Zn2+ -Ion Sensing by Fluorescent Schiff Base Calix[4]arene Macrocycles.

A macrocyclic ligand (H2 L) containing two o,o'-bis(iminomethyl)phenol and two calix[4]arene head units has been synthesized and its coordination chemistry towards divalent Ni and Zn investigated. The new macrocycle forms complexes of composition [ML] (M=Zn, M=Ni) and [ZnL(py)2 ], which were characterized by elemental analysis; IR, UV/Vis, and NMR spectroscopy; electrospray ionization mass spectrometry (ESI-MS); and X-ray crystallography (for [ZnL(py)2 ] and [NiL]). H2 L allows the sensitive optical detection of Zn2+ among a series of biologically relevant metal ions by a dual fluorescence enhancement/quenching effect in solution. The fluorescence intensity of the macrocycle increases by a factor of ten in the presence of Zn2+ with a detection limit in the lower nanomolar region.

Endocyclic P-P bond cleavage in carbaborane-substituted 1,2-diphosphetane: a new route to secondary phosphinocarbaboranes.

Carbaborane-substituted 1,2-diphosphetane reacts with elemental lithium and hydrogen chloride to give exclusively secondary mono- and bis(phosphino)carbaboranes. The latter reacts with two equivalents of formaldehyde and one equivalent of aniline to give a carbaborane-substituted 1-aza-3,6-diphosphepane.

Aligned deuterochloroform in cross-linked polystyrene as a new sample for adjusting the magic angle in HR-MAS.

A new and easily usable sample for adjusting the magic angle in a high resolution magic angle spinning (HR-MAS) probe head is a swollen polymer stick in CDCl(3) . The deuterium resonance shows a quadrupolar splitting if the rotor assembly is not at the magic angle, but a sharp singlet if the magic angle is correctly adjusted.

Mechanistic and kinetic insights into the thermally induced rearrangement of alpha-pinene.

The thermal rearrangement of alpha-pinene (1) is interesting from mechanistic as well as kinetic point of view. Carrier gas pyrolyses with 1 and its acyclic isomers ocimene (2) and alloocimene (3) were performed to investigate the thermal network of these hydrocarbons. Kinetic analysis of the major reaction steps allows for a deeper insight in the reaction mechanism. Thus it was possible to explain the racemization of 1, the formation of racemic limonene (4), and the absence of the primary pyrolysis product 2 in the reaction mixture resulting from thermal rearrangement of 1. Results supported the conclusion that the reactions starting with 1 involve biradical transition states.

Thermal isomerization of (+)-cis- and (-)-trans-pinane leading to (-)-beta-citronellene and (+)-isocitronellene.

Catalyzed and uncatalyzed rearrangement reactions of terpenoids play a major role in laboratory and industrial-scale synthesis of fine chemicals. Herein, we present our results on the thermally induced isomerization of pinane (1). Investigation of the thermal behavior of (+)-cis- (1 a) and (-)-trans-pinane (1 b) in a flow-type reactor reveals significant differences in both reactivity and selectivity concerning the formation of (-)-beta-citronellene (2) and (+)-isocitronellene (3) as main products. Possible explanations for these results are discussed on the basis of reaction mechanism and ground-state geometries for 1 a and 1 b. To identify side reactions caused from ene cyclizations of 2 and 3, additional pyrolysis experiments were conducted that enabled the identification of almost all compounds in the network of C(10)H(18)-hydrocarbon products formed from 1.

Can one gain spectral information plus time by 3D HMBC via back-projection?

The 3D HMBC technique is compared with a time saving technique in which the projection-reconstruction (PR) principle is applied. Using strychnine as an example we demonstrate that after recording essentially three planes of the 3D cuboid a comparable result can be obtained, if certain constraints of the data dimensions are obeyed.

Evidence for the combined participation of a C10 and a C15 precursor in the biosynthesis of moenocinol, the lipid part of the moenomycin antibiotics.

Upon feeding of [2-(13)C,4-(2)H]-1-deoxy-D-xylulose to Streptomyces ghanaensis, the deuterium label was retained exclusively at positions C-7 and C-17 in the moenocinol part of the moenomycin antibiotics. This result vindicates the hypothesis that the C(25) structure of moenocinol is assembled from a C(10) and a C(15) precursor, each of which requires for its formation the involvement of a dimethylallyl diphosphate starter unit.

Studies on the interaction of the antibiotic moenomycin A with the enzyme penicillin-binding protein 1b.

The interaction of a moenomycin derivative with the enzyme penicillin binding protein 1b (PBP 1b) has been studied by means of STD NMR. The results obtained initiated the synthesis of a number of moenomycin derivatives modified in unit A including a moenomycin-ampicillin conjugate and determination of their antibiotic activities. A protocol is described that allows studying the interaction of moenomycin analogues with PBP 1b by fluorescence correlation spectroscopy.

Tandem Protocol for the Stereoselective Synthesis of Different Polyfunctional beta-Amino Acids and 3-Amino-Substituted Carbohydrates.

Conjugate addition of homochiral amidocuprates or lithium amides based on (R)-N-(1-phenylethyl)(trimethylsilyl)amine to alpha,beta-unsaturated esters proceeds stereoselectively and allows the synthesis of beta-amino acids. Trapping of the intermediate ester enolate with D(2)O affords the corresponding deuterated compounds. anti-alpha-Alkyl-beta-amino acids are obtained stereoselectively after transmetalation of the lithium/copper ester enolate to the titanium ester enolate and trapping with carbon electrophiles. Both diastereomers of beta-homothreonine, other precursors of 3-amino-substituted carbohydrates, and stereoselectively in position 2 deuterated analogues are formed from enantiomerically pure gamma-alkoxy-substituted enoates. The product distribution observed is complementary to published results regarding 1,4-addition to gamma-silyloxy-substituted enoates. The anti/syn selectivity can be explained by assuming transition state geometries where the delivery of the nitrogen nucleophile is controlled by lithium "chelation" between reagent and substrate. In one case the product configuration can be controlled by the reagent irrespective of the substrate stereochemistry; in other cases the topicity of the addition is complementary to published results. For instance, erythro- or threo-configured 2,3-dideoxy-3-aminopentoses are accessible via this route.