DNA encodes the genetic information; recently, it has also become a key player in material science. Given the specific Watson-Crick base-pairing interactions between only four types of nucleotides, well-designed DNA self-assembly can be programmable and predictable. Stem-loops, sticky ends, Holliday junctions, DNA tiles, and lattices are typical motifs for forming DNA-based structures. The oligonucleotides experience thermal annealing in a near-neutral buffer containing a divalent cation (usually Mg ) to produce a variety of DNA nanostructures. These structures not only show beautiful landscape, but can also be endowed with multifaceted functionalities. This Review begins with the fundamental characterization and evolutionary trajectory of DNA-based artificial structures, but concentrates on their biomedical applications. The coverage spans from controlled drug delivery to high therapeutic profile and accurate diagnosis. A variety of DNA-based materials, including aptamers, hydrogels, origamis, and tetrahedrons, are widely utilized in different biomedical fields. In addition, to achieve better performance and functionality, material hybridization is widely witnessed, and DNA nanostructure modification is also discussed. Although there are impressive advances and high expectations, the development of DNA-based structures/technologies is still hindered by several commonly recognized challenges, such as nuclease instability, lack of pharmacokinetics data, and relatively high synthesis cost.

An oligonucleotide incorporating a palladacyclic nucleobase has been prepared by ligand-directed metalation of a phenylpyridine moiety. This oligonucleotide hybridized with natural counterparts placing any of the canonical nucleobases opposite to the palladacyclic residue. The palladated duplexes had B-type conformation and melting temperatures comparable to those of respective unmodified duplexes with a single mismatch. In the duplexes placing C, G or T (but not A) opposite to the palladacyclic residue, greatly increased absorptivity suggested formation of a Pd -mediated base pair. Absorptivity and ellipticity of these duplexes persisted even at the highest temperatures applicable in T and CD experiments (90 °C). Evidently the Pd -mediated base pairs do not dissociate under the experimental conditions.

In article number https://doi.org/10.1002/adma.201703658, Yuezhou Zhang, Hongbo Zhang, and co‐workers discuss the biomedical applications of DNA‐based materials. Due to the well understood interactions of four types of nucleotides, which serve as the building blocks of DNA, the programmable and versatile structure is readily achieved and multifaceted functionalities are assigned. DNA nanomaterials are very promising in biomedical applications.

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SummaryThe present work describes efficient avenues for the synthesis of the trisaccharide repeating unit [α-D-Rhap-(1→3)-α-D-Rhap-(1→3)-α-D-Rhap] associated with the A-band polysaccharide of Pseudomonas aeruginosa. One of the key steps involved 6-O-deoxygenation of either partially or fully acylated 4,6-O-benzylidene-1-thiomannopyranoside by radical-mediated redox rearrangement in high yields and regioselectivity. The D-rhamno-thioglycosides so obtained allowed efficient access to the trisaccharide target via stepwise glycosylation as well as a one-pot glycosylation protocol. In a different approach, a 4,6-O-benzylidene D-manno-trisaccharide derivative was synthesized, which upon global 6-O-deoxygenation followed by deprotection generated the target D-rhamno-trisaccharide. The application of the reported regioselective radical-mediated deoxygenation on 4,6-O-benzylidene D-manno thioglycoside (hitherto unexplored) has potential for ramification in the field of synthesis of oligosaccharides based on 6-deoxy hexoses.

Oligonucleotides incorporating a central C‐nucleoside with either a rigid or flexible benzaldoxime base moiety have been synthesized, and the hybridization properties of their metallacyclic derivatives have been studied by UV melting experiments. In all cases, the metallated duplexes were less stable than their unmetallated counterparts, and the metallacyclic nucleobases did not show a clear preference for any of the canonical nucleobases as a base‐pairing partner. With palladated oligonucleotides, increased flexibility translated to less severe destabilization, whereas the opposite was true for the mercurated oligonucleotides; this reflects the greater difficulties in accommodating a rigid Pd II ‐mediated base pair than a rigid Hg II ‐mediated base pair within the base stack of a double helix.

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