Oxidative Spirocyclization of β-Furyl Amides for the Assembly of Spiro-γ-butenolide-γ-butyrolactones

The synthesis of heretofore unknown γ-spirobutenolides has been achieved via an m-CPBA-mediated oxidation of β-furyl amides. The reaction employs a tethered amide, ostensibly a poorly reactive carbonyl, as a nontraditional nucleophile resulting in spirolactone formation and concurrent amide cleavage. The transformation exhibits functional group tolerance and compatibility with complex compounds. In situ 1H NMR spectroscopic studies reveal the identities of key intermediates in the oxidation-spirolactonization-oxidation cascade, suggesting a plausible mechanistic pathway. The distinct diastereofaces of the electrophilic butenolide product may be used for diastereoselective cycloaddition and conjugate addition reactions.

A Photosensitized Singlet Oxygen (1O2) Toolbox for Bio-Organic Applications: Tailoring 1O2 Generation for DNA and Protein Labelling, Targeting and Biosensing

Singlet oxygen (1O2) is the excited state of ground, triplet state, molecular oxygen (O2). Photosensitized 1O2 has been extensively studied as one of the reactive oxygen species (ROS), responsible for damage of cellular components (protein, DNA, lipids). On the other hand, its generation has been exploited in organic synthesis, as well as in photodynamic therapy for the treatment of various forms of cancer. The aim of this review is to highlight the versatility of 1O2, discussing the main bioorganic applications reported over the past decades, which rely on its production. After a brief introduction on the photosensitized production of 1O2, we will describe the main aspects involving the biologically relevant damage that can accompany an uncontrolled, aspecific generation of this ROS. We then discuss in more detail a series of biological applications featuring 1O2 generation, including protein and DNA labelling, cross-linking and biosensing. Finally, we will highlight the methodologies available to tailor 1O2 generation, in order to accomplish the proposed bioorganic transformations while avoiding, at the same time, collateral damage related to an untamed production of this reactive species.

Pyrrolidinyl Peptide Nucleic Acid Probes Capable of Crosslinking with DNA: Effects of Terminal and Internal Modifications on Crosslink Efficiency

In this study, we describe a furan-modified acpcPNA as a probe that can form an interstrand crosslink (ICL) with its DNA target upon activation with N-bromosuccinimide (NBS). To overcome the problem of furan instability under acidic conditions, a simple and versatile post-synthetic methodology for the attachment of the furan group to the PNA probe was developed. Unlike in other designs, the furan was placed at the end of the PNA molecule or tethered to the PNA backbone with all the base pairs in the PNA ⋅ DNA duplexes fully preserved. Hence, the true reactivity of each nucleobase towards the crosslinking could be compared. We show that all DNA bases except T could participate in the crosslinking reaction when the furan was placed at the end of the PNA strand. The crosslinking process was sensitive to mispairing, and lower crosslinking efficiency was observed in the presence of a base-mismatch in the PNA ⋅ DNA duplex. In contrast, when the furan was placed at internal positions of the acpcPNA ⋅ DNA duplex, no ICL was observed; this was explained by the inability of a hydrogen-bonded nucleobase to participate in the crosslinking reaction. The crosslinking efficiency was considerably improved, despite lower duplex stability, when an unpaired base (in the form of C-insertion) was present in the complementary DNA strand close to the furan modification site.

Furan-PNA: a mildly inducible irreversible interstrand crosslinking system targeting single and double stranded DNA

We here report on the design and synthesis of tailor-made furan-modified peptide nucleic acid (PNA) probes for covalent targeting of single stranded DNA through a crosslinking strategy. After introducing furan-containing building blocks into a PNA sequence, hybridization and furan-oxidation based crosslinking to DNA is investigated. The structure of the crosslinked products is characterized and preliminary investigations concerning the application of these systems to double stranded DNA are shown.

Furan oxidation based cross-linking: a new approach for the study and targeting of nucleic acid and protein interactions

The coming of age story of furan oxidation cross-linking.

On-Resin Conjugation of Diene-Polyamides and Maleimides via Diels-Alder Cycloaddition

The reaction between maleimides and resin-linked diene-polyamides allows the latter to be used in the preparation of conjugates. Conjugation takes place by reacting the insoluble, hydrophobic diene component either with water-soluble dienophiles or with dienophiles requiring mixtures of water and organic solvents. Experimental conditions can be adjusted to furnish the target conjugate in good yield with no need of adding large excesses of soluble reagent. In case protected maleimides are used, maleimide deprotection and Diels-Alder cycloaddition can be simultaneously carried out to render conjugates with different linking positions. On-resin conjugation is followed by an acidic treatment that removes the polyamide protecting groups with no harm to the cycloadduct, in contrast with the unreacted diene that is indeed degraded under these conditions. Cycloadducts incorporating suitable functional groups can undergo subsequent additional conjugation reactions in solution to furnish double conjugates.