Understand the Specific Regio- and Enantioselectivity of Fluostatin Conjugation in the Post-Biosynthesis

Fluostatins, benzofluorene-containing aromatic polyketides in the atypical angucycline family, conjugate into dimeric and even trimeric compounds in the post-biosynthesis. The formation of the C-C bond involves a non-enzymatic stereospecific coupling reaction. In this work, the unusual regio- and enantioselectivities were rationalized by density functional theory calculations with the M06-2X (SMD, water)/6-311 + G(d,p)//6-31G(d) method. These DFT calculations reproduce the lowest energy C1-(R)-C10'-(S) coupling pathway observed in a nonenzymatic reaction. Bonding of the reactive carbon atoms (C1 and C10') of the two reactant molecules maximizes the HOMO-LUMO interactions and Fukui function involving the highest occupied molecular orbital (HOMO) of nucleophile p-QM and lowest unoccupied molecular orbital (LUMO) of electrophile FST2- anion. In particular, the significant π-π stacking interactions of the low-energy pre-reaction state are retained in the lowest energy pathway for C-C coupling. The distortion/interaction-activation strain analysis indicates that the transition state (TScp-I) of the lowest energy pathway involves the highest stabilizing interactions and small distortion among all possible C-C coupling reactions. One of the two chiral centers generated in this step is lost upon aromatization of the phenol ring in the final difluostatin products. Thus, the π-π stacking interactions between the fluostatin 6-5-6 aromatic ring system play a critical role in the stereoselectivity of the nonenzymatic fluostatin conjugation.

RK, Pillegowda M, Periyasamy G, Suchetan PA, Butcher RJ, Foro S, Nagaraju G. Synthesis, crystal structures, photophysical, electrochemical studies, DFT and TD-DFT calculations and Hirshfeld analysis of new 2,2′:6′,2′′-terpyridine ligands with pendant 4′-(trimethoxyphenyl) groups and their homoleptic ruthenium complexes

[Ru(L1)₂](PF₆)₂ (1) and [Ru(L2)₂](PF₆)₂ (2): X-ray structures, CH⋯F/O, OH⋯F/N, CH⋯O/π, π⋯π interactions, absorption and emission spectra, DFT/TD-DFT, Hirshfeld analysis.

The effect of alkyl chain tethers on the kinetics and mechanistic behaviour of bifunctional dinuclear platinum(ii) complexes bearing N,N′-dipyridylamine ligands

This study reports on non-classical dinuclear platinum(ii) complexes, with the ability to bind to DNA strands in a different manner from cisplatin and its analogues. This is an effort to design dinuclear Pt(ii) complexes that target DNA and are bifunctional.

Straightforward synthesis of 1,2-dicyanoalkanes from nitroalkenes and silyl cyanide mediated by tetrabutylammonium fluoride

A straightforward synthesis of 1,2-dicyanoalkanes by reacting nitroalkenes with trimethylsilyl cyanide in the presence of tetrabutylammonium fluoride is described. The reaction proceeds through a tandem double Michael addition under mild conditions. Employing the hypervalent silicate generated from trimethylsilyl cyanide and tetrabutylammonium fluoride is essential for achieving this transformation. Mechanistic studies suggest that a small amount of water included in the reaction media plays a key role. This protocol is applicable to various types of substrates including electron-rich and electron-deficient aromatic nitroalkenes, and aliphatic nitroalkenes. Moreover, vinyl sulfones were found to be good alternatives, particularly for electron-deficient nitroalkenes. The broad substrate scope and functional group tolerance of the reaction makes this approach a practical method for the synthesis of valuable 1,2-dicyanoalkanes.

Stereoselective reaction of 2-carboxythioesters-1,3-dithiane with nitroalkenes: an organocatalytic strategy for the asymmetric addition of a glyoxylate anion equivalent

Under mild reaction conditions γ-nitro-β-aryl-α-keto esters with up to 92% ee were obtained, realizing a formal catalytic stereoselective conjugate addition of the glyoxylate anion synthon.

Selective amination reactions of α-nitro aryl and heteroaryl enoates

Highly functionalized tetrasubstituted alkenes were obtained by an unexpected amination reaction promoted by ethyl nosyloxycarbamate on various α-nitro aryl and heteroaryl enoates. A nitrene is likely the aminating species responsible for the observed insertion reaction leading to (E)-β-amino α-nitro enoates as the major products, regardless of the substrate configuration. The compounds, bearing two nitrogenous functional groups in different oxidation states, can be regarded as interesting synthons. In contrast, aziridination was observed for α-nitro alkyl enoates or β-nitro allylic alcohols.

Structure-activity relationship in the interaction of substituted perinaphthenones with Mycosphaerella fijiensis

The levels of native fungitoxic perinaphthenone phytoalexins in susceptible Musa varieties (banana), which are commercially grown in large plantations, are too low to provide plants with long-lasting protection against highly pathogenic fungi. Novel strategies for plant protection are necessary to reduce crop losses and to prevent the development of resistant fungal strains. The synthesis of novel fungicides based on the structures of perinaphthenone natural products is considered to be a promising strategy. Thirteen substituted perinaphthenones, among them two known natural products (1, 2) and 11 synthetics (3-13), were evaluated for their activity against Mycosphaerella fijiensis , and their half-maximal inhibitory concentrations (IC(50)) were calculated to establish structure-activity relationships (SAR). A SAR trend was hypothesized, leading to the design of a new compound, 4-methoxy-2-nitro-1H-phenalen-1-one (14); the new compound displayed significantly enhanced in vitro activity against M. fijiensis compared to other perinaphthenone derivatives. The activity of 14 was comparable to that of two commercial fungicides.

Physical basis of structural and catalytic Zn-binding sites in proteins

Zn(2+), an element that is essential to all life forms, can play a catalytic or a solely structural role. Previous works have shown that Zn(2+) binds preferentially to water molecules and His in catalytic sites, but to Cys(-) instructural sites, but the molecular basis for the observed ligand preference is unclear. Here, we show that the different Zn(2+) roles are also reflected in the different bond distances to Zn(2+) in structural and catalytic sites. We reveal the physical basis for the observed differences between structural and catalytic Zn sites: In most catalytic sites, water is found bound to Zn(2+) as it transfers the least charge to Zn(2+) and is less bulky compared to the protein ligands, enabling Zn(2+) to serve as a Lewis acid in catalysis. In most structural sites, however, >/= 2 Cys(-) are found bound to Zn(2+), as Cys(-) transfers the most charge to Zn(2+) and reduces the Zn charge to such an extent that Zn(2+) can no longer act as a Lewis acid; furthermore, steric repulsion among the bulky Cys(S(-)) prevents Zn(2+) from accommodating another ligand. Based on the observed ligand preference and Zn-ligand distance differences between structural and catalytic Zn sites, we present a simple method for distinguishing the two types of sites and for verifying the catalytic role of Zn(2+). Finally, we discuss how the physical bases revealed aid in designing potential drug molecules that target Zn proteins.