Further Insight into the Castagnoli-Cushman-type Synthesis of 1,4,6-Trisubstituted 1,6-Dihydropyridin-2-(3H)-ones from 3-Arylglutaconic Acid Anhydrides

The earlier reported three-component Castagnoli-Cushman-type synthesis of 1,4,6-trisubstituted 1,6-dihydropyridin-2-(3H)-ones from 3-arylglutaconic acids, primary amines, and aromatic aldehydes has been further investigated. It was shown to proceed via 3-arylglutaconic anhydrides, which, in turn, were found to give superior results in the two-component reactions with imines. The initial formation of the Castagnoli-Cushman carboxylic acids was shown to be the case, and their decarboxylation was found to follow a complex, "forked" pathway, which was confirmed by deuterium incorporation experiments.

Facile One-Pot Access to α-Diazo-β-ketosulfones from Sulfonyl Chlorides and α-Haloketones

A convenient one-pot approach to the preparation of α-diazo-β-ketosulfones from sulfonyl chlorides is described. It involves the conversion of the sulfonyl chloride to sodium sulfinate, alkylation of the latter with α-haloketones followed by diazo transfer using the ‘sulfonyl-azide-free’ (‘SAFE’) protocol in aqueous medium. The simple and expedient method relies on readily available starting materials and provides facile access to a wide variety of valuable diazo reagents for organic synthesis.

Preparation and in situ use of unstable N-alkyl α-diazo-γ-butyrolactams in RhII-catalyzed X-H insertion reactions

N-Alkyl α-diazo-γ-butyrolactams, previously found to be unstable and to undergo unproductive dimerization to bishydrazones, were successfully converted immediately to various X–H insertion products with alcohols, aromatic amines and thiols via an in situ Rh^II-catalyzed reaction. With aliphatic amines or unreactive, sterically hindered anilines, the reactions tended to yield enamine adducts.

Realizing the Trifunctional Potential of Alkyl 4-Chloro-2-diazo-3-oxobutanoates: Convenient Assembly of 6,7-Dihydro-4H-[1,2,3]triazolo[5,1-c][1,4]thiazine Core

The first example of exploiting the trifunctional character of alkyl 4-chloro-2-diazo-3-oxobutanoates in the reactions with vicinal N,S-bis-nucleophiles leading to the formation of bicyclic 6,7-dihydro-4H-[1,2,3]triazolo[5,1-c][1,4]thiazines is presented. The key to the successful realization of the atom-economical synthetic strategy is the initial S N 2 event, which facilitates the subsequent domino 1,2,3-triazole formation via the Wolff reaction. Equally important is the choice of sodium acetate as the base: acetic acid formed in the course of the initial nucleophilic substitution acts as an efficient catalyst for the Wolff reaction, which suppresses the competing, unwanted fragmentation path (observed when other bases are used).

Sulfocoumarins as dual inhibitors of human carbonic anhydrase isoforms IX/XII and of human thioredoxin reductase

The hypothesis that sulfocoumarin acting as inhibitors of human carbonic anhydrase (CA, EC 4.2.1.1) cancer-associated isoforms hCA IX and – hCA XII is being able to also inhibit thioredoxin reductase was verified and confirmed. The dual targeting of two cancer cell defence mechanisms, i.e. hypoxia and oxidative stress, may both contribute to the observed antiproliferative profile of these compounds against many cancer cell lines. This unprecedented dual anticancer mechanism may lead to a new approach for designing innovative therapeutic agents.

α-Diazoacetamides in Sc(OTf)3-Catalyzed Tiffeneau–Demjanov Ring Expansion: Application towards the Synthesis of Rare Bicyclic Pyrazoles

A novel Sc(OTf)3-catalyzed Tiffeneau–Demjanov ring expansion of six-membered cyclic ketones has been developed. The resulting seven-membered cyclic β-keto carboxamides were found to be versatile precursors to rare bicyclic pyrazoles obtained in modest to good yields via condensation with aryl hydrazines in the presence of Lawesson’s reagent.

7-Acylamino-3H-1,2-benzoxathiepine 2,2-dioxides as new isoform-selective carbonic anhydrase IX and XII inhibitors

A series of 3H-1,2-benzoxathiepine 2,2-dioxides incorporating 7-acylamino moieties were obtained by an original procedure starting from 5-nitrosalicylaldehyde, which was treated with propenylsulfonyl chloride followed by Wittig reaction of the bis-olefin intermediate. The new derivatives, belonging to the homosulfocoumarin chemotype, were assayed as inhibitors of the zinc metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). Four pharmacologically relevant human (h) isoforms were investigated, the cytosolic hCA I and II and the transmembrane, tumour-associated hCA IX and XII. No relevant inhibition of hCA I and II was observed, whereas some of the new derivatives were effective, low nanomolar hCA IX/XII inhibitors, making them of interest for investigations in situations in which the activity of these isoforms is overexpressed, such as hypoxic tumours, arthritis or cerebral ischaemia.

Plants of the Russian Federation pharmacopeia: an unexhausted natural products research opportunity?

32 medicinal plants that are unique to the Russian Pharmacopeia have 693 isolated natural products associated with them (an average of 21.66 compounds per plant). This is in contrast to the US Pharmacopeia plants that have delivered 2366 known natural products (an average of 42.25 compounds per plant).

Further exploration of DVD-445 as a lead thioredoxin reductase (TrxR) inhibitor for cancer therapy: Optimization of potency and evaluation of anticancer potential

A series of analogs of the earlier reported lead compound DVD-445 (thioredoxin reductase inhibitor with anticancer activity) has been synthesized via a modified Ugi reaction and investigated. Seven most potent compounds (with IC₅₀ below 5.00 μM against recombinant rTrxR1 enzyme) were examined for their effect on cell growth and viability, oxidative stress induction and P-glycoprotein (P-gp) inhibition in human glioblastoma cells cell line U87 and its corresponding multidrug resistant (MDR) cell line U87-TxR. Several of these frontrunner compounds were shown to be superior over DVD-445. Besides providing promising candidates for anticancer therapy, our study further validates the small electrophilic Ugi Michael acceptor (UMA) chemotype as efficacious inhibitor of thioredoxin reductase.

Aryl derivatives of 3H-1,2-benzoxathiepine 2,2-dioxide as carbonic anhydrase inhibitors

A new series of homosulfocoumarins (3H-1,2-benzoxathiepine 2,2-dioxides) possessing various substitution patterns and moieties in the 7, 8 or 9 position of the heterocylic ring were prepared by original procedures and investigated for the inhibition of four physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the human (h) hCA I, II, IX and XII. The 8-substituted homosulfocoumarins were the most effective hCA IX/XII inhibitors followed by the 7-substituted derivatives, whereas the substitution pattern in position 9 led to less effective binders for the transmembrane, tumour-associated isoforms IX/XII. The cytosolic isoforms hCA I and II were not inhibited by these compounds, similar to the sulfocoumarins/coumarins investigated earlier. As hCA IX and XII are validated anti-tumour targets, with one sulphonamide (SLC-0111) in Phase Ib/II clinical trials, finding derivatives with better selectivity for inhibiting the tumour-associated isoforms over the cytosolic ones, as the homosulfocoumarins reported here, is of crucial importance.

Further validation of strecker-type α-aminonitriles as a new class of potent human carbonic anhydrase II inhibitors: hit expansion within the public domain using differential scanning fluorimetry leads to chemotype refinement

Testing of an expanded, 800-compound set of analogues of the earlier described Strecker-type α-aminonitriles (selected from publicly available Enamine Ltd. Screening Collection) in thermal shift assay against bovine carbonic anhydrase (bCA) led to further validation of this new class of inhibitors and identification a new, refined chemotype represented by inhibitors with 10-improved potency.

Spirocyclic Motifs in Natural Products

Spirocyclic motifs are emerging privileged structures for drug discovery. They are also omnipresent in the natural products domain. However, until today, no attempt to analyze the structural diversity of various spirocyclic motifs occurring in natural products and their relative populations with unique compounds reported in the literature has been undertaken. This review aims to fill that void and analyze the diversity of structurally unique natural products containing spirocyclic moieties of various sizes.

Practical Application of the Aqueous ‘Sulfonyl-Azide-Free’ (SAFE) Diazo Transfer Protocol to Less α-C–H Acidic Ketones and Esters

The earlier described ‘sulfonyl-azide-free’ (‘SAFE’) protocol for diazo transfer to CH-acidic 1,3-dicarbonyl compounds (and their similarly activated congeners) has been extended to the less reactive monocarbonyl substrates, which previously required a separate activation step. Formylation in situ, followed by the addition of an optimized amount of the ‘SAFE cocktail’ (obtained by mixing sodium azide, potassium carbonate, and m-carboxybenzenesulfonyl chloride in water) led to the formation of the desired diazo compounds, which were isolated by extraction in moderate to excellent yields, and, in most cases, with no need for additional purification.