Die absolute Konfiguration der Iridale und Cycloiridale unterschiedlicher Herkunft

The Absolute Configuration of Iridals and Cycloiridals of Different Origin Natural irones are known to occur in enantiomeric forms within Iris oils of different origin. They are formed by oxidative degradation of the cycloiridals (C₃₁-triterpenoids) found in rhizomes of various Iris species. The absolute configuration of iridals from different varieties is determined by ozonolysis of the triterpenoids and comparison of their degradation products with authentic samples of known configuration. It is shown that the initial cyclization of squalene resulting in the formation of a monocyclic seco-ring-A iridal has the same stereo-chemical course throughout all Iris species studied. The subsequent cyclization of the homofarnesyl side chain of the iridals, however, produces cycloiridals with enantiomeric irone moieties within different subspecies of the sword lilies.     

Konstitution und absolute Konfiguration der Rhoeadin-Alkaloide (+)-Alpinigenin und (+)-cis-Alpinigenin

The constitution and absolute configuration of the rhoeadine alkaloids (+)-alpinigenine and (+)-cis-alpinigenine. The fundamental structure of the hemi-acetal phenylbenzazepine alkaloid (+)-alpinigenine ( 1 ), isolated from Papaver bracteatum LINDL ., was derived essentially from ¹H-NMR.- and mass-spectra of 1 and its derivatives 7, 10 and 14 (cf. Scheme 2). The positioning of the four methoxy groups in the two aromatic rings could be deduced from the ¹H-NMR.-spectra of the N-oxides 14 and 15 in which, as a result of favourable sterical and conformational behaviour, an interaction exists between the N-oxide oxygen atom and one of the two ortho protons in ring C. The B/D-trans-fused 1 undergoes isomerization in 1N HCl to cis-alpinigenine ( 16 ). A stereochemical correlation between bases in the trans-and cis-series was enabled via an Emde degradation of the corresponding methylacetal-methyliodides 21 resp. 19 leading to the enantiomeric isochroman derivatives 22 resp. 23 which are achiral at C (2) (Scheme 4). The configuration at C (14) in the hemi-acetals (eg. 1 and 16 ) and the methyl ethers (eg. 7 and 8 ) is discussed in detail (cf. Scheme 7). (+)-Alpinigenine ( 1 ) has the (1S, 2R, 14R) configuration and (+)-cis-alpinigenine ( 16 ), in chloroform or acetone solution, the (1R, 2R, 14R) configuration.     

Die diastereomeren Mutatochrome. Trennung,absolute Konfiguration sowie chiroptische,spektroskopische und chromatographische Charakterisierung

Diastereoisomeric Mutatochromes: Separation, Absolute Configuration, and Spectra and Chromatographic Behaviour (5S, 6R)-5, 6-Epoxy-5, 6-dihydro-β, β-carotent ( 2 ), prepared from azafrinal ( 1 ) was rearranged in an acid-catalyzed reaction into the mixture of (5S, 8S)- and (5S, 8 R)-5, 8-epox-5, 8-dihydro-β, β-carotenes = ‘mutatochrome’. HPLC separation of the individual diastereoisomers led to the pure isomers for the first time. Their structures were assigned by analysis of the characteristic pattern of the signals of H? C(7) and H? C(8), respectively, in ¹H-NMR spectra. Although many reports of the occurrence of ‘mutatochrome’ exist, it is as yet not clear whether optically active or racemic forms predominate in nature. Combination of HPLC separations with UV/VIS and CD spectra should now allow an unambigous identification of the isomer in question.     

Die Kristallstruktur und absolute Konfiguration von Mikrolin

The Crystal Structure and Absolute Configuration of Mikrolin. The crystal structure and absolute configuration of mikrolin has been determined by X-ray diffraction. Crystals of mikrolin belong to space group P2₁2₁2₁ with a = 17.867, b = 7.947, c = 9.824 Å, Z = 4. The structure was solved by multi-solution method, and refined to R = 0.060. The anomalous scattering of CuKα-radiation by chlorine was used to determine the absolute configuration of the molecule.     

Nachweis von C (15)-epimeren Coleonen C und D in der Natur und ihre Bedeutung für den sterischen Verlauf der Bildung des Spirocyclopropanrings

Natural Occurrence of C(15)-Epimeric Coleons C and D and its Significance to the Stereochemistry of the Formation of a Spirocyclopropanring In a previous paper some evidence was presented for a predominant occurrence of epimeric coleons ((15S)-coleon C ((15 S)- 1a ), and (15S)-coleon D ((15S)- 2a )) in Plectranthus lanuginosus [1], The proposed structures have now been proven by careful comparison of their physical data with those of the already described C(15)-epimers whose structures were deduced by X-ray analysis of a derived cis-diketone 3 [5], Examination of the epimeric purity of coleons possessing a 2-hydroxy-1-methylethyl side-chain (coleons C , D , H , I , I ′ and derivatives) isolated from seven different species (Coleus, Plectranthus and Solenostemon) has shown that these coleons always occur as a mixture of C(15)-epimers, although in most cases with one predominant epimer. The consequences for the stereochemistry of the postulated in vivo formation of the methyl-substituted spirocyclopropane substructure is discussed.     

Über die absolute Konfiguration der Visnagane

(+)-cis-Khellactone methyl ether ( 4 ) and (?)-trans-khellactone methyl ether ( 6 ) had earlier been assigned the absolute configurations 3′-S; 4′-S and 3′-S; 4′-R, respectively, on the basis of the FREUDENBERG , rule. Both compounds together with their defunctionalised derivatives (?)- 7 and (+)- 8 (=(+)-lomatin), obtained from a mixture of (+)-visnadin ( 1 ) and (+)-samidin ( 2 ), were investigated by the HOREAU method. A conformational analytical study showed that the optical yield should rise in the order 4 < 6 < 7 , 8. This order was found and the α-phenylbutyric acid liberated was always dextrorotatory. The centre 3′ of the khellactones and their derivatives must be R-chiral and not S. Treatment of (?)- 6 with pyridinium perbromide gave (?)-trans-3-bromokhellactone methyl ether ( 11 ) as orthorhombic crystals. The X-ray crystal structure determination was made using the anomalous scattering of the Mo-K α radiation by Br. The result, — centre 3′ R-chiral (fig. g) — showed that the HOREAU method was correct.     

Die absolute Konfiguration von Carquejol und verwandten o-Menthan-Derivaten

The structure of carquejol is amended to that of cis-3-hydroxy-o-mentha-1(7),4,8-triene; the chirality has been confirmed as 2 R, 3 S by correlation with the (?)-cis-o-menthane obtained from carquejol and that from (+)-verbenene of known absolute configuration. The two double bonds of the dihydrocarquejol system ( 15 and 16 ) constitute a helical system, that especially in the case of the acetate ( 16 ) fixes the isopropenyl group in such a way that a very high Δ? value in the CD. curve is observed. The conformational significance of this phenomenon is discussed.     

Über die absolute Konfiguration der Cantharsäure und des Palasonins

The absolute configurations of (+)-cantharic acid, a chiral derivative of the achiral insect defensive substance cantharidin ( 1 ), and of palasonin, a lower homologue of 1 occurring in the plant Butea frondosa, were shown to be represented by formulas 2 and 3 , respectively (scheme 1). These results were obtained by application of the Horeau method (table 1) on the (+)-cantharic acid derivatives (+)- 5 , (?)- 7 , and (?) 11 (scheme 2), and the palasonin derivatives (+)- 29 and (+)- 30 (scheme 4), as well as by comparison of the chiroptical properties (tables 2 and 3) of a number of derivatives, prepared from either cantharic acid or palasonin. – Attempts to incorporate various radioactively labelled precursors into palasonin ( 3 ), using young and adult plants, have been so far unsuccessful.     

Bildung,Kristallstruktur und absolute Konfiguration von (−)-N-(Chloromethyl)galanthaminium-chlorid

Formation, X-Ray Crystal Structure, and Absolute Configuration of (?)-N-(Chloromethyl)galanthaminium Chloride The acetylcholinesterase inhibitor galanthamine ( 1 ), main alkaloid of several Narcissus species, readily forms a quaternary ammonium salt by reaction with the solvent CH₂Cl₂. The structure and absolute configuration of (?)-N-(chloromethyl)galanthaminium chloride ( 2 ) were determined by X-ray diffraction (R = 0.075 for 2775 observed independent reflexions) and NMR spectroscopy. The tetragonal crystals (space group P4₃) contain two crystallographically independent cations which do not differ significantly from one another. The CH₂Cl group is attached to the quaternary N-atom in stereospecific (R)-configuration. In the crystal, the configurational position of the Me group at the N-atom of 2 differs from that of the crystalline free base 1 . Hydrogen bonding is observed from the OH group at C(3) of 2 to the Cl^? anion or to the Cl-atom of an adjacent cation.     

Totalsynthese und absolute Konfiguration von natürlichem Multifloramin

The diphenol 1 was resolved into its antipodes and their absolute configuration was established. The levorotatory isomer R-(?)- 1 was oxidized to the dienone R-(?)- 6 , which was rearranged to afford natural (?)-multifloramine (R-(?)- 7 ), thus establishing that the latter has the R-configuration. By the same reaction sequences, the enantiomeric diphenol S-(+)- 1 was transformed to provide (+)-multifloramine (S-(+)- 7 ) of the S-configuration.     

Anreicherung der Enantiomeren,Circulardichroismus und absolute Konfiguration vonN,N,N′,N′-Tetramethyldithiooxamid

(+)- and (?)-1 (N,N,N′,N′-Tetramethyldithiooxamide) were enriched by semipreparative liquid chromatography on triacetylcellulose. According to¹HNMR in the presence of an optically active auxiliary, the sample of (+)₃₆₅-1 had an enantiomeric purity of 0,50±0,01, thus permitting to calculate the CD spectrum for the pure enantiomer. The CD and UV spectra are discussed in terms of qualitative MO theory. Thereby, the absolute configuration of (+)₃₆₅-1 is determined to be (R).     

Trennung und Bestimmung der DDT-Isomeren

Ohne Zusammenfassung     

Trennung und Bestimmung der Metalle der Schwefelammoniumgruppe

Ohne Zusammenfassung