Synthesis of Spironucleosides: Past and Future Perspectives

Gold(I)-Catalyzed Reactions of exo-Glycals with Propargyl Esters toward C-1 Alkenyl Spirocyclopropyl Carbohydrates

An atom-economic and diazo-free strategy for the construction of novel pseudo anomeric C-1 alkenyl spirocyclopropyl sugars is described. Leveraging the 1,2-migration pathway of propargyl esters under gold(I) catalysis, easily available exo-glycals undergo β-selective alkenylcarbenoid insertion in moderate to excellent yields. Preferential activation of propargyl moieties and concerted [2 + 1] insertion are both favored through ligand choice and electron enrichment of esters. Stereocontrol using conformational bias and rearrangement are also demonstrated.

Recent advances in microwave-assisted multicomponent synthesis of spiro heterocycles

Spiro heterocycle frameworks are a class of organic compounds that possesses unique structural features making them highly sought-after targets in drug discovery due to their diverse biological and pharmacological activities. Microwave-assisted organic synthesis has emerged as a powerful tool for assembling complex molecular architectures. The use of microwave irradiation in synthetic chemistry is a promising method for accelerating reaction rates and improving yields. This review provides insights into the current state of the art and highlights the potential of microwave-assisted multicomponent reactions in the synthesis of novel spiro heterocyclic compounds that were reported between 2017 and 2023.

Recent developments using malononitrile in ultrasound-assisted multicomponent synthesis of heterocycles

Ultrasonic irradiation serves as a vigorous and environmentally sustainable approach for augmenting multicomponent reactions (MCRs), offering benefits such as thermal enhancement, agitation, and activation, among others. Malononitrile emerges as a versatile reagent in this context, participating in a myriad of MCRs to produce structurally diverse heterocyclic frameworks. This review encapsulates the critical role of malononitrile in the sonochemical multicomponent synthesis of these heterocyclic structures. The paper further delves into the biochemical and pharmacological implications of these heterocycles, elucidating their reaction mechanisms as well as delineating the method's scope and limitations. We furnish an overview of the merits and challenges inherent to this synthetic approach and offer insights for potential avenues in future research.

[4+2]-Cycloaddition to 5-Methylidene-Hydantoins and 5-Methylidene-2-Thiohydantoins in the Synthesis of Spiro-2-Chalcogenimidazolones

Novel hydantion and thiohydantoin-based spiro-compounds were prepared via theDiels-Alder reactions between 5-methylidene-hydantoins or 5-methylidene-2-thiohydantoins and 1,3-dienes (cyclopentadiene, cyclohexadiene, 2,3-dimethylbutadiene, isoprene). It was shown that the cycloaddition reactions proceed regioselectively and stereoselectively with the formation of exo-isomers in the reactions with cyclic dienes andthe less sterically hindered products in the reactions with isoprene. Reactions of methylideneimidazolones with cyclopentadiene proceed viaco-heating the reactants; reactions with cyclohexadiene, 2,3-dimethylbutadiene, and isoprene require catalysis by Lewis acids. It was demonstrated that ZnI₂ is an effective catalyst in the Diels-Alder reactions of methylidenethiohydantoins with non-activated dienes. The possibility of alkylation and acylation of the obtained spiro-hydantoinsat the N(1)nitrogen atoms with PhCH₂Cl or Boc₂O and the alkylation of the spiro-thiohydantoinsat the S atoms with MeI or PhCH₂Cl in high yields have been demonstrated. The preparativetransformation of spiro-thiohydantoins into corresponding spiro-hydantoinsin mild conditions by treating with 35% aqueous H₂O₂ or nitrile oxide has been carried out. The obtained compounds show moderate cytotoxicity in the MTT test on MCF7, A549, HEK293T, and VA13 cell lines. Some of the tested compounds demonstrated some antibacterial effect against Escherichia coli (E. coli) BW25113 DTC-pDualrep2 but were almost inactive against E. coli BW25113 LPTD-pDualrep2.

Spiro Derivatives in the Discovery of New Pesticides: A Research Review

Spiro compounds are biologically active organic compounds with unique structures, found in a wide variety of natural products and drugs. They do not readily lead to drug resistance due to their unique mechanisms of action and have, therefore, attracted considerable attention regarding pesticide development. Analyzing structure-activity relationships (SARs) and summarizing the characteristics of spiro compounds with high activity are crucial steps in the design and development of new pesticides. This review mainly summarizes spiro compounds with insecticidal, bactericidal, fungicidal, herbicidal, antiviral, and plant growth regulating functions to provide insight for the creation of new spiro compound pesticides.

Synthesis of Spirocyclic Cyclopropyl Glycosyl-1-phosphate Analogues

A general methodology allowing the preparation of phosphonylated 1-spirocyclopropyl analogues of glycosyl-1-phosphates is reported. The scope of this reaction has been assessed using various exo-glycals easily obtained from the corresponding pyranoses and furanoses. The cyclopropanation was found to be stereospecific, and the cis/trans selectivity only depends on the E/Z configuration of the starting exo-glycal. The four possible isomers of spirocyclopropyl ribose-1-phosphonate could thus be prepared in a controlled manner, protected and deprotected.

Regio- and Stereoselective Synthesis of C-4' Spirocyclobutyl Ribofuranose Scaffolds and Their Use as Biologically Active Nucleoside Analogues

Novel C-4',C-5' cyclobutane-fused spirocyclic ribonucleoside analogues were prepared. Thermal [2 + 2] cycloaddition between dichloroketene and readily derived 4'-exo-methylene furanoses afforded a first entry to the required constrained ribofuranoses, relying on a carbonyl transposition sequence. Alternatively, an unusual stereoselective ionic [2 + 2] cycloaddition using methyl propiolate promoted by methylaluminoxane gave a complementary, more direct approach to such ribofuranoses. Further conversion to the constrained adenosine analogues revealed promising structure-dependent inhibition of the protein methyltransferase PRMT5:MEP50 complex in the (sub)micromolar range.

Ultrasound-assisted synthesis of pyrimidines and their fused derivatives: A review

The pyrimidine scaffold is present in many bioactive drugs; therefore, efficient synthetic routes that provide shorter reaction times, higher yields, and site-selective reactions are constantly being sought. Ultrasound (US) irradiation has emerged as an alternative energy source in the synthesis of these heterocyclic scaffolds, and over the last ten years there has been a significant increase in the number of publications mentioning US in either the construction or derivatization of the pyrimidine core. This review presents a detailed summary (with 140 references) of the effects of US (synergic or not) on the construction and derivatization of the pyrimidine core through classical reactions (e.g., multicomponent, cyclocondensation, cycloaddition, and alkylation reactions). The main points that were taken into consideration are as follows: chemo- and regioselectivity issues, and the results of conventional heating methods compared to US and mechanistic insights that are also presented and discussed for key reactions.

Chemo-enzymatic access to C-4′-hydroxyl-tetrahydrofurano-spironucleosides

The biocatalytic synthesis of C-4′-hydroxyl-tetrahydrofurano-spironucleosides where the tetrahydrofuranospirocyclic ring at C-4′ position locks the furanose ring of nucleosides in the NE-conformation (C4′-exo).

Glucopyranosylidene-spiro-benzo[ b][1,4]oxazinones and -benzo[ b][1,4]thiazinones: Synthesis and Investigation of Their Effects on Glycogen Phosphorylase and Plant Growth Inhibition

Glucopyranosylidene-spiro-benzo[ b][1,4]oxazinones were obtained via the corresponding 2-nitrophenyl glycosides obtained by two methods: (a) AgOTf-promoted glycosylation of 2-nitrophenol derivatives by O-perbenzoylated methyl (α-d-gluculopyranosyl bromide)heptonate or (b) Mitsunobu-type reactions of O-perbenzoylated methyl (α-d-gluculopyranose)heptonate with bulky 2-nitrophenols in the presence of diethyl azodicarboxylate (DEAD) and PPh₃. Catalytic hydrogenation (H₂-Pd/C) or partial reduction (e.g., H₂-Pd/C, pyridine) of the 2-nitro groups led to spiro-benzo[ b][1,4]oxazinones and spiro-benzo[ b][1,4]-4-hydroxyoxazinones by spontaneous ring closure of the intermediate 2-aminophenyl or 2-hydroxylamino glycosides, respectively. The analogous 2-aminophenyl thioglycosides, prepared by reactions of O-perbenzoylated methyl (α-d-gluculopyranosyl bromide)heptonate with 2-aminothiophenols, were cyclized in m-xylene at reflux temperature to the corresponding spiro-benzo[ b][1,4]thiazinones. O-Debenzoylation was effected by Zemplén transesterification in both series. Spiro-configurations were determined by NMR and electronic circular dichroism time-dependent density functional theory (ECD-TDDFT) methods. Inhibition assays with rabbit muscle glycogen phosphorylase b showed (1' R)-spiro{1',5'-anhydro-d-glucitol-1',2-benzo[ b][1,4]oxazin-3(4 H)-one} and (1' R)-spiro{1',5'-anhydro-d-glucitol-1',2-benzo[ b][1,4]thiazin-3(4 H)-one} to be the most efficient inhibitors (27 and 28% inhibition at 625 μM, respectively). Plant growth tests with white mustard and garden cress indicated no effect except for (1' R)-4-hydroxyspiro{1',5'-anhydro-d-glucitol-1',2-benzo[ b][1,4]oxazin-3(4 H)-one} with the latter plant to show modest inhibition of germination (95% relative to control).