Reaction of Boranephosphonate Diesters with Amines in the Presence of Iodine: The Case for the Intermediacy of H-Phosphonate Derivatives

Synthesis of P-Modified DNA from Boranophosphate DNA as a Precursor via Acyl Phosphite Intermediates

In this study, we successfully synthesized several kinds of P-modified nucleic acids from boranophosphate DNAs via an acyl phosphite intermediate in solution and on a solid support. In the solution-phase synthesis, phosphorothioate diester, phosphotriester, and phosphoramidate diester were synthesized in a one-pot reaction from boranophosphodiester via the conversion of an acyl phosphite as a key intermediate. In addition, doubly P-modified nucleic acid derivatives which were difficult to synthesize by the phosphoramidite and H-phosphonate methods were also obtained by the conversion reaction. In the solid-phase synthesis, a boranophosphate derivative was synthesized on a solid support using the H-boranophosphonate method. Then, an acyl phosphite intermediate was formed by treatment with pivaloyl chloride in pyridine, followed by appropriate transformations to obtain the P-modified derivatives such as phosphotriester and phosphorothioate diester. Notably, it was suggested that the conversion reaction of a boranophosphate to a phosphorothioate diester proceeded with retention of the stereochemistry of the phosphorous center. In addition, a phosphorothioate/phosphate chimeric dodecamer was successfully synthesized from a boranophosphate/phosphate chimeric dodecamer using the same strategy. Therefore, boranophosphate derivatives are versatile precursors for the synthesis of P-modified DNA, including chimeric derivatives.

Convenient Solid-Phase Attachment of Small-Molecule Ligands to Oligonucleotides via a Biodegradable Acid-Labile P-N-Bond

One of the key problems in the design of therapeutic and diagnostic oligonucleotides is the attachment of small-molecule ligands for targeted deliveries in such a manner that provides the controlled release of the oligonucleotide at a certain moment. Here, we propose a novel, convenient approach for attaching ligands to the 5'-end of the oligonucleotide via biodegradable, acid-labile phosphoramide linkage. The method includes the activation of the 5'-terminal phosphate of the fully protected, support-bound oligonucleotide, followed by interaction with a ligand bearing the primary amino group. This technique is simple to perform, allows for forcing the reaction to completion by adding excess soluble reactant, eliminates the problem of the limited solubility of reagents, and affords the possibility of using different solvents, including water/organic media. We demonstrated the advantages of this approach by synthesizing and characterizing a wide variety of oligonucleotide 5'-conjugates with different ligands, such as cholesterol, aliphatic oleylamine, and p-anisic acid. The developed method suits different types of oligonucleotides (deoxyribo-, 2'-O-methylribo-, ribo-, and others).

A greener protocol for the synthesis of phosphorochalcogenoates: Antioxidant and free radical scavenging activities

In this contribution, a metal- and base-free protocol has been developed for the synthesis of phosphorochalcogenoates (Se and Te) by using DMSO as solvent at 50 °C. A variety of phosphorochalcogenoates were prepared from diorganyl dichalcogenides and H-phosphonates, leading to the formation of a Chal-P(O) bond, in a rapid procedure with good to excellent yields. A full structural elucidation of products was accessed by 1D and 2D NMR, IR, CGMS, and HRMS analyses, and a stability evaluation of the phosphorochalcogenoates was performed for an effective operational description of this simple and feasible method. Typical ⁷⁷Se{¹H} (δ_Se = 866.0 ppm), ¹²⁵Te{¹H} (δ_Te = 422.0 ppm) and ³¹P{¹H} (δ_P = -1.0, -13.0 and -15.0 ppm) NMR chemical shifts were imperative to confirm the byproducts, in which this stability study was also important to select some products for pharmacological screening. The phosphorochalcogenoates were screened in vitro and ex vivo tests for the antioxidant potential and free radical scavenging activity, as well as to investigation toxicity in mice through of the plasma levels of markers of renal and hepatic damage. The pharmacological screening of phosphorochalcogenoates indicated that compounds have antioxidant propriety in different assays and not changes plasma levels of markers of renal and hepatic damage, with excision of 3g compound that increased plasma creatinine levels and decreased plasma urea levels when compared to control group in the blood mice. Thus, these compounds can be promising synthetic antioxidants that provide protection against oxidative diseases.

H-Phosphonate Chemistry in the Synthesis of Electrically Neutral and Charged Antiviral and Anticancer Pronucleotides

In this review a short account of our work on the synthesis and biological activity of electrically neutral and charged anti-HIV and anticancer pronucleotides, presented on the background of the contemporary research in this area, is given.

Reaction of Boranephosphonate Diesters with Pyridines or Tertiary Amines in the Presence of Iodine: Synthetic and Mechanistic Studies

Boranephosphonate diesters react with heteroaromatic and certain tertiary amines in the presence of an oxidant (I₂) to afford the boron-modified phosphodiester analogues containing a P-B-N structural motif. Our multinuclear ³¹P and ¹¹B NMR spectroscopy studies lend support for a two-step mechanism involving generation of a λ³-boranephosphonate intermediate that immediately coordinates an amine in the solvent cage, leading to B-pyridinium or B-ammonium boranephosphonate betaine derivatives. We found that the type of the solvent used (e.g., dichloromethane vs acetonitrile) significantly affected the course of the reaction, resulting in either formation of boron-modified derivatives or loss of the boron group with a subsequent oxidation of the phosphorus atom. In aprotic, electron-donating, polar solvents., e.g., acetonitrile (ACN) and tetrahydrofuran (THF), a λ³-boranephosphonate intermediate can also coordinate solvent molecules forming P-B-ACN or P-B-THF complexes that may influence the type of the products formed.