Synthesis of vinca alakaloids and realated compounds 98. Oxidation with dimethyldioxirane of compounds containing the aspidospermane and quebrachamine ring system. A simple synthesis of (7S,20S)‐(+)‐rhazidigenine and (2R,7S,20S)‐(+)‐rhazidine

The oxidation of (‐)‐tabersonine ( 1 ) with dimethyldioxirane (DMD) in neutral and acidic medium gave 16‐hydroxytabersonine‐N‐oxide ( 3 ) and the didehydrovincamine isomers 4 and 5 , respectively. (+)‐14,15‐Didehydro‐quebrachamine ( 7 ) furnished the hydroxyindolenine 9 , and the pentacyclic derivative 11 . (+)‐Quebrachamine ( 8 ) and DMD in neutral medium gave (7S,20S)‐(+)‐rhazidigenine ( 12 ) which was converted to (2R,7S,20S)‐(+)‐rhazidine ( 13b ) with hydrochloric acid.     

Stabilization and Solubilization of Lipophilic Natural Colorants with Cyclodextrins

The paper provides data on the practical utilization of the benefits of the molecular encapsulation of natural colorants by cyclodextrins. Experimental results on the stability of cyclodextrin complexed curcumin, curcuma oleoresin, -carotene and carotenoid oleoresins against light-, heat- and oxygen prove the benefits of molecular encapsulation of colorants. The parent -cyclodextrin stabilized most effectively the curcumines, while the stability of carotenoids was most effectively achieved by -cyclodextrin complexation. Methylated -cyclodextrin was found to be the most potent solubilizing agent for both carotenoids and curcuminoids.     

Uncommon Interactions of Aliphatic Dicarboxylic Acids with Cyclodextrins

A relatively high and unexpected increase of inclusion complex stabilities could be detected in some half dissociated dicarboxylic acids (HA⁻ ions) with intramolecular H-bonding. The intermolecular hydrogen bonds between the protruding functional groups of the guest and the hydroxy groups of the host are known to enhance the stability of the cyclodextrin (CD) inclusion complexes. The enhanced inclusion of HA⁻ species is promoted, not by the intermolecular but by the intramolecular H-bond indirectly, resulting in a compact shape of the guest with more favourable space filling.     

Ring transformations of 1,3-benzothiazine derivatives II conversion of 6α-aryl-7α-chloro-2,3(2′,3′-dialkqxybenzo)-1-thiaoctems3 into 2-carbomethoxy-3-aryl-7,8-dialkoxy-4.5-dihydro-1,4-benzothiazepines

6,7-Dialkoxy-2-aryl-4$\text{H}$1-1,3-benzothiazines (1a?) react with chloroacetyl chlorlde to give condensed β-lactam derivatives (2a?). Basic treatment of 2a? in methanol led to the corresponding 1,4-banzothiazepine derivativee (3a?) $\text{via}$ring expansion. The structures of the products were determined by IR, NMR and MS studies     

Determination of N9/N7-isomer ratio of alkyl (guaninyl)acetates by electrospray ionization tandem mass spectrometry

N9- and N7-substituted (guaninyl)acetic esters were studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in order to determine their ratio in alkylation reactions. The loss of ammonia is significantly different for the N9- and N7-alkylated guanine regioisomer pairs. More importantly, the abundance of the [MH-17]+ ion is in linear correlation with the N9-isomer content. Therefore, the ratio of regioisomers can be determined in a mixture containing these compounds.     

Emissions-spektralanalytische Methode zur Bestimmung des Spurenelementgehaltes in geringen Pulvermengen und Lösungen

Zusammenfassung Für die spektrographische und spektrometrische Bestimmung nicht leitender Stoffe wurde ein Elektrodensystem mit Kunststoffbindung entwickelt. In einem Konzentrationsbereich von 0,01–1,0% ließ sich damit der relative Fehler von 4–15% auf 0,5–4,0% herabsetzen. Die Selbstabsorption wird in erheblichem Ausmaß zurückgedrängt; demzufolge werden die Eichkurven in einem größeren Konzentrationsbereich linear.

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A method of emission spectrum analysis for determining the trace element content in small amounts of powder and solutions

Summary An electrode system with plastic binding was developed for spectrographic and spectrometric determination of non-conducting substances. In a concentration range of 0.01–1.0%, the relative error of 4–15% could thereby be reduced to 0.5–4.0%. The autoabsorption is suppressed to an appreciable extent; in consequence, the calibration curves become linear in a larger concentration range.

     

Limit theorems for permutations of empirical processes with applications to change point analysis

Theorems of approximation of Gaussian processes for the sequential empirical process of the permutations of independent random variables are established. The results are applied to simulate critical values for the functionals of sequential empirical processes used in change point analysis. The proofs are based on the properties of rank statistics and negatively associated random variables.     

An Improved Esterification of Carboxylic Acids Using Phase Transfer Conditions Without Solvents

Esterification of sodium salt of carboxilic acids were performed with alkyl bromide in phase-transfer conditions without solvent.