Ring Opening Reactions of 1,2-Didehydroprolines. Part II. Synthesis of 5-Amino-2,4-dihydroxypentanoic Acids,their 2-Piperidones and Pentanolides [1]

Summary. NMR spectroscopic investigations on 1,2-didehydroproline in alkaline deuterium oxide revealed incorporation of deuterium at position C-3, presumably due to the presence of acyclic 5-amino-2-oxopentanoate in solution. Reduction of this equilibrium mixture with hydride reagents generally yields prolines together with the 2-hydroxy acids. It could be shown that the ratio of the two products depends strongly on the pH. This allowed the optimization of reaction conditions for the preparation of the target compounds (2R,4R)- and (2S,4R)-5-amino-2,4-dihydroxypentanoic acid. In order to separate these isomers and unambiguously assign their respective structures, the (3R,5R)- and (3S,5R)-3,5-dibenzoyloxy-2-piperidones were synthesized as the key intermediates by lactamization and benzoylation. Lactames were also directly transformed to the corresponding lactones.     

Near-Hartree—Fock calculation of the electric field gradient tensor at the hydrogen nucleus in water

The electric field gradient tensor at the hydrogen nucleus in water has been calculated in an SCF calculation with local near-Hartree—Fock quality using asymmetric basis sets. The results are in excellent agreement with results obtained by Davidson and Feller with a basis set of uniform near-Hartree—Fock quality and deviate only a few percent from experimental results. Calculated and experimental data are combined to improve the transformed experimental values.     

Citrus-Carotinoide. 2. Mitteilung. Synthese von (3R)-β-Citraurin, (3R)-β-Citraurol und (3R)-β-Citraurinin; Aufklärung der Konfiguration von Citrus-Carotinoiden

Citrus-Carotenoids. Synthesis of (3R)-β-Citraurin, (3R)-β-Citraurol and (3R)-β-Citraurinene; Determination of the Configuration of Citrus-Carotenoids (3R)-β-Citraurin, (3R)-β-citraurol and (3R)-β-citraurinene were prepared starting from (3R)-3-acetoxy-β-ionone. Comparison of the chiroptical data of β-citraurin from orange peels with those of the synthetic compound confirmed the 3R-configuration of the natural pigment.     

Isolierung und Strukturaufklärung von Neapolitanose (O-β-D-Glucopyranosyl-(1→2)-O-[β-D-glucopyranosyl-(1→6)]-(D-glucose), einem neuen Trisaccharid aus den Stempeln von Gartenkrokussen (Crocus neapolitanus var.)

Isolation and Structure Elucidation of Neapolitanose (O-β-D -Glucopyranosyl-(1→2)-O-[β-D -glucopyranosyl-(1→6)]-D -glucose), New Trisaccharide from the Stigmas of Garden Crocusses (Crocus neapolitanus var.) From the stigmas of Crocus neapolitanus var. ‘Blue Bird’ two new crocetin glycosyl esters were isolated. They contained a hitherto unknown trisaccharide. For the structure elucidation a homonuclear 2D-¹H-NMR-shift-correlation experiment was carried out with the peracetate of the isolated trisaccharide. This experiment revealed that the carbohydrate is O-β-D -glucopyranosyl-(1→2)-O-[β-D -glucopyranosyl-(1→6))]-D -glucose, for which we suggest the name ‘neapolitanose’. The two new C₂₀-carotenoids from Crocus neapolitanus are crocetin (β-gentiobiosyl) (β-neapolitanosyl) ester ( 4 ) and crocetin di(β-neapolitanosyl) ester ( 5 ).     

1,2-Epoxycarotinoide. 4. Mitteilung. Synthese, 1H-NMR- und CD-Studien von (S)-1,2-Epoxy-1,2-dihydrolycopin und (S)-1′,2′-Epoxy-1′,2′-dihydro-γ-carotin

1,2-Epoxycarotenoids: Synthesis, ¹H-NMR and CD Studies of (S)-1,2-Epoxy-1,2-dihydrolycopene and (S)-1′,2′-Epoxy-1′, 2′ -dihydro-γ-carotene The synthesis of (S)-1,2-epoxy-1,2-dihydrolycopene (^(S)- 1 ) and (S)-1′, 2′ -epoxy- 1′, 2′ -dihydro-γ-carotene ((S)- 2 ) are described. The CD spectra of the (all-E)-isomers and of the isomers (7Z, S)- 1 and (7′Z, S)- 2 are discussed. The comparison of the CD spectra of the synthetic (S)- 1 and the compound isolated from the tomatoes proves the (S)-configuration of the natural product.     

1,2-Epoxycarotinoide. 2. Mitteilung. Synthese der 1′,2′-Epoxide von β,ψ- und ε,ψ-Carotin (= γ- bzw. δ-Carotin)

The synthesis of the naturally occurring 1′,2′-epoxy-1′,2′-dihydro-β, δ-carotene and 1′,2′-epoxy-1′,2′-dihydro-ε, ψ-carotene is described.     

Optisch aktive C5-Bausteine zur Synthese von natürlich vorkommenden Terpenen

Optically Active C₅-Synthons for the Synthesis of Naturally Occurring Terpenes The optically active synthons (S)- 22 , (R)- 23 , (R)- 25 and (R)- 26 were prepared from L -serine. Furthermore the tertiary alcohol 6 was synthesized from L -serine (→(S)- 6 ) and D -mannitol (→(R)- 6 ). These compounds are suitable for the synthesis of optically active natural products.     

Studies of a nickel-based single-molecule magnet

A cyclic complex [Ni(12)(chp)(12)(O(2)CMe)(12)(thf)(6)(H(2)O)(6)] (1) has been synthesised and studied (chp=6-chloro-2-pyridonate). Complex 1 exhibits ferromagnetic exchange between the S=1 centres, giving an S=12 spin ground state. Detailed studies demonstrate that it is a single-molecule magnet with an energy barrier of approximately 10 K for reorientation of magnetisation. Resonant quantum tunnelling is also observed. The field between resonances allows accurate measurement of D, which is 0.067 K. Inelastic neutron scattering studies have allowed exchange parameters to be derived accurately, which was impossible from susceptibility data alone. Three exchange interactions are required: two ferromagnetic nearest neighbour interactions of approximately 11 and 2 cm(-1) and an anti-ferromagnetic next nearest neighbour interaction of -0.9 cm(-1).     

C45- and C50-Carotinoide. 1. Mitteilung. Synthese von (R)- and (S)-Lavandulol

C₄₅- and C₅₀-Carotenoids, 1st Communication. Synthesis of (R)- and (S)-Lavandulol Starting with methyl (3 R)-3-hydroxybutanoate ((R)-7) and ethyl (3 S)-3- hydroxybutanoate ((S)- 11 ), respectively, (R)- and (S)-lavandulol ((R)- 1 and (S)- 1 ) were synthesized with high optical purity. The synthesized key intermediates (R)- 6 and (S)- 6 are suitable compounds for the synthesis of optically active acyclic C₄₅- and C₅₀-carotenoids.     

Nonlinear dynamics of the voice: Signal analysis and biomechanical modeling

Irregularities in voiced speech are often observed as a consequence of vocal fold lesions, paralyses, and other pathological conditions. Many of these instabilities are related to the intrinsic nonlinearities in the vibrations of the vocal folds. In this paper, bifurcations in voice signals are analyzed using narrow-band spectrograms. We study sustained phonation of patients with laryngeal paralysis and data from an excised larynx experiment. These spectrograms are compared with computer simulations of an asymmetric 2-mass model of the vocal folds. (c) 1995 American Institute of Physics.