Peter Bladon

Optisch aktive Übergangsmetall-Komplexe: XCX. Optisch reines 3a,4,5,6,7,7a-Hexahydro-2-phenyl-4,7-methano-1H-inden-1-on durch asymmetrische Khand-Reaktion

Abstract The prochiral complex Co2(CO)6(HC2Ph) (I) obtained from the reaction of Co2(CO)8 with phenylacetylene, after reaction with the optical active phosphane Glyphos (II) gives the complex Co2(CO)5(HC2Ph)(Glyphos) which consists of two diastereomers (IIIa and IIIb) differing only in the chirality of the Co2C2 cluster. IIIa and IIIb can be separated by preparative liquid chromatography. They epimerize at higher temperatures, with the half life of the approach to the equilibrium IIIa/IIIb = 60 40 , at 60°C in toluene, being approximately 170 min. IN the Khand reaction of III with norbornene (IV) the cyclopentenone 3a,4,5,6,7,7a-hexahydro-2-phenyl-4,7-methano-1H-inden-1-one (V) is formed. The optical purity of V can be determined with the optishift reagent Pr(tfc)3. The equilibrium mixture IIIa/IIIb = 60 40 gives the (−)-cyclopentenone V in an enantiomeric purity of 36% ee. The optically pure (−)589-diasstereomer IIIb yields the enantiomerically pure (+)-cyclopentenone V, provided the epimerization is slow under the reaction conditions used.

Distichol an antibacterial polyphenol from Shorea disticha

Abstract The structure of distichol, a new hexadehydrotrimer of resveratrol isolated from the bark of Shorea disticha , has been established on the basis of spectroscopic evidence, chemical degradations and biosynthetic considerations.

A rapid method for comparing and matching the spherical parameter surfaces of molecules and other irregular objects

This paper describes a method for the rapid searching of rotational three-dimensional space, relying on the symmetries of the regular icosahedron and dodecahedron. This can be used to compare the spherical parameter surfaces of two molecules.

Polyphenols from dipterocarp species. Vaticaffinol and ε-viniferin

A dipterocarp endemic to Sri Lanka, Vatica affinis, yielded three phenols. Two of them showed anti-bacterial properties and have been shown to be the dimer and tetramer of 3,5,4′-trihydroxystilbene.

Another antibacterial polyphenol, copalliferol B, from Vateria copallifera (dipterocarpaceae)

Abstract Another new resveratrol trimer, copalliferol B, isolated from Vateria copallifera , has been characterized on the basis of chemical, spectroscopic and biogenetic evidence.

The lithium aluminium hydride reduction of cyclohexadienylmanganese complexes

Abstract Reduction of cyclohexadienyltricarbonylmanganese or its ring-substituted derivatives with lithium aluminium hydride leads to dihydro-derivatives. Preparative and NMR spectral information is presented and interpreted on the basis of the CH-bridged cyclohexenyl structure recently established for these products by Lamanna and Brookhart [3].

Identification of a locality in snake venomα-neurotoxins with a singificant compositional similarity to marine snailα-conotoxins: Implications for evolution and structure/activity

Summaryα-neurotoxins from elapid snake venoms andα-conotoxins from marine snails bind specifically and with high affinity to nicotinic cholinoceptors. Although both types of toxin are polypeptides, there is more than a fourfold difference in size between the two and no clear sequence homology is evident. A systematic computer search of the three-dimensional structure of erabutoxin b (anα-neurotoxin from the false sea snakeLaticauda semifasciata) was performed to identify the locality that most closely matched the amino acid compositions of the smallerα-conotoxins (from the marine snailsConus magus andConus geographus). The area of greatest similarity centered on residue position 25 of erabutoxin b, a locale that is conserved throughout the snakeα-neurotoxins and their homologues. Six Proteins unrelated to erabutoxin b were compared to theα-conotoxins to show that the extent of the erabutoxin b/α-conotoxin match was too high to be coincidental. Homologues of erabutoxin b, namelyα-cobratoxin fromNaja naja siamensis and cytotoxin VII4 fromNaja mossambica mossambica, were also analyzed. The extent of the matching with theα-conotoxins decreased in the series erabutoxin b>α-cobratoxin>cytotoxin VII4, and this also relates the order of similarity to the pharmacological properties of theα-conotoxins.Theα-conotoxin-like area of the snakeα-neurotoxins is peripheral to the site previously considered important for binding to the cholinoceptor, even though it seems to represent the focus of evolutionary convergence between the two types of neurotoxin. The area of resemblance does, however, have strong associations with the conformational behavior of the snake toxins. Hence, the outcome of this study has important consequences for the current ideas on snakeα-neurotoxin structure/activity relationships and the evolutionary origins of neurotoxicity.

Synthesis and spectroscopy of 1,2,5-selenadiazolo-[3.4-b]-pyridine and 1,2,5-selenadiazolo-[3.4-c]-pyridine

Abstract The novel 1,2,5-selenadiazolo[3.4-b]pyridine and 1,2,5-selenadiazolo[3.4-c]pridine have been synthesized. Their IR, UV and PMR spectra are reported and discussed.

The NMR spectra of some 2-substituted indanes and their tricarbonylchromium complexes

Abstract The NMR spectra of 2-indanol and its acetate indicate that the cyclopentane ring is non-planar and that the substituent group adopts a pseudo -equatorial position. The cyclopentene ring in cis -tricarbonyl(2-indanol)chromium (II, R  OH) and its acetate (II, R  OAc) appears to be even more distorted but almost planar in the corresponding trans -compounds. No evidence could be found for strong intramolecular hydrogen bonds in the cis -alcohol compound. The spectra of methyl 2-indanecarboxylate and its carbonylchromium complexes are also discussed. Relative signs of coupling constants in the five-membered ring have been determined.

General Review of Proton Magnetic Resonance

Publisher Summary This chapter presents a general review of proton magnetic resonance (PMR). The chemical-shift effects are discussed in the chapter. It also describes the anisotropy of bonds and systems, and anisotropy due to aromatic systems. Later, the chemical shift non-equivalence of methylene and methyl is discussed in this chapter. The presence of an asymmetric centre in the molecule gives conditions, under which the methylene protons in an ethyl group or the methyl protons in an isopropyl group are potentially non-equivalent. The chapter also illustrates the coupling-constant effects that include vicinal coupling constants, long-range coupling, and coupling between protons and other nuclei. The methods of sub-spectral analysis and the use of computers in spectral analysis are reviewed in the chapter. An alternative representation of energy-level diagrams is also described. Among the compounds whose spectra have been completely analyzed are, allyl iodide, benzene, pyridine, cyclobutene, alicyclic protons of 1-indanone, and cyclopropenone. Finally, the chapter presents the equilibrium problems studied by PMR