Codinaeopsin, an antimalarial fungal polyketide

A new tryptophan-polyketide hybrid, codinaeopsin, was isolated from an endophytic fungus collected in Costa Rica. The structure of codinaeopsin, which was deduced from NMR and mass spectral data, contains an unusual heterocyclic unit linking indole and decalin fragments. Codinaeopsin is active against Plasmodium falciparum, the causative agent of the most lethal form of malaria (IC50 = 2.3 microg/mL or 4.7 microM).     

N-(p-methoxyphenyl)-N-prop-2-ynyl-urea: a crystal structure with the rare Z′=5, and statistical data on Z′ values

The crystal structure of N-(p-methoxyphenyl)-N-prop-2-ynyl-urea contains five symmetry-independent molecules (Z′=5), which is a high and rarely occurring value. The five molecules have similar but not identical conformations, and form similar but not identical intermolecular interactions. The terminal alkyne groups of the five molecules are oriented differently, and form different hydrogen bond interactions (C–HO and C–Hπ). This is an example of how simple molecules can form a highly complicated solid state structure.     

Strong intramolecular O—H⋯O hydrogen bonds in quinaldic acid N‐oxide and picolinic acid N‐oxide

The title compounds contain very short intramolecular hydrogen bonds of the type C—O—H?O—N. The O?O distances are 2.425 (2) Å in picolinic acid N‐oxide (2‐carboxy­pyridine N‐oxide), C₆H₅NO₃, (I), and 2.435 (2) Å in quinaldic acid N‐oxide (2‐carboxy­quinoline N‐oxide), C₁₀H₇NO₃, (II). In (II), this is associated with slight molecular distortion from planarity, while in (I), such an effect cannot be observed because the mol­ecule crystallizes on a mirror plane.     

Arm-first star-polymer synthesis in one-pot via alkylborane-initiated RAFT

An alkylborane initiated reversible addition-fragmentation chain transfer (AI-RAFT) process was developed for the synthesis of star-polymers using a one-pot approach at room-temperature in the presence of oxygen. Linear poly(tert-butyl acrylate) arms were first polymerized using a latent trialkylborane-amine initiator, which generated trialkylborane, in situ, and subsequently radicals after reaction with oxygen. Polymerizations were optimized to maximize monomer conversion (~70–80%) and minimize arm-dispersity (~1.10) through the oxygen concentration, initiator concentration, and polymerization time. The oxygen concentration was a critical AI-RAFT parameter, providing maximum conversion at a ~0.5:1 molar ratio of oxygen-to-initiator. After arm-polymerization, multifunctional acrylates were injected into the reactor to commence crosslinking without intermediate purification. The impact of the crosslinking time and the crosslinker's functionality, concentration, and injection time were investigated to enhance arm incorporation and diminish star-polymer dispersity, quantified by deconvolution of size-exclusion chromatography data. Crosslinker concentration had the largest influence on arm conversion with optimal concentrations at a 20-25-fold excess to chain transfer agent. Under optimal conditions, arm conversions were maximized to ~75–85% and star-dispersity minimized to ~1.35–1.50. Herein an initial effort is made toward the synthesis of star-polymers with well-defined structures and high-arm conversions, while also striving for oxygen tolerance, minimal purification, low-temperatures, and metal-free conditions.     

Fast clustering of equivalent structures in crystal structure prediction

Most methods of crystal structure prediction generate many trial structures. Because these may differ in choice of unit cell, it is not always immediately obvious whether or not two such structures are equivalent. A method to answer this question is described for the case where the asymmetric unit contains one molecule in a general position, defined by the rotation and translation of that molecule with respect to some reference geometry. In the comparison of two structures, the rotation needed to transform one orientation into the other is determined first. Then it is checked whether this rotation corresponds to a transformation that is compatible with the imposed space group symmetry. A final test compares the cell lengths, the cell angles, and the molecular centers of gravity after the transformation of one structure into the other. The method is implemented for triclinic, monoclinic, and orthorhombic systems and is found to be very fast in tests on hypothetical crystal structures of acetic acid. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 :1036–1042, 1997     

Synthesis,structures and luminescence properties of two gallium(III) complexes with 5,7-dimethyl-8-hydroxyquinoline

Luminescent gallium(III) complexes featuring 5,7-dimethyl-8-hydroxyquinoline (DimOx) are systematically compared and their structural features are correlated with their photophysical properties. The two complexes are chemically identical; however, contain various number of solvent molecules in the crystalline lattice which is representative of the bulk material confirmed by both nuclear magnetic resonance and elemental analysis. Detailed structural comparisons highlight the effect which the solvent molecules have on the intra- and intermolecular interactions. A distinct number of interactions are found for the gallium complex (1) containing more than one solvent molecule for unit cell. Variation in complex morphology is similarly observed via SEM micrographs. The distinct luminescent properties of the two gallium complexes appear directly related to octahedral coordination of the 8-hydroxyquinoline ligand as well as the number of identical coordinated solvent molecules.     

Fragmentation of Electrospray-Produced Deprotonated Ions of Oligodeoxyribonucleotides Containing an Alkylated or Oxidized Thymidine

Alkylation and oxidation constitute major routes of DNA damage induced by endogenous and exogenous genotoxic agents. Understanding the biological consequences of DNA lesions often necessitates the availability of oligodeoxyribonucleotide (ODN) substrates harboring these lesions, and sensitive and robust methods for validating the identities of these ODNs. Tandem mass spectrometry is well suited for meeting these latter analytical needs. In the present study, we evaluated how the incorporation of an ethyl group to different positions (i.e., O ², N3, and O ⁴) of thymine and the oxidation of its 5-methyl carbon impact collisionally activated dissociation (CAD) pathways of electrospray-produced deprotonated ions of ODNs harboring these thymine modifications. Unlike an unmodified thymine, which often manifests poor cleavage of the C3′–O3′ bond, the incorporation of an alkyl group to the O ² position and, to a much lesser extent, the O ⁴ position, but not the N3 position of thymine, led to facile cleavage of the C3′–O3′ bond on the 3′ side of the modified thymine. Similar efficient chain cleavage was observed when thymine was oxidized to 5-formyluracil or 5-carboxyluracil, but not 5-hydroxymethyluracil. Additionally, with the support of computational modeling, we revealed that proton affinity and acidity of the modified nucleobases govern the fragmentation of ODNs containing the alkylated and oxidized thymidine derivatives, respectively. These results provided important insights into the effects of thymine modifications on ODN fragmentation.