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.     

Zur Kenntnis der β-Lysin-Mutase-Reaktion: Mechanismus und sterischer Verlauf

Investigations on the β-lysine mutase reaction: Mechanism and steric course The steric course and some mechanistic aspects of the coenzyme-B₁₂-dependent β-lysine-mutase reaction, in which (3 S)-β-lysine is converted to (3 S, 5 S)-3, 5-diaminohexanoate, have been investigated by means of tritium labelling. The reaction involves migration of an hydrogen atom from C(5) of the substrate to C(5′) of coenzyme B₁₂ and back-transfer to C(6) of the product. In the presence of [5′-³H]-coenzyme B₁₂ the enzyme catalyzes the exchange of label between the cofactor and one of the diastereotopic H-atoms at C(5) of the substrate. The exchangeable hydrogen atom is identical with the one specifically involved in the migration reaction. Degradation of the tritiated β-lysine obtained in such experiments yielded a sample of tritiated succinic acid which was shown in an enzymic assay involving partial oxidation with succinate dehydrogenase, to possess the (S)-configuration. Thus, the overall substitution at C(5) occurs with inversion of configuration.     

Doppelt und dreifach funktionalisierte,enantiomerenreine C4-Synthesebausteine aus β-Hydroxybuttersäure, Äpfelsäure und Weinsäure

Enantiomerically Pure Synthetic Building Blocks with Four C-Atoms and Two or Three Functional Groups from β-Hydroxy-butanoic, Malic, and Tartaric Acid The pool of chiral, non-racemic electrophilic building blocks, which are available from simple natural products in both enantiomeric forms is enlarged by the epoxides 3, 5 , and 10 , by the tosylate 12a , and by the aldehydes 18 (cf. symbols A-D , 14 , and Scheme 1). Key steps of the conversions leading from hydroxyacids to the building blocks are: epoxide-opening by triethylborohydride ( 1 → 2a ) and tosylate reduction ( 12a → 12b ); the Mitsunobu inversion ( 2a → 4a ); the reduction of (R, R)-tartaric ester to (R)-malic ester by NBS (N-bromosuccinimide) opening of the benzaldehyde acetal 8 and tin hydride reduction ( 6c → 7c ); the enantiomer enrichment of optically active ethyl β-hydroxy-butanoate through the crystalline dinitrobenzoate 21b . Detailed procedures are given for large scale preparations of the key intermediates. The enantiomeric purities of the building blocks are secured by correlations.     

Die absolute Konfiguration von 1-2H1-Äthanol

(S)-l-²H₁-Ethanol (6) has been prepared in three steps from (–)-erythro-(2R,3S)-3-²H₁-butan-2-ol (2) , itself available from cis-butene by asymmetric hydroboration. In enzymatic tests with yeast alcohol dehydrogenase this deuterated ethanol proved to be indistinguishable from the laevorotatory isomer. This establishes the (S)-chirality of the latter and at the same time defines the stereospecificity of the yeast alcohol dehydrogenase.     

Herstellung enantiomerenreiner Derivate von 3-Amino- und 3-Mercaptobuttersäure durch SN2-Ringöffnung des β-Lactons und eines 1,3-Dixoanons aus der 3-Hydroxybuttersä ure

Preparation of Enantiomerically Pure Derivatives of 3-Amino- and 3-Mercaptobutanoic Acid by S_N2 Ring Opening of the β-Lactone and a 1,3-Dioxanone Derived from 3-Hydroxybutanoic Acid From (S)-4-methyloxetan-2-one ( 1 ), the β-butyrolactone readily available from the biopolymer ( R )-polyhydroxybutyrate (PHB) and various C, N, O and S nucleophiles, the following compounds are prepared:(s)-2-hydroxy-4-octanone ( 3 ), (R)-3-aminobutanoic acid ( 7 ) and its N-benzyl derivative 5 , (R)-3-azidobutanoic acid ( 6 ) (R)-3-mercaptobutanoic acid ( 10 ), (R)-3-(phenylthio)butanoic acid ( 8 ) and its sulfoxide 9 . The (6R)-2,6-dimethyl-2-ethoxy-1,3-dioxan-4-one ( 4 ) from (R)-3-hydroxybutanoic acid undergoes S^N2 ring opening with benzylamine to give the N-benzyl derivative (ent- 5 ) of (S)-3-aminobutanoic acid in 30?40% yield.     

Neue Diterpene aus Blattdrüsen von Plectranthus barbatus (Labiatae). Die absolute Konfiguration der 2-Hydroxypropyl-Seitenkette in Coleon E

Novel Diterpenoids from Leaf Glands of Plectranthus barbatus (Labiatae). The Absolute Configuration of the 2-Hydroxypropyl Group in Coleon E In addition to the previously reported quinone methides coleon E ( 1a ), coleon F ( 2a ) and the spirocoleon 9 (plectrin), novel rearranged abietanoid dienediones, called (16R)-plectrinon A ( 3a ) and plectrinon B ( 5 ) as well as the allylroyleanone 8a have been isolated from Plectranthus barbatus and their structures elucidated mainly by spectroscopy. Closer investigation of acetylations of 1a and 2a established the hitherto unknown structures 1c , 2c , 3b , 10a , 10b , 11a , 11b , 12a , and 12b . The derivatives 3b , 11a , 11b , 12a , and 12a , and 12b are the products of a nucleophilic attack at the quinone methide system. The analysis of the ¹³C-NMR spectra led to the full assignment of the signals in 1a , 1b , 2a , 3a , and 8a . Correlations by partial syntheses of 3a , from coleon E( 1a ), after oxidation or acetylation/saponification of the latter, established the (R)-configuration of the 2-hydroxypropyl group in 1a . The biomimetic transformation of plectrin ( 9 ) into (16R)-coleon E ( 1a ) is shown to proceed via the unexpected, highly reactive 2-methylspiro[cyclopropane-1,2′-(2′H)-phenanthrene]-1′,3′, 6′-trione 13 . The solvolysis of the spiro(methylcyclopropane) moiety takes place with inversion of the configuration at the attacked C-atom, as established in a previous communication. The 1,3,6-trione 13 is supposed to be also the key intermediate in the biosynthesis of the allyl group in coleon F ( 2a ) which proceeds via a homosigmatropic [1,5]-H shift.     

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.     

Diterpenoide Drüsenfarbstoffe aus Labiaten: 3β-Acetoxyfuerstion,Nilgherron A und Nilgherron B,neue Chinomethane aus Plectranthus nilgherricus BENTH.; absolute Konfiguration von Fuerstion

Leaf-gland Pigments: 3β-Acetoxyfuerstione, Nilgherron A and Nilgherron B, New Quinomethanes from Plectranthus nilgherricus BENTH . (Labiatae); Absolute Configuration of Fuerstione We have isolated from leaf-glands of the above mentioned plant the following deeply coloured quino-methane derivatives: (1) traces of the already known fuerstione ( 1a ); 11,15-dihydroxy-5,7,9 (11), 13-abietatetraen-12-one; (2) the new 3β-acetoxy-fuerstione ( 1b ); (3) nilgherron A ( 5a , I or II), a new dimeric diterpenoid quinomethane, C₄₀H₅₂O₇, formed in the plant obviously by cycloaddition of the o-quinone 8 (9aS, 11R)-11 -hydroxy-2-(1-hydroxy-1-methylethyl-9,9-dimethyl-3,4,7,8,9,9a,10,11- octahydro-5H-dibenzo [a, d]cycloheptene-3,4-dione) with fuerstione; (4) nilgherron B ( 5b , I or II), C₄₂H₅₄O₉, likewise a new compound, formed by the same type of cycloaddition (heterodiene synthesis) of 8 with 3β-acetoxyfuerstione. On the basis of ¹H-NMR. shift arguments structure I is slightly preferred to II for 5a and 5b . Model experiments have shown the easy formation of the dihydrodioxin ring by reaction of an o-benzoquinone with p-quinomethanes. The absolute configuration of fuerstione and 3β-acetoxyfuerstione has been determined by chiroptical methods.     

Absolute Konfiguration der enantiomeren α-CyclogeraniumsäUren, α-Cyclogeraniale, α-Jonone, γ-Jonone, α-und ϵ-Carotine

By chemical correlation with manool and ambrein the absolute configurations of the enantiomeric α-cyclogeranic acids, α-cyclogeranials, α-ionones and α- and ?-carotenes have been elucidated.     

Notiz über die Bestimmung der absoluten Konfiguration von (+)-2-Hydroxy-2, 3-dimethylbuttersäure

Note on the Determination of the Absolute Configuration of (+)-2-Hydroxy-2, 3-dimethylbutyric Acid Chemical correlation of the title compound 1 with (S)-3-isopropyl-3-methyl-5-trimethylsilyl-4-penten-2-one ( 2 ) showed (+)- 1 to have (S)-configuration. Key step was the Baeyer-Villiger oxidation of a very hindered, optically active methyl keton to the corresponding acetoxy compound with trifluoroperacetic acid using slightly modified buffer conditions. It is found, that the erythro/threo assignment of an α, α-disubstituted β-hydroxyester intermediate can be based on the observation, that the ¹H-NMR. signal of H? C(β) of the erythro isomer appears at lower field than that of the threo isomer.