Total synthesis and biological evaluation of neodysiherbaine A and analogues

Dysiherbaine (1) and its congener neodysiherbaine A (2) are naturally occurring excitatory amino acids with selective and potent agonistic activity for ionotropic glutamate receptors. We describe herein the total synthesis of 2 and its structural analogues 3-8. Advanced key intermediate 16 was employed as a branching point to assemble a series of these analogues 3-8 with respect to the C8 and C9 functionalities, which would not have been accessible through manipulations of the natural product itself. The synthesis of key intermediate 16 features (i) stereocontrolled C-glycosylation to set the C6 stereocenter, (ii) concise synthesis of the bicyclic ether skeleton through chemo- and stereoselective dihydroxylation of the exo-olefin and stereoselective epoxidation of the endo-olefin, followed by epoxide ring opening/5-exo ring closure, and (iii) catalytic asymmetric hydrogenation of enamide ester to construct the amino acid appendage. A preliminary biological evaluation of analogues for their in vivo toxicity against mice and binding affinity for glutamate receptors showed that both the type and stereochemistry of the C8 and C9 functional groups affected the subtype selectivity of dysiherbaine analogues for members of the kainic acid receptor family.     

Bis(2,2′:6′,2′′-ter­pyridine-κ3N)­manganese(II) tetra­thionate trihydrate

The structure of the title compound, [Mn(tpy)₂](S₄O₆)·3H₂O (tpy is 2,2′:6′,2′′-ter­pyridine, C₁₅H₁₁N₃), consists of monomeric [Mn(tpy)₂]²⁺ units embedded in a complex anionic network made up of tetra­thionate ions and hydration water mol­ecules connected via a complex hydrogen-bonding scheme.     

Synthesis of [FeFe] Hydrogenase Mimics with Lipoic acid and its Selenium Analogue as Anchor Groups

[FeFe] hydrogenase (H₂ase) mimicking complexes containing lipoic and selenolipoic acid moieties connected to 2-hydroxy-1,3-dithiopropane and 2-hydroxy-1,3-diselenopropane bridging ligands were synthesized and characterized using different spectroscopic methods. X-ray diffraction analysis was utilized to determine the molecular structure of a triphenylphosphane substituted analogue. Cyclic voltammetry (CV) investigations on the redox chemistry in presence and absence of acetic acid (AcOH) revealed differing behaviours among the mimics. IR spectroelectrochemistry (IR SEC) enabled deeper insights of structural changes during electrochemical measurements. The elaboration of surface confined systems was studied in preliminary experiments. CV experiments showed that the lipoic acid derivatives of the [FeFe] H₂ase mimics formed well-organized self-assembled monolayers (SAMs) on Pt electrodes, a promising result for future work.     

Synthesis of Unprotected Carboxy Indazoles via Pd-Catalyzed Carbonylation

The first published synthesis of unprotected carboxy indazoles from the corresponding bromoindazoles is described. This is achieved via Pd(II)-catalyzed carbonylation and is demonstrated to work on a variety of indazoles.     

Electron Counting in Carbaalane Clusters with Cubic Aluminum Core

Extended Hückel Theory (EHT) and Density Functional Theory (DFT) calculations on hexacapped cubic aluminum clusters of the type [(AlH)₈(μ₄-CH)_6−n (μ₄-H) _n ]^+/−q (n ≤ 6) indicate that their favored number of skeletal electron pairs (SEP), 12 SEPs for n ≥ 3, 14 SEPs for n = 2, 16 SEPs for n = 1 and 18 SEPs for n = 0, depends on the relative number of the two types of capping ligands: one-orbital ligands such as H and conical three-orbital CH units. Although only 16- and 18-SEP species have been isolated so far, DFT calculations indicate that 14-SEP clusters of the type [(AlR′)₈(μ₄-CR)₄(μ₄-X)₂]²⁺ (X = one-orbital ligand) should be synthesized. Computed 12-SEP models were not found to be energy minima, but this should not preclude the possibility for stabilizing such species, for example with bulky substituents. Changing the CR capping ligands into AlR units in the above series is expected to limit their electron counts to 12 SEPs. The incorporation of a main-group atom in the middle of the cube does not change the favored cluster electron count. However, calculations indicate that only 12-SEP species are likely to be synthesized. Dedicated to Professor Günter Schmid on the occasion of his 70th birthday     

catena‐Poly[[aqua­(3,4,7,8‐tetra­methyl‐1,10‐phenanthroline‐κ2N,N′)cadmium(II)]‐μ3‐thio­sulfato‐κ3S:S:O]

The title compound, [Cd(S₂O₃)(C₁₆H₁₆N₂)(H₂O)]_n, presents a polymeric one‐dimensional structure running along the P2₁/c glide direction, with elementary units defined by six‐coordinate Cd^II atoms bonded to three symmetry‐related thio­sulfate groups, a bidentate tetra­methyl­phenanthroline ligand and one aqua ligand. The bridging thio­sulfates bind metal centers through two different sequences, viz. Cd—S—Cd′ and Cd′—S′—S′—O′—Cd, defining a closed six‐membered ring. Individual chains are held together viaπ–π inter­actions to generate two‐dimensional networks parallel to the (100) plane. These, in turn, are connected by much weaker van der Waals inter­actions.     

Bis[(acetato‐κ2O,O′)bis­(4,4′‐dimeth­yl‐2,2′‐bipyrid­yl‐κ2N,N′)zinc(II)] trithion­ate penta­hydrate

The title ionic zinc–acetate complex, [Zn(C₂H₃O₂)(C₁₂H₁₂N₂)₂]₂(S₃O₆)·5H₂O, contains a ZnN₄O₂ nucleus provided by the three bidentate ligands acting in a chelating mode. The trithio­nate unit, in turn, acts as an isolated charge‐balancing counter‐ion. The structure has a three‐dimensional assembly achieved through three different inter­action types, viz. Coulomb, hydrogen bonding and π–π. The trithio­nate group and one of the solvent water mol­ecules are disordered around inversion centers.