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1. A versatile approach to the synthesis of glycans containing mannuronic acid residues

   https://doi.org/10.1039/D1OB00188D  

   Alex, Catherine; Visansirikul, Satsawat; Demchenko, Alexei V. (April 2021, Organic & Biomolecular Chemistry)

   null (Ed.)

   Reported herein is a new method for a highly effective synthesis of β-glycosides from mannuronic acid donors equipped with the 3- O -picoloyl group. The stereocontrol of glycosylations was achieved by means of the H-bond-mediated aglycone delivery (HAD). The method was utilized for the synthesis of a tetrasaccharide linked via β-(1 → 3)-mannuronic linkages. We have also investigated 3,6-lactonized glycosyl donors that provided moderate to high β-manno stereoselectivity in glycosylations. A method to achieve complete α-manno stereoselectivity with mannuronic acid donors equipped with 3- O -benzoyl group is also reported. 

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2. Catalysis‐Enabled Concise and Stereoselective Total Synthesis of the Tricyclic Prostaglandin D ₂ Metabolite Methyl Ester

   https://doi.org/10.1002/anie.202115633  

   Sims, Hunter S.; de Andrade Horn, Pedro; Isshiki, Ryota; Lim, Melissa; Xu, Yan; Grubbs, Robert H.; Dai, Mingji (December 2021, Angewandte Chemie International Edition)

   Abstract A concise and stereoselective total synthesis of the clinically relevant tricyclic prostaglandin D₂metabolite (tricyclic‐PGDM) methyl ester in racemic form was accomplished in eight steps from a readily available known cyclopentene‐diol derivative. The synthesis features a nickel‐catalyzed Ueno–Stork‐type dicarbofunctionalization to generate two consecutive stereocenters, a palladium‐catalyzed carbonylative spirolactonization to build the core oxaspirolactone, and aZ‐selective cross‐metathesis to introduce the (Z)‐3‐butenoate side chain, a group challenging to introduce through traditional Wittig protocols and troublesome for the two previous total syntheses. A generalZ‐selective cross‐metathesis protocol to construct (Z)‐β,γ‐unsaturated esters was also developed that has broad functional group tolerance and high stereoselectivity. Additionally, our synthesis already accumulated 75 mg of valuable material for an¹⁸O‐tricyclic‐PGDM‐based assay used in clinical settings for inflammation. 

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3. Synthesis of alpha-Gal C-disaccharides

   https://doi.org/10.1016/j.bmc.2024.117903  

   Ann, Alex; Truong, Steven; Peters, Jiwani; Mootoo, David R (October 2024, Bioorganic & Medicinal Chemistry)

   The synthesis of C-disaccharides of α-D-galactopyranosyl-(1 → 3)-D-galactopyranose (α-Gal), potential tools for studying the biology of α-Gal glycans, is described. The synthetic strategy, centers on the reaction of two easily available precursors 1,2-O-isopropylidene-D-glyceraldehyde and an α-C-glactosyl-E-crotylboronate, which affords a mixture of two diastereomeric anti-crotylation products. The stereoselectivity of this reaction was controlled with (R)- and (S)-TRIP catalysts, and the appropriate diastereomer was transformed to C-linked disaccharides of α-Gal, in which the aglycone segment comprised O-, C- and S-glycoside entities that can enable glycoconjugate synthesis. 

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4. A General Framework for Robust G-Invariance in G-Equivariant Networks

   Sanborn, Sophia; Miolane, Nina (December 2023, NeurIPS 2023)

   We introduce a general method for achieving robust group-invariance in group-equivariant convolutional neural networks (G-CNNs), which we call the G-triple-correlation (G-TC) layer. The approach leverages the theory of the triple-correlation on groups, which is the unique, lowest-degree polynomial invariant map that is also complete. Many commonly used invariant maps--such as the max--are incomplete: they remove both group and signal structure. A complete invariant, by contrast, removes only the variation due to the actions of the group, while preserving all information about the structure of the signal. The completeness of the triple correlation endows the G-TC layer with strong robustness, which can be observed in its resistance to invariance-based adversarial attacks. In addition, we observe that it yields measurable improvements in classification accuracy over standard Max G-Pooling in G-CNN architectures. We provide a general and efficient implementation of the method for any discretized group, which requires only a table defining the group's product structure. We demonstrate the benefits of this method for G-CNNs defined on both commutative and non-commutative groups--SO(2), O(2), SO(3), and O(3) (discretized as the cyclic C8, dihedral D16, chiral octahedral O and full octahedral Oh groups)--acting on ℝ2 and ℝ3 on both G-MNIST and G-ModelNet10 datasets. 

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5. Regioselective Formation of Substituted Indoles: Formal Synthesis of Lysergic Acid

   https://doi.org/10.1002/chem.202004107  

   Points, III, Gary_L; Stout, Kenneth_T; Beaudry, Christopher_M (November 2020, Chemistry – A European Journal)

   Abstract A Diels–Alder reaction‐based strategy for the synthesis of indoles and related heterocycles is reported. An intramolecular cycloaddition of alkyne‐tethered 3‐aminopyrones gives 4‐substituted indolines in good yield and with complete regioselectivity. Additional substitution is readily tolerated in the transformation, allowing synthesis of complex and non‐canonical substitution patterns. Oxidative conditions give the corresponding indoles. The strategy also allows the synthesis of carbazoles. The method was showcased in a formal synthesis of lysergic acid. 

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