10.1016/j.tetlet.2011.07.035
The research presents a stereoselective synthesis of the naturally occurring pyrrolidine alkaloid, (+)-radicamine B, which possesses significant biological properties. The synthesis involves 13 steps, starting from commercially available p-hydroxybenzaldehyde, with an overall yield of 9.75%. Key reactions include Sharpless asymmetric epoxidation and Horner–Wadsworth–Emmons (HWE) olefination. Reactants used throughout the synthesis include p-hydroxybenzaldehyde, tosyl chloride, (+)-DET, NaN3, PPh3, Boc anhydride, benzaldehyde dimethylacetal, DIBAL-H, IBX, (OEt)2PO(CH2COOEt), and (+)-DIPT, among others. Analytical techniques employed to characterize the intermediates and final product included 1H NMR, 13C NMR, Mass spectrometry, and IR spectroscopy, with enantioselectivity determined by chiral HPLC. The study also discusses the biological significance of radicamine B and the challenges in its asymmetric synthesis, highlighting the efficiency and linearity of their developed synthetic protocol.
10.1016/j.tet.2005.12.002
The study focuses on the synthesis and characterization of a novel cationic, chiral peptide nucleic acid (PNA) analogue known as backbone extended pyrrolidine PNA (bepPNA), which is designed for selective recognition of RNA over DNA. The bepPNA features an additional carbon atom in the backbone and a (2S,4S) geometry of the pyrrolidine ring, optimizing the internucleobase distance for triplex mode binding. The researchers used various chemicals in the synthesis process, including trans-4-hydroxy-L-proline, LiCl/NaBH4 for reduction, p-TsCl for tosylation, NaN3 for azide formation, Raney Ni for reduction, BocN3 for protection, and Pd–C catalyst for hydrogenation. These chemicals served to protect, modify, and transform the PNA structure at different stages of the synthesis. The study also involved the use of UV–Tm measurements, gel electrophoretic shift assays, and circular dichroism analysis to evaluate the binding properties of bepPNA in both triplex and duplex modes. The purpose of these chemicals and methods was to create a PNA analogue with improved binding affinity and selectivity towards RNA, which has potential applications in gene-targeted therapeutics and molecular diagnostics.
10.1016/S0957-4166(97)00121-3
The research aimed to develop a stereocontrolled synthesis method for producing stereoregular, chiral analogs of nylon 5,5 and nylon 5,6, utilizing L-glutamic acid as a chiral template. The study focused on achieving stereocontrol in the synthesis of these polymers through chemoselective condensation of the ester group with aminoalcohols, leading to the formation of N-(hydroxyalkyl)amides. These amides were further functionalized by converting the alcohol function into an amine through a series of reactions involving tosylation, azide substitution, and hydrogenolysis. The resulting amino lactones were then used in polycondensation to yield the final crystalline polyamides. The chemicals used in this process included L-glutamic acid, pentachlorophenyl ester, aminoalcohols, ethyldiisopropylamine (EDPA), tosyl chloride, sodium azide, and palladium on carbon for hydrogenolysis, among others. The conclusions of the research were that the synthesized polyamides displayed high optical rotation values, indicating their stereoregularity, and were highly crystalline as confirmed by X-ray diffraction and DSC analysis.
10.1021/jo0618730
The study presents a novel and efficient method for synthesizing 2-amino-1,3,4-oxadiazoles, which are important pharmacophores due to their metabolic stability and hydrogen bonding capabilities. The key chemicals involved include thiosemicarbazides, which are prepared by acylating hydrazides with isothiocyanates. The thiosemicarbazides are then cyclized using tosyl chloride and pyridine in THF under reflux conditions to form the desired 2-amino-1,3,4-oxadiazoles. This method consistently outperforms the analogous semicarbazide cyclization, yielding 5-alkyl- and 5-aryl-2-amino-1,3,4-oxadiazoles in high yields (78-99%). The study highlights the superior reactivity of thiosemicarbazides compared to semicarbazides in this cyclization process, and it demonstrates the generality of this approach with various substituents. Additionally, the study shows that the thiosemicarbazides can be used directly from the crude acylation reaction mixture without purification, making the synthesis a convenient two-step, one-pot process. This method provides an efficient and robust route for the preparation of a wide variety of 2-amino-1,3,4-oxadiazoles, which are valuable in medicinal chemistry for their diverse biological activities.
10.1016/S0040-4039(01)91879-9
The study details the synthesis of 5-acetoxy-9-oxotridecanolactone as a model for erythronolide B, the aglycone of erythromycin B. The researchers aimed to develop a route to 5-acetoxy-13-hydroxy-9-oxotridecanoic acid, with the intention of lactonization at the final stage of macrolide synthesis. The synthesis involved assembling a thirteen-carbon backbone from two cyclopentanoid and one propanoid unit. Key steps included alkylation of the potassio salt of cyclopentanone carboxylic ester with 1,3-dibromopropane, decarboxylation with HBr, Baeyer-Villiger oxidation using CF3CO3H, and further alkylation and decarboxylation steps. The study also involved protecting and unmasking the cyclopentanone carbonyl group, reduction of an ester group with LiAlH4, and oxidation with Collins' reagent. The final lactonization was achieved using p-toluenesulfonyl chloride and Et3N, or alternatively, 1,1'-carbonyldiimidazole and sodium t-amylate. The synthetic route demonstrated potential applicability to erythronolide and other macrolide systems.
10.1016/S0040-4020(00)00626-8
The study presents an eco-friendly and cost-effective method for the tosylation of alcohols and selective monotosylation of diols using p-toluenesulfonic acid with metal-exchanged montmorillonite clay as a catalyst. The Fe3+-montmorillonite clay demonstrated the highest effectiveness among the tested catalysts, outperforming Zn2+, Cu2+, Al3+-exchanged montmorillonites and K10 montmorillonite. This method allows for the regioselective tosylation of diols to monotosylated derivatives with high purity, favoring the primary hydroxy group in the presence of secondary hydroxy groups. The catalyst's reusability over several cycles was consistent, as shown in the tosylation of cyclohexanol. This approach minimizes by-product formation, typically just water, and offers advantages such as ease of catalyst recovery, recyclability, and enhanced stability compared to traditional methods using sulfonyl chloride or anhydride with organic bases.
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