The sulfonimidamide as a novel transition state analog for aspartic acid and metallo proteases

Unifying N-Sulfinylamines with Alkyltrifluoroborates by Organophotoredox Catalysis: Access to Functionalized Alkylsulfinamides and High-Valent S(VI) Analogues

We describe an organophotoredox-catalyzed sp3 C-S coupling of N-sulfinylamines with bench-stable alkyltrifluoroborates as a latent nucleophilic counterpart en route to alkylsulfinamides in high efficiency. In contrast to the two-electron reactivity of traditional organometallic reagents, this catalytic method reports the single-electron process of an organometallic reagent with N-sulfinylamines in C-S coupling. This mild and scalable protocol offers operational simplicity and exceptional functional group compatibility, including ketone, ester, amide, nitrile, and halides, that is vulnerable to organolithium or Grignard reagents. Additionally, the sulfinamides are conveniently converted to a variety of important S(VI) compounds, like sulfonamides, sulfonimidamides, and sulfonimidates, among others.

Mechanochemical Iron-Catalyzed Nitrene Transfer Reactions: Direct Synthesis of N-Acyl Sulfonimidamides from Sulfinamides and Dioxazolones

A mechanochemical synthesis of sulfonimidamides by iron(II)-catalyzed exogenous ligand-free N-acyl nitrene transfer to sulfinamides is reported. The one-step method tolerates a wide range of sulfinamides with various substituents under solvent-free ambient conditions. Compared to its solution-phase counterpart, this mechanochemical approach shows better conversion and chemoselectivity. Mechanistic investigations by ESI-MS revealed the generation of crucial nitrene iron intermediates.

Exploiting Configurational Lability in Aza-Sulfur Compounds for the Organocatalytic Enantioselective Synthesis of Sulfonimidamides

Methods for establishing the absolute configuration of sulfur‐stereogenic aza‐sulfur derivatives are scarce, often relying on cumbersome protocols and a limited pool of enantioenriched starting materials. We have addressed this by exploiting, for the first time, a feature of sulfonimidamides in which it is possible for tautomeric structures to also be enantiomeric. Such sulfonimidamides can readily generate prochiral ions, which we have exploited in an enantioselective alkylation process. Selectivity is achieved using a readily prepared bis‐quaternized phase‐transfer catalyst. The overall process establishes the capability of configurationally labile aza‐sulfur species to be used in asymmetric catalysis.

Recent Developments in the Practical Application of Novel Carboxylic Acid Bioisosteres

BACKGROUND

The carboxylic acid is an important functional group which features in the pharmacophore of some 450 drugs. Unfortunately, some carboxylic acid-containing drugs have been withdrawn from market due to unforeseen toxicity issues. Other issues associated with the carboxylate moiety include reduced metabolic stability or limited passive diffusion across biological membranes. Medicinal chemists often turn to bioisosteres to circumvent such obstacles.

OBJECTIVE

The aim of this review is to provide a summary of the various applications of novel carboxylic acid bioisosteres which have appeared in the literature since 2013.

RESULTS

We have summarised the most recent developments in carboxylic acid bioisosterism. In particular, we focus on the changes in bioactivity, selectivity or physiochemical properties brought about by these substitutions, as well as the advantages and disadvantages of each isostere.

CONCLUSION

The topics discussed herein highlight the continued interest in carboxylate bioisosteres. The development of novel carboxylic acid substitutes which display improved pharmacological profiles is testament to the innovation and creativity required to overcome the challenges faced in modern drug design.

Modern Stereoselective Synthesis of Chiral Sulfinyl Compounds

Chiral sulfinyl compounds, sulfoxides, sulfoximines, sulfinamides, and other derivatives, play an important role in asymmetric synthesis as versatile auxiliaries, ligands, and catalysts. They are also recognized as pharmacophores found in already marketed and well-sold drugs (e.g., esomeprazole) and used in drug design. This review is devoted to the modern methods of preparation of sulfinyl derivatives in enantiopure or enantiomerically enriched form. Selected new approaches leading to racemic products for which the asymmetric variant can be developed in the future are mentioned as well.

Synthesis and functionalization of cyclic sulfonimidamides: a novel chiral heterocyclic carboxylic Acid bioisostere

An efficient synthesis of aryl substituted cyclic sulfonimidamides designed as chiral nonplanar heterocyclic carboxylic acid bioisosteres is described. The cyclic sulfonimidamide ring system could be prepared in two steps from a trifluoroacetyl protected sulfinamide and methyl ester protected amino acids. By varying the amino acid, a range of different C-3 substituted sulfonimidamides could be prepared. The compounds could be further derivatized in the aryl ring using standard cross-coupling reactions to yield highly substituted cyclic sulfonimidamides in excellent yields. The physicochemical properties of the final compounds were examined and compared to those of the corresponding carboxylic acid and tetrazole derivatives. The unique nonplanar shape in combination with the relatively strong acidity (pK a 5-6) and the ease of modifying the chemical structure to fine-tune the physicochemical properties suggest that this heterocycle can be a valuable addition to the range of available carboxylic acid isosteres.

Progress in metallocarboxypeptidases and their small molecular weight inhibitors

In what corresponds to a life span, metallocarboxypeptidases (MCPs) have jumped from being mere contaminants in animal pancreas powders (in depression year 1929) to be key players in cellular and molecular processes (in yet-another-depression years 2009-2010). MCPs are unique zinc-dependent enzymes that catalyze the breakdown of the amide bond at the C-terminus of peptide and protein substrates and participate in the recovery of dietary amino acids, tissue organogenesis, neurohormone and cytokine maturation and other important physiological processes. More than 26 genes code for MCPs in the human genome, many of them still waiting to be fully understood in terms of physiological function. A variety of MCPs have been linked to diseases in man: acute pancreatitis and pancreas cancer, type 2 diabetes, Alzheimer's Disease, various types of cancer, and fibrinolysis and inflammation. Many of these discoveries have been made possible thanks to recent advances, as exemplified by plasma carboxypeptidases N and B, known for fifty and twenty years, respectively, which have had their structures released only very recently. Plasma carboxypeptidase B is a biological target for therapy because of its involvement in the coagulation/fibrinolysis processes. Besides, the widespread use of carboxypeptidase A as a benchmark metalloprotease since the early days of Biochemistry has allowed the identification and design of an increasingly vast repertory of small molecular weight inhibitors. With these two examples we wish to emphasize that MCPs have become part of the drug discovery portfolio of pharmaceutical companies and academic research laboratories. This paper will review key developments in the discovery and design of MCP small molecular weight inhibitors, with an emphasis on the discovery of chemically diverse entities. Although encouraging advances have been achieved in the last few years, the specificity and oral bioavailability of the new chemotherapeutic agents seem to pose a challenge to medicinal chemists.

Synthesis of enantiopure sulfonimidamides and elucidation of their absolute configuration by comparison of measured and calculated CD spectra and X-ray crystal structure determination

Straightforward syntheses of enantiopure N-benzoyl- and N-tert-butyloxycarbonyl-protected sulfonimidamides, which can be used as building blocks in newly designed catalysts, are presented. Key synthetic step is a dynamic resolution of a racemic sulfinic acid sodium salt. All subsequent transformations proceed stereospecifically. The absolute configurations at the sulfur atoms of both sulfonimidamides were determined by comparison of measured and calculated CD spectra. An X-ray crystal structure determination of a sulfonimidoylguanidine derivative confirmed this result.

Toward a synthetically useful stereoselective C-H amination of hydrocarbons

Reaction between a sulfur(VI) compound and an iodine(III) oxidant in the presence of a catalytic quantity (<=3 mol %) of a rhodium(II) catalyst leads to the formation of a chiral metallanitrene of unprecedented reactivity. The latter allows intermolecular C-H amination to proceed in very high yields up to 92% and excellent diastereoselectivities up to 99% with C-H bond containing starting materials as the limiting component. The scope of this C-H functionalization includes benzylic and allylic substrates as well as alkanes. Secondary positions react preferentially, but insertion into activated primary C-H bonds or sterically accessible tertiary sites is also possible. Cooperative effects between the nitrene precursor and the chiral catalyst at the origin of these good results have also been applied to kinetic resolution of racemic sulfonimidamide. This methodology paves the way to the use of Csp3-H bonds as synthetic precursors for the introduction of a nitrogen functionality into selected positions.

Synthesis of sulfonimidamides from sulfinamides by oxidation with N-chlorosuccinimide

BACKGROUND

The synthesis of sulfonimidamides involves the nucleophilic substitution of a sulfonimidoyl chloride with an amine. However, only four chlorinating systems have been reported for the preparation of the sulfonimidoyl chloride intermediates. Whereas some of them have shown a rather limited substrate spectrum, the most versatile and commonly used tert-butyl hypochlorite is known to be explosive. To establish alternative methods for the synthesis of these molecules is therefore desirable.

RESULTS

The preparation of various p-tolylsulfonimidamides through the reaction of the corresponding N-protected p-tolylsulfinamides and a number of amines in the presence of N-chlorosuccinimide was achieved at room temperature in 50-97% yield.

CONCLUSION

A convenient alternative procedure for the synthesis of sulfonimidamides from sulfinamides and various amines and sulfonamides using N-chlorosuccinimide as halogenating agent has been developed.

Sulfonimidamides: Efficient Chiral Iminoiodane Precursors for Diastereoselective Copper-Catalyzed Aziridination of Olefins

N-(p-Toluenesulfonyl)-p-toluenesulfonimidamide reacts with iodosylbenzene to afford in situ a chiral iminoiodane. The latter gives, in the presence of a copper(I) catalyst, a nitrene that is very efficiently transferred under stoichiometric conditions to a variety of alkenes with diastereoselectivities up to 60%. [reaction: see text]

Sulfamide-based inhibitors for carboxypeptidase A. Novel type transition state analogue inhibitors for zinc proteases

N-Sulfamoylphenylalanine and its derivatives having varied alkyl groups on the terminal amino group were designed rationally as transition state analogue inhibitors for carboxypeptidase A (CPA) and synthesized. In CPA inhibitory assays the parent compound having the (S)-configuration, i.e., (S)-1a, showed potent inhibitory activity with the K(i) value of 0.64 microM. Its enantiomer was shown to be much less potent (K(i) = 470 microM). Introduction of an alkyl group such as methyl or isopropyl group on the terminal amino group of (S)-1a lowered the inhibitory potency drastically. Introduction of a methyl group on the internal amino group of (S)-1a also caused a drastic reduction of the inhibitory activity. The structure of the CPA x(S)-1a complex determined by single-crystal X-ray diffraction reveals that the sulfamoyl moiety interacts with the zinc ion and functional groups at the active site of CPA, which is reminiscent of the postulated stabilization mode of a tetrahedral transition state in the CPA-catalyzed hydrolysis of a peptide substrate. On the basis of the design rationale and the binding mode of (S)-1a to CPA shown by X-ray crystallographic analysis, the present inhibitors are inferred to be a novel type of transition state analogue inhibitor for CPA.