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Understanding how enzymes have been repurposed by evolution to carry out new functions is a key goal of mechanistic enzymology. In this study we aimed to identify the adaptations required to allow the 3-hydroxy-3-methylglutaryl (HMG)-CoA synthase (HMGCS) enzymes of primary isoprenoid assembly to function in specialized polyketide biosynthetic pathways, where they initiate β-branching. This role notably necessitates that the HMG synthases (HMGSs) act on substrates tethered to noncatalytic acyl carrier protein (ACP) domains instead of coenzyme A, and accommodation of substantially larger chains within the active sites. Here, we show using a combination of X-ray crystallography and small-angle X-ray scattering, that a model HMGS from the virginiamycin system exhibits markedly increased flexibility relative to its characterized HMGCS counterparts. This mobility encompasses multiple secondary structural elements that define the dimensions and chemical nature of the active site, as well the catalytic residues themselves. This result was unexpected given the well-ordered character of the HMGS within the context of an HMGS/ACP complex, but analysis by synchrotron radiation circular dichroism demonstrates that this interaction leads to increased HMGS folding. This flexible to more rigid transition is notably not accounted for by AlphaFold2, which yielded a structural model incompatible with binding of the native substrates. Taken together, these results illustrate the continued necessity of an integrative structural biology approach combining crystallographic and solution-phase data for elucidating the mechanisms underlying enzyme remodeling, information which can inform strategies to replicate such evolution effectively in the laboratory.

With growing efforts pushing toward sustainable catalysis, using earth-abundant metals has become increasingly important. Here, we present the first examples of cobalt PC_NHCP pincer complexes that demonstrate dual stereoselectivity for allyl ether isomerization. While the cationic cobalt complex [((PC_NHCP)Co)₂-μ-N₂][BAr₄^F]₂ (3) mainly favors the Z-isomer of the enol ether, the corresponding methyl complex [(PC_NHCP)CoMe] (4) mostly gives the E-isomer. The dichotomy in selectivity was investigated computationally, revealing important contributions from the substituents on the metal (N₂ vs Me), including a 1,2-alkyl migration from cobalt to the N-heterocyclic carbene (NHC) of the methyl substituent, which is further explored in this report.

Site-selective C–H borylation is an important strategy for constructing molecular diversity in arenes and heteroarenes. Although transition-metal-catalyzed borylation is well explored, developing metal-free strategies remains scarce. Herein, we developed a straightforward approach for BBr₃-mediated selective C–H borylation of naphthamide and phenyl acetamide derivatives under metal-free conditions. This methodology appears to be economical and cost-effective. Successful borylation of drug molecules such as ibuprofen and indoprofen demonstrates the versatility and utility of this metal-free borylation. An exclusive monoselectivity was observed without a trace of diboration. Despite the possibility of forming a 5-membered boronated intermediate at the ortho-position, the selectively 6-membered intermediate paved the way for the formation of the peri-product, which was further supported by detailed computational investigation.

The GalNAc-transferase (GalNAc-T) family, consisting of 20 isoenzymes, regulates the O-glycosylation process of mucin glycopeptides by transferring GalNAc units to serine/threonine residues. Dysregulation of specific GalNAc-Ts is associated with various diseases, making these enzymes attractive targets for drug development. The development of inhibitors is key to understanding the implications of GalNAc-Ts in human diseases. However, developing selective inhibitors for individual GalNAc-Ts represents a major challenge due to shared structural similarities among the isoenzymes and some degree of redundancy among the natural substrates. Herein, we report the development of a GalNAc-T2 inhibitor with higher potency compared to those of the T1 and T3 isoforms. The most promising candidate features bivalent GalNAc and thiophene moieties on a peptide chain, enabling binding to both the lectin and catalytic domains of the enzyme. The binding mode was confirmed by competitive saturation transfer difference NMR experiments and validated through molecular dynamics simulations. The inhibitor demonstrated an IC₅₀ of 21.4 μM for GalNAc-T2, with 8- and 32-fold higher selectivity over the T3 and T1 isoforms, respectively, representing a significant step forward in the synthesis of specific GalNAc-T inhibitors tailored to the unique structural features of the targeted isoform.

Trioxacarcin A (TXN) is a highly potent cytotoxic antibiotic with remarkable structural complexity. The crystal structure of TXN bound to double-stranded DNA (dsDNA) suggested that the TXN interaction might depend on positions of two sugar subunits on the minor and major grooves of dsDNA. LL-D49194α1 (LLD) is a TXN analogue bearing the same polycyclic polyketide scaffold with a distinct glycosylation pattern. Although LLD was in a phase I clinical trial, how LLD binds to dsDNA remains unclear. Here, we solved the solution structures at high resolutions of palindromic 2″-fluorine-labeled guanine-containing duplex d(A₁A₂C₃C₄G^FG^FT₇T₈)₂ and of its stable LLD and TXN covalently bound complexes. Combined with biochemical assays, we found that TXN-alkylated dsDNA would tend to keep DNA helix conformation, while LLD-alkylated dsDNA lost its stability more than TXN-alkylated dsDNA, leading to dsDNA denaturation. Thus, despite lower cytotoxicity in vitro, the differences of sugar substitutions in LLD caused greater DNA damage than TXN, thereby bringing about a completely new biological effect.

Over the past several decades, there has been a surge of interest in harnessing the functionalization of C(sp³)–H bonds due to their promising applications across various domains. Yet, traditional methodologies have heavily leaned on stoichiometric quantities of costly and often environmentally harmful metal oxidants, posing sustainability challenges for C–H activation chemistry at large. In stark contrast, the emergence of electro-photocatalytic-driven C(sp³)–H bond activation presents a transformative alternative. This approach offers a viable route for forging carbon–carbon and carbon–heteroatom bonds. It stands out by directly engaging inert C(sp³)–H bonds, prevalent in organic compounds, without the necessity for prefunctionalization or harsh reaction conditions. Such methodology simplifies the synthesis of intricate organic compounds and facilitates the creation of novel chemical architectures with remarkable efficiency and precision. This review aims to shed light on the notable strides achieved in recent years in the realm of C(sp³)–H bond functionalization through organic electro-photochemistry.

Small-angle X-ray scattering (SAXS) is a characterization technique that allows for the study of colloidal interactions by fitting the structure factor of the SAXS profile with a selected model and closure relation. However, the applicability of this approach is constrained by the limited number of existing models that can be fitted analytically, as well as the narrow operating range for which the models are valid. In this work, we demonstrate a proof of concept for using an artificial neural network (ANN) trained on SAXS curves obtained from Monte Carlo (MC) simulations to predict values of the effective macroion valency (Z_eff) and the Debye length (κ^–1) for a given SAXS profile. This ANN, which was trained on 200,000 simulated SAXS curves, was able to predict values of Z_eff and κ^–1 for a test set containing 25,000 simulated SAXS curves, where most predicted values had errors smaller than 20%. Subsequently, an ANN was used as a surrogate model in a Markov chain Monte Carlo sampling algorithm to obtain maximum a posteriori estimates of Z_eff and κ^–1, as well as the associated confidence intervals and correlations between Z_eff and κ^–1 for an experimentally obtained SAXS profile.

The structural, photophysical, and photochemical properties of Ln(depma)(hmpa)₂(NO₃)₃ (Ln = La, Ce, Nd, Sm, Eu, Tb, Ho, Er, and Yb) complexes 1-Ln were investigated with a multidisciplinary approach involving synthesis, photocycloaddition-based crystal engineering, spectroscopic analytical techniques and quantum chemical ab initio calculations. Depending on the Ln³⁺ ion the isostructural 1-Ln complexes exhibit quite different behavior upon excitation at 350–400 nm. Some 1-Ln complexes (Ln = La, Ce, Sm, Tb, Yb) emit a broad and strong band near 533 nm arising from paired anthracene moieties, whereas others (Ln = Nd, Eu, Ho, Er) do not. 1-Eu is not emissive at all, whereas 1-Nd, 1-Ho, and 1-Er exhibit a Ln³⁺ based luminescence. Upon irradiation with 365 nm ultraviolet (UV) light 1-Ln (Ln = La, Ce, Sm, Tb, Yb) dimerize by means of a photochemically induced [4 + 4] cycloaddition of the anthracene moieties, whereas 1-Ln (Ln = Nd, Eu, Ho, Er) remain monomers. We propose three models, based on the matching of the energy levels between the Ln³⁺ ion and the paired or dimerized anthracene units in the energy-resonance crossing region, as well as on internal conversion-driven and intersystem crossing-driven energy transfer, which explain the Ln³⁺ ion regulated photophysics and photochemistry of the 1-Ln complexes.