C45- und C50-Carotinoide. 5. Mitteilung

C₄₅- and C₅₀-Carotenoids. Synthesis of an Optically Active Cyclic C₂₀-Building Block and of (2R,2′S)-3′,4′-Didehydro-1′,2′-dihydro-2-(4-hydroxy-3-methylbut-2-enyl)-2′-(3-methylbut-2-enyl)-β,ψ-caroten-1′-ol (= C. p. 473) The synthesis of the optically active C₂₀-building block (R)- 16 and of the optically active C₅₀-carotenoid C.p. 473 ( 1 ) starting from (?)-β-pinene is reported.     

C45- and C50-Carotinoide. 1. Mitteilung. Synthese von (R)- and (S)-Lavandulol

C₄₅- and C₅₀-Carotenoids, 1st Communication. Synthesis of (R)- and (S)-Lavandulol Starting with methyl (3 R)-3-hydroxybutanoate ((R)-7) and ethyl (3 S)-3- hydroxybutanoate ((S)- 11 ), respectively, (R)- and (S)-lavandulol ((R)- 1 and (S)- 1 ) were synthesized with high optical purity. The synthesized key intermediates (R)- 6 and (S)- 6 are suitable compounds for the synthesis of optically active acyclic C₄₅- and C₅₀-carotenoids.     

C45 und C50-Carotinoide. 6. Mitteilung. Synthese eines optisch aktiven cyclischen C20-Bausteins und von Decaprenoxanthin (= (2R, 6R, 2′R, 6′R)-2,2′-Bis(4-hydroxy-3-methylbut-2-enyl)-ϵ, ϵ-carotin)

C₄₅- and C₅₀-Carotenoids: Synthesis of an Optically Active Cyclic C₂₀-Building Block and of Decaprenoxanthin ( = (2R, 6R, 2′R, 6′R)-2,2′-Bis(4-hydroxy-3-methylbut-2-enyl)-?, ?-carotene) The synthesis of the optically active cyclic C₂₀-building block (R, R) -15 and of the optically active C₅₀-carotenoid (2R, 6R, 2′R, 6′R)-decaprenoxanthin ( 1 ) starting from (-)-β-pinene ((S)- 2 ) is reported.     

C45- und C50-Carotinoide. 4. Mitteilung. Synthese von optisch aktiven cyclischen C20-Bausteinen und von (2R,2′R)-2,2′-Bis(4-hydroxy-3-methyl-2-butenyl)-β,β-carotin ( = C.p. 450)

C₄₅- and C₅₀-Carotenoids: Synthesis of Optically Active Cyclic C₂₀-Building Blocks and of (2R,2′R)-2,2′-Bis(4-hydroxy-3-methyl-2-butenyl)-β,β-carotene ( = C.p. 450) The synthesis of the optically active C₂₀-building blocks (R)- 26 and (R)- 39 and of the optically active cyclic C₅₀-carotenoid C.p. 450 ( 3 ) starting from (?)-β-pinene is reported.     

C45- und C50-Carotinoide. 3. Mitteilung. Synthese von (S)-Trisanhydrobacterioruberin

C₄₅-and C₅₀-Carotenoids: Synthesis of (S)-Trisanhydrobacterioruberin The Synthesis of (S)-trisanhydrobacterioruberin ((S)- 1 ) is reported.     

Totalsynthese von natürlichem α-Tocopherol. 4. Mitteilung. Aufbau des Chromanringsystems aus Trimethylhydrochinon und einem optisch aktiven C4- bzw. C5-Synthon

Total Synthesis of Natural α-Tocopherol Two independent syntheses of (S)-6-hydroxy-2,5,7,8-tetramethylchroman-2-yl-methanol ( 8b ), (Scheme 6 resp. 9) as optically active chroman moiety for the preparation of natural vitamin E via (S)-6-acetoxy-2,5,7,8-tetramethylchroman-2-carboaldehyde ( 2a ) (Scheme 1) and a corresponding side chain are described. Both reaction sequences use trimethyl-hydroquinone as starting material; one approach employs an optically active C₄ unit ( 10a ) (Schemes 5 and 6) to introduce the required configuration at C(2), the other uses an optically active C₅-synthon ( 11a ) (Schemes 8 and 9) to build the optically active chroman unit. The correct configuration and optical purity of the chroman synthesized is established by correlation with optically pure material of known configuration from which natural vitamin E had already been derived [2].     

Optisch aktive C5-Bausteine zur Synthese von natürlich vorkommenden Terpenen

Optically Active C₅-Synthons for the Synthesis of Naturally Occurring Terpenes The optically active synthons (S)- 22 , (R)- 23 , (R)- 25 and (R)- 26 were prepared from L -serine. Furthermore the tertiary alcohol 6 was synthesized from L -serine (→(S)- 6 ) and D -mannitol (→(R)- 6 ). These compounds are suitable for the synthesis of optically active natural products.     

Synthese von optisch aktiven,natürlichen Carotinoiden und strukturell verwandten Naturprodukten. VII. Synthese von (3R)-3-Hydroxyretinol, (3R)-3-Hydroxyretinal und (3R)-3-Hydroxyretinsäure

Synthesis of optically active natural carotenoids and structurally related compounds. VII. Synthesis of (3R)-3-hydroxyretinol, (3R)-3-hydroxyretinal and (3R)-3-hydroxyretinoic acid The synthesis of (3R)-3-hydroxyretinol, ( 7 ), (3R)-3-hydroxyretinal ( 9 ) and (3R)-3-hydroxyretinoic acid ( 5 ) according to the building principle C₁₅ + C₅ = C₂₀ is reported utilizing the optically active C₁₅-phosphonium salt 2 and the C₅-aldehyde ester 3 .     

Synthese von optisch aktiven,natürlichen Carotinoiden und strukturell verwandten Naturprodukten. IX. Synthese von (3R)-Hydroxyechinenon, (3R, 3′R)- und (3R, 3′S)-Adonixanthin, (3R)-Adonirubin,deren optischen Antipoden und verwandten Verbindungen

Synthesis of Optically Active Natural Carotenoids and Structurally Related Compounds. IX. Synthesis of (3R)-Hydroxyechinenone, (3R, 3′R)- and (3R, 3′S)-Adonixanthin, (3R)-Adonirubin, Their Optical Antipodes and Related Compounds The synthesis of racemic and optically active hydroxyechinenone ( 12–14 ), adonixanthin ( 16–19 ), adonirubin ( 22–24 ), meso-astaxanthin ( 26 ) and their corresponding diosphenols 15, 20, 21, 25, 27, 28 , and 29 ) by Wittig reaction is reported, starting from suitable C₁₅-phosphonium salts and C₁₀-aldehydes.     

Synthesis,Separation, and Characterization of Optically Pure C76 Mono-Adducts

Nucleophilic Bingel cyclopropanation of D₂-C₇₆ with bis[(S)-1-phenylbutyl] 2-bromomalonate in toluene in the presence of base yielded three constitutionally isomeric pairs of diastereoisomeric mono-adducts together with one other constitutional isomer. All seven mono-adducts were isolated in optically pure form by prep. HPLC on a (S,S)-Whelk-O1 chiral stationary phase. They represent the first optically pure adducts of an inherently chiral fullerene. Characterization by UV/VIS, CD, ¹³C- and ¹H-NMR spectroscopy allowed identification of pairs of stereoisomers and symmetry assignments: the two pairs of diastereoisomers which were isolated as the major product possess C₁ symmetry, whereas the third pair of diastereoisomers, which is a minor product, is C₂-symmetrical. The circular dichroism spectra of the optically active C₇₆-adducts showed very pronounced Cotton effects resulting from strong chiroptical contributions of the chiral fullerene chromophore with the maximum observed Δε values being twice as high than those previously measured for optically active adducts of achiral fullerenes with a chiral addition pattern. Whereas the regioselectivity of mono-additions to C₇₀ correlates with the degree of local bond curvature and the regioselectivity of multiple Bingel cyclopropanations of C₆₀ with electronic parameters such as coefficients of the lowest unoccupied molecular orbital (LUMO), no such simple predictive correlations exist for the nucleophilic addition to C₇₆. Despite full spectral characterization, an unambiguous structural assignment of the isolated compounds was not possible, except for the two C₂-symmetrical isomers. Based on considerations of local bond curvature and the previous experiences with the chemistry of C₇₀, the structures of the C₂-symmetrical stereoisomers were assigned as (S,S,^fC)- 3 and (S,S,^fA)- 3 , resulting from addition to the polar α-type C(1)? C(6) bond.     

Totalsynthese von natürlichem α-Tocopherol. 1. Mitteilung. Herstellung bifunktioneller,optisch aktiver Synthesebausteine für die Seitenkette mit Hilfe mikrobiologischer Umwandlungen

Total Synthesis of Natural α-Tocopherol. I. Preparation of Bifunctional Optically Active Precursors for the Synthesis of the Side Chain by Means of Microbiological Transformations Our concept for a new total synthesis of natural α-tocopherol includes the synthesis of a corresponding (3 R, 7 R)-configurated C₁₅ side chain to be built up by using twice an optically active C₅ unit together with an achiral C₅ end part. (S)-3-methyl-γ-butyrolactone ( 11 ) and (S)-2-methyl-γ-butyrolactone ( 9 ) represent suitable bifunctional C₅-precursors for this purpose. These two key compounds have been prepared by fermentative transformation including the enantioselective hydrogenation of the double bond of ethyl-4, 4-dimethoxy-3-methylcrotonate ( 5 ) by bakers yeast (yielding 11 after ester hydrolysis and cyclization of the fermentation product) and (E)-3-(1′, 3′-dioxolan-2′-yl)-2-buten-1-ol ( 8 ) by the fungus Geotrichum candidum (yielding directly 9 ).     

Synthese von optisch aktiven Carotinoiden mit 3,5,6-Trihydroxy-5-6-dihydro-β-Endgruppen

Syntheses of Optically Active Carotenoids with 3,5,6-Trihydroxy-5,6-dihydro β-End Groups For the specification of the relative and absolute configuration in carotenoids with 3,5,6-trihydroxy-5-6-dihydro β-end groups, several ionone derivatives and carotenoids bearing this end group were synthesized. Acid-catalyzed hydrolysis of (3S,5S,6R)– acetoxy-5,6-epoxy-5,6-dihydro-β-ionone ( 7 ) and of its (3S,5R,6S)-isomer ( 13 ) gave the diols 8 and 15 , respectively, with exclusive inversion at c(5) (Scheme 2). Compared to this, mild acid hydrolysis of caroten-5-6-expoxides in the presence of H₂O resulted in the formation of 5,6-diols with either inversion or retention of the configuration at C(6) (Scheme 3). Spectroscopic data allowed us to distinguish the relative configurations (3R*,5S*,6S*) (see A ), (3R*,5R*,6R*) (see B ), (3R*,5S*,6R*) (see C ), and (3R*,5R*,6S*) (see D ), of the 3,5,6-trihydroxy-5-6-dihydro β-end groups. Syntheses of the optically active carotene-hexols 20 and 21 and comparison with published data led to a revision of the structure of mectrazanthin (now formulated as 20 ), heteroxanthin (now formulated as 28 ), and further carotenoids with 3,5,6-trihydroxy end groups.     

C45- and C50-Carotehoids. Part 8. Synthesis of (all-E,2S,2′S)-bacterioruberin, (all-E,2S,2′S)-monoanhydrobacterioruberin, (all-E,2S,2′S)-bisanhydrobacterioruberin, (all- E,2R,2′R)-3,4,3′,4′-tetrahydrobisanhydro- bacterioruberin,and (all-E,S)-2-isopentenyl-3,4-dehydrorhodopin

Starting from (R)-3-hydroxybutyric acid ((R)- 10 ) the C₄₅- and C₅₀-carotenoids (all-E,2S,2′S)-bacterioruberm ( 1 ), (all-E,2S,2′S)-monoanhydrobacterioruberin ( 2 ), (all-E,2S,2′S)-bisanhydrobacterioruberin ( 3 ), (all-E,2R,2′R)-3,4,3′,4′-tetrahydrobisanhydrobacterioruberin ( 5 ), and (all-E,S)-2-isopentenyl-3,4-dehydrorhodopin ( 6 ) were synthesized. By comparison of the chiroptical data of the natural and the synthetic compounds, the (2S)- and (2′S)-configuration of the natural products 1–3 and 6 was established.     

Totalsynthese von natürlichem α-Tocopherol. 2. Mitteilung. Aufbau der Seitenkette aus (−)-(S)-3-Methyl-γ-butyrolacton

Total Synthesis of Natural α-Tocopherol A short and efficient route to optically pure (+)-(3 R, 7 R)-trimethyldodecanol ( 14 ) is demonstrated, 14 serving as side chain unit in the preparation of natural vitamin E. The synthesis of 14 is based on the concept of using a single optically active C₅-synthon of suitable configuration and functionalization to introduce both asymmetric centres in 14 . (?)-(S)-3-Methyl-γ-butyrolacton ( 1 ) and ethyl (?)-(S)-4-bromo-3-methylbutyrate ( 2 ), respectively, is used in a sequence of either two Grignard C,C-coupling reactions 5 → 8 and 12 → 13 or two Wittig reactions 17a → 18 and 20 → 21 to achieve this goal. 14 is converted to (2 R, 4′R, 8′R)-α-tocopherol (= vitamin E) by coupling with a chroman unit in known manner. Optical purity of products and intermediates is established.     

Stable frustrated phases in chiral liquid crystals derived from optically active (R)- and (S)-3-ethylmercapto-2-methylpropionic acids

Highly optically pure (R)- and (S)-3-ethylmercapto-2-methylpropionic acids were synthesized by using optically active (D)- and (L)-2,10-camphorsultams as chiral auxiliaries, respectively. Their derivatives, (R)- and (S)-EMMPNmB (m=6-12), were prepared for investigation. Microscopic texture observations demonstrated that the materials possess three stable frustrated phases: BP, TGB_A* and TGB_C* phases. Interestingly, it was found that the N* phase behaves as an intermediary phase between BP and TGB_A* phases in a rather narrow temperature range (calc. 0.5-1.4°C). A study of the racemic mixture, (±)-EMMPNmB (m=10), indicated that the chirality of the molecule could suppress the formation of smectic phases in the heating process. An increase of alkyl chain length favoured the formation of the TGB phases particularly, in accompaniment with a change of TGB phases from monotropic to enantiotropic. Moderate maximum P _S values (calc. 14-19 nC cm^-2) and apparent tilt angle (calc. 20°) were obtained for the TGB_C* phase in a surface stabilized ferroelectric liquid crystal geometry.     

C45- and C50-Carotenoids Part7 Total synthesis of (all-E,2R,6R,2′R,6′R)- and (all-E,2R,6S,2′R,6′S)-2,2′-Bis(4-hydroxy-3-methylbut-2-enyl)-γ,γ-carotene (sarcinaxanthin)

The synthesis of sarcinaxanthin ((2R,6R,2′R,6′R)- 1 ), a symmetrical C₅₀-carotenoid with two γ-end groups, isolated from Sarcina lutea and from Cellulomonas biazotea as major pigment, was based on the strategy C₂₀ + C₁₀ + C₂₀ = C₅₀ using camphoric acid as starting material for the C₂₀-end group 3. The key step of the synthesis is a ring enlargement of the cyclopentane derivative 10 with 2,4,4,6-tetrabromocyclohexa-2,5-dien-1-one (TBCO) to give the cyclohexane derivative 11 (Scheme 1). The spectroscopic data of the synthetic compound are in full agreement with the data of the isolated product and give the final proof for the (2R,6R,2′R,6′R) chirality of natural sarcinaxanthin.     

Optically active organoaluminum based inclusion compounds. Synthesis and characterization of (S)-(−)-α-[(C6H5)CH(CH3)N(CH3)3][Al2R6I] (R=CH3, C2H5)

The optically active quaternary ammonium salt (S)-(?)-α-[(C₆H₅)CH(CH₃)N(CH₃)₃I] reacts with AlR₃ to afford optically active organoaluminum based inclusion compounds, liquid clathrates, of the formula (S)-(?)-α-[(C₆H₅)CH(CH₃)N(CH₃)₃][Al₂R₆I] (R=CH₃, C₂H₅). Specific rotation ([α] ₂₅ ^D ) for the Al(CH₃)₃ compound was determined to be ?13.19° while that for the Al(C₂H₅)₃ analog was determined to be ?14.30°. There are 13.8 toluene molecules per anionic moiety for the trimethylaluminum based liquid clathrate while there are 15.0 toluene molecules per anion for the corresponding triethylaluminum inclusion compound.     

Biosynthesis of the Irregular C12-Terpenoid Dehydrogeosmin in Flower Heads of Rebutia marsoneri WERD. (Cactaceae)

Farnesol ( 3a ) is the precursor to the irregular C₁₂ terpenoid (4S, 4aS, 8aS)-1,2,3,4,4a,5,8,8a-octahydro-4,8a-dimethylnaphthalen-4a-ol (= dehydrogeosmin; 1 ). The irregular C-backbone originates from the oxidative removal of a C₃ side chain from a C₁₅ eudesmane-type intermediate (Scheme 2). The bicyclic C-framework is assembled by a formal addition of H₂O across the endocyclic double bonds of a monocyclic germacradiene-type precursor. The biosynthetic pathway follows from administration of the deuteriated farnesols 3b–e to flower heads of the cactaceae Rebutia marsoneri Werd. and mass-spectroscopic analysis of the collected volatiles.     

Synthese von optisch aktiven,natürlichen Carotinoiden und strukturell verwandten Naturprodukten. IV. Synthese von (3R, 3′R, 6′R)-Lutein. Vorläufige Mitteilung

Synthesis of optically active natural carotenoids and structurally related compounds. IV. Synthesis of (3R, 3′R, 6′R)-lutein The synthesis of (3R, 3′R, 6′R)-lutein ( 19 ) according to the building principle C₂₅+C₁₅?C₄₀ is reported utilizing (R)-4-hydroxy-2,6,6-trimethyl-2-cyclohexen-1-one ( 4 ) as a readily available key intermediate.     

Technical Procedures for the Syntheses of Carotenoids and Related Compounds from 6-Oxo-isophorone: Syntheses of (3R,3′R)-Zeaxanthin. Part I

Starting from the readily available, optically active (4R)-4-hydroxy-2,2,6-trimethylcyclohexanone ( 1 ), a new technical synthesis of (3R,3′R)-zeaxanthin is described. According to a 2(C₉ + C₆) + C₁₀ = C₄₀ construction scheme, the ketone 1 was first transformed with (E)-3-methylpent-2-en-4-yn-1-ol ( 5 ) into a C₁₅-intermediate which, by a three-step sequence, could be converted into the known olefinic C₁₅-Wittig salt 4 . Optimized conditions for the final Wittig reaction of 4 with the C₁₀-dialdehyde 3 are discussed. Based on 1 , the overall yield of the entire technical process is ca. 40%.