The Use of Chloroformamidine Hydrochloride as a Reagent for the Synthesis of Guanidines from Electron Deficient Aromatic Amines

Abstract

in Wiley Online Library (wileyonlinelibrary.com).In efforts to optimize a manufacturing process for an internal development compound, a clean, efficient approach to guanidine synthesis using chloroformamidine hydrochloride was identified. To investigate the general utility of this methodology towards electron-deficient aromatic amines, a set of favorable conditions were developed from a series of screens, and the scope of the reaction was probed. The successful application of this chemistry to a variety of pyridines, anilines, and heterocyclic compounds highlights its use as an improved, alternative guanylation method for this often challenging set of aromatic amines.J. Heterocyclic Chem., 00, 00 (2015).Guanidines are of great importance in the pharmaceutical industry due to their many synthetic applications, often being utilized as heterocyclic precursors, strong bases and catalysts, and their alkaloids have exhibited a broad range of antimicrobial and antitumor activities [1]. For these reasons, much effort has gone into the development of facile, efficient guanylating reagents. Many methods for the synthesis of substituted guanidines reported in the literature often perform well with electron-rich amines, but only modestly, if at all, with electron-deficient aromatic amines [1]. This paper reports a clean, convenient one-pot synthesis of guanidines from electron-deficient aromatic amines using chloroformamidine hydrochloride as the guanylating reagent.The methodology presented herein evolved from the need to identify and develop a scalable synthesis for a guanidine intermediate 2 associated with an internal development project (Scheme 1) [2]. The initial focus for this transformation was on utilizing the two most common approaches to guanidines from electron-deficient aromatic amines. Our first attempts involved the reaction of pyridine amine 1 with bis-Boc-thiourea in the presence of activating agents such as HgCl 2 , CuCl 2 , or Mukaiyama's reagent, followed by deprotection of the resulting Boc-protected guanidine (Scheme 1, Method A) [3]. The use of stoichiometric amounts of metal salts, removal of by-products, poor atom efficiency, column chromatography, and low yields made this method inappropriate for further scale up.The second guanylation strategy utilized cyanamide activated by an acid, often HCl, to generate the formamidine species in situ followed by reaction with an amine to affect guanidine formation (Scheme 1, Method B) [4]. The main limitation encountered was the small number of solvent options associated with commercially available acid solutions and water in aqueous acids. Many of those solvents hindered reagent and substrate solubility, reaction temperature, and hence reaction completion. In addition, degradation of the active formamidine reagent occurred over time as a result of reaction with the nucleophilic solvents used. When this method was attempted on starting material 1, this degradation was significant with EtOH as solvent and portionwise dosing of 12 equivalents of cyanamide over 26...

Improved Synthesis of the Selected Serine Protease uPA Inhibitor UAMC-00050, a Lead Compound for the Treatment of Dry Eye Disease

“…We investigated a direct way to convert aniline HCl salt 24 to product 1 , reducing the step count, increasing the overall yield, and cutting the cost. A range of literature methods is available for the direct transformation of aniline to aryl guanidine. − From these, guanylation with cyanamide was selected to develop the protocol with the best atom economy and costs. , However, heating aniline HCl salt 24 with cyanamide in a protic solvent in the presence of a Brønsted or a Lewis acid led to a decomposition of the α-aminophosphonate. Therefore, we investigated the guanylation of aniline salt 24 with 1.2 equiv of cyanamide in the presence of 0.1 equiv of Sc­(OTf) 3 in a panel of solvents and solvent mixtures at room temperature (see the Supporting Information).…”

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“…Previously, few reports have described this compound. Its chemical structure is similar to that of aniline [ 2 ], which is oxidized into phenylhydroxylamine analogs after entering the human body, thereby causing methemoglobinemia, hemolytic anemia, abnormal liver and kidney function, and nervous system damage [ 4 , 5 ]. Our patient experienced similar symptoms, and laboratory findings confirmed the diagnosis of methemoglobinemia [ 6 ].…”

“…It causes severe eye, skin, and respiratory tract irritation as well as allergic skin reactions, or even death if ingested [ 1 ]. It acts as an intermediate in medicine and various chemical products [ 2 , 3 ]. However, to our knowledge, there are no systematic studies on the toxicology profile of 5-amino-2-(trifluoromethyl)pyridine, nor a relevant clinical profile.…”

Regioisomer Formation with Agmatine Guanidino Group, Its Implications for Agmatine Peptide Cyclization, and Application of Bis-Boc-Agmatine

“…Amidination of amine is one of the most prominent guanidine synthetic methodologies to build agmatine structure. Direct or indirect electrophilic guanylating agents including carbodiimide, O -methylisourea, thiourea, isothiourea, amino­(imino)­methanesulfonic acid, chloroformamidine, 1 H -pyrazole-1-carboxamidine, N -triflylguanidine, and cyanamide have been traditionally employed to transform amines to the corresponding protected or nonprotected guanidine compounds.…”