Gd-TEMDO: Design, Synthesis, and MRI Application

Multicomponent reaction-derived covalent inhibitor space

The area of covalent inhibitors is gaining momentum due to recently introduced clinical drugs, but libraries of these compounds are scarce. Multicomponent reaction (MCR) chemistry is well known for its easy access to a very large and diverse chemical space. Here, we show that MCRs are highly suitable to generate libraries of electrophiles based on different scaffolds and three-dimensional shapes and highly compatible with multiple functional groups. According to the building block principle of MCR, acrylamide, acrylic acid ester, sulfurylfluoride, chloroacetic acid amide, nitrile, and α,β-unsaturated sulfonamide warheads can be easily incorporated into many different scaffolds. We show examples of each electrophile on 10 different scaffolds on a preparative scale as well as in a high-throughput synthesis mode on a nanoscale to produce libraries of potential covalent binders in a resource- and time-saving manner. Our operational procedure is simple, mild, and step economical to facilitate future covalent library synthesis.

Ruthenium-Catalyzed Deaminative Hydrogenation of Amino Nitriles: Direct Access to 1,2-Amino Alcohols

A new approach for the efficient and highly selective synthesis of 1,2-amino alcohols by direct reductive hydrolysis of N-formyl-protected α-amino nitriles is reported. The commercially available RuHCl(CO)(PPh₃ )₃ complex was found to be a suitable catalyst for this operationally simple protocol, in which no stoichiometric amounts of undesired metal waste are generated. The deaminative hydrogenation is performed at 55 bar of H₂ , using a 6:1 mixture of 1,4-dioxane/water as solvent. In addition, hydroxymethyl alcohols were prepared from cyanoketones under very similar conditions.

Tetrazoles via Multicomponent Reactions

Tetrazole derivatives are a prime class of heterocycles, very important to medicinal chemistry and drug design due to not only their bioisosterism to carboxylic acid and amide moieties but also to their metabolic stability and other beneficial physicochemical properties. Although more than 20 FDA-approved drugs contain 1 H- or 2 H-tetrazole substituents, their exact binding mode, structural biology, 3D conformations, and in general their chemical behavior is not fully understood. Importantly, multicomponent reaction (MCR) chemistry offers convergent access to multiple tetrazole scaffolds providing the three important elements of novelty, diversity, and complexity, yet MCR pathways to tetrazoles are far from completely explored. Here, we review the use of multicomponent reactions for the preparation of substituted tetrazole derivatives. We highlight specific applications and general trends holding therein and discuss synthetic approaches and their value by analyzing scope and limitations, and also enlighten their receptor binding mode. Finally, we estimated the prospects of further research in this field.

Composed in the f-block: solution structure and function of kinetically inert lanthanide(iii) complexes

An induction to the wonders of lanthanides, and a call for standardised methods for characterisation of lanthanide complexes in solution.

Cyclen-based Gd3+ complexes as MRI contrast agents: Relaxivity enhancement and ligand design

Magnetic Resonance Imaging (MRI) is a noninvasive radiology technique used to examine the internal organs of human body. It is useful for the diagnosis of structural abnormalities in the body. Contrast agents are used to increase the sensitivity of this technique. 1,4,7,10-Tetraazacyclododecane (cyclen) is a macrocyclic tetraamine. Its derivatives act as useful ligands to produce stable complexes with Gd³⁺ ion. Such chelates are investigated as MRI contrast agents. Free Gd³⁺ ion is extremely toxic for in vivo use. Upon complexation with a cyclen-based ligand, it is trapped in the preformed central cavity of the ligand resulting in the formation of a highly stable Gd³⁺-chelate. Better kinetic and thermodynamic stability of cyclen-based MRI contrast agents decrease their potential toxicity for in vivo use. Consequently, such agents have proved to be safest for clinical applications. Relaxivity is the most important parameter used to measure the effectiveness of a contrast agent. A number of factors influence this parameter. This article elucidates detailed strategies to increase relaxivity of cyclen-based MRI contrast agents. 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) are two key ligands derived from cyclen. They also act as building blocks for the synthesis of novel ligands. A few important methodologies for the synthesis of DOTA and DO3A derivatives are described. Moreover, the coordination geometry of chelates formed by these ligands and their derivatives is discussed as well. Novel ligands can be developed by the appropriate derivatization of DOTA and DO3A. Gd³⁺-chelates of such ligands prove to be useful MRI contrast agents of enhanced relaxivity, greater stability, better clearance, lesser toxicity and higher water solubility.

Cleavable β-Cyanoethyl Isocyanide in the Ugi Tetrazole Reaction

β-Cyanoethyl isocyanide is introduced as a cleavable isocyanide in the Ugi tetrazole reaction. Eleven examples are described that exhibit a broad scope and are obtained in good overall yields. The obtained 1H-tetrazole scaffold is an important bioisostere for carboxylic acids, and the method described here is a valuable alternative route to known procedures.