Camphanic Acid Research Articles

Die bestimmung der absoluten konfigurationen der enantiomeren 3,6-hexanooxepin-4-carbonsäuren und [6]paracyclophan-8-carbonsäuren

The absolute configurations of the title compounds were determined by X-ray structural analysis of one of the (-)-camphanic acid esters of the hydroxymethyl-oxepin (=10a) and the conversion of (M)-(=10a) to (+)-(M)-(=10b) and (+)-(P)-(=2b).

The Preparation of Optically Pure 7‐Oxabicyclo [2.2.1]hept‐2‐ene Derivatives. The CD Spectrum of (+)‐(1R)‐7‐Oxabicyclo [2.2.1]hept‐5‐en‐2‐one

Abstract(−)‐1‐Camphanoyloxyacrylonitrile (=(−)‐1‐cyanovinyl camphanate; 1) obtained from the commercially available (−)‐camphanoyl chloride and 2‐oxo‐propiononitrile added to furan at 20° in the presence of Cu (BF4)2 · 6H2O or ZnI2 and gave a mixture of 2‐cyano‐7‐oxabicyclo [2.2.1]hept‐5‐en‐2‐yl camphanates (2–5) from which isomer 5 could be obtained pure by crystallization. The latter was transformed into (+)‐(1R)‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (6) in high yield and optical purity. Adducts 2–4 were recycled into 1+furan by heating in toluene, and (−)‐camphanic acid was recovered after saponification of 5. The absolute configuration of 6 was deduced from its CD spectrum which showed two 1200‐cm−1 Franck‐Condon series for its n→π transition.

PREPARATION OF ENANTIOMERICALLY PURE 1-HYDROXY-NEOCEMBRENES TO DETERMINE THE UNSOLVED ABSOLUTE CONFIGURATION OF CEMBRENOIDS

Abstract Cis and trans 1-hydroxy-neocembrenes were prepared in an enantiomerically pure form by reduction of dl-ketone with respective (+)- and (−)-Darvon-LiAlH4 complex followed by purification with the aids of esterification with d- and l-menthoxyacetyl chlorides and (−)-camphanic acid chloride, respectively. Absolute configuration of naturally occurring (+)-mayol and (+)-cembrenene was determined by correlation with enantiomerically pure compounds.

ChemInform Abstract: NATURAL OCCURRENCE OF ENANTIOMERIC AND MESO‐ASTAXANTHIN. 5. EX WILD SALMON (SALMO SALAR AND ONCORHYNCHUS)

The configurational isomers of astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′-dione) from the flesh of salmon (Salmo salar and Oncorhynchus) caught at different places in Europe and Canada were isolated and analyzed as (−)-camphanic acid diesters by means of HPLC. The biological variation in the composition of the configurational isomers in seven fish was surprisingly similar: 78 to 85% of (3S, 3′S)-astaxanthin, 12 to 17% (3R, 3′R)-astaxanthin and 2 to 6% meso-astaxanthin.

Natural Occurrence of Enantiomeric and meso‐Astaxanthin. 5. Ex wild salmon (Salmo salar and Oncorhynchus)

AbstractThe configurational isomers of astaxanthin (3,3′‐dihydroxy‐β,β‐carotene‐4,4′‐dione) from the flesh of salmon (Salmo salar and Oncorhynchus) caught at different places in Europe and Canada were isolated and analyzed as (−)‐camphanic acid diesters by means of HPLC. The biological variation in the composition of the configurational isomers in seven fish was surprisingly similar: 78 to 85% of (3S, 3′S)‐astaxanthin, 12 to 17% (3R, 3′R)‐astaxanthin and 2 to 6% meso‐astaxanthin.

Optical purity of (3 S,3' S)-astaxanthin from Haematococcus pluvialis

Haematococcus pluvialis cultivated in a N-deficient medium produced astaxanthin (1 % of total carotenoids), the monoester (76 %) and diester (7 %) of astaxanthin, β,β-carotene (1 %), an adonirubin ester (3 %), (3 R,3′ R,6′ R)-lutein (7 %), violaxanthin (2 %) and neoxanthin (1 %). The CD values of the mono- and diesters of astaxanthin, the HPLC properties of astaxanthin monoester further esterified with (−)-camphanic acid and the optical purity of astaxanthin [determined by HPLC analysis of the diester of(−)-camphanic acid] produced by saponification of the natural mono- and diesters of astaxanthin in the absence of oxygen showed that this green alga synthesizes pure (3 S,3′ S)-astaxanthin esters.

Esterified, optical pure (3 S, 3′ S)-astaxanthin from flowers of Adonis annua

The quantitative carotenoid composition of the red flower petals of Adonis annua is reported. Optically pure (3 S, 3′ S)-astaxanthin occurs both as a diester (64% of total carotenoid) and as a monoester (11%). The optical purity was determined by hydrolysis of the natural esters in the absence of oxygen and subsequent HPLC analysis of the paren α-ketol esterified with (−)-camphanic acid. All non-animal sources hitherto examined synthesize pure 3 S,3′ S- or 3 R,3′ R-isomers of astaxanthin, whereas marine animal sources contain mixtures of all three optical isomers, including the meso form.

Natural occurrence of enantiomeric and meso-astaxanthin 4. Ex shrimps ( Pandalus borealis)

1. 1. The quantitative carotenoid composition of shells of the common northern circumpolar shrimp Pandalus borealis (Crustaceae Malacostraca, order Decapoda) (i) fresh frozen, (ii) boiled and (iii) processed shrimp meal, is reported. Astaxanthin, present as the free diol, mono-and diester with higher fatty acids, was identified by co-chromatography with authentic standards, conversion to astacene and spectral criteria (electronic-, mass- and CD spectra). 2. 2. By conversion to its diester with (−) camphanic acid astaxanthin from unboiled shells was shown by HPLC analysis to consist of the (3S, 3′S), ( 3R,3′R; meso) and ( 3R,3′R) isomers in ratio 25:52:23. 3. 3. Natural astaxanthin monoester was by similar procedure found to consist of the ( 3S)-ol and the ( 3R)-ol in ration 47:53, Saponification of the monoester in the absence of oxygen provided astaxanthin, shown by the above HPLC method to consist of the ( 3S,3′S), ( 3R,3′S;meso) and ( 3R,3′R) isomers in ration 17:50:33. Natural astaxanthin diester provided astaxanthin, containing the optical isomers ( 3S,3′S), ( 3R,3′S; meso) and ( 3R,3′R) in ratio 12:46:43. 4. 4. The strongly racemized nature of astaxanthin and its monoester was confirmed by the chiroptical data. The CD data for the natural astaxanthin diester confirmed a high degree of racemization with some preference for R- configuration ( ca, 13% optical purity ). 5. 5. The data suggest some preference for 3R- configuration of astaxanthin in the in vivo acylation reaction.

Natural Occurrence of Enantiomeric and meso‐Astaxanthin 1. Ex Lobster Eggs (Homarus gammarus)

AbstractAstaxanthin (1; 3,3′‐dihydroxy‐β,β‐carotene‐4,4′‐dione) isolated from lobster eggs (Homarus gammarus) was unexpectedly found to be a mixture of all three optical isomers as determined by HPLC. analysis of the corresponding diesters of (–)‐camphanic acid. This is the first finding of meso‐astaxanthin and a meso‐carotenoid in general in nature.

Some recent advances in the synthesis of natural carotenoids

The total syntheses of naturally occurring (3R,3′R)-zeaxanthin, (3S,3′S)-astaxanthin, (3S,3′S)-asterinic acid and of some related xanthophylls are discussed. Asymmetric hydroboration has been applied to the total synthesis of all configurational isomers of zeaxanthin. The total synthesis of natural actinioerythrin is described and the absolute configuration confirmed by X-ray crystallographic analysis of an intermediate. The optical resolution of α-hydroxy-carbonyl compounds via (−)-camphanic acid esters appears to be generally applicable and can be used as an analytical method for the determination of the optical purity of α-hydroxy-carbonyl carotenoids. Some technological applications are indicated.

Separation of (3S, 3′S)‐, (3R 3′R)‐ and (3S, 3′R)‐astaxanthin via (−)‐camphanic acid esters

AbstractA method is described for the qualitative and quantitative determination of configurational isomers of astaxanthin. It is based on the esterification of astaxanthin with (—)‐camphanic acid chloride and analysis of the corresponding diesters by HPLC.

Racematspaltung und Bestimmung der absoluten Konfiguration von 2, 6‐disubstituierten Bicyclo [3.3.1]nonanen

Resolution and Determination of the Absolute Configuration of 2,6‐Disubstituted Bicyclo[3.3.1]nonanes(±)‐endo, endo‐Bicyclo [3.3.1]nonane‐2,6‐diol was resolved via diastereomeric camphanic acid esters. Conversion of the (+)‐enantiomer 2 via (+)‐5 and (+)‐6 as key intermediates gave (+) methyl 3‐(3‐oxocyclohexyl)‐propionate (7) which independently could be prepared also from the known (+)‐(R)‐3‐oxo‐cyclohexane‐carboxylic acid (8). These chemical correlations establish the absolute configuration of (+)‐2, (+)‐5 and (+)‐6 as well as that of (+)‐bicyclo [3.3.1]nonane‐2,6‐dione (1) obtained by oxidation of (+)‐2. The chiroptical properties of 1 and 6 are discussed.

Synthese des (R)‐trans‐11‐Hydroxy‐8‐dodecensäure‐lactons (Recieifeiolid)

Synthesis of RecifeiolideThe synthesis of the mould metabolite recifeiolide (VIII), a 12‐membered ring lactone, is described. 1,3‐Butandiol was resolved with (−)‐camphanic acid via (R)‐1‐iodo‐3‐butanol (II) into (R)‐3‐hydroxybutyl triphenyl phosphonium iodide (III). Wittig condensation of the phosphorane derived from III with methyl 8‐oxo‐octanoate (V) led to the methyl trans‐11‐hydroxy‐8‐dodecenoate (VI). The corresponding hydroxy acid VII was transformed into the S‐(2‐pyridyl) carbothioate which cyclizes under the influence of silver ion to the lactone VIII. With (−)‐(R)‐1,3‐butandiol (I) as starting material the naturally occurring (+)‐(R)‐recifeiolide (VIII) is produced in 70% yield from VII.

Determination of the enantiomeric purity and absolute configuration of α-deuteriated primary alcohols

The enantiomeric purity and absolute configuration of α-deuteriated primary alcohols can be ascertained by n.m.r. spectroscopy of the corresponding esters with camphanic acid in the presence of Eu(dpm)3.

Synthese der enantiomeren 1,6‐Spiro[4.4]nonadiene

AbstractTwo new syntheses of spiro[4.4]nonane‐1, 6‐dione (I) are described: one by rearrangement of 1,6‐epoxy‐bicyclo[4.3.0]‐nonane‐2‐one (IV) with boron trifluoride, the other by an acid catalyzed, intramolecular Claisen condensation of 4‐(2‐oxocyclopentyl)‐butyric acid. Spiro[4.4]‐nonane‐1,6‐dione is converted into trans, trans‐spiro[4.4]nonane‐1,6‐diol which is resolved into enantiomers via the diastereomeric esters with (−)‐camphanic acid. (+)‐(5S)‐Spiro[4.4]nona‐1,6‐diene (III) is prepared from (1R, 6R)‐trans,trans‐spiro[4.4]nonane‐1,6‐diol (II) by pyrolysis of the corresponding bis‐4‐methylphenyl‐thionocarbonate. This modification of the Chugaev reaction is particularly useful with sterically hindered alcohols which cannot be converted into S‐me‐thylxanthates. The circular dichroism, UV.‐ and NMR.‐spectrum of optically active spiro[4.4]‐nonane‐1,6‐diene are discussed.