Mechanism and synthetic use of Paterno-Büchi reactions: spin-mapping and photo-aldol reactions

The concentration dependence of the diastereoselectivity of the Paternò- Büchi reaction of a series of cyclic enolethers, cyclooctene, allylic alcohols and acetates, respectively, with aromatic as well as aliphatic aldehydes was studied. For most aliphatic aldehydes, a sharp transition from low to high diastereoselectivity was observed, indicating a distinct switch from singlet to triplet photocycloaddition with different selectivity controlling mechanisms. Furthermore, the effect of solvent viscosity and temperature on the spin- directed stereoselectivity of the carbonyl-ene photocycloaddition was investigated. The variation of the solvent viscosity over a large range resulted in a weak but significant increase in the endo-selectivity of triplet benzaldehyde cycloaddition to 2,3-dihydrofuran from 82 to 91 %. For aliphatic aldehydes, the diastereoselectivity strongly increased with increasing solvent viscosity. The temperature dependence of the endo/exo- selectivity with aliphatic aldehydes RCHO (R = Me, Et, i-Bu) showed characteristic non-linear behavoir with inversion points from which activation parameters for singlet as well as the triplet photocycloaddition were determined. 5-Methoxyoxazole derivatives were prepared and evaluated with respect to their use as diene components in stereoselective Paternò-Büchi reaction. These oxazoles were versatile synthetic building blocks that reacted with various photoexcited aliphatic as well as aromatic carbonyl compounds with high regioselectvity and excellent exo-diastereoselectvity. Hydrolysis of the primary photoadducts resulted in twofold ring-opening and provided a convenient and high yielding access to erythro (S*,S*) (-amino-(-hydroxy carboxylic acid derivatives

Benzaldehyde thio­semicarbazone monohydrate

In the title compound, C8H9N3S·H2O, intra­molecular N—H⋯N hydrogen bonding contributes to the mol­ecular conformation. Water mol­ecules are involved in inter­molecular N—H⋯O and O—H⋯S hydrogen bonds, which link the mol­ecules into ribbons extended along the a axis. Weak inter­molecular N—H⋯S hydrogen bonds link these ribbons into layers parallel to the ab plane with the phenyl rings pointing up and down

Spin-dependent diastereoselectivity in the photocycloaddition of aldehydes to 2,2-dimethyl-2,3-dihydrofuran

The simple (non-induced) diastereoselectivity of the photocycloaddition of aliphatic as well as aromatic aldehydes to 2,2-dimethyl-2,3-dihydrofuran (1) was analyzed as a function of the substrate concentration (spin mapping) and rationalized in terms of optimal spin-orbit coupling controlled triplet biradical geometries

1,5-Dimethyl-4-(1-methyl-3-oxo-3-phenylprop-1-enyl­amino)-2-phenyl-1H-pyrazol-3(2H)-one

In the title compound, C21H21N3O2, an intra­molecular N—H⋯O inter­action generates an S(6) ring, which stablizes the enamine–keto tautomer. The S(6) ring makes dihedral angles of 33.07 (7), 56.50 (8) and 38.59 (8)°, respectively, with the benzoyl­acetone benzene ring and the anti­pyrine pyrazole and benzene rings

Advancements in tetronic acid chemistry. Part 1: Synthesis and reactions

AbstractThe preparation and the properties of the elusive tetronic acid are reviewed, including its synthesis, chemical reactivity and reactions

4-[(1-Hy­droxy-2-naphth­yl)methyl­ene­amino]-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one

The title anti­pyrine derivative, C22H19N3O2, was synthesized by the reaction of 4-amino-1,5-dimethyl-2-phenyl-1,2-dihydro­pyrazol-3-one and 1-hy­droxy­naphthalene-2-carbaldehyde in methanol solution. As expected, the compound adopts a trans configuration about the central C=N bond. The N atom is involved in an intra­molecular O—H⋯N bond which stabilizes the mol­ecular configuration. In the crystal structure, adjacent mol­ecules stack with no short contacts

Volatile Compounds in Honey: A Review on Their Involvement in Aroma, Botanical Origin Determination and Potential Biomedical Activities

Volatile organic compounds (VOCs) in honey are obtained from diverse biosynthetic pathways and extracted by using various methods associated with varying degrees of selectivity and effectiveness. These compounds are grouped into chemical categories such as aldehyde, ketone, acid, alcohol, hydrocarbon, norisoprenoids, terpenes and benzene compounds and their derivatives, furan and pyran derivatives. They represent a fingerprint of a specific honey and therefore could be used to differentiate between monofloral honeys from different floral sources, thus providing valuable information concerning the honey’s botanical and geographical origin. However, only plant derived compounds and their metabolites (terpenes, norisoprenoids and benzene compounds and their derivatives) must be employed to discriminate among floral origins of honey. Notwithstanding, many authors have reported different floral markers for honey of the same floral origin, consequently sensory analysis, in conjunction with analysis of VOCs could help to clear this ambiguity. Furthermore, VOCs influence honey’s aroma described as sweet, citrus, floral, almond, rancid, etc. Clearly, the contribution of a volatile compound to honey aroma is determined by its odor activity value. Elucidation of the aroma compounds along with floral origins of a particular honey can help to standardize its quality and avoid fraudulent labeling of the product. Although only present in low concentrations, VOCS could contribute to biomedical activities of honey, especially the antioxidant effect due to their natural radical scavenging potential

Identification and characterization of antibacterial compound(s) of cockroaches (Periplaneta americana)

Infectious diseases remain a significant threat to human health, contributing to more than 17 million deaths, annually. With the worsening trends of drug resistance, there is a need for newer and more powerful antimicrobial agents. We hypothesized that animals living in polluted environments are potential source of antimicrobials. Under polluted milieus, organisms such as cockroaches encounter different types of microbes, including superbugs. Such creatures survive the onslaught of superbugs and are able to ward off disease by producing antimicrobial substances. Here, we characterized antibacterial properties in extracts of various body organs of cockroaches (Periplaneta americana) and showed potent antibacterial activity in crude brain extract against methicillin-resistant Staphylococcus aureus and neuropathogenic E. coli K1. The size-exclusion spin columns revealed that the active compound(s) are less than 10 kDa in molecular mass. Using cytotoxicity assays, it was observed that pre-treatment of bacteria with lysates inhibited bacteria-mediated host cell cytotoxicity. Using spectra obtained with LC-MS on Agilent 1290 infinity liquid chromatograph, coupled with an Agilent 6460 triple quadruple mass spectrometer, tissues lysates were analyzed. Among hundreds of compounds, only a few homologous compounds were identified that contained isoquinoline group, chromene derivatives, thiazine groups, imidazoles, pyrrole containing analogs, sulfonamides, furanones, flavanones, and known to possess broad-spectrum antimicrobial properties, and possess anti-inflammatory, anti-tumour, and analgesic properties. Further identification, characterization and functional studies using individual compounds can act as a breakthrough in developing novel therapeutics against various pathogens including superbugs