Jürgen Voss

EPR-untersuchungen an carbonsäureestern—II : Radikalanionen der thion- und dithiobenzoesäureester

Zusammenfassung Thion- ( 2 ) und Dithiobenzoesaureester ( 3 ) sowie ihre kernsubstituierten Derivate 4 und 5 lassen sich durch in situ-Elektroreduktion in Radikalanionen uberfuhren.—Die EPR-Spektren von 2–5 werden aufgenommen. Aus den Hyperfeinstrukturkopplungskonstanten und g-Werten sowie polarographischen Halbstufenpotentialen werden Ruckschlusse uber die Spindichteverteilung im aromatischen Ring und in der funktionellen Gruppe gezogen, wobei insbesondere die Wirkung von ortho -Substituenten (Verdrillung der Molekulhalften) untersucht wird.—Die Ergebnisse stimmen befriedigend mit MO-Rechnungen vom McLachlan-Typ uberein. Aus der Abstufung der Alkylkopplungskonstanten kann geschlossen werden, dass die Alkylreste eine Konformation mit minimaler sterischer Behinderung der Thiocarbonylgruppe einnehmen.

EPR-untersuchungen an carbonsäureestern—I : Oxalsäureester-radikalanionen (dialkoxysemidione)

Zusammenfassung Oxalsauredialkyl- und -diphenylester werden durch interne Elektrolyse zu den entsprechenden Radikalanionen 3a–3p (“Dialkoxysemidionen”) reduziert.—Die EPR-Spektren dieser Spezies, d.h. die HFS-Kopplungskonstanten der α-standigen Protonen werden im Hinblick auf die Spindichteverteilung und Konformation interpretiert. Es wird gezeigt, dass primare Alkylgruppen zeitgemittelte Diederwinkel Θ zwischen der Richtung der α—CH-Bindung und der z-Achse des π-Elektronensystems von 42–47°, abhangend von der Grosse des β-Substituenten. aufweisen, wahrend die CH-Bindung sekundarer Reste um ungefahr 60° aus der z-Richtung herausgedreht ist.

Synthesis and Structural Elucidation of 2′‐Deoxy‐4′‐thio‐L‐threo‐pentofuranosylpyrimidine and ‐purine Nucleosides

Benzyl 3,5-di-O-benzyl-2-deoxy-1,4-dithio-L-threo-pentofuranoside (13) was used as glycosyl donor for the synthesis of 4′-thio-L-threo-pentofuranosyluracil derivatives 23−29. The corresponding cytidine analogue 33 was prepared from 13 via the triazolo derivative 31. Adenine and hypoxanthine did not react with 13. Therefore, 13 was transformed into the 1-O-acetate 15, which was a sufficiently reactive donor for the purine bases, yielding 4′-thio-L-threo-pentofuranosylpurines 36 and 37. In most cases it was possible to obtain pure anomers of the deprotected nucleoside analogues, three of which were suitable for X-ray structural analyses.

EPR-untersuchungen an carbonsäureestern—III: Thiooxalsäureester-radikalanionen

Zusammenfassung Die polarographische und cyclovoltammetrische Untersuchung der Thiooxalsaureester 1–6 zeigt, dass diese reversibel zu Radikalanionen reduzierbar sind. Dementsprechend liefern sie nach in-situ-Elektroreduktion EPR-Spektren, aus denen sich unter Zuhilfenahme der Elektronenspektren Ruckschlusse auf die Spindichteverteilung ziehen lassen. Dabei zeigt sich, dass pπ am Sauerstoff der Oxoester hoher ist als am Schwefel der entsprechenden Thionester.

Preparation of 2,3,5-Tri-O-benzyl-4-thio-L-arabino-furanosides and the Corresponding 4′-Thionucleoside Analogues

1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-arabino-furanose (9) has been prepared from D-xylose via the 1,4-dithio-L-arabino-furanoside 8. The crucial step of the reaction, i.e. the intramolecular cyclization of the open-chain dithioacetal 5, has been achieved in a yield of 90% by applying tetrabutylammonium iodide as promoter. Reaction of 9 with bis(trimethylsilyl)uracil or -thymine led to the benzyl derivatives 12 and 13 from which the deprotected 4′-thionucleoside analogues 14 and 15 have been prepared by debenzylation with boron tribromide.

RADICAL IONS 561,2 ONE-ELECTRON OXIDATION OF 1,2-DITHIETE DERIVATIVES

Abstract Novel 1,2-dithiete derivatives R2C2S2 with R = [sbnd]C(CH3)3 and [sbnd]C(CH3)2[sbnd]CH2[sbnd]CH2[sbnd]CH2[sbnd]C(CH3)2[sbnd] are readily oxidized by the one-electron transfer system AlCl3/H2CCl2 to their radical cations. The single line ESR spectra, on high amplification, exhibit 33S satellites in natural abundance. Both the ESR data, i.e. rather large g values and 33S hyperfine coupling constants as well as MNDO closed and open shell calculations for the parent molecule H2C2S2 illustrate that spin and positive charge are predominantly located in the SS bridge of the four-membered ring.

Preparation of selenoanhydro- and telluroanhydroglycofuranosides and some corresponding nucleosides.

Methyl 2,3-anhydro-alpha-D-ribofuranoside (3a) was transformed into methyl 2-seleno-2,5-anhydro-alpha-D-arabinofuranoside (5a) and methyl 3-seleno-3,5-anhydro-alpha-D-xylofuranoside (6a) in two steps via the reaction of the C-5 mesylate of 3a, methyl 2,3-anhydro-5-O-mesyl-alpha-D-ribofuranoside (4a), with sodium hydrogen selenide. The corresponding beta anomer of 3a yielded methyl 3-seleno-3,5-anhydro-beta-D-xylofuranoside as the main product and only traces of methyl 2-seleno-2,5-anhydro-beta-D-arabinofuranoside. Sodium hydrogen telluride transformed 4a into methyl 2-telluro-2,5-anhydro-alpha-D-arabinofuranoside. Starting from 5a we prepared 1-(2-seleno-2,5-anhydro-alpha-D-arabinofuranosyl)uracil and the analogous thymidine nucleoside. Compound 6a could not be transformed into nucleosides.

C,C-coupling with sulfur-stabilized carbanions — 6. Preparation and electrophilic substitution of 1-[3-methyl-2-(2-thiolanylthio)-butyl]piperidine and dethioacetalization of semicyclic dithioacetals☆☆☆

Abstract 1-[3-Methyl-2-(2-thiolanylthio)butyl]piperidine ( 8 ) is obtained from L-valine via enantiomerically pure 1-(2-mercapto-3-methylbutyl)piperidine ( 6 ). The diastereoisomers are separated by column chromatography and the reactions of the carbanion 8a with electrophiles are studied. Semicyclic dithioacetals 12 – 15 are converted into the corresponding carbonyl compounds with [bis(trifluoroacetoxy)iodo]benzene (PIFA). Phenyl dichlorophosphate (PDCP) in the presence of sodium iodide and DMF is found to be a reagent for selective cleavage of the exocyclic CS bond. By using DOWEX 50W and paraformaldehyde in acetone/water a cleavage of both acetalic CS bonds is achieved in certain cases.

Preparation, structural elucidation and reactions of benzyl 2-deoxy-3,5-di-O-methyl-1,4-dithio-l-threo-pentofuranoside and synthesis of the corresponding 2′-deoxy-4′-thionucleosides

Abstract Benzyl 2- deoxy-3,5-di -O- methyl-1,4-dithio- l -threo- pentofuranoside (5) is synthesized in five steps starting with 2-deoxy- d -ribose. The anomers 5α and 5β are separated and their configuration is unequivocally assigned by use of NOE measurements. 2- Deoxy-3,5-di -O- methyl-4-thio- l -threo- pentofuranose is obtained from 5 and mercuric 4-nitrobenzoate. The corresponding nucleosides are prepared from 5 and bis-(trimethylsilyl)uracil or bis-(trimethylsilyl)thymine in the presence of N -iodosuccinimide.

A new method for the assay of aminoacylase: Elaboration of a fixed-incubation method for routine measurements

A simple method suitable for routine determinations of aminoacylase (EC 3.5.1.14) in serum and tissue homogenates is described. It is based on the formation of red charge-transfer complexes from p-benzoquinone and amino acids liberated by cleavage of acylamino acids. Optimal substrates are trifluoroacetyl-L-methionine and chloroacetyl-L-methionine, the first being rapidly hydrolyzed by pancreatic tissue, the latter by liver and kidney homogenates. Sera preferentially split the chloroacetyl compound. Optimal conditions for the assay of serum activity are: 18-20 mm9l/l substrate concentration, 50 mmol/l phosphate buffer pH 6.0, no additives.