Cubane-type clusters [Fe4S4(SR*)4]2− containing chiral thiolate ligands with R* = CH(Me)Ph (1), CH2CH(Me)Et (2), and CH2CH(OH)CH2OH (3) have been prepared by ligand substitution in the reaction systems [Fe4S4(SEt)4]/R*SH (1–3, acetonitrile) and [Fe4S4Cl4]2−/NaSR*(3, Me2SO). Reactions with successive equivalents of thiol or thiolate generate the species [Fe4S4L4-n(SR*)n]2− (L = SEt, Cl) with n = 1–4. Clusters 1 and 2 were prepared with racemic thiols leading to the possible formation of one enantiomeric pair (n = 1) and seven diastereomers and their enantiomers (n = 2–4). Reactions were monitored by isotropically shifted 1H NMR spectra in acetonitrile or Me2SO. In systems affording 1 and 2 as final products, individual mixed-ligand species could not be detected. However, crystallization of (Et4N)2[1] afforded 1-[SS(RS)(RS)] in which two sites are disordered because of occupancy of R and S ligands. Similarly, (Et4N)2[2] led to 2-[SSSS], a consequence of spontaneous resolution upon crystallization. The clusters 3-[RRRR] and 3- [SSSS] were obtained from enantiomerically pure thiols. Successive reactions lead to detection of species with n = 1–4 by appearance of four pairs of diastereotopic SCH2 signals in both acetonitrile and Me2SO reaction systems. Identical spectra were obtained with racemic, R-(−), and S-(+) thiols, indicating that ligand-ligand interactions are too weak to allow detection of diastereomers (e.g., [SSSS] vs. [SSRR]). The stability of 3 in Me2SO/H2O media is described.

Utilizing a hexadentate ligand platform, a high-spin trinuclear iron complex of the type (tbsL)Fe3(thf) was synthesized and characterized ([tbsL]6− = [1,3,5-C6H9(NPh-o-NSitBuMe2)3]6−). The silyl-amide groups only permit ligation of one solvent molecule to the tri-iron core, resulting in an asymmetric core wherein each iron ion exhibits a distinct local coordination environment. The triiron complex (tbsL)Fe3(thf) rapidly consumes inorganic azide ([N3]NBu4) to afford an anionic, trinuclear nitride complex [(tbsL)Fe3(μ3-N)]NBu4. The nearly C3-symmetric complex exhibits a highly pyramidalized nitride ligand that resides 1.205(3) Å above the mean triiron plane with short Fe–N (1.871(3) Å) distances and Fe–Fe separation (2.480(1) Å). The nucleophilic nitride can be readily alkylated via reaction with methyl iodide to afford the neutral, trinuclear methylimide complex (tbsL)Fe3(μ3-NCH3). Alkylation of the nitride maintains the approximate C3-symmetry in the imide complex, where the imide ligand resides 1.265(9) Å above the mean triiron plane featuring lengthened Fe–Nimide bond distances (1.892(3) Å) with nearly equal Fe–Fe separation (2.483(1) Å).

Excited-state geometries determined by time-resolved synchrotron diffraction are summarized with emphasis on their comparison with a series of theoretical results. The relative merits of monochromatic and polychromatic (Laue) techniques are discussed.

Definitive experimental results on the geometry of fleeting species are at the time of writing still limited to monochromatic data collection, but methods for modifications of the polychromatic Laue data to increase their accuracy and their suitability for pump–probe experiments have been implemented and are reviewed. In the monochromatic experiments summarized, excited-state conversion percentages are small when neat crystals are used, but are higher when photoactive species are embedded in an inert framework in supramolecular crystals. With polychromatic techniques and increasing source brightness, smaller samples down to tenths of a micrometre or less can be used, increasing homogeneity of exposure and the fractional population of the excited species. Experiments described include a series of transition metal complexes and a fully organic example involving excimer formation. In the final section, experimental findings are compared with those from theoretical calculations on the isolated species. Qualitative agreement is generally obtained, but the theoretical results are strongly dependent on the details of the calculation, indicating the need for further systematic analysis.

We report the direct observation of a bent geometry for a non-stabilized nitrile imine in a metal-coordination crystal. The photoinduced tetrazole ring rupture to release N2 appears to depend on the size of voids around the N3-N4 bond in the crystal lattice. We further observed the selective formation of 1,3-addition product when a reactive nitrile imine was photo-generated in water. Taken together, the bent nitrile imine geometry agrees with the 1,3-dipolar structure, a transient reactive species that mediates the photoinduced 1,3-dipolar cycloaddition in the aqueous medium.

Sequential alkyne activation of terminal alkynes and propiolic acids by gold(I) catalysts yields compounds having α-pyrone skeletons. Novel cascade reactions involving propiolic acids are reported that give rise to α-pyrones with different substitution patterns.

Actinobacteria generate a large number of structurally diverse small molecules with potential therapeutic value. Genomic analyses of this productive group of bacteria show that their genetic potential to manufacture small molecules exceeds their observed ability by roughly an order of magnitude, and this revelation has prompted a number of studies to identify members of the unknown majority. As a potential window into this cryptic secondary metabolome, pairwise assays for developmental interactions within a set of 20 sequenced actinomycetes were carried out. These assays revealed that Amycolatopsis sp. AA4, a so-called “rare” actinomycete, produces a novel siderophore, amychelin, which alters the developmental processes of several neighboring streptomycetes. Using this phenotype as an assay, we isolated amychelin and solved its structure by NMR and MS methods coupled with an X-ray crystallographic analysis of its Fe-complex. The iron binding affinity of amychelin was determined using EDTA competition assays, and a biosynthetic cluster was identified and annotated to provide a tentative biosynthetic scheme for amychelin.

We propose a novel pathway for the prebiotic synthesis of 2′-deoxynucleotides. Consideration of the constitutional chemical relationships between glycolaldehyde and β-mercapto-acetaldehyde, and the corresponding proteinogenic amino acids, serine and cysteine, led us to explore the consequences of the corresponding sulfur substitution for our previously proposed pathways leading to the canonical ribonucleotides. We demonstrate that just as 2-aminooxazole–an important prebiotic ribonucleotide precursor–is readily formed from glycolaldehyde and cyanamide, so is 2-aminothiazole formed from β-mercapto-acetaldehyde and cyanamide in water at neutral pH. Indeed, both the oxazole and the thiazole can be formed together in a one-pot reaction, and can be co-purified by crystallization or sublimation. We then show that 2-aminothiazole can take part in a 3-component carbon–carbon bond-forming reaction in water that leads to the diastereoselective synthesis of masked 2′-thiosugars regiospecifically tethered to purine precursors, which would lead to 2′-deoxynucleotides upon desulfurization. The possibility of an abiotic route to the 2′-deoxynucleotides provides a new perspective on the evolutionary origins of DNA. We also show that 2-aminothiazole is able to sequester, through reversible aminal formation, the important nucleotide precursors glycolaldehyde and glyceraldehyde in a stable, crystalline form.