Deoxynucleoside Triphosphate Containing Pyridazin-3-one Aglycon as a Thymidine Triphosphate Substitute for Primer Extension and Chain Elongation by Klenow Fragments

Synthesis of C4-Acyl Glycosides by Cross-Ketonization: The Importance of Precise Temperature Control in Photochemistry

We describe herein a method for the synthesis of reversed C-acyl glycosides by direct cross-ketonization of linear carboxylic acids with carboxy sugars under metallaphotoredox conditions. This reaction proves to be highly sensitive to reaction temperature, with the reproducibility and yield of ketonization highly dependent upon precise temperature control. Analysis of the reaction mechanism suggests this sensitivity reflects the need to match the rate of Ni catalytic turnover with the rate of photocatalytic decarboxylation of the carboxy sugar. The insights gained from this study have important implications for the study of all metallaphotoredox reactions as well as other photoreactions that involve dual catalytic cycles.

Rhizoaspergillin A and Rhizoaspergillinol A, including a Unique Orsellinic Acid-Ribose-Pyridazinone-N-Oxide Hybrid, from the Mangrove Endophytic Fungus Aspergillus sp. A1E3

Two new compounds, named rhizoaspergillin A (1) and rhizoaspergillinol A (2), were isolated from the mangrove endophytic fungus Aspergillus sp. A1E3, associated with the fruit of Rhizophora mucronata, together with averufanin (3). The planar structures and absolute configurations of rhizoaspergillinol A (2) and averufanin (3) were established by extensive NMR investigations and quantum-chemical electronic circular dichroism (ECD) calculations. Most notably, the constitution and absolute configuration of rhizoaspergillin A (1) were unambiguously determined by single-crystal X-ray diffraction analysis of its tri-pivaloyl derivative 4, conducted with Cu Kα radiation, whereas those of averufanin (3) were first clarified by quantum-chemical ECD calculations. Rhizoaspergillin A is the first orsellinic acid-ribose-pyridazinone-N-oxide hybrid containing a unique β-oxo-2,3-dihydropyridazine 1-oxide moiety, whereas rhizoaspergillinol A (2) and averufanin (3) are sterigmatocystin and anthraquinone derivatives, respectively. From the perspective of biosynthesis, rhizoaspergillin A (1) could be originated from the combined assembly of three building blocks, viz., orsellinic acid, β-D-ribofuranose, and L-glutamine. It is an unprecedented alkaloid-N-oxide involving biosynthetic pathways of polyketides, pentose, and amino acids. In addition, rhizoaspergillinol A (2) exhibited potent antiproliferative activity against four cancer cell lines. It could dose-dependently induce G2/M phase arrest in HepG2 cells.

Diversification of Glycosyl Compounds via Glycosyl Radicals

Glycosyl radical functionalization is one of the central topics in synthetic carbohydrate chemistry. Recent advances in metal-catalyzed cross-coupling chemistry and metallaphotoredox catalysis provided powerful platforms for glycosyl radical diversification. In particular, the discovery of new glycosyl radical precursors in conjunction with these advanced reaction technologies have significantly expanded the space for glycosyl compound synthesis. In this Review, we highlight the most recent progress in this area starting from 2021, and the reports included will be categorized based on different reaction types for better clarity.

Synthesis of C-acyl furanosides via the cross-coupling of glycosyl esters with carboxylic acids

C-Acyl furanosides are versatile synthetic precursors to a variety of natural products, nucleoside analogues, and pharmaceutical molecules. This report addresses the unmet challenge in preparing C-acyl furanosides by developing a cross-coupling reaction between glycosyl esters and carboxylic acids. A key step is the photoredox activation of the glycosyl ester, which promotes the homolysis of the strong anomeric C–O bond through CO₂ evolution to afford glycosyl radicals. This method embraces a large scope of furanoses, pyranoses, and carboxylic acids, and is readily applicable to the synthesis of a thymidine analogue and diplobifuranylone B, as well as the late-stage modification of (+)-sclareolide. The convenient preparation of the redox active glycosyl ester from native sugars and the compatibility with common furanoses exemplifies the potential of this method in medicinal chemistry.

A cross-coupling of glycosyl esters with carboxylic acids to prepare C-acyl furanosides and pyranosides. The reaction proceeds through photoredox activation of the glycosyl ester to afford glycosyl radicals.

Double-headed nucleotides as xeno nucleic acids: information storage and polymerase recognition

Xeno nucleic acids (XNAs) are artificial genetic systems based on sugar-modified nucleotides. Herein, we investigate double-headed nucleotides as a new XNA. A new monomer, AT, is presented, and together with previous double-headed nucleotide monomers, new nucleic acid motifs consisting of up to five consecutive A·T base pairs have been obtained. Sections composed entirely of double-headed nucleotides are well-tolerated within a DNA duplex and can condense the genetic information. For instance, a 13-mer duplex is condensed to an 11-mer modified duplex containing four double-headed nucleotides while simultaneously improving duplex thermal stability with +14.0 °C. Also, the transfer of information from double-headed to natural nucleotides by DNA polymerases has been examined. The first double-headed nucleoside triphosphate was prepared but could not be recognized and incorporated by the tested DNA polymerases. On the other hand, it proved possible for Therminator DNA polymerase to transfer the information of a double-headed nucleotide in a template sequence to natural DNA under controlled conditions.