Synthetic and natural guanidine derivatives as antitumor and antimicrobial agents: A review

Guanidines are fascinating small nitrogen-rich organic compounds, which have been frequently associated with a wide range of biological activities. This is mainly due to their interesting chemical features. For these reasons, for the past decades, researchers have been synthesizing and evaluating guanidine derivatives. In fact, there are currently on the market several guanidine-bearing drugs. Given the broad panoply of pharmacological activities displayed by guanidine compounds, in this review, we chose to focus on antitumor, antibacterial, antiviral, antifungal, and antiprotozoal activities presented by several natural and synthetic guanidine derivatives, which are undergoing preclinical and clinical studies from January 2010 to January 2023. Moreover, we also present guanidine-containing drugs currently in the market for the treatment of cancer and several infectious diseases. In the preclinical and clinical setting, most of the synthesized and natural guanidine derivatives are being evaluated as antitumor and antibacterial agents. Even though DNA is the most known target of this type of compounds, their cytotoxicity also involves several other different mechanisms, such as interference with bacterial cell membranes, reactive oxygen species (ROS) formation, mitochondrial-mediated apoptosis, mediated-Rac1 inhibition, among others. As for the compounds already used as pharmacological drugs, their main application is in the treatment of different types of cancer, such as breast, lung, prostate, and leukemia. Guanidine-containing drugs are also being used for the treatment of bacterial, antiprotozoal, antiviral infections and, recently, have been proposed for the treatment of COVID-19. To conclude, the guanidine group is a privileged scaffold in drug design. Its remarkable cytotoxic activities, especially in the field of oncology, still make it suitable for a deeper investigation to afford more efficient and target-specific drugs.

Catalytic Carbodiimide Guanylation by a Nucleophilic, High Spin Iron(II) Imido Complex

Reduction of the three-coordinate iron(III) imido [Ph₂B(^tBuIm)₂Fe═NDipp] (1) affords [Ph₂B(^tBuIm)₂Fe═NDipp][K(18-C-6)THF₂] (2), a rare example of a high-spin (S = 2) iron(II) imido complex. Unusually for a late metal imido complex, the imido ligand in 2 has nucleophilic character, as demonstrated by the reaction with DippNH₂, which establishes an equilibrium with the bis(anilido) complex [Ph₂B(^tBuIm)₂Fe(NHDipp)₂][K(18-C-6)THF₂] (3). In an unusual transformation, formal insertion of ⁱPrN═C═NⁱPr into the Fe═N(imido) bond yields the guanidinate [Ph₂B(^tBuIm)₂Fe(ⁱPrN)₂CNDipp][K(18-C-6)THF₂] (4). Reaction of 4 with excess DippNH₂ provides 3, along with the guanidine (ⁱPrNH)₂C═NDipp. As suggested by these stoichiometric reactions, 2 is an efficient catalyst for the guanylation of carbodiimides, converting a wide range of aniline substrates under mild conditions.

Reactivity of terminal imido complexes of group 4-6 metals: stoichiometric and catalytic reactions involving cycloaddition with unsaturated organic molecules

Imido complexes of early transition metals are key intermediates in the synthesis of many nitrogen-containing organic compounds. The metal-nitrogen double bond of the imido moiety undergoes [2+2] cycloaddition reactions with various unsaturated organic molecules to form new nitrogen-carbon and nitrogen-heteroatom bonds. This review article focuses on reactivity of the terminal imido complexes of Group 4-6 metals, summarizing their stoichiometric reactions and catalytic applications for a variety of reactions including alkyne hydroamination, alkyne carboamination, pyrrole formation, imine metathesis, and condensation reactions of carbonyl compounds with isocyanates.

Insertion reactions of small unsaturated molecules in the N-B bonds of boron guanidinates

We report here 1,1- and 1,2-insertion reactions of small unsaturated molecules in the N-B bonds of two boron guanidinates, (Me₂N)C(NⁱPr)₂BCy₂ (1) and {ⁱPr(H)N}C(NⁱPr){N(p-^tBu-C₆H₄)}BCy₂ (2), and two bisboron guanidinates(2-), {ⁱPr(BCy₂)N}C(NⁱPr){N(p-^tBu-C₆H₄)}BCy₂ (3) and {ⁱPr(C₈H₁₄B)N}C(NⁱPr){N(p-Me-C₆H₄)}BC₈H₁₄ (4), the latter being prepared for the first time by double deprotonation of the corresponding guanidine with the 9-borabicyclo[3.3.1]nonane dimer, (H-BC₈H₁₄)₂. Compounds 1-4 easily insert aromatic isonitriles, XylNC (Xyl = 2,6-Me₂-C₆H₃) and (p-MeO-C₆H₄)NC, to give the expected diazaboroles 5-12, some of them being structurally characterised by X-ray diffraction. Interestingly, the BC₈H₁₄ derivatives 11 and 12 are in a fast temperature-dependent equilibrium with the de-insertion products, whose thermodynamic parameters are reported here. A correlation between these equilibria and the puckered heterocyclic structure found in the solid state for 11, and confirmed by DFT calculations, is also established. Reactions of the aforementioned guanidinates with CO are more sluggish or even precluded, and only one product, {ⁱPr(H)N}C{N(p-^tBu-C₆H₄)}(NⁱPr)(CO)BCy₂ (13), could be isolated in moderate yields. The 1,2-insertions of benzaldehyde in compounds 1, 2 and 4 are reversible reactions in all cases, and only one of the insertion products, {ⁱPr(H)N}C{N(p-^tBu-C₆H₄)}(NⁱPr)(PhHCO)BCy₂ (16a), was isolated and diffractrometrically characterised. Likewise, CO₂ reversibly inserts into a N-B bond of 2 to give {ⁱPr(H)N}C{N(p-^tBu-C₆H₄)}(NⁱPr)(CO₂)BCy₂ (19) with a conversion of ca. 9%. In all these equilibria, de-insertion is always favoured upon increasing the temperature.

Structural and Mechanistic Insights into s-Block Bimetallic Catalysis: Sodium Magnesiate-Catalyzed Guanylation of Amines

To advance the catalytic applications of s-block mixed-metal complexes, sodium magnesiate [NaMg(CH₂ SiMe₃ )₃ ] (1) is reported as an efficient precatalyst for the guanylation of a variety of anilines and secondary amines with carbodiimides. First examples of hydrophosphination of carbodiimides by using a Mg catalyst are also described. The catalytic ability of the mixed-metal system is much greater than that of its homometallic components [NaCH₂ SiMe₃ ] and [Mg(CH₂ SiMe₃ )₂ ]. Stoichiometric studies suggest that magnesiate amido and guanidinate complexes are intermediates in these catalytic routes. Reactivity and kinetic studies imply that these guanylation reactions occur via (tris)amide intermediates that react with carbodiiimides in insertion steps. The rate law for the guanylation of N,N'-diisopropylcarbodiimide with 4-tert-butylaniline catalyzed by 1 is first order with respect to [amine], [carbodiimide], and [catalyst], and the reaction shows a large kinetic isotopic effect, which is consistent with an amine-assisted rate-determining carbodiimide insertion transition state. Studies to assess the effect of sodium in these transformations denote a secondary role with little involvement in the catalytic cycle.

Tris(pentafluorophenyl)borane as an efficient catalyst in the guanylation reaction of amines

Tris(pentafluorophenyl)borane, [B(C6F5)3], has been used as an efficient catalyst in the guanylation reaction of amines with carbodiimide under mild conditions. A combined approach involving NMR spectroscopy and DFT calculations was employed to gain a better insight into the mechanistic features of this process. The results allowed us to propose a new Lewis acid-assisted Brønsted acidic pathway for the guanylation reaction. The process starts with the interaction of tris(pentafluorphenyl)borane and the amine to form the corresponding adduct, [(C6F5)3B-NRH2] , followed by a straightforward proton transfer to one of the nitrogen atoms of the carbodiimide, (i)PrN[double bond, length as m-dash]C[double bond, length as m-dash]N(i)Pr, to produce, in two consequent steps, a guanidine-borane adduct, [(C6F5)3B-NRC(N(i)PrH)2] . The rupture of this adduct liberates the guanidine product RNC(N(i)PrH)2 and interaction with additional amine restarts the catalytic cycle. DFT studies have been carried out in order to study the thermodynamic characteristics of the proposed pathway. Significant borane adducts with amines and guanidines have been isolated and characterized by multinuclear NMR in order to study the N-B interaction and to propose the existence of possible Frustrated Lewis Pairs. Additionally, the molecular structures of significant components of the catalytic cycle, namely 4-tert-butylaniline-[B(C6F5)3] adduct and both free and [B(C6F5)3]-bonded 1-(phenyl)-2,3-diisopropylguanidine, and respectively, have been established by X-ray diffraction.

A non-oxo methanolate-bridged divanadium(IV) complex with tris(2-sulfanidylphenyl)phosphane ligands: synthesis, structural characterization and magnetic investigation

Vanadium chemistry is of interest due its biological relevance and medical applications. In particular, the interactions of high-valent vanadium ions with sulfur-containing biologically important molecules, such as cysteine and glutathione, might be related to the redox conversion of vanadium in ascidians, the function of amavadin (a vanadium-containing anion) and the antidiabetic behaviour of vanadium compounds. A mechanistic understanding of these aspects is important. In an effort to investigate high-valent vanadium-sulfur chemistry, we have synthesized and characterized the non-oxo divanadium(IV) complex salt tetraphenylphosphonium tri-μ-<!?tlsb=-0.11pt>methanolato-κ(6)O:O-bis({tris[2-sulfanidyl-3-(trimethylsilyl)phenyl]phosphane-κ(4)P,S,S',S''}vanadium(IV)) methanol disolvate, (C24H20P)[V(IV)2(μ-OCH3)3(C27H36PS3)2]·2CH3OH. Two V(IV) metal centres are bridged by three methanolate ligands, giving a C2-symmetric V2(μ-OMe)3 core structure. Each V(IV) centre adopts a monocapped trigonal antiprismatic geometry, with the P atom situated in the capping position and the three S atoms and three O atoms forming two triangular faces of the trigonal antiprism. The magnetic data indicate a paramagnetic nature of the salt, with an S = 1 spin state.

Dialkylboron guanidinates: syntheses, structures and carbodiimide de-insertion reactions

Solutions of some of the title compounds reached an equilibrium with the aminoboranes and the corresponding carbodiimides at room temperature.

Recent development of synthetic preparation methods for guanidines via transition metal catalysis

This article provides an overview of guanidine synthesis via transition-metal-catalyzed reactions including cycloaddition, guanylation and tandem guanylation/cyclization.

Catalyst free C–N bond formation by the reaction of amines with diimides: bulky guanidines

Catalyst free direct addition of cyclic secondary amines to various N,N′-bisaryl substituted carbodiimides led to the formation of bulky guanidines. Furthermore, two equivalents of N,N′-bisaryl substituted carbodiimides upon treatment with piperazine led to the formation of bis guanidines.

Guanidines: from classical approaches to efficient catalytic syntheses

This review focuses on the metal-mediated catalytic addition of amines to carbodiimides as an atom-economical alternative to the classical synthesis of guanidines.