Helvetica Chimica Acta

Ohloff, Günther; Vial, Christian; Demole, Edouard; Enggist, Paul; Giersch, Wolfgang; Jégou, Elise; Caruso, Andrew J.; Polonsky, Judith; Lederer, Edgar

doi: 10.1002/hlca.19860690120pmid: N/A

Conformational factors have been found responsible for the dramatic change in odor between (−)‐deoxyambreinolide (12) and its (+)‐epi derivative 13. The presumably molecular event during the receptor interaction has been simulated by the diastereoisomeric 11‐methyl‐ambrox derivatives 3 and 5 as model compounds.

Fehr, Charles; Galindo, José

doi: 10.1002/hlca.19860690127pmid: N/A

The novel reagents formed by combination of allylmagnesium chloride and a strong non‐nucleophilic lithium base (LiNR2) convert non‐ or slowly enolizable carboxylic esters or carboxamides into 2‐propenyl ketones which are protected from further reaction by their in situ conversion into enolates. This modified Grignard reaction is applied to efficient syntheses of α‐damascone, β‐damascone, β‐damascenone, and various other (E)‐1‐propenyl ketones.

Sakai, Ryuichi; Higa, Tatsuo; Jefford, Charles W.; Bernardinelli, GéRald

doi: 10.1002/hlca.19860690113pmid: N/A

Four new halogenated chamigrenes have been isolated from the sea hare, the (E)‐ and (Z)‐9‐(bromomethylidene)‐1,2,5‐trimethylspiro[5.5]undeca‐1,7‐dien‐3‐ones (11 and 10, resp.) the structures of which were deduced by NMR spectroscopy and by comparison with a known relative, the (8R,9R)‐8‐bromo‐9‐chloro‐5,5,9‐trimethyl‐1‐methylidenespiro[5,5]undec‐3‐en‐2‐one (12), and its (11 R)‐11‐acetoxy‐substituted derivative 13. Their structures and absolute configurations were determined and deduced by X‐ray using the absolute‐structure parameter. The configurations were remarkable in being enantiomeric to those of the tertiary chlorochamigrenes isolated so far. Consequently, a more general scheme is proposed to account for their biogenesis.

Hilpert, Hans; Hollenstein, Roger

doi: 10.1002/hlca.19860690116pmid: N/A

The 15N‐NMR spectra of cis‐ and trans‐2,3‐dialkyl‐substituted triaziridines are reported. The assignment of the 15N‐NMR resonances is described, and the chemical‐shift and coupling data are compared with those of aziridines and diaziridines. The 1J(N,H) coupling constants allow one to deduce the relative configuration of the involved N‐atom. In CDCl3, a 1J(N,H) value of 58.1 ± 0.5 Hz is assigned to an NH bond cis to two lone‐pairs of electrons at neighboring N‐atoms, i.e. to the cis,trans‐triaziridines The first stereodescriptor denotes the relative configuration of the two equal alkyl substituents, the second the relative configuration of one alkyl substituent and the H‐atom. , and a value of 51.7 ± 0.5 Hz is assigned to a NH bond cis to only one lone‐pair of electrons, i.e. to trans, cis‐triaziridines.

Ćavara, Luka; Gerson, Fabian; Cowan, Dwaine O.; Lerstrup, Knud

doi: 10.1002/hlca.19860690117pmid: N/A

Hyperfine data and g factors are reported for the radical cations of tetrathiafulvalene (TTF; 1) and of its derivatives 2–13. From the intense satellite spectra of 1+–13+ not only the coupling constants of the 33S isotopes in the TTF moiety could be determined, but also, in favourable cases, those of the 13C isotopes in the central double bond. The former values range from 0.370 (8+) to 0.470 mT (4+) and the latter from 0.255 (8+) to 0.360 mT (4+) in the radical cations of bis(ethylenedithio)‐TTF (8+) and tetracyano‐TTF (4+). The radical cation of TTF (1+) exhibits intermediate values, 0.425 for the 33S and 0.285 mT for the 13C isotopes. The spin population in 1+–13+ resides, to a large extent, in the central S2C  CS2 part of the π‐system. It tends to increase (decrease) by substitution with electron‐accepting (donating) groups in the 2,3,6,7‐positions of TTF.

Milon, Alain; Wolff, Geneviève; Ourisson, Guy; Nakatani, Yoichi

doi: 10.1002/hlca.19860690104pmid: N/A

Four carotenoids (zeaxanthin 1, astaxanthin 2, and their C50 synthetic isoprene‐homologues 3 und 4) have been incorporated into bilayer unilamellar vescles of dimyristoylphospatidylcholine as proved by coelution on a Sepharose column. The incorporation into the bilayer proper has been proved by the sensitivity to phase transition of UV/VIS spectra and circular dichroism. The UV/VIS absorptions of the carotenoids are typical of a lipidic environment. At the temperature of phase transition occur both intermolecular phenomena (aggregation of carotenoid molecules) and intramolecular changes (conformational change). The relative solubilities of the various carotenoids in this phospholipid membrane can be fitted with molecular parameters (length of the lipophilic carotenoid segment vs. lipid bilayer thickness).

Wolf, Jean‐Pierre; Pfander, Hanspeter

doi: 10.1002/hlca.19860690109pmid: N/A

C45‐and C50‐Carotenoids: Synthesis of (S)‐Trisanhydrobacterioruberin

Hamburger, Matthias; Hostettmann, Kurt

doi: 10.1002/hlca.19860690126pmid: N/A

Two glycosides 2 and 3 of the formerly undescribed triterpene 3β,23,27,29‐tetrahydroxyolean‐12‐en‐28‐oic acid (4) have been isolated from the aerial parts of Polygala chamaebuxus L. In addition, a prosapogenin, obtained by basic hydrolysis of a mixture of bidesmosidic saponins, has been identified as tenuifolin (1). The structures have been established by spectroscopic (IR, 1H‐and 13‐C‐NMR, DCI‐ and FAB‐MS) and chemical methods (acid, basic, and enzymatic hydrolysis, acetylation, bromination).

Antoulas, Syméon; Prewo, Roland; Bieri, Jost H.; Viscontini, Max

doi: 10.1002/hlca.19860690125pmid: N/A

Polyacetylated 5,6,7,8‐Tetrahydro‐D‐ and L‐neopterins. A Special Case of N(5)‐Alkylation of 5,6,7,8‐Tetrahydroneopterins

Scheller, Markus E.; Frei, Bruno

doi: 10.1002/hlca.19860690107pmid: N/A

The synthesis of the cyclopropyl silyl ketones 1–4 is described. The trimethylsilyl ketone 1 was prepared from geraniol ((E)‐5) in ca. 10% overall yield by cyclopropanation leading to 6, CrO3 oxidation to the aldehyde 8, reaction of the latter with trimethylsilyl anion to 14A+B, and CrO3 oxidation to 1. Also for the (t‐butyl)dimethylsilyl ketones 2–4, an efficient four‐step synthesis with overall yields of 48%, 85%, and 13%, respectively, was elaborated, starting from the allylic alcohols (E)‐5, and 23. The method of preparation involves as the key step a Wittig rearrangement of the silylallyl ethers ((E/Z)‐20, 24) to the silyl alcohols ((E/Z)‐21, 25), subsequent cyclopropanation (19A + B, 22A + B, 26), and oxidation to the cyclopropyl silyl ketones 2–4.