New methodology for the synthesis of 25-hydroxyvitamin D conjugates

A new method for synthesizing regiospecific 3-position vitamin D conjugates is described. Reaction of either 25-dihydroxyvitamin D2 or 25-dihydroxyvitamin D3 with p-nitrophenylchloroformate resulted in conversion to the respective 3-p-nitrophenylcarbonates. Reaction of the p-nitrophenylcarbonates with amines produced the 3-carbamates in good yield. Careful selection of commercially available amines and non-acidic conditions made this pathway amenable to the preparation of fluorescent, chemiluminescent, or biotinylated conjugates. This strategy offers a general method for the preparation of vitamin D conjugates.     

Comparison of sample digestion procedures for the determination of arsenic in certified marine samples using the FI-HG-AAS-technique

 High-pressure digestion and a closed-vessel microwave heated system, both employing a mixture of nitric acid and hydrogen peroxide as digesting agent, were tested for decomposing the certified samples of BCR 278 mussel tissue (Mytilus edulis) and of BCR 422 cod muscle to determine arsenic by use of FI-HG-AAS. While the microwave system is insufficient to mineralize arsenic in marine samples (arsenic recoveries of 13±10% in BCR 278, 2±1% in BCR 422; n=4), high-pressure ashing at 300 °C results in recovery percentages of 56±15% (n=4) in mussel tissue (BCR 278) and of 25±10% (n=4) in cod muscle (BCR 422). A dry ashing procedure is given as a reference digestion, yielding complete recoveries of arsenic for both materials. The nitrite interference arising during measurement can be entirely overcome by using an amino sulfuric acid concentration of about 350 mmol/L in the solutions for measurement. Received: 30 April 1996/Revised: 12 July 1996/Accepted: 16 July 1996     

Auf eine Verf?lschung des Perubalsams

Ohne Zusammenfassung     

Copaiva-Balsam

Ohne Zusammenfassung     

Das Enolisierungsverhalten des 2-Benzoylacetoacetanilids

A study of the NMR and IR spectra shows 2-benzoylacetoacetanilide existing in the enol form in a rate of 85% (solvent acetone). Only two of the three possible enol tautomers can be proved in a rate of 38%: 47%. Because of steric hindrance the third tautomere cannot be formed. There is some evidence for a chelated ketamine structure in the keto form and in one of the enol forms.     

Further Expansion of the trans-Diels-Alder Paradigm: Reductive Alkylation of α-Cyanoketones

Reductive alkylation of Diels-Alder-derived ring junction α-cyanoketones provides a route to trans-fused bicyclic systems.     

Bridged dihydroxypyridine ligands for the synthesis of expanded helicates

The assembly of organometallic half-sandwich complexes with bis(dihydroxypyridine) ligands gives hexanuclear structures, which can be regarded as expanded triple-stranded helicates.     

Cembranoid diterpenes and a briarane diterpene from corals

Two new cembrane diterpenes (+)-polydactylide (1) and (+)-7alpha,8beta-dihydroxydeepoxysarcophine (2) together with (+)-sarcophine (3) and (+)-sarcophytoxide (4) have been isolated from the soft coral Sinularia polydactyla. The new cembrane diterpene (-)-7beta-hydroxy-8alpha-methoxydeepoxysarcophine (5) has been obtained from the soft coral Sarcophyton trocheliophorum and the known briarane diterpene briaexcavatolide W (6) from the gorgonian coral Briareum sp.The structures were determined primarily by NMR spectroscopy. The assignment of NMR signals was performed by means of (1)H-(1)H COSY, ROESY, HMQC and HMBC experiments.