Illuminating Stannylation

Photocatalytic Generation of Germyl Radicals from Digermanes Enabling the Hydro/Deuteriogermylation of Alkenes

We have developed a visible-light-induced method to photolyze digermanes through single-electron oxidation using a photocatalyst, in contrast to direct excitation, to generate germyl radicals and achieve the hydro/deuteriogermylation of alkenes. This protocol allows the previously elusive incorporation of the small trimethylgermyl group and deuterium, metabolically stable bioisosteres of tert-butyl and hydrogen, respectively, making this approach attractive in not only organic synthesis but also medicinal chemistry.

Surefire generation of stannylpotassium: highly reactive stannyl anions and applications

Organometallic reagents such as organolithium and Grignard reagents have long been esteemed in chemical synthesis for their exceptional reactivity. In contrast, the application of their sodium and potassium counterparts has been comparatively sluggish, notwithstanding their augmented reactivity stemming from their heightened ionic character. This inertia persists due to the constrained accessibility of these heavy alkali metal reagents. In this study, our focus was directed towards devising a convenient and pragmatic approach for fabricating heavy alkali metal-based reagents, particularly those grounded in potassium. Herein, we present a novel, direct method for generating stannylpotassium (Sn-K) reagents through the simple combination of readily available silylstannanes and t-BuOK. Subsequently, the generated Sn-K reagents were effectively harnessed for stannylative substitution of aryl halides, furnishing an array of arylstannanes straightforwardly under transition metal-free conditions. This application distinctly underscores the potential utility of highly reactive Sn-K species, hitherto sparingly tapped into within the realm of synthetic organic chemistry. Furthermore, our investigation confirms that Sn-K reagents manifest notably superior reactivity compared with their well-established stannyllithium (Sn-Li) counterparts. This heightened reactivity can be ascribed to the increasing ionic character of Sn-K, which was supported by computational experiments.

Photocatalytic Generations of Secondary and Tertiary Silyl Radicals from Silylboranes Using an Alkoxide Cocatalyst

Silyl radicals are valuable species to prepare diverse organosilicon compounds. However, unlike stable tertiary silyl radicals, the use of secondary silyl radicals has been problematic in silylation reactions due to their instability. Here, we present photocatalytic in situ generations of both secondary and tertiary silyl radicals by one-electron oxidation of ate complexes, formed from silylboranes and an alkoxide cocatalyst, achieving highly efficient hydrosilylation and deuterosilylation of electron-rich alkenes and dienes as well as electron-deficient alkenes. The theoretical studies show that anionic borate complexes activated with an alkoxide have lower oxidation potentials than neutral borate complexes, allowing the formation of secondary silyl radicals. The calculated reaction pathways reveal that anionic conditions using the conjugate acid-base pair of NaOEt (cocatalyst) and EtOH (solvent) are the key to expanding the scope of silyl radicals and alkenes.

Synthesis and Evaluation of a Dimeric RGD Peptide as a Preliminary Study for Radiotheranostics with Radiohalogens

We recently developed ¹²⁵I- and ²¹¹At-labeled monomer RGD peptides using a novel radiolabeling method. Both labeled peptides showed high accumulation in the tumor and exhibited similar biodistribution, demonstrating their usefulness for radiotheranostics. This study applied the labeling method to a dimer RGD peptide with the aim of gaining higher accumulation in tumor tissues based on improved affinity with α_vβ₃ integrin. We synthesized an iodine-introduced dimer RGD peptide, E[c(RGDfK)] (6), and an ^125/131I-labeled dimer RGD peptide, E[c(RGDfK)]{[^125/131I]c[RGDf(4-I)K]} ([^125/131I]6), and evaluated them as a preliminary step to the synthesis of an ²¹¹At-labeled dimer RGD peptide. The affinity of 6 for α_vβ₃ integrin was higher than that of a monomer RGD peptide. In the biodistribution experiment at 4 h postinjection, the accumulation of [¹²⁵I]6 (4.12 ± 0.42% ID/g) in the tumor was significantly increased compared with that of ¹²⁵I-labeled monomer RGD peptide (2.93 ± 0.08% ID/g). Moreover, the accumulation of [¹²⁵I]6 in the tumor was greatly inhibited by co-injection of an excess RGD peptide. However, a single injection of [¹³¹I]6 (11.1 MBq) did not inhibit tumor growth in tumor-bearing mice. We expect that the labeling method for targeted alpha therapy with ²¹¹At using a dimer RGD peptide could prove useful in future clinical applications.