Acid-Promoted Cyclization Reaction of the Guanine Base with 1,1,3,3-Tetramethoxypropane: A Method for the Preparation of M1 dG and its Derivatives

Despite the importance of nucleosides and nucleotides for drug discovery, only a few practical methods to prepare tricyclic nucleosides have been reported. Here, we describe a synthetic strategy for late-stage functionalization of nucleosides and nucleotides via chemo- and site-selective acid-promoted intermolecular cyclization. The nucleoside analogs with an additional ring were obtained in moderate-to-high yields, including some antiviral drugs (acyclovir, ganciclovir, and penciclovir) derivatives, endogenous fused ring nucleoside (M₁ dG) and its derivatives, and nucleotide derivatives. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Synthesis of tricyclic acyclovir analogs (3a-3c) Basic Protocol 2: Synthesis of tricyclic nucleosides M₁ dG (6) and M₁ G (9) Basic Protocol 3: Synthesis of tricyclic nucleotide (12).

Bifunctional thiourea-catalyzed asymmetric [3 + 2] annulation reactions of 2-isothiocyanato-1-indanones with barbiturate-based olefins

Bifunctional thiourea-catalyzed asymmetric [3 + 2] annulation reactions of 2-isothiocyanato-1-indanones with barbiturate-based olefins have been developed to afford chiral dispiro[indene-pyrrolidine-pyrimidine]s. Through this strategy, the target products could be obtained in good to excellent yields with excellent stereoselectivities. In addition, the synthetic utility was verified through a gram-scale synthesis, one-pot three-component reactions and further transformation experiments of the products.

The crystal structure of benzophenone synthase from Garcinia mangostana L. pericarps reveals the basis for substrate specificity and catalysis

Benzophenone synthase (BPS) catalyzes the production of 2,4,6-trihydroxybenzophenone via the condensation of benzoyl-CoA and three units of malonyl-CoA. The biosynthetic pathway proceeds with the formation of the prenylated xanthone α-mangostin from 2,4,6-trihydroxybenzophenone. Structural elucidation was performed to gain a better understanding of the structural basis of the function of Garcinia mangostana L. (mangosteen) BPS (GmBPS). The structure reveals the common core consisting of a five-layer αβαβα fold as found in other type III polyketide synthase enzymes. The three residues Met264, Tyr266 and Gly339 are proposed to have a significant impact on the substrate-binding specificity of the active site. Crystallographic and docking studies indicate why benzoyl-CoA is preferred over 4-coumaroyl-CoA as the substrate for GmBPS. Met264 and Tyr266 in GmBPS are properly oriented for accommodation of the 2,4,6-trihydroxybenzophenone product but not of naringenin. Gly339 offers a minimal steric hindrance to accommodate the extended substrate. Moreover, the structural arrangement of Thr133 provides the elongation activity and consequently facilitates extension of the polyketide chain. In addition to its impact on the substrate selectivity, Ala257 expands the horizontal cavity and might serve to facilitate the initiation/cyclization reaction. The detailed structure of GmBPS explains its catalytic function, facilitating further structure-based engineering to alter its substrate specificity and obtain the desired products.

Selective Synthesis of Benzimidazoles from o-Phenylenediamine and Aldehydes Promoted by Supported Gold Nanoparticles

We investigated the catalytic efficacy of supported gold nanoparticles (AuNPs) towards the selective reaction between o-phenylenediamine and aldehydes that yields 2-substituted benzimidazoles. Among several supported gold nanoparticle platforms, the Au/TiO₂ provides a series of 2-aryl and 2-alkyl substituted benzimidazoles at ambient conditions, in the absence of additives and in high yields, using the mixture CHCl₃:MeOH in ratio 3:1 as the reaction solvent. Among the AuNPs catalysts used herein, the Au/TiO₂ containing small-size nanoparticles is found to be the most active towards the present catalytic methodology. The Au/TiO₂ can be recovered and reused at least five times without a significant loss of its catalytic efficacy. The present catalytic synthetic protocol applies to a broad substrate scope and represents an efficient method for the formation of a C–N bond under mild reaction conditions. Notably, this catalytic methodology provides the regio-isomer of the anthelmintic drug, Thiabendazole, in a lab-scale showing its applicability in the efficient synthesis of such N-heterocyclic molecules at industrial levels.

Study on the Changes of Structures and Properties of PAN Fibers during the Cyclic Reaction in Supercritical Carbon Dioxide

Thermal pre-oxidation of polyacrylonitrile (PAN) fibers is a time-consuming and energy-consuming step in the production of PAN-based carbon fibers. In this paper, the effect of temperature on the structures and properties of PAN fibers cyclized in the supercritical carbon dioxide (Sc-CO₂) medium was studied. The thermal behaviors of the PAN fibers were investigated by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The cyclization reaction was sensitive to the heating temperature and gas atmosphere. The FT-IR results of the PAN fibers treated in the Sc-CO₂ confirmed that the degree of cyclization increased with the increase of the cyclization temperature. Compared with the PAN fibers treated in the air, the PAN fibers treated in the Sc-CO₂ showed a higher degree of cyclization even at the same temperature. These findings might be related to the osmotic action of Sc-CO₂ causing the fibers to be further arranged in a regular manner, which was favorable for the cyclization reaction. Moreover, as one kind of high diffusion and high heat transfer media, the heat release during the cyclization of PAN fibers could be quickly removed by Sc-CO₂, which achieved the progress of the rapid-entry cyclization reaction.

Rewritable Optical Memory Through High-Registry Orthogonal Upconversion

An experimental design, based on a combination of core-shell-structured upconversion nanoparticles and diarylethene photochromic molecules, for achieving rewritable optical memory is reported. This core-shell design enables the nanoparticles to emit two sets of distinct emission bands with ultrahigh spectral purity through laser excitation at 980 and 1532 nm. Importantly, the ultraviolet emission of the nanoparticles under 980 nm irradiation is used to activate the cyclization reaction of diarylethene through CC bond formation, while the green emission from the nanoparticles upon 1532 nm excitation leads to the cleavage of the newly formed CC bond. This pathway offers a convenient and versatile optical method for controlling the process of data writing and erasing with high spatiotemporal resolution.