been used for a range of organic transformations; however, in carbohydrate chemistry they have primarily been applied to the generation of oxocarbenium ion intermediates in the ubiquitous glycosylation reaction. In this Review, we present more intricate light-induced synthetic strategies to modify native carbohydrates through homolytic C-H and C-C bond cleavage. These strategies allow access to glycans and glycoconjugates with profoundly altered carbohydrate skeletons, which are challenging to obtain through conventional synthetic means. Carbohydrate derivatives with such structural motifs represent a broad class of natural products integral to numerous biochemical processes and can be found in active pharmaceutical substances. Here we present progress made in C-H and C-C bond activation of carbohydrates through photoredox catalysis, focusing on the operational mechanisms and the scope of the described methodologies.

Synthesis and Exploitation of the Biological Profile of Novel Guanidino Xylofuranose Derivatives

The synthesis and biological evaluation of novel guanidino sugars as isonucleoside analogs is described. 5-Guanidino xylofuranoses containing 3- O -saturated/unsaturated hydrocarbon or aromatic-containing moieties were accessed from 5-azido xylofuranoses via reduction followed by guanidinylation with N , N '-bis( tert -butoxycarbonyl)- N ''-triflylguanidine. Molecules comprising novel types of isonucleosidic structures including 5-guanidino 3- O -methyl-branched N -benzyltriazole isonucleosides and a guanidinomethyltriazole 3'- O -dodecyl xylofuranos-5'-yl isonucleoside were accessed. The guanidinomethyltriazole derivative and a 3- O -dodecyl ( N -Boc)guanidino xylofuranose were revealed as selective inhibitors of acetylcholinesterase ( K i = 22.87 and 7.49 µM, respectively). The latter also showed moderate antiproliferative effects in chronic myeloid leukemia (K562) and breast cancer (MCF-7) cells. An aminomethyltriazole 5'-isonucleoside was the most potent molecule with low micromolar GI 50 values in both cells (GI 50 = 6.33 μM, 8.45 μM), similar to that of the drug 5-fluorouracil in MCF-7 cells. Moreover, the most bioactive compounds showed low toxicity in human fibroblasts, further indicating their interest as promising lead molecules.

Samarium(ii) iodide-mediated reactions applied to natural product total synthesis

Natural product synthesis remains a field in which new synthetic methods and reagents are continually being evaluated. Due to the demanding structures and complex functionality of many natural products, only powerful and selective methods and reagents will be highlighted in this proceeding. Since its introduction by Henri Kagan, samarium(ii) iodide (SmI2, Kagan's reagent) has found increasing use in chemical synthesis. Over the years, many reviews have been published on the application of SmI2 in numerous reductive coupling procedures as well as in natural product total synthesis. This review highlights recent advances in SmI2-mediated synthetic strategies, as applied in the total synthesis of natural products since 2004.

Silane promoted glycosylation and its applications for synthesis of sugar compounds and active pharmaceutical ingredients (APIs)

Silane promoted glycosylation and its applications for preparation of active pharmaceutical ingredients.

Study of the N7 Regioselective Glycosylation of 6-Chloropurine and 2,6-Dichloropurine with Tin and Titanium Tetrachloride

6-Chloropurine and 2,6-dichloropurine were regioselectively glycosylated at position 7 to give the corresponding peracetylated N⁷-nucleosides, which can be suitable for other purine transformations. In this work, we study the distribution of N⁷/N⁹-isomers produced via the Vorbrüggen method under different conditions, using an N-trimethylsilylated purine derivative and SnCl₄ or TiCl₄ as a catalyst. The main effort is devoted to reversing the disadvantageous predominant selectivity of most glycosylation reactions at the N⁹ position and thus to determining conditions that maximize the regioselectivity of glycosylation toward the desired N⁷-isomer.

Solving the Structural Puzzles of Amipurimycin and Miharamycins Enabled by Stereodivergent Total Synthesis

The efforts toward the synthesis of amipurimycin and miharamycin A/B, two peptidyl nucleoside antibiotics bearing a unique nine carbon C3-branched pyranosyl amino acid core, are accounted. Highlighted is our stereodivergent total synthesis of all the possible diastereoisomers of amipurimycin, which has enabled us to solve the structural puzzles of amipurimycin and miharamycin A/B after ∼50 years of their discovery.

NIS/TMSOTf-Promoted Glycosidation of Glycosyl ortho-Hexynylbenzoates for Versatile Synthesis of O-Glycosides and Nucleosides

Glycosidation plays a pivotal role in the synthesis of O-glycosides and nucleosides that mediate a diverse range of biological processes. However, efficient glycosidation approach for the synthesis of both O-glycosides and nucleosides remains challenging in terms of glycosidation yields, mild reaction conditions, readily available glycosyl donors, and cheap promoters. Here, we report a versatile N-iodosuccinimide/trimethylsilyl triflate (NIS/TMSOTf)-promoted glycosidation approach with glycosyl ortho-hexynylbenzoates as donors for the highly efficient synthesis of O-glycosides and nucleosides. The glycosidation approach highlights the merits of mild reaction conditions, cheap promoters, extremely wide substrate scope, and good to excellent yields. Notably, the glycosidation approach performs very well in the construction of a series of challenging O- and N-glycosidic linkages. The glycosidation approach is then applied to the efficient synthesis of oligosaccharides via the one-pot strategy and the stepwise strategy. On the basis of the isolation and characterization of the departure species derived from the leaving group, a plausible mechanism of NIS/TMSOTf-promoted glycosidation of glycosyl ortho-hexynylbenzoates is proposed.

Synthesis of Azido Acids and Their Application in the Preparation of Complex Peptides

Azido acids are important synthons for the synthesis of complex peptides. As a protecting group, the azide moiety is atom-efficient, easy to install and can be reduced in the presence of many other protecting groups, making it ideal for the synthesis of branched and/or cyclic peptides. α-Azido acids are less bulky than urethane-protected counterparts and react more effectively in coupling reactions of difficult-to-form peptide and ester bonds. Azido acids can also be used to form azoles on complex intermediates. This review covers the synthesis of azido acids and their application to the total synthesis of complex peptide natural products.

1 Introduction

2 Synthesis of α-Azido Acids

2.1 From α-Amino Acids or Esters

2.2 Via α-Substitution

2.3 Via Electrophilic Azidation

2.4 Via Condensation of N-2-Azidoacetyl-4-Phenylthiazolidin- 2-Thi one Enolates with Aldehydes and Acetals

2.5 Synthesis of α,β-Unsaturated α-Azido Acids and Esters

3 Synthesis of β-Azido Acids

3.1 Preparation of Azidoalanine and 3-Azido-2-aminobutanoic Acids

3.2 General Approaches to Preparing β-Azido Acids Other Than Azi doalanine­ and AABA

4 Azido Acids in Total Synthesis

4.1 α-Azido Acids

4.2 β-Azido Acids and Azido Acids Containing an Azide on the Side Chain

5 Conclusions

Glycosyl ortho-(1-phenylvinyl)benzoates versatile glycosyl donors for highly efficient synthesis of both O-glycosides and nucleosides

Both of O-glycosides and nucleosides are important biomolecules with crucial rules in numerous biological processes. Chemical synthesis is an efficient and scalable method to produce well-defined and pure carbohydrate-containing molecules for deciphering their functions and developing therapeutic agents. However, the development of glycosylation methods for efficient synthesis of both O-glycosides and nucleosides is one of the long-standing challenges in chemistry. Here, we report a highly efficient and versatile glycosylation method for efficient synthesis of both O-glycosides and nucleosides, which uses glycosyl ortho-(1-phenylvinyl)benzoates as donors. This glycosylation protocol enjoys the various features, including readily prepared and stable donors, cheap and readily available promoters, mild reaction conditions, good to excellent yields, and broad substrate scopes. In particular, the applications of the current glycosylation protocol are demonstrated by one-pot synthesis of several bioactive oligosaccharides and highly efficient synthesis of nucleosides drugs capecitabine, galocitabine and doxifluridine.

The Miharamycins and Amipurimycin: their Structural Revision and the Total Synthesis of the Latter

The structural puzzle of amipurimycin, a peptidyl nucleoside antibiotic, is solved by total synthesis and X-ray diffraction analysis, with the originally proposed configurations at C3' and C8' inverted and those at C6', C2'', and C3'' corrected. A similar structural revision of the relevant miharamycins is proposed via chemical transformations and then validated by X-ray diffraction analysis. The miharamycins bear an unusual trans-fused dioxabicyclo[4.3.0]nonane sugar scaffold, which was previously assigned as being in the cis configuration.

Synthesis and conformational analysis of linear homo- and heterooligomers from novel 2-C-branched sugar amino acids (SAAs)

Sugar amino acids (SAAs), as biologically interesting structures bearing both amino and carboxylic acid functional groups represent an important class of multifunctional building blocks. In this study, we develop an easy access to novel SAAs in only three steps starting from nitro compounds in high yields in analytically pure form, easily available by ceric (IV) mediated radical additions. Such novel SAAs have been applied in the assembly of total nine carbopeptoids with the form of linear homo- and heterooligomers for the structural investigations employing circular dichroism (CD) spectroscopy, which suggest that the carbopeptoids emerge a well-extended, left (or right)-handed conformation similar to polyproline II (PPII) helices. NMR studies also clearly demonstrated the presence of ordered secondary structural elements. 2D-ROESY spectra were acquired to identify ⁱ⁺¹ NH ↔  ⁱ C ₁ H, ⁱ C ₂ H correlations which support the conformational analysis of tetramers by CD spectroscopy. These findings provide interesting information of SAAs and their oligomers as potential scaffolds for discovering new drugs and materials.

Nucleoside Derived Antibiotics to Fight Microbial Drug Resistance: New Utilities for an Established Class of Drugs?

Novel antibiotics are urgently needed to combat the rise of infections due to drug-resistant microorganisms. Numerous natural nucleosides and their synthetically modified analogues have been reported to have moderate to good antibiotic activity against different bacterial and fungal strains. Nucleoside-based compounds target several crucial processes of bacterial and fungal cells such as nucleoside metabolism and cell wall, nucleic acid, and protein biosynthesis. Nucleoside analogues have also been shown to target many other bacterial and fungal cellular processes although these are not well characterized and may therefore represent opportunities to discover new drugs with unique mechanisms of action. In this Perspective, we demonstrate that nucleoside analogues, cornerstones of anticancer and antiviral treatments, also have great potential to be repurposed as antibiotics so that an old drug can learn new tricks.