Total synthesis of (3R,3′R,6′R)-lutein and its stereoisomers

Article abstract of DOI:10.1021/jo900432r

(Chemical Equation Presented) (3R,3′R,6′R)-Lutein (1) is a major dietary carotenoid that is abundant in most fruits and vegetables commonly consumed in the U.S. and that accumulates in the human plasma, major organs, and ocular tissues. Numerous epidemiol

Full text of DOI:10.1021/jo900432r

Total Synthesis of (3R,3′R,6′R)-Lutein and Its Stereoisomers
Frederick Khachik* and An-Ni Chang
Department of Chemistry and Biochemistry, UniVersity of Maryland, College Park, Maryland 20742
khachik@umd.edu
ReceiVed February 25, 2009
(3R,3′R,6′R)-Lutein (1) is a major dietary carotenoid that is abundant in most fruits and vegetables
commonly consumed in the U.S. and that accumulates in the human plasma, major organs, and ocular
tissues. Numerous epidemiological and experimental studies have shown that 1 has important biological
activities and may play an important role in the prevention of age-related macular degeneration (AMD).
While the total synthesis of 1 has been previously reported in a poor overall yield, the total synthesis of
the other seven stereoisomers of lutein has not yet been accomplished. We have developed a relatively
straightforward methodology for the total synthesis of 1 and three of its stereoisomers, (3R,3′S,6′S)-
lutein (2), (3R,3′S,6′R)-lutein or 3′-epilutein (3), and (3R,3′R,6′S)-lutein (4) by C15 + C10 + C15 Wittig
coupling reactions. Employing this methodology, the other four stereoisomers of lutein that are enantiomeric
to the aforementioned lutein isomers can be similarly prepared. One of the important features of this
strategy is its application to the total synthesis of 13C-labeled luteins and their metabolites with appropriate
stereochemistry for metabolic studies in animals and humans. This synthesis also provides access to the
C15-precursors of optically active carotenoids with a 3-hydroxy-ε end group that are otherwise difficult
to synthesize.
Introduction
than two decades, the industrial production of 1 by chemical
synthesis has not yet materialized.5 Consequently, this carotenoid
is commercially produced from saponified extracts of marigold
flowers (Tagetes erecta, variety orangeade).6 The major dif-
ficulty with the total synthesis of 1 is due to the presence of
three stereogenic centers at the C3, C3′, and C6′ positions in
this carotenoid that can result in eight possible stereoisomers
(Figure 1).
(3R,3′R,6′R)-Lutein (1) and (3R,3′R)-zeaxanthin are two
dietary carotenoids that are present in most fruits and vegetables
commonly consumed in the U.S.1 These carotenoids accumulate
in human plasma and breast milk,2 major organs, and ocular
tissues3 and have been implicated in the prevention of age-
related macular degeneration (AMD).4 While (3R,3′R)-zeaxan-
thin has been commercially available by total synthesis for more
(1) (a) Khachik, F.; Beecher, G. R.; Goli, M. B.; Lusby, W. R. Pure Appl.
Chem. 1991, 63, 71–80. (b) Humphries, J. M.; Khachik, F. J. Agric. Food Chem.
2003, 51, 1322–1327. (c) Khachik, F. Pure Appl. Chem. 2006, 78, 1551–1557.
(2) (a) Khachik, F.; Beecher, G. R.; Goli, M. B.; Lusby, W. R.; Smith, J. C.
Anal. Chem. 1992, 64, 2111–2122. (b) Khachik, F.; Spangler, C. J.; Smith, J. C.,
Jr.; Canfield, L. M.; Pfander, H.; Steck, A. Anal. Chem. 1997, 69, 1873–1881.
(3) (a) Bone, R. A.; Landrum, J. T.; Hime, G. W.; Cains, A. InVest.
Ophthalmol. Visual Sci. 1993, 34, 2033–2040. (b) Khachik, F.; Bernstein, P.;
Garland, D. L. InVest. Ophthalmol. Visual Sci. 1997, 38, 1802–1811. (c)
Bernstein, P. S.; Khachik, F.; Carvalho, L. S.; Muir, G. J.; Zhao, D. Y.; Katz,
N. B. Exp. Eye Res. 2001, 72 (3), 215–223.
(4) (a) Schalch, W.; Dayhaw-Barker, P.; Barker, F. M. The Carotenoids of
Human Macula (Nutritional and EnVironmental Influences on the Eye); Taylor,
A., Ed.; CRC Press: Boca Raton, FL, 1999; pp 215-250. (b) Snodderly, D. M.;
Auran, J. D.; Delori, F. C. InVest. Ophthalmol. Visual Sci. 1984, 25, 674–685.
(5) (a) Widmer, E.; Soukup, M.; Zell, R.; Broger, E.; Wagner, H. P.; Imfeld,
M. HelV. Chim. Acta 1990, 73, 861–867. (b) Soukup, M.; Widmer, E.; Luka´c,
T. HelV. Chim. Acta 1990, 73, 868–873.
(6) (a) Khachik, F. Process for isolation, purification, and recrystallization
of lutein from saponified marigolds oleoresin and uses thereof. U.S. Patent,
5,382,714, 1995.
10.1021/jo900432r CCC: $40.75
Published on Web 04/24/2009
2009 American Chemical Society
J. Org. Chem. 2009, 74, 3875–3885 3875

Khachik and Chang
Retrosynthetic Analysis
Mayer and Ru¨ttimann employed a C15 + C10 + C15 Wittig
coupling reaction for the synthesis of 1 according to Scheme
1.7 Despite the difficulties encountered in the synthesis of
unsymmetrical C40-carotenoids, the C15 + C10 + C15 building
block strategy is, in most cases, the method of choice. This is
because the formation of the double bonds at the 11 and 11′
positions due to steric interaction yields predominantly the (all-
E)-isomer of carotenoids.9
The (3R,6R)-3-acetoxy-(R-ionylideneethyl)triphenylphospho-
nium chloride that was used in the final step of the reported
synthesis of 1 was prepared in poor yield and involved numerous
steps. In addition, according to Mayer and Ru¨ttimann, the final
olefination reaction with this Wittig salt only gave 25% yield
of 1. Therefore, in our synthetic strategy, we employed slightly
different C15 and C10 building blocks to arrive at luteins 1-4
(Scheme 2). We anticipated that the final step of our synthesis
could be best accomplished by elongation of the optically pure
C25-hydroxyaldehydes 6-9 with the Wittig salt 5 that could be
readily prepared according to the known processes.5 We
rationalized that the optically pure C25-hydroxyaldehydes 6-9
could be prepared from deprotection of their corresponding
dimethylacetals 10-13 under mild acidic conditions without
epimerization of their allylic hydroxyl groups at C3. These
acetals could in turn be prepared from the reaction of protected
Wittig salt 14 with the optically pure C15-hydroxyaldehydes
15-18 with the required stereochemistry at C3 and C6. The
protected Wittig salt 14 was readily accessible according to
published methods.10
The application of this Wittig salt 14 in the synthesis of
unsymmetrical carotenoids with a variety of sensitive functional
groups has been well documented in the literature.10a,11 How-
ever, this building block has not been employed in the synthesis
of lutein or its precursors. The C15-hydroxynitriles 19-22 with
the appropriate stereochemistry at C3 and C6 could serve as
the precursors of C15-hydroxyaldehydes 15-18. We envisioned
that either the diastereomeric hydroxynitriles or hydroxyalde-
hydes could be first separated from their respective racemic
mixtures into two pairs of enantiomers by chromatography and
each pair could then be resolved by enzyme-mediated acylation.
(7E,9E)-3-Keto-R-ionylideneacetonitrile (23a) and its (7E,9Z)-
isomer (23b), prepared from nitriles 24a and 24b, could be
transformed into C15-hydroxynitriles 19-22. However, the
(7E,9E)-isomer (23a) would be preferable in order to avoid the
difficulties associated with the separation of optically active E/Z-
isomers throughout our entire synthetic strategy. The com-
mercially available and inexpensive (()-R-ionone was selected
as the starting material for the synthesis of nitriles 24a/24b.
Ketonitriles 23a and 23b have been previously synthesized as
a mixture of E/Z-isomers from (()-R-ionone by Horner-
Wadsworth-Emmons (HWE) olefination.12 Therefore, we had
FIGURE 1. Chemical structures of four stereoisomers of lutein.
The other four stereoisomers of lutein (structures not shown)
are those in which the configuration at the C3 position is S while
the stereochemistry at C3′ and C6′ remains the same as in luteins
1-4. Among these stereoisomers, only 1 is of dietary origin,
and 3, a presumed metabolite of 1, has been identified in human
plasma and ocular tissues.2,3 However, it is not known whether
the other lutein stereoisomers could be formed in humans as a
consequence of metabolic transformation of 1. Therefore, the
fate and biological activity of lutein stereoisomers in humans
remain unexplored due to the lack of availability of these
carotenoids. In 1980, Mayer and Ru¨ttimann reported the only
total synthesis of 1 in an overall yield of 1%, and since then no
attempt has been made to synthesize this important carotenoid
and its stereoisomers. However, it should be noted that
3′-epilutein (3) has been prepared by partial synthesis from 1.8
In this paper, we report the total synthesis of luteins 1-4 by
employing a divergent synthetic strategy that can be extended
to the synthesis of the other four stereoisomers of these
carotenoids. Our methodology can be applied to the synthesis
of 13C-labeled luteins for metabolic studies and provides access
to the precursors of optically active carotenoids with a 3-hy-
droxy-ε end group that are otherwise difficult to prepare.
Nomenclature
The carotenoid numbering system has been used for com-
pounds 15-24 to allow comparison of their stereochemical
transformations to compounds 1-10. The correct systematic
names of these carotenoid precursors followed by their common
names are shown in brackets as follows: 15-18, (2E,4E)-3-methyl-
5-(2,6,6-trimethyl-4-hydroxy-2-cyclohexen-1-yl)penta-2,4-dienal
[(7E,9E)-3-hydroxy-R-ionylideneacetaldehyde]; 19-22, (2E,4E)-
3-methyl-5-(2,6,6-trimethyl-4-hydroxy-2-cyclohexen-1-yl)penta-
2,4-dienenitrile [(7E,9E)-3-hydroxy-R-ionylideneacetonitrile];
23a: (2E,4E)-, 23b: (2Z,4E)-3-methyl-5-(2,6,6-trimethyl-4-oxo-
2-cyclohexen-1-yl)penta-2,4-dienenitrile, [23a: (7E,9E)-, 23b:
(7E,9Z)-3-keto-R-ionylideneacetonitrile]; 24a: (2E,4E)-, 24b:
(2Z,4E)-3-methyl-5-(2,6,6-trimethyl-2-cyclohexen-1-yl)penta-
2,4-dienenitrile, [24a: (7E,9E)-, 24b: (7E,9Z)-R-ionylideneac-
etonitrile].
(8) Khachik, F. J. Nat. Prod. 2003, 66, 67–72.
(9) Soukup, M.; Spurr, P.; Widmer, E. In Carotenoids, Synthesis; Britton,
G., Liaaen-Jensen, S., Pfander, H., Eds.; Birkha¨user: Basel, 1995; Vol. 2; pp
7-14.
(10) (a) Bernhard, K.; Kienzle, F.; Mayer, H.; Mu¨ller, R. K. HelV. Chim.
Acta 1980, 63, 1473–1490. (b) Haugen, J. A. Acta Chim. Scand. 1994, 48, 657–
664.
(11) (a) Haag, A.; Eugster, C. H. HelV. Chim. Acta 1985, 68, 1897–1906.
(b) Yamano, Y.; Sakai, Y.; Yamashita, S.; Ito, M. Heterocycles 2000, 52, 141–
146. (c) Tode, C.; Yamano, Y.; Ito, M. J. Chem. Soc., Perkin Trans. 1 2002,
1581–1587.
(12) Imai, H.; Hirano, T.; Terakita, A.; Shichida, Y.; Muthyala, R. S.; Chen,
R. L.; Colmenares, L. U.; Liu, R. S. H. Photochem. Photobiol. 1999, 70, 111–
115.
(7) Mayer, H.; Ru¨ttimann, A. HelV. Chim. Acta 1980, 63 (6), 1451–1455.
3876 J. Org. Chem. Vol. 74, No. 10, 2009

Total Synthesis of Lutein Stereoisomers
SCHEME 1
SCHEME 2
to develop a methodology that could provide 24a as a single
isomer and transform this nitrile into 23a without stereoisomer-
ization. Other challenges with our synthetic approach were
separation of C15-hydroxyaldehydes 15-18 or their precursors,
C15-hydroxyanitriles 19-22, in high optical purity and maintain-
ing their stereochemical integrity throughout the synthesis of
luteins 1-4.
nitrile which had to be preferentially synthesized as the (7E,9E)-
isomer (23a) at the expense of its (7E,9Z)-isomer (23b). This
is because when (()-ketonitrile 23a is reduced in the following
step, a new stereogenic center at C3 is generated that results in
the formation of four stereoisomers, namely, rac-hydroxynitriles
19-22. Consequently, the reduction of a mixture of ketonitriles
23a and 23b could afford as many as eight stereoisomeric
hydroxynitriles that would be difficult to separate in high
optically purity. Therefore, our initial goal was to explore the
possible routes by which (()-R-ionone could be transformed
into ketonitrile 23a. Three synthetic routes were employed for
Results and Discussion
One of the key starting materials in the retrosynthetic
pathways shown in Scheme 2 is (()-3-keto-R-ionylideneaceto-
J. Org. Chem. Vol. 74, No. 10, 2009 3877

Khachik and Chang
SCHEME 3a
tic acid in boiling pyridine and catalytic amounts of piperidinium
acetate has been shown to afford ꢀ-ionylideneacetonitrile in high
yield, predominantly as the (7E,9E)-isomer.17 When we applied
these conditions to the condensation of (()-R-ionone with
cyanoacetic acid, no reaction was observed. After examining
this reaction with a number of organic amines, we discovered
that cyclohexylamine could promote this reaction under mild
conditions to give a 75% yield of 24a: 24b ) 12: 1 as a colorless
oil after distillation (Route 2, Scheme 3). In the following step,
the mixture of these nitriles in CH3CN was oxidized with TBHP
and household bleach as described earlier to yield ketonitriles
23a (92%) and 23b (8%) in 53% isolated yield. After low
temperature (-15 °C) crystallization from ethanol, (7E,9E)-
ketonitrile 23a was obtained as white crystals in 37% isolated
yield and contained no measurable amounts of 23b.
We also investigated the HWE reaction of (()-3-keto-R-
ionone with diethyl cyanomethylphosphonate in THF according
to the method of Imai et al.12 and obtained 23a: 23b ) 3: 1 in
81% yield (Route 3, Scheme 3). After purification by chroma-
tography and crystallization from ethanol, 23a was obtained as
white crystals in 40% isolated yield. It should be noted that
Imai et al. prepared 23a and 23b as a mixture and the isomeric
ratio of these ketonitriles were not reported. (()-3-Keto-R-
ionone was first prepared in 1952 from allylic oxidation of (()-
R-ionone in 14% isolated yield by Prelog and Osgan.18 Widmer
et al. employed Ac2Co.4H2O/NH4Br/O2 to improve the yield
of this reaction to 31%.19 More recently, another procedure for
allylic oxidation of ionone-like dienes with TBHP catalyzed by
CaCl2 and MgCl2.6H2O at 60 °C has also been reported that
can afford (()-3-keto-R-ionone in 67% isolated yield.20 Em-
ploying bleach oxidation, we were able to prepare crystalline
(()-3-keto-R-ionone from (()-R-ionone in 64% isolated yield.
The palladium(II)-mediated oxidation of (()-R-ionone with
TBHP in CH2Cl2 also afforded this ketone in 53% isolated yield.
a Reagents and conditions: (a) (EtO)2P(O)CH2CN or (iPrO)2P(O)CH2CN/
NaH, TBME; (b) BuOOH (TBHP), bleach (5.25% NaOCl), CH3CN, -5
to 0 °C; (c) CH2(CN)CO2H, cyclohexylamine, 80-85 °C, 3.5 h.
t
transformation of (()-R-ionone to ketonitrile 23a (Scheme 3).
According to the first route, the HWE reaction of (()-R-ionone
with diethyl cyanomethylphosphonate in TBME using NaH as
base gave nitriles 24a:24b ) 3:1 in 74% isolated yield after
distillation. The use of diisopropyl cyanomethylphosphonate has
been shown to increase the E/Z ratio in HWE reaction with
ꢀ-ionone, but in our case this phosphonate only marginally
improved the E/Z ratio.13
A mixture of nitriles 24a and 24b was oxidized with tBuOOH
(TBHP, 70% in water), bleach, and catalytic amounts of K2CO3
in CH3CN at -5 to 0 °C to yield 23a:23b ) 3:1. After
purification by chromatography, a mixture of these ketonitriles
was obtained in 57% yield. This mixture was crystallized from
ethanol at -15 °C to give 23a as white crystals free from 23b
in 37% isolated yield. This water-based oxidation system, using
household laundry bleach and aqueous TBHP, has been shown
to convert steroidal olefins to R,ꢀ-enones by an economical and
environmentally friendly methodology.14 Ketonitriles 23a and
23b were also prepared in 53% yield by palladium(II)-mediated
oxidation of nitriles 24a and 24b with TBHP in CH2Cl2 at 0
°C, a methodology similar to one that has been employed for
allylic oxidation of olefins.15 However, to date there is no
literature report on the direct oxidation of nitriles 24a and 24b
to ketonitriles 23a and 23b. These reactions clearly revealed
that oxidation of a mixture of 24a and 24b to 23a and 23b is
not accompanied by E/Z-isomerization and the isomeric ratio
of these nitriles remained unchanged.
In search of an alternative process that could provide 24a as
a single isomer, we turned our attention to Knoevenagel
condensation. In 1944, Young et al. prepared R-ionylideneac-
etonitrile from condensation of R-ionone with cyanoacetic acid
using a mixture of acetamide and ammonium acetate as
catalyst.16 Unfortunately, due to the old nature of this publication
and lack of sophisticated analytical methods at that time, the
E/Z-ratio of these nitriles could not be determined. More
recently, Knoevenagel condensation of ꢀ-ionone with cyanoace-
While the overall yield of the three routes discussed above
were comparable, route 2 proved to be easier to scale up and
due to the high E-stereoselectivity of the Knoevenagel conden-
sation, 23a could be crystallized from the isomeric mixture more
expeditiously.
Reduction of (7E,9E)-3-Keto-r-ionylideneacetonitrile (23a)
to (7E,9E)-3-Hydroxy-r-ionylideneacetaldehydes 15-18 via
(7E,9E)-3-Hydroxy-r-ionylideneacetonitriles 19-22. (7E,9E)-
Ketonitrile 23a was reduced to four stereoisomeric hydroxyni-
triles 19-22 with a number of reagents in high yields (see Table
1S, Supporting Information). Because (3R,6R)-hydroxynitrile
19 with a trans relationship between the OH at C3 and C6-
dienenitrile side chain is the precursor of the naturally occurring
(3R,3′R,6′R)-lutein (1), it was desirable to increase the composi-
tion of the (3,6-trans)-hydroxynitriles 19 and 20 relative to the
(3,6-cis)-hydroxynitriles 21 and 22. Among the reducing agents
employed, potassium tri-sec-butylborohydride (K-Selectride)21
produced the greatest amounts of the (3,6-trans)-hydroxynitriles
relative to the (3,6-cis)-hydroxynitriles [(19+20):(21+22) ) 6:1]
(17) Andriamialisoa, Z.; Valla, A.; Zennache, S.; Giraud, M.; Potier, P.
Tetrahedron Lett. 1993, 34, 8091–8092.
(18) Prelog, V.; Osgan, M. HelV. Chim. Acta 1952, 35, 986–992.
(19) Widmer, E.; Soukup, M.; Zell, R.; Broger, E.; Lohri, B.; Marbet, R.;
Luka´c, T. HelV. Chim. Acta 1982, 65, 944–957.
(20) Yang, M.; Peng, Q. R.; Lan, J. B.; Song, G. F.; Xie, R. G. Synlett 2006,
16, 2617–2620.
(21) (a) Dauben, W. G.; Ashmore, J. W. Tetrahedron Lett. 1978, 4487–4490.
(b) Bell, R. A.; Turner, J. V. Tetrahedron Lett. 1981, 22, 4871–4872. (c) Go¨ndo¨s,
G.; Orr, J. C. J. Chem. Soc., Chem. Commun. 1982, 1239–1240. (d) Tal, D. M.;
Frisch, G. D.; Elliott, W. H. Tetrahedron 1984, 40, 851–854.
(13) Dugger, R. W.; Heathcock, C. H. Synth. Commun. 1980, 10, 509–515.
(14) Marwah, P.; Marwah, A.; Lardy, H. A. Green Chem. 2004, 6, 570–
577.
(15) Yu, J. Q.; Corey, E. J. Org. Lett. 2002, 4, 2727–2730.
(16) Young, W. G.; Andrews, L. J.; Cristol, S. J. J. Am. Chem. Soc. 1944,
66, 520–524.
3878 J. Org. Chem. Vol. 74, No. 10, 2009

Total Synthesis of Lutein Stereoisomers
TABLE 1. Reduction of Ketonitrile 23a to Aldehydes 15-18 via Nitriles 19-22
entry
1
conditions
yield,a (19+20):(21+22)b
yield,a (15+16):(17+18)b
KB[CHMeC2H5]3H, TBME, -30 °C, 4 h
94%, 6:1
70%, 6:1
83%, 6:1 (one-pot process)
2
(R)-2-methyl-CBS-oxaza-borolidine/BH3, TBME, 0 °C, 1.5 h
97%, 1:6
80%, 1:6
a Isolated yield after chromatography. b Ratios were determined by HPLC on a silica-based nitrile bonded column and a chiral column (see Supporting
Information).
SCHEME 4a
a Reagents and conditions: (a) lipase AK (Pseudomonas fluorescens), vinyl acetate, pentane (reflux), 48 h, 43% conversion; (b) chromatography (n-Si,
hexane/EtOAc, 98:2 to 85:15); (c) KOH/MeOH (10%, w:v), 0 °C, 2 h, 97%.
(Table 1). When Corey’s enantiomerically pure (R)-2-methyl-
CBS-oxazaborolidine22 was used as the reducing agent, this
diastereoselectivity was reversed and the (3,6-cis)-hydroxyni-
triles were the major products [(19+20):(21+22) ) 1:6].
Hydroxynitriles 19-22 were subsequently reduced to their
corresponding hydroxyaldehydes 15-18 (Table 1).
Separation of Hydroxyaldehydes 15-18 in High Optical
Purity by Enzyme-Mediated Acylation. We have previously
demonstrated that when a diastereomeric mixture of (3R,3′R,6′R)-
lutein (1) and (3R,3′S,6′R)-lutein (3) is subjected to enzyme-
mediated acylation with lipase AK (Pseudomonas fluorescens),
1 remains unreacted while the allylic hydroxyl group in 3 is
readily acylated. This allowed the separation of 3 from 1 in
diastereomeric ratio (dr) of 95:5.8 Because the allylic hydroxyl
group in 3 with 3S configuration was shown to be highly reactive
toward enzymatic acylation while the 3R-hydroxyl group in 1
was unreactive, this approach was used to resolve the racemic
mixture of hydroxyaldehydes 15-18. When a racemic mixture
of 15 and 16 was subjected to enzyme-mediated acylation with
lipase AK in the presence of vinyl acetate in refluxing pentane,
16 was acylated to acetoxyaldehyde 25 within 48 h, while 15
remained unchanged and was obtained in high optical purity
(er 97:3) (Scheme 4). Acetoxyaldehydes 25 was then readily
separated from 15 by column chromatography and was subjected
to saponification with KOH/MeOH at 0 °C to afford 16 (er 97:3).
Similarly, the resolution of a racemic mixture of 17 and 18 was
accomplished with enzymatic acylation under the same condi-
tions. Hydroxyaldehyde 17 underwent acylation to acetoxyal-
dehyde 26, while 18 was found to be unreactive. After column
chromatography and saponification of 26, hydroxyaldehydes 17
(er 96:4) and 18 (er 96:4) were obtained in high optical purity.
Interestingly, the reduction of 23a with (S)-2-methyl-CBS-
oxazaborolidine under the same conditions (Table 1) gave
(15+16):(17+18) ) 1:3 and stereoselectivity was not reversed.
The separation of the (3,6-trans)-hydroxynitriles (19+20) from
the (3,6-cis)-hydroxynitriles (21+22) by column chromatogra-
phy proved to be challenging and could only be accomplished
with repeated chromatography. Therefore, the hydroxynitriles
19-22 were first transformed into a racemic mixture of
hydroxyaldehydes 15-18 by DIBAL-H and the mixture was
then subjected to column chromatography. Unlike hydroxyni-
triles, the (3,6-trans)-hydroxyaldehydes (15+16) were readily
separated from the (3,6-cis)-hydroxyaldehydes (17+18) by
chromatography. In an alternative one-pot reaction, ketonitrile
23a was reduced to hydroxynitriles 19-22 with K-Selectride
followed by the reduction with DIBAL-H to afford hydroxy-
aldehydes 15-18 in one convenient step (Table 1).
(22) (a) Corey, E. J.; Bakshi, R. K.; Shibata, S. J. Am. Chem. Soc. 1987,
109, 5551–5553. (b) Corey, E. J.; Bakshi, R. K.; Shibata, S.; Chen, C. P.; Singh,
V. K. J. Am. Chem. Soc. 1987, 109, 7925–7926.
J. Org. Chem. Vol. 74, No. 10, 2009 3879

Khachik and Chang
SCHEME 5
from their NMR, MS, UV-vis, and CD spectra. The CD spectra
of (3,6-trans)-aldehydes 15 (3R,6R) [281 nm (+18 mdeg), 242
nm (-1.3 mdeg)] and 16 (3S,6S) [281 nm (-13 mdeg), 242
nm (+1.0 mdeg)] in ether-hexane-methanol (10:3:1) with
strong opposite Cotton effects clearly indicated that these
aldehydes were enantiomeric. The absolute configuration of 15
was assigned as (3R,6R) by comparison of its CD spectrum with
that of hydroxyketone 27 (3R,6R) [320 nm (+10.6 mdeg)] that
similar to this aldehyde showed a positive Cotton effect.
To establish the absolute configuration of 17 and 18,
aldehydes 15 and 17 were separately epimerized in dilute
aqueous HCl similarly to our previously reported epimerization
of (3R,3′R,6′R)-lutein (1) to 3′-epilutein (3).8 Under identical
reaction conditions, the HPLC analysis of the crude product
revealed that hydroxyaldehydes 15 (32%) and 17 (68%) had
reached an equilibrium that favored the (3,6-cis)-aldehyde 17
(Scheme 6).
The products of these reactions were then separated by
semipreparative HPLC, and their absolute configurations were
determined by NMR and CD. The H-6 chemical shift of the
epimer of 15 appeared at δ ) 2.25 ppm, indicating a trans-
geometry between H-6 and OH, and on this basis this epimer
was identified as 17 (3S,6R). The CD spectrum of the epimer
of 15 was also identical to that of the synthetic sample of 17
that was prepared in high optical purity by enzymatic acylation
of the racemic mixture of 17 and 18 (Scheme 4). Similarly, the
epimer of 17 was shown by NMR and CD to be identical to
15. Because the CD spectra of 17 (3S,6R) and 18 indicated that
these aldehydes were enantiomeric, the absolute configuration
of 18 was assigned as 3R,6S.
Synthesis of Luteins 1-4 via C25-Hydroxy-apocarote-
nals 6-9. The C15-hydroxyaldehydes 15-18 prepared in high
optical purities were each elongated to their corresponding
protected C25-aldehydes 10-13 by olefination with the protected
Wittig salt 14 in the presence of NaOMe/MeOH at rt (Scheme
7). After solvent evaporation and without isolation of the
products, acetals 10-13 that were obtained as a mixture of all-E
and 11Z were deprotected in dilute aqueous HCl (0.3 N) in
acetone to give C25-aldehydes 6-9 as a mixture of all-E and
11Z. Fortunately, the (11Z)-isomers of carotenoids and apo-
carotenoids are sterically hindered and are readily converted to
their (all-E)-isomers.25 Thus, prior to purification, the crude
mixture of (all-E)- and (11Z)-isomers of each of these aldehydes
were catalytically isomerized to their corresponding (all-E)-
isomers in the presence of Pd(OAc)2 in refluxing EtOAc within
2 h. In the following step, the individual aldehydes were purified
by column chromatography to afford 6-9 in isolated yields
ranging from 53-85%. Aldehydes 6 and 7 were each obtained
in an er of 97:3, and similarly 8 and 9 were each prepared in
an er of 96:4. It should be noted that under the acidic conditions
employed for the deprotection of acetals 10-13, the hydroxyl
group at C3 did not undergo epimerization and the optical
purities of the resulting C25-aldehydes 6-9 were not compro-
mised. This was confirmed by chiral HPLC (Supporting
Information) of the individually synthesized (all-E)-C25-alde-
hydes.
Determination of the Absolute Configuration of Hydroxy-
aldehydes 15-18. Hydroxyldehydes 15-18 were fully char-
1
acterized from their H and 13C NMR as well as MS and UV
spectra. The relative stereochemistry of these aldehydes at C-3
and C-6 was established from comparison of the proton NMR
chemical shifts of H-6 with published values for (3R,3′R,6′R)-
lutein (1) and (3R,3′S,6′R)-lutein (3).23 It has been well
documented that when H-6 and the hydroxyl group at C-3 in
lutein are in a cis-geometry, the chemical shift of H-6 is shifted
downfield by 0.25 ppm in comparison with the chemical shift
of this proton when it is in a trans-geometry with OH at C-3.
The chemical shift of H-6 proton in (3,6-trans)-aldehydes 15
and 16 in which this proton is in a cis-geometry with the
hydroxyl group at C-3 appeared at δ ) 2.50 ppm while this
chemical shift in (3,6-cis)-aldehydes 17 and 18 (H-6 and OH
in trans-geometry) moved upfield to δ ) 2.25 ppm. Therefore,
the relative stereochemistry of hydroxyldehydes 15-18 was
assigned on this basis. However, the absolute configuration of
these aldehydes could only be unequivocally determined with
comparison of the circular dichroism (CD) data with a model
compound in which the stereochemistry at C3 and C6 was
known. We prepared this model compound by oxidative
cleavage of the polyene chain of naturally occurring (3R,3′R,6′R)-
lutein (1) in which the stereochemistry in the ε-end group of
this carotenoid at C3′ and C6′ is known to be R (Scheme 5).24
Prior to oxidative cleavage of 1, the hydroxyl groups were
protected by acylation with Ac2O-pyridine and the resulting
(3R,3′R,6′R)-lutein diacetate was then oxidized with TBHP/
bleach. After saponification and column chromatography, HPLC
analysis of the product showed the presence of unreacted 1
(80%) and a number of oxidation products. Among these,
(3R,6R)-3-hydroxy-13-apo-ε-caroten-13-one (27) with an ε end
group and (3R)-3-hydroxy-ꢀ-ionone (28) with a ꢀ end group
were the only major stable products (27:28 ) 3:1). These were
separated by semipreparative HPLC and were fully characterized
(23) (a) Buchecker, R.; Eugster, C. H. HelV. Chim. Acta 1979, 62, 2817–24.
(b) Englert, G. In Carotenoid Chemistry and Biochemistry; Britton, G., Goodwin,
T. W., Eds.; Pergammon: Oxford, 1982; pp 107-134. (c) Englert, G. In
Carotenoids; Britton, G., Liaaen-Jensen, S., Pfander, H., Eds.; Birkha¨user: Basel,
1995; Vol. 1B, pp 147-260. (d) Khachik, F.; Englert, G.; Daitch, C. E.; Beecher,
G. R.; Lusby, W. R.; Tonucci, L. H. J. Chromatogr. Biomed. Appl. 1992, 582,
153–166.
(24) (a) Buchecker, R.; Hamm, P.; Eugster, C. H. Chimia 1971, 25, 192–
194. (b) Buchecker, R.; Hamm, P.; Eugster, C. H. Chimia 1972, 26, 134–136.
(c) Buchecker, R.; Hamm, P.; Eugster, C. H. HelV. Chim. Acta 1974, 57, 631–
656.
Although the (11Z)-isomers of C25-hydroxyaldehydes 6-9
were readily isomerized into their corresponding (all-E)-isomers,
this step was shown to be unnecessary and could be postponed
until after preparation of luteins 1-4.
(25) Soukup, M.; Spurr, P.; Widmer, E. In Carotenoids; Britton, G., Liaaen-
Jensen, S., Pfander, H., Eds.; Birkha¨user: Basel, 1995; Vol. 2, pp 7-14.
3880 J. Org. Chem. Vol. 74, No. 10, 2009

Total Synthesis of Lutein Stereoisomers
SCHEME 6
SCHEME 7
After chromatography and crystallization, luteins 1 (74%, dr
99:1), 2 (82%, dr 99:1), 3 (85%, dr 96:4), and 4 (80%, dr 97:3)
1
were prepared in high optical purities. The H and 13C NMR
spectra of luteins 1-4 were in agreement with the published
NMR data of the polyene chain and the end groups of these
carotenoids.7,23 The CD spectrum of 1 was also in agreement
with that of naturally occurring (3R,3′R,6′R)-lutein, as well as
the CD spectrum of this carotenoid reported by Mayer.23c
The overall yield of luteins 1-4 according to our synthetic
strategy can be determined on the basis of the stereochemistry of
the targeted lutein. For example, if the synthesis of (3R,3′R,6′R)-
lutein (1) and (3R,3′S,6′S)-lutein (2) is of particular interest, the
one-pot reduction of ketonitrile 23a with K-Selectride followed
by DIBAL-H would be the preferred route. This is because this
reduction predominantly provides the (3,6-trans)-hydroxyalde-
hydes 15 and 16 that are precursors to the ε end group of luteins
1 and 2, respectively. Using this approach, the overall yields
for luteins 1 and 2 from ketonitrile 23a were determined as
follows: 23a f (15 + 16), 71% f 15 (30%) and 16 (31%) f
6 (26%) and 7 (28%) f 1 (18%) and 2 (20%). Because the
isolated yield of ketonitrile 23a from (()-R-ionone was 28%
after crystallization, the overall yields of luteins 1 and 2 from
(()-R-ionone were 5% and 6%, respectively.
Similarly, if luteins 3 and 4 are the target carotenoids, the
reduction of 23a with (R)-2-methyl-CBS-oxazaborolidine is
preferred because this reagent provides the (3,6-cis)-hydroxy-
aldehydes 17 and 18 as the major products. According to this
route, the overall yields of luteins 3 and 4 based on ketonitrile
23a were 17% and 19%, respectively. However, the calculated
yields of 3 (5%) and 4 (6%) based on (()-R-ionone were
significantly lower.
SCHEME 8
Although 23a served as the key starting material in our
synthesis, the preparation and crystallization of this (7E,9E)-
isomer from (()-R-ionone in a low yield (28%) contributed to
the low overall yield of luteins 1-4.
Conclusion
The same strategy that we have employed for the synthesis
of luteins 1-4 can also be used to elongate C25-hydroxyalde-
hydes 6-9 with the S-enantiomer of Wittig salt 5 to synthesize
the other four stereoisomers of luteins; these are (3S,3′S,6′S)-
lutein, (3S,3′R,6′R)-lutein, (3S,3′R,6′S)-lutein, and (3S,3′S,6′R)-
lutein. Further, the hydroxyaldehydes 15-18 provide access to
the synthesis of all eight stereoisomers of lutein labeled with
carbon-13 for metabolic studies. This is because we have
previously demonstrated that 2,7-dimethylocta-2,4,6-triene-1,8-
dial, the precursor to Wittig salt 14, can be labeled with 4-6
carbon-13 and employed in the synthesis of (3R,3′R)-zeaxanthin
by C15 + C10 + C15 Wittig coupling strategy.26 This will allow
(26) Khachik, F.; Beecher, G. R.; Li, B. W.; Englert, G. J. Labelled Compd.
Radiopharm. 1995, 36, 1157–1172.
Therefore in a simplified process, each of the (all-E + 11Z)-
C25-hydroxyaldehydes 6-9 were allowed to react with the Wittig
salt 55 to yield their corresponding luteins 1-4 as a mixture of
(all-E)- and (11Z,11′Z)-isomers (Scheme 8). The crude mixture
of each E/Z-lutein was then thermally isomerized in a refluxing
solution of EtOAc to afford its corresponding (all-E)-isomer.
(27) (a) Khachik, F.; Beecher, G. R.; Smith, J. C., Jr. J. Cell. Biochem. 1995,
22, 236–246. (b) Khachik, F.; De Moura, F.; Zhao, D. Y.; Aebischer, C. P.;
Bernstein, P. S. InVest. Ophthalmol. Visual Sci. 2002, 43, 3383–3392. (c)
Khachik, F.; London, E.; De Moura, F.; Johnson, M.; Steidl, S.; DeTolla, L.;
Shipley, S.; Sanchez, R.; Chen, X. Q.; Flaws, J.; Lutty, G.; McLeod, S.; Fowler,
B. InVest. Ophthalmol. Visual Sci. 2006, 47, 5476–86.
J. Org. Chem. Vol. 74, No. 10, 2009 3881

Khachik and Chang
was quenched with water and extracted with hexane. The combined
organic solution was dried and concentrated to give 38.00 g of a
pale yellow oil that was purified by fractional distillation to yield
a mixture of 24a/24b ) 12/1 (bp ) 105-110 °C at 10 mm) as a
colorless oil (30.00 g, 0.139 mol, 75%). The NMR data were shown
to be identical with those of 24a/24b characterized earlier.
the introduction of 4-6 carbon-13 into the polyene chain of
luteins 1-4 according to our synthetic methodology. Based on
our human and animal supplementation studies with naturally
occurring lutein, we have previously demonstrated that a
minimum of 4-6 carbon-13 randomly located in the lutein
polyene chain would be sufficient for investigating the ocular
metabolism of this carotenoid.27
The U.S. National Eye Institute is currently conducting a
multicenter, randomized clinical trial to assess the effects of
oral supplementation of (3R,3′R,6′R)-lutein (1) and (3S,3′R)-
zeaxanthin on the progression to advanced age-related macular
degeneration (AMD) (http://www.areds2.org). Therefore, the
availability of a methodology that can be applied to the synthesis
of isotopically labeled lutein and its stereoisomers for metabolic
studies in an appropriate animal model is essential. Finally, our
synthesis provides a relatively easy access to hydroxyaldehydes
15-18 that are key starting materials in the synthesis of naturally
occurring carotenoids with 3-hydroxy-ε end groups.
Bleach Oxidation of (()-r-Ionylideneacetonitrile to 3-Keto-
r-ionylideneacetonitrile (23a/23b) (Route 2). A mixture of (()-
R-ionylideneacetonitrile (27.00 g, 0.125 mol; 24a:24b ) 12:1) and
K2CO3 (1.71 g, 12.37 mmol) in acetonitrile (103.0 mL, 80.95 g,
1.972 mol) was cooled to 0 °C under N2, and a 70% solution of
TBHP in water (124 mL, 111.6 g, 70% ≈ 78.12 g, 0.867 mol) was
added dropwise in 30 min. Household bleach containing 5.25%
NaOCl (386 g, 20.265 g NaOCl, 0.272 mol) was added over a
period of 8 h at -5 to 0 °C. After the addition was completed, the
reaction mixture was stirred at 0 °C for 1 h, the product was
extracted with hexane and washed with water, and the combined
organic solution was dried and concentrated to give 36.7 g of a
yellow oil. The crude product was purified by column chromatog-
raphy (n-silica, hexane/ethyl acetate, from 98:2 to 92:8) to yield a
mixture of (7E,9E)-3-keto-R-ionylideneacetonitrile (23a) and (7E,9Z)-
3-keto-R-ionylideneacetonitrile (23b) (15.19 g, 66.24 mmol, 53%,
23a:23b ) 12:1) as a yellow oil. Crystallization from ethanol at
-15 °C gave 23a (10.50 g, 45.79 mmol, 37%) as a white solid,
Experimental Section
General Materials and Methods. See Supporting Information.
(()-R-Ionone is commercially available. Compounds 55 and
1410a were prepared according to published procedures. Naturally
occurring (3R,3′R,6′R)-lutein (1) was isolated from a saponified
extracts of marigold flowers and was purified by crystallization.6a
Circular dichroism (CD) spectra were obtained in a mixture of
hexane, ether, and methanol (10:3:1).
1
mp 93-95 °C. H NMR (400 MHz, CDCl3): δ 0.97 (s, 3H), 1.06
(s, 3H), 1.89 (d, J ) 1.2 Hz, 3H), 2.13 (d, J ) 16.8 Hz, 1H), 2.16
(d, J ) 1.0 Hz, 3H), 2.33 (d, J ) 16.8 Hz, 1H), 2.66 (d, J ) 9.4
Hz, 1H), 5.23 (s, 1H), 5.95 (s, 1H), 5.98 (dd, J ) 15.5, 9.4 Hz,
1H), 6.25 (d, J ) 15.5 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ
16.8, 23.5, 27.3, 27.9, 36.7, 47.3, 55.9, 98.4, 117.2, 126.5, 133.7,
135.2, 155.8, 160.0, 198.5. UV λmax ) 260 nm (hexane). HRMS
(ESI+) calcd for C15H19NO [M + H]+ 230.15394, found 230.15272.
The mother liquor from the above crystallization was subjected to
semipreparative HPLC to yield an analytically pure sample of 23b.
1H NMR (400 MHz, CDCl3): δ 0.98 (s, 3H), 1.08 (s, 3H), 1.92 (d,
J ) 1.3, 3H), 2.02 (d, J ) 1.5, 3H), 2.17 (d, J ) 17.1, 1H), 2.36
(d, J ) 17.1, 1H), 2.73 (d, J ) 9.9, 1H), 5.21 (s, 1H), 5.95 (s, 1H),
5.98 (dd, J ) 15.3, 9.9, 1H), 6.80 (d, J ) 15.3, 1H). 13C NMR
(100 MHz, CDCl3): δ 19.6, 23.5, 27.4, 27.8, 36.5, 47.5, 56.3, 97.0,
116.6, 126.3, 131.3, 136.1, 155.3, 160.3, 198.5. UV λmax ) 260
nm (hexane). HRMS (ESI+) calcd for C15H19NO [M + H]+
230.15394, found 230.15330.
r-Ionylideneacetonitrile (24a/24b) from (()-r-Ionone by
WHE Coupling (Route 1). To a freshly prepared solution of
NaOMe, prepared from Na (5.47 mol) and MeOH (70 mL), was
added a solution of diisopropyl cyanomethylphosphonate (47 g of
95% pure, 44.65 g, 0.218 mol) in TBME (20 mL) at 0-5 °C in 20
min under N2. After stirring at rt for 1 h, the mixture was cooled
in an ice bath, and freshly distilled (()-R-ionone (38.10 g, 0.198
mol) in TBME (20 mL) was added in 45 min at 0-5 °C. The
mixture was stirred at rt for 4 h, and the product was quenched
with water, extracted with TBME, dried, and concentrated to give
45.4 g of a pale yellow oil. The crude product was purified by
fractional distillation to yield a mixture of 24a and 24b (bp )
107-110 °C at 10 mm) as a colorless oil (31.60 g, 0.147 mol,
74%); 24a:24b ) 3:1 (determined by HPLC). The 1H and 13C NMR
peak assignments were made by comparison of the spectra of the
3:1 mixture with those of a mixture of 24a:24b ) 12:1 that was
prepared by an alternative method (Route 2, described later).
24a: 1H NMR (400 MHz, CDCl3): δ 0.81 (s, 3H), 0.91 (s, 3H),
1.20 (m, 1H), 1.46 (m, 1H), 1.55 (d, J ) 2.0 Hz, 3H), 2.02 (m,
2H), 2.13 (d, J ) 1.0 Hz, 3H), 2.22 (d, J ) 9.8 Hz, 1H), 5.15 (s,
1H), 5.46 (m, 1H), 5.94 (dd, J ) 15.5, 9.4 Hz, 1H), 6.12 (d, J )
15.5 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ 156.9, 140.5, 135.6,
132.7, 131.5, 122.1, 96.3, 54.6, 32.5, 31.3, 27.7, 26.8, 23.0, 22.8,
16.8. UV λmax ) 260 nm (hexane); HRMS (ESI+) calcd for C15H21N
216.17468 [M + H]+, found 216.17268.
Reduction of (7E,9E)-3-Keto-r-ionylideneacetonitrile (23a)
to Hydroxynitriles 19-22 with K-Selectride. A solution of 23a
(3.00 g, 13.08 mmol) in TBME (25 mL) at -30 °C under N2 was
treated dropwise with a 1 M solution of K-Selectride in THF (20
mL, 20 mmol) in TBME (10 mL) in 40 min. After 4 h at this
temperature, the product was quenched with 15 mL of 3 N NaOH
followed by 15 mL of 30% H2O2 and stirred at rt for 30 min. The
product was extracted with TBME, washed with brine, dried, and
concentrated to give a colorless oil that was passed through a short
silica gel column (hexane/acetone ) 97:3) to afford 3-hydroxy-R-
ionylideneacetonitriles 19-22 (2.85 g, 12.32 mmol, 94%). The
isomeric ratio of hydroxynitriles (19+20):(21+22) ) 6:1 was
established by normal phase HPLC. The mixture was subjected to
three additional column chromatography separations (hexane/
acetone ) 97:3) to separate (3,6-trans)-hydroxynitriles 19 + 20
(2.14 g) from (3,6-cis)-hydroxynitriles 21 + 22 (0.36 g). Hydrox-
ynitriles 19 + 20 and 21 + 22 were each shown by chiral HPLC
to consist of an approximately 1:1 mixture of enantiomers.
(3,6-trans,7E,9E)-3-Hydroxy-r-ionylideneacetonitriles (19 +
24b: 1H NMR (400 MHz, CDCl3): δ 0.83 (s, 3H), 0.92 (s, 3H),
1.20 (m, 1H), 1.46 (m, 1H), 1.57 (d, J ) 2.0 Hz, 3H), 2.02 (m,
2H), 2.14 (d, J ) 1.0 Hz, 3H), 2.30 (d, J ) 10 Hz, 1H), 5.08 (s,
1H), 5.46 (m, 1H), 5.96 (dd, J ) 15.6, 9.6 Hz, 1H), 6.65 (d, J )
15.6 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ 156.5, 141.3, 136.1,
132.8, 128.9, 121.9, 94.9, 54.8, 32.4, 31.5, 27.8, 26.8, 23.0, 22.8,
16.5. UV λmax ) 258 nm (hexane); HRMS (ESI+) calcd for C15H21N
216.17468 [M + H]+, found 216.17423.
r-Ionylideneacetonitrile (24a/24b) from (()-r-Ionone and
Cyanoacetic Acid (Route 2). Freshly distilled (()-R-ionone (36.00
g, 0.187 mol) in cyclohexylamine (62.0 mL, 53.75 g, 0.542 mol)
was treated with cyanoacetic acid (20.25 g, 0.238 mol), and the
mixture was heated at 80-85 °C under N2. After 3.5 h, the mixture
was allowed to cool down to room temperature and the product
1
20). H NMR (400 MHz, CDCl3): δ 0.84 (s, 3H), 0.99 (s, 3H),
1.37 (dd, J ) 13.3, 6.4, 1H), 1.59 (s, 3H), 1.81 (dd, J ) 13.3, 6.4,
1H), 2.13 (s, 1H), 2.44 (d, J ) 10.0, 1H), 4.25 (m, 1H), 5.17 (s,
1H), 5.58 (s, 1H), 5.85 (dd, J ) 15.4, 10.0, 1H), 6.15 (d, J ) 15.4,
1H). 13C NMR (100 MHz, CDCl3): δ 16.8, 22.7, 24.3, 29.3, 34.0,
44.1, 54.7, 65.4, 96.9, 117.6, 125.5, 133.0, 135.9, 138.5, 156.4.
UV λmax ) 260 nm (hexane). HRMS (ESI+) calcd for C15H21NO
[M + H]+ 232.16959, found 232.16997.
3882 J. Org. Chem. Vol. 74, No. 10, 2009

Total Synthesis of Lutein Stereoisomers
(3,6-cis,7E,9E)-3-Hydroxy-r-ionylideneacetonitriles (21 +
A solution of 25 in CH2Cl2 (25 mL) was saponified with KOH/
MeOH (2.3 mL, 10 wt %/v) at 0 °C for 2 h. The product was
washed with water, dried, and concentrated to give (3S,6S)-3-
hydroxy-R-ionylideneacetaldehyde (16) (1.00 g, 4.27 mmol; 42%).
The second fraction was fully characterized as (3R,6R)-3-hydroxy-
R-ionylideneacetaldehyde (15) (1.00 g, 4.27 mmol, 42%). The
optical purities of 15 (er 97:3) and 16 (er 97:3) were established
by chiral HPLC. The absolute configurations of 15 and 16 were
1
22). H NMR (400 MHz, CDCl3): δ 0.83 (s, 3H), 0.94 (s, 3H),
1.35 (dd, J ) 12.9, 9.8, 1H), 1.60 (t, J ) 1.5, 3H), 1.64 (dd, J )
12.9, 6.5, 1H), 2.12 (d, J ) 1.0, 3H), 2.19 (d, J ) 9.3, 1H), 4.23
(m, 1H), 5.17 (s, 1H), 5.53 (s, 1H), 5.95 (dd, J ) 15.3, 9.3, 1H),
6.14 (d, J ) 15.3, 1H). 13C NMR (100 MHz, CDCl3): δ 16.8, 22.4,
26.9, 29.1, 34.9, 40.5, 54.6, 66.3, 96.8, 117.6, 125.8, 131.9, 136.0,
139.2, 156.7. UV λmax ) 260 nm (hexane). HRMS (ESI+) calcd
for C15H21NO [M + H]+ 232.16959, found 232.17062, and [(M +
H) - H2O]+ 214.15944.
1
assigned by comparison of their H NMR and CD spectra with
those of a C18-ketone that was prepared by oxidative cleavage of
naturally occurring (3R,3′R,6′R)-lutein (1); details are described later
in this section.
Reduction of (7E,9E)-3-Hydroxy-r-ionylideneacetonitriles
19-22 to (7E,9E)-3-Hydroxy-r-ionylideneacetaldehydes 15-18.
To a solution of hydroxynitriles 19-22 [2.30 g, 9.94 mmol,
(19+20):(21+22) ) 6:1] in CH2Cl2 (10 mL) was added a 1 M
solution of DIBAL-H in CH2Cl2 (33 mL, 33 mmol) at -40 °C
under N2 in 1 h. The reaction mixture was stirred at -30 °C for
1 h, and the mixture was very slowly treated with a homogeneous
mixture of 26 g of water absorbed on n-silica (0.3 g of water/g of
silica) at a rate such that the temperature remained below -10 °C.
Caution: the addition of silica/water results in rapid elevation of
the temperature. The reaction mixture was then allowed to stir at
0 °C for 2 h. Na2SO4 (3.0 g) was added, and the solids were filtered
off and washed with CH2Cl2. The organic solution was washed
with water, dried, and concentrated to give a pale yellow oil (2.00
g) that was purified by column chromatography (hexane/ethyl
acetate, 95:5 to 80:20) to yield (3,6-trans)-hydroxyaldehydes 15
+ 16 (1.40 g, 5.97 mmol, 60%) and (3,6-cis)-hydroxyaldehydes
17 + 18 (0.23 g, 0.98 mmol, 10%).
1
(3R,6R)-3-Hydroxy-r-ionylideneacetaldehyde (15). H NMR
(400 MHz, CDCl3): δ 0.87 (s, 3H), 1.03 (s, 3H), 1.40 (dd, J )
13.3, 6.8, 1H), 1.62 (s, 3H), 1.85 (dd, J ) 13.3, 5.8, 1H), 2.0 (d,
J ) 1.3, 1H), 2.26 (d, J ) 1, 3H), 2.50 (d, J ) 10, 1H), 4.27 (s,
1H), 5.61 (s, 1H), 5.93 (d, J ) 8.0, 1H), 6.01 (dd, J ) 15.6, 10,
1H), 6.23 (d, J ) 15.6, 1H), 10.12 (d, J ) 8.0, 1H). 13C NMR
(100 MHz, CDCl3): δ 13.3, 22.7, 24.4, 29.4, 34.1, 44.3, 55.0, 65.4,
125.3, 128.9, 136.0, 136.3, 138.3, 153.9, 191.4. UV λmax ) 280
nm (hexane). HRMS (ESI+) calcd for C15H22O2 [M + H]+
235.16926, found 235.17023, and [(M + H) - H2O]+ 217.15886.
CD: 281 nm (+18 mdeg), 242 nm (-1.3 mdeg).
1
(3S,6S)-3-Hydroxy-r-ionylideneacetaldehyde (16). H NMR
and 13C NMR, UV, and MS spectra of 16 were identical with those
of 15. CD: 281 nm (-13 mdeg), 242 nm (+1.0 mdeg).
Enzyme-Mediated Acylation of (3,6-cis,7E,9E)-3-Hydroxy-
r-ionylideneacetaldehydes 17 + 18 with Lipase AK (Pseudomo-
nas fluorescens). To a solution of (3,6-cis)-hydroxyaldehydes 17
+ 18 (1.68 g, 7.17 mmol) in 15 mL of pentane were added 1.10 g
of lipase AK (Pseudomonas fluorescens) and vinyl acetate (2.00
mL, 1.87 g, 21.72 mmol). The mixture was refluxed (35-36 °C)
under N2, and the course of the acylation was monitored by chiral
HPLC. After 50 h, the product was filtered through Celite, and the
filtrate was concentrated to give a yellow oil (2.0 g). Column
chromatography (hexane/ethyl acetate, 98:2 to 85:15) of the product
gave two major fractions. The first fraction was identified as
(3S,6R)-3-acetoxy-R-ionylideneacetaldehyde (26) (0.85 g, 3.08
mmol; 43%). 1H NMR (400 MHz, CDCl3): δ 0.88 (s, 3H), 1.02 (s,
3H), 1.52 (dd, J ) 23.0, 13.0, 1H), 1.66 (t, J ) 1.51, 3H), 1.73
(dd, J ) 13.0, 6.8, 1H), 2.08 (s, 3H), 2.27 (d, J ) 1.0, 3H), 2.31
(d, J ) 9.0, 1H), 5.35 (m, 1H), 5.51 (s, 1H), 5.95 (d, J ) 8.0, 1H),
6.12 (dd, J ) 15.6, 9.0, 1H), 6.37 (d, J ) 15.6, 1H), 10.13 (d, J )
8.0, 1H). 13C NMR (100 MHz, CDCl3): δ 13.7, 21.8, 23.0, 27.5,
29.3, 35.2, 37.0, 55.3, 70.1, 121.8, 129.6, 135.8, 138.9, 139.0, 154.4,
191.8. UV λmax ) 282 nm (hexane). HRMS (ESI+) calcd for
C17H24O3 [M + H]+ 277.17982, found 277.18092.
(3,6-trans,7E,9E)-3-Hydroxy-r-ionylideneacetaldehyde (15 +
1
16). H NMR (400 MHz, CDCl3): δ 0.87 (s, 3H), 1.03 (s, 3H),
1.40 (dd, J ) 13.3, 6.8, 1H), 1.62 (s, 3H), 1.85 (dd, J ) 13.3, 5.8,
1H), 2.00 (d, J ) 1.3, 1H), 2.26 (d, J ) 1.0, 3H), 2.50 (d, J ) 10,
1H), 4.27 (s, 1H), 5.61 (s, 1H), 5.93 (d, J ) 8.0, 1H), 6.02 (dd, J
) 15.6, 10.0, 1H), 6.23 (d, J ) 15.6, 1H), 10.12 (d, J ) 8.0, 1H).
13C NMR (100 MHz, CDCl3): δ 13.3, 22.7, 24.4, 29.4, 34.1, 44.3,
55.0, 65.4, 125.3, 128.9, 136.0, 136.3, 138.3, 153.9, 191.4. UV
λmax ) 280 nm (hexane). HRMS (ESI+) calcd for C15H22O2 [M +
H]+ 235.16926, found 235.17037, and [(M + H) - H2O]+
217.15933.
(3,6-cis,7E,9E)-3-Hydroxy-r-ionylideneacetaldehyde (17 +
1
18). H NMR (400 MHz, CDCl3): δ 0.86 (s, 3H), 0.96 (s, 3H),
1.39 (dd, J ) 12.3, 9.9, 1H), 1.63 (d, J ) 0.8, 3H), 1.68 (dd, J )
12.3, 6.4, 1H), 2.25 (d, J ) 9.3, 1H), 2.25 (s, 3H), 4.26 (m, 1H),
5.55 (s, 1H), 5.92 (d, J ) 8.3, 1H), 6.11 (dd, J ) 15.6, 9.3, 1H),
6.22 (d, J ) 15.6, 1H), 10.11 (d, J ) 8.3, 1H). 13C NMR (100
MHz, CDCl3): δ 13.3, 22.5, 27.0, 29.2, 34.9, 40.8, 55.1, 66.4, 125.6,
128.9, 135.0, 136.4, 139.2, 154.3, 191.5. UV λmax ) 282 nm
(hexane). HRMS (ESI+) calcd for C15H22O2 [M + H]+ 235.16926,
found 235.16888, and [(M + H) - H2O]+ 217.15927.
A solution of 26 in CH2Cl2 (15 mL) was hydrolyzed with KOH/
MeOH (1.6 mL, 10 wt %/v) at 0 °C for 2 h. The product was
washed with water, dried, and concentrated to give (3S,6R)-3-
hydroxy-R-ionylideneacetaldehyde (17) (0.70 g, 2.99 mmol; 42%).
The second fraction was fully characterized as (3R,6S)-3-hydroxy-
R-ionylideneacetaldehyde (18) (0.68 g, 2.90 mmol, 40%). The
optical purities of 17 (er 96:4) and 18 (er 96:4) were established
by chiral HPLC. The absolute configurations of 17 and 18 were
Enzyme-Mediated Acylation of (3,6-trans,7E,9E)-3-Hydroxy-
r-ionylideneacetaldehydes 15 + 16 with Lipase AK (Pseudomo-
nas fluorescens). To a solution of (3,6-trans)-hydroxyaldehydes
15 + 16 (2.40 g, 10.24 mmol) in 20 mL of pentane were added
1.5 g of lipase AK (Pseudomonas fluorescens) and vinyl acetate
(2.84 mL, 2.65 g, 30.78 mmol). The mixture was refluxed (35-36
°C) under N2, and the course of the acylation was monitored by
chiral HPLC. After 48 h, the product was filtered through Celite,
and the filtrate was concentrated to give a yellow oil (2.7 g). Column
chromatography (hexane/ethyl acetate, 98:2 to 85:15) of the product
gave two major fractions. The first fraction was identified as (3S,6S)-
3-acetoxy-R-ionylideneacetaldehyde (25) (1.22 g, 4.41 mmol; 43%).
1H NMR (400 MHz, CDCl3): δ 0.90 (s, 3H), 1.02 (s, 3H), 1.49
(dd, J ) 14.0, 5.3, 1H), 1.65 (s, 3H), 1.84 (dd, J ) 14.0, 6.0, 1H),
2.05 (s, 3H), 2.26 (s, 3H), 2.50 (d, J ) 9.8, 1H), 5.33 (m, 1H),
5.55 (s, 1H), 6.01 (dd, J ) 15.6, 9.8, 1H), 6.22 (d, J ) 15.6, 1H),
10.12 (d, J ) 8.0, 1H). 13C NMR (100 MHz, CDCl3): δ 13.2, 21.4,
22.8, 25.4, 28.8, 33.5, 39.3, 54.9, 68.3, 120.9, 129.1, 136.0, 137.8,
138.8, 153.8, 170.8, 191.4. UV λmax ) 282 nm (hexane). HRMS
(ESI+) calcd for C17H24O3 [M + H]+ 277.17982, found 277.17888.
1
assigned by comparison of their H NMR and CD spectra with
those of the acid-catalyzed epimerization products of 15.
1
(3S,6R)-3-Hydroxy-r-ionylideneacetaldehyde (17). H NMR
(400 MHz, CDCl3): δ 0.86 (s, 3H), 0.96 (s, 3H), 1.39 (dd, J )
12.3, 9.8, 1H), 1.63 (s, 3H), 1.68 (dd, J ) 12.3, 6.3, 1H), 2.25 (d,
J ) 9.3, 1H), 2.25 (s, 3H), 4.25 (m, 1H), 5.55 (s, 1H), 5.92 (d, J
) 8.3, 1H), 6.11 (dd, J ) 15.6, 9.3, 1H), 6.22 (d, J ) 15.6, 1H),
10.11 (d, J ) 8.3, 1H). 13C NMR (100 MHz, CDCl3): δ 13.2, 22.5,
27.0, 29.2, 34.9, 40.8, 55.1, 66.4, 125.6, 128.9, 135.0, 136.4, 139.2,
154.3, 191.5. UV λmax ) 282 nm (hexane). HRMS (ESI+) calcd
for C15H22O2 [M + H]+ 235.16926, found 235.17121, and [(M +
H) - H2O]+ 217.15762. CD: 280 nm (+17.8 mdeg).
J. Org. Chem. Vol. 74, No. 10, 2009 3883

Khachik and Chang
1
(3R,6S)-3-Hydroxy-r-ionylideneacetaldehyde (18). H NMR
equilibrium had been established between hydroxyaldehydes 15
(32%) and 17 (68%). After removal of water and solvent evapora-
tion, the hydroxyaldehydes were separated by semipreparative
and 13C NMR, UV, and MS spectra were identical with those of
17. CD: 280 nm (-7 mdeg).
1
HPLC and characterized by H NMR and CD as 15 and 17.
Oxidative Cleavage of (3R,3′R,6′R)-Lutein Diacetate to (3R,6R)-
3-Hydroxy-13-apo-ε-caroten-13-one (27) and (3R)-3-Hydroxy-
ꢀ-ionone (28). Preparation of (3R,3′R,6′R)-Lutein Diacetate. A
solution of naturally occurring (3R,3′R,6′R)-lutein (1) (2.30 g, 4.04
mmol) in 20 mL of THF was treated with pyridine (2.5 mL, 2.45 g,
30.97 mmol) and acetic anhydride (2.50 mL, 2.70 g, 26.45 mmol),
and the mixtue was heated at 45 °C under N2 for 6 h. The product
was extracted with hexane, and the organic solution was washed
sequentially with aqueous HCl (5%, v/v), saturated NaHCO3
solution, and water. After drying, the organic solution was
concentrated to give a red solid that was purified by column
chromatography on n-silica (hexane/acetone, from 90:10 to 70:30)
to yield (3R,3′R,6′R)-lutein diacetate (2.35 g, 3.60 mmol; 89%).
Epimerization of (3S,6R)-3-Hydroxy-r-ionylideneacetalde-
hydes (17) to (3R,6R)-3-Hydroxy-r-ionylideneacetaldehydes
(15). A solution of 17 (4.7 mg, 0.020 mmol; er 96:4) in acetone (1
mL) and H2O (0.5 mL) was epimerized with 0.24 mL of 0.1 N
HCl similarly to the previous experiment. After 28 h, HPLC showed
an equilibrium between hydroxyaldehydes 15 (31%) and 17 (69%).
These hydroxyaldehydes were separated by semipreparative HPLC
1
and characterized by H NMR and CD as 15 and 17.
General Procedure for the Synthesis of C25-Hydroxy-apoc-
arotenals 6-9. Synthesis of (3R,6R)-3-Hydroxy-12′-apo-ε-caro-
ten-12′-al (6). A solution of (3R,6R)-3-hydroxy-R-ionylideneace-
taldehyde (15) (0.25 g, 1.1 mmol) in MeOH (3 mL) was treated
with the protected Wittig salt 14 (0.82 g, 1.66 mmol) in MeOH (2
mL) at rt under N2. One milliliter of a freshly prepared 0.42 M
solution of NaOMe (0.42 mmol) in MeOH was added, and the
mixture was stirred at rt for 4 h. The product was diluted with
CH2Cl2, washed with water, and concentrated to give a red solid
(1.30 g). The solids were dissolved in acetone (4 mL) and water (1
mL) and stirred with 0.3 N HCl (75 µL) at rt for 1 h under N2. The
product was extracted with CH2Cl2 and sequentially washed with
a saturated solution of NaHCO3 and water, dried, and concentrated
to give a red oil. The crude product was refluxed in EtOAc in the
presence of catalytic amounts of Pd(OAc)2 for 2 h; in a simplified
procedure, this step was omitted. After solvent evaporation, column
chromatography (hexane/ethyl acetate, 95:5 to 80:20) gave (all-
E,3R,6R)-3-hydroxy-12′-apo-ε-caroten-12′-al (6) (0.34 g, 0.93
mmol; 85%, er 97:3) as a red oil.
Following the above procedure, (3S,6S)-3-hydroxy-12′-apo-ε-
caroten-12′-al (7, 61%, er 97:3), (3S,6R)-3-hydroxy-12′-apo-ε-
caroten-12′-al (8, 53%, er 96:4), and (3R,6S)-3-hydroxy-12′-apo-
ε-caroten-12′-al (9, 69%, er 96:4) were similarly prepared.
(3R,6R)-3-Hydroxy-12′-apo-ε-caroten-12′-al (6). 1H NMR (400
MHz, CDCl3): δ 0.86 (s, 3H), 1.00 (s, 3H), 1.38 (dd, J ) 13.3,
6.9, 1H), 1.63 (dd, J ) 2.3, 1.6, 3H), 1.85 (dd, J ) 13.3, 5.9, 1H),
1.89 (d, J ) 0.7, 3H), 1.94 (d, J ) 0.9, 3H), 2.04 (s, 3H), 2.43 (d,
J ) 9.9, 1H), 4.26 (s, 1H), 5.50 (dd, J ) 15.4, 9.9, 1H), 5.56 (d,
J ) 1.4, 1H), 6.16 (d, J ) 15.4, 2H), 6.31 (d, J ) 11.9, 1H), 6.38
(d, J ) 15.0, 1H), 6.69 (dd, J ) 14.4, 11.5, 1H), 6.76 (dd, J )
15.0, 11.3, 1H), 6.97 (d, J ) 11.5, 1H), 7.03 (dd, J ) 11.9, 14.4,
1H), 9.46 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 9.6, 13.0, 13.2,
22.8, 24.2, 29.5, 34.0, 44.6, 55.0, 65.9, 124.6, 127.4, 130.0, 130.3,
131.0, 136.7, 136.9, 137.0, 137.5, 137.7, 141.6, 148.9, 194.5.
UV-vis λmax ) 416 nm (ethanol). HRMS (ESI+) calcd for C25H34O2
[M + H]+ 367.26316, found 367.26098, and [(M + H) - H2O]+
349.25053. CD: 292 nm (+5.82 mdeg), 236 nm (+5.32 mdeg),
212 nm (+4.54 mdeg).
1
Mp 154-155 °C. H NMR (400 MHz, CDCl3): δ 0.86 (s, 3H),
0.98 (s, 3H), 1.06 (s, 6H), 1.09 (s, 3H), 1.44 (dd, J ) 13.9, 5.5,
1H), 1.57 (t, J ) 12.3, 1H), 1.63 (s, 3H), 1.71 (s, 3H), 1.76 (m,
1H), 1.83 (dd, J ) 13.9, 6.0, 1H), 1.89 (s, 3H), 1.95 (s, 6H), 2.00
(s, 3H), 2.03 (s, 3H), 2.10 (d, J ) 16.1, 8.5, 1H), 2.39 (d, J ) 9.3,
1H), 2.45 (d, J ) 5.5, 1H), 5.04 (m, 1H), 5.30 (s, 1H), 5.41 (dd, J
) 15.5, 9.8, 1H), 5.47 (m, 1H), 6.10 (m, 2H), 6.15 (m, 3H), 6.27
(m, 2H), 6.34 (m, 2H), 6.61 (m, 4H). 13C NMR (100 MHz, CDCl3):
δ 12.7, 13.0, 21.4, 22.9, 25.2, 28.4, 28.9, 29.9, 33.3, 36.6, 38.3,
39.4, 43.9, 54.8, 68.3, 68.8, 119.8, 124.7, 124.8, 125.2, 125.5, 128.2,
130.0, 130.9, 131.4, 132.5, 134.9, 135.5, 136.4, 137.5, 137.7, 138.6,
140.4, 170.8. UV-vis λmax ) 444 nm (ethanol). HRMS (ESI+)
calcd for C44H60O4 652.44861, found 652.43484.
Oxidative Cleavage of (3R,3′R,6′R)-Lutein Diacetate. A solu-
tion of (3R,3′R,6′R)-lutein diacetate (1.00 g, 1.53 mmol) in ethyl
acetate (30 mL) at 0 °C was treated with a 70% solution of TBHP
in water (2.7 mL, 2.4 g 70% ≈ 1.7 g, 19 mmol) under N2.
Household bleach containing 5.25% NaOCl (8.8 g, 0.46 g NaOCl,
6.2 mmol) was added in 20 min at 0 °C, and the mixture was stirred
at rt for 3 h. The organic solution was washed with water and
concentrated, and the residue was dissolved in CH2Cl2 (20 mL)
and saponified with KOH/MeOH (20 mL, 10%, wt/v) at rt for 2 h.
The CH2Cl2 layer was washed with water, dried, and concentrated
to give an orange solid (1.2 g). Column chromatography of the
product on n-silica (hexane/acetone, from 95:5 to 70:30) gave
unreacted 1 (0.69 g, 1.22 mmol; 80%) and a fraction that was shown
by HPLC to consist of two major products. These were separated
by semipreparative HPLC and identified as (3R,6R)-3-hydroxy-13-
apo-ε-caroten-13-one (27) and (3R)-3-hydroxy-ꢀ-ionone (28).
(3R,6R)-3-Hydroxy-13-apo-ε-caroten-13-one (27). 1H NMR
(400 MHz, CDCl3): δ 0.84 (s, 3H), 0.99 (s, 3H), 1.37 (dd, J )
13.3, 6.8, 1H), 1.60 (s, 3H), 1.82 (dd, J ) 13.3, 6.0, 1H), 1.99 (s,
3H), 2.28 (s, 3H), 2.43 (d, J ) 9.5, 1H), 4.24 (s, 1H), 5.56 (s, 1H),
5.68 (dd, J ) 15.6, 10.0, 1H), 6.16 (d, J ) 15.3, 1H), 6.16 (m,
2H), 7.52 (dd, J ) 11.8, 15.3, 1H). 13C NMR (100 MHz, CDCl3):
δ 13.4, 22.7, 24.2, 27.6, 29.4, 34.0, 44.4, 54.9, 65.6, 125.0, 127.7,
129.7, 133.6, 136.8, 136.9, 139.0, 144.4, 198.5. UV λmax ) 322
nm (hexane). CD: 320 nm (+10.6 mdeg). HRMS (ESI+) calcd for
C18H26O2 [M + H]+ 275.20056, found 275.19999.
(3S,6S)-3-Hydroxy-12′-apo-ε-caroten-12′-al (7). 1H NMR (400
MHz, CDCl3): δ 0.86 (s, 3H), 1.01 (s, 3H), 1.38 (dd, J ) 13.3,
6.9, 1H), 1.63 (s, 3H), 1.85 (dd, J ) 13.3, 5.8, 1H), 1.89 (s, 3H),
1.94 (s, 3H), 2.04 (s, 3H), 2.43 (d, J ) 9.9, 1H), 4.26 (s, 1H), 5.51
(dd, J ) 15.4, 9.9, 1H), 5.56 (s, 1H), 6.16 (d, J ) 15.4, 2H), 6.31
(d, J ) 11.9, 1H), 6.38 (d, J ) 15.0, 1H), 6.70 (dd, J ) 14.4, 11.6,
1H), 6.77 (dd, J ) 15.0, 11.3, 1H), 6.97 (d, J ) 11.7, 1H), 7.04
(dd, J ) 14.4, 12.0, 1H), 9.46 (s, 1H). 13C NMR (100 MHz,
CDCl3): δ 9.6, 13.0, 13.2, 22.8, 24.3, 29.5, 34.0, 44.6, 55.0, 65.9,
124.6, 127.4, 130.0, 130.4, 131.0, 136.7, 137.0, 137.5, 137.7, 141.6,
148.9, 194.5. UV-vis λmax ) 416 nm (ethanol). HRMS (ESI+)
calcd for C25H34O2 [M + H]+ 367.26316, found 367.26242, and
[(M + H) - H2O]+ 349.25188. CD: 292 nm (-4.32 mdeg), 238
nm (-4.86 mdeg), 210 nm (-4.72 mdeg).
1
(3R)-3-Hydroxy-ꢀ-ionone (28). H NMR (400 MHz, CDCl3):
δ 1.11 (s, 3H), 1.12 (s, 3H), 1.25 (s, 1H), 1.49 (t, J ) 12.0, 1H),
1.77 (s, 3H), 1.80 (dd, J ) 2.0, 3.6, 1H), 2.09 (dd, J ) 9.5, 17.5,
1H), 2.30 (s, 3H), 2.43 (dd, J ) 5.6, 17.5, 1H), 4.00 (m, 1H), 6.11
(d, J ) 16.5, 1H), 7.21 (d, J ) 16.5, 1H). 13C NMR (100 MHz,
CDCl3): δ 21.6, 27.3, 28.5, 30.0, 36.9, 42.7, 48.4, 64.5, 132.3, 135.6,
142.3, 198.6. UV λmax ) 290 nm (ethanol). HRMS (ESI+) calcd
for C13H20O2 [M + H]+ 209.15361, found 209.151363. CD: 310
nm (+2.98 mdeg), 270 nm (-2.87 mdeg).
Epimerization of (3R,6R)-3-Hydroxy-r-ionylideneacetalde-
hydes (15) to (3S,6R)-3-Hydroxy-r-ionylideneacetaldehydes
(17). To a solution of 15 (3.2 mg, 0.014 mmol; er 97:3) in acetone
(1 mL) and H2O (0.5 mL) was added 0.12 mL of 0.1 N HCl, and
the mixture was stirred at rt. After 28 h, HPLC showed that
(3S,6R)-3-Hydroxy-12′-apo-ε-caroten-12′-al (8). 1H NMR (400
MHz, CDCl3): δ 0.86 (s, 3H), 0.95 (s, 3H), 1.40 (dd, J ) 12.6,
9.8, 1H), 1.65 (s, 3H), 1.66 (m, 1H), 1.89 (s, 3H), 1.94 (s, 3H),
2.04 (s, 3H), 2.18 (d, J ) 9.4, 1H), 4.25 (m, 1H), 5.50 (s, 1H),
5.61 (dd, J ) 15.6, 9.4, 1H), 6.15 (d, J ) 15.6, 1H), 6.16 (d, J )
3884 J. Org. Chem. Vol. 74, No. 10, 2009

Total Synthesis of Lutein Stereoisomers
10.8, 1H), 6.31 (d, J ) 11.9, 1H), 6.37 (d, J ) 15.2, 1H), 6.69 (dd,
J ) 14.8, 11.8, 1H), 6.76 (dd, J ) 15.2, 10.8, 1H), 6.97 (d, J )
11.8, 1H), 7.03 (dd, J ) 14.8, 11., 1H), 9.46 (s, 1H). 13C NMR
(100 MHz, CDCl3) δ 9.6, 13.0, 13.2, 14.1, 22.6, 27.0, 29.3, 34.8,
40.9, 55.0, 66.7, 124.6, 127.4, 127.5, 130.4, 130.9, 131.0, 136.5,
136.6, 136.9, 137.1, 137.7, 137.8, 141.6, 148.9, 194.5. UV-vis
λmax ) 418 nm (ethanol). HRMS (ESI+) calcd for C25H34O2 [M +
H]+ 367.26316, found 367.26519, and [(M + H) - H2O]+
349.25091. CD: 402 nm (+3.73 mdeg), 235 nm (+8.57 mdeg).
(3R,6S)-3-Hydroxy-12′-apo-ε-caroten-12′-al (9). 1H NMR (400
MHz, CDCl3): δ 0.86 (s, 3H), 0.96 (s, 3H), 1.40 (dd, J ) 12.8,
9.8, 1H), 1.64 (m, 1H), 1.65 (t, J ) 1.6, 3H), 1.89 (d, J ) 0.8,
3H), 1.94 (d, J ) 0.8, 3H), 2.04 (s, 3H), 2.18 (d, J ) 9.3, 1H),
4.25 (m, 1H), 5.50 (s, 1H), 5.61 (dd, J ) 15.4, 9.3, 1H), 6.15 (d,
J ) 15.4, 1H), 6.16 (d, J ) 11.0, 1H), 6.31 (d, J ) 11.9, 1H), 6.38
(d, J ) 15.0, 1H), 6.69 (dd, J ) 14.4, 11.7, 1H), 6.77 (dd, J )
15.0, 11.0, 1H), 6.97 (d, J ) 11.7, 1H), 7.04 (dd, J ) 14.4, 11.9,
1H), 9.46 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 9.6, 13.0, 13.2,
14.1, 22.6, 27.0, 29.3, 34.8, 41.0, 55.0, 66.8, 124.6, 127.4, 127.5,
130.4, 130.9, 131.0, 136.5, 136.6, 136.9, 137.1, 137.7, 137.8, 141.6,
148.9, 194.5. UV-vis λmax ) 416 nm (ethanol). HRMS (ESI+)
calcd for C25H34O2 [M + H]+ 367.26316, found 367.26380, and
[(M + H) - H2O]+ 349.25028. CD: 406 nm (-4.32 mdeg), 235
nm (-11.23 mdeg).
General Procedure for the Synthesis of Luteins 1-4. Syn-
thesis of (3R,3′R,6′R)-Lutein (1). A solution of (3R,6R)-3-hydroxy-
12′-apo-ε-caroten-12′-al (6) (0.26 g, 0.70 mmol) [mixture of (all-
E)- and (11Z)-isomers] and (3R)-3-hydroxy-(ꢀ-ionylideneethyl)-
triphenylphosphonium chloride (5) (0.41 g, 0.79 mmol) in CH2Cl2
(5 mL) was cooled to -5 °C under N2. A solution of KOH (0.13
g, 2.32 mmol) in H2O (0.5 mL) was added, and the mixture was
stirred for 30 min at -5 °C and 3 h at rt. The product was diluted
with CH2Cl2, washed with water, dried, and concentrated to give
1.0 g of a red oil. The crude product was thermally isomerized in
a refluxing solution of EtOAc for 4 h under N2. After solvent
evaporation, the product was purified by column chromatography
(hexane/ethyl acetate, from 90:10 to 50:50) followed by crystal-
lization (hexane/acetone ) 4:1) to yield (3R,3′R,6′R)-lutein (1)
(0.296 g, 0.52 mmol; 74%, dr 99:1) as red solids.
13.2, 6.9, 1H), 1.49 (t, J ) 11.8, 1H), 1.63 (s, 3H), 1.74 (s, 3H),
1.78 (dd, J ) 11.8, 2.8, 1H), 1.85 (dd, J ) 13.2, 5.8, 1H), 1.92 (s,
3H), 1.98 (s, 9H), 2.05 (dd, J ) 16.4, 9.7, 1H), 2.40 (dd, J ) 16.4,
6.8, 1H), 2.41 (d, J ) 9.9, 1H), 4.01 (m, 1H), 4.26 (s, 1H), 5.44
(dd, J ) 15.5, 9.9, 1H), 5.56 (s, 1H), 6.13 (m, 2H), 6.17 (m, 3H),
6.27 (m, 2H), 6.37 (m, 2H), 6.64 (m, 4H). 13C NMR (100 MHz,
CDCl3): δ 12.7, 12.8, 13.1, 21.6, 22.9, 24.3, 28.7, 29.5, 30.2, 34.0,
37.1, 42.5, 44.6, 48.4, 54.9, 65.1, 65.9, 124.5, 124.8, 124.9, 125.6,
126.2, 128.7, 130.0, 130.1, 130.8, 131.3, 132.6, 135.1, 135.7, 136.4,
136.5, 137.6, 137.7, 138.0, 138.5. UV-vis λmax ) 446 nm (ethanol).
HRMS (ESI+) calcd for C40H56O2 568.42748, found 568.42135,
and [(M - H2O) + H]+ 551.41944. CD: 272 nm (-6.19 mdeg),
238 nm (+0.41 mdeg), 214 nm (-4.73 mdeg).
(3R,3′S,6′R)-Lutein (3). Mp 145-146 °C. 1H NMR (400 MHz,
CDCl3): δ 0.86 (s, 3H), 0.95 (s, 3H), 1.08 (s, 6H), 1.42 (dd, J )
11.8, 3.5, 1H), 1.49 (t, J ) 11.9, 1H), 1.65 (s, 3H), 1.75 (s, 3H),
1.78 (m, 1H), 1.85 (dd, J ) 12.7, 7.0, 1H), 1.98 (s, 9H), 2.06 (dd,
J ) 16.0, 10.9, 1H), 2.17 (d, J ) 9.4, 1H), 2.40 (dd, J ) 16.0, 5.0,
1H), 4.01 (m, 1H), 4.24, (m, 1H), 5.49 (s, 1H), 5.54 (dd, J ) 15.4,
9.4, 1H), 6.14 (m, 3H), 6.26 (d, 2H), 6.36 (m, 2H), 6.63 (m, 4H).
13C NMR (100 MHz, CDCl3): δ 12.8, 13.1, 21.6, 22.6, 27.0, 28.7,
29.3, 30.3, 34.8, 37.1, 41.0, 42.5, 48.4, 55.0, 65.1, 66.8, 124.4,
124.8, 124.9, 125.6, 126.2, 128.5, 129.8, 130.1, 130.8, 131.3, 132.5,
132.6, 135.3, 135.7,136.5, 136.7, 137.5, 137.6, 137.7, 138.0, 138.5.
UV-vis λmax ) 446 nm (ethanol). HRMS (ESI+) calcd for C40H56O2
568.42748, found 568.41427, and [(M - H2O) + H]+ 551.41547.
CD: 333 nm (+1.79 mdeg), 280 nm (-2.71 mdeg), 242 nm (+4.92
mdeg).
(3R,3′R,6′S)-Lutein (4). Mp 114-116 °C. 1H NMR (400 MHz,
CDCl3): δ 0.86 (s, 3H), 0.95 (s, 3H), 1.08 (s, 6H), 1.41 (m, 1H),
1.49 (t, J ) 11.9, 1H) 1.65 (s, 3H), 1.75 (s, 3H), 1.80 (m, 1H),
1.92 (m, 1H), 1.98 (s, 9H), 2.05 (dd, J ) 16.6, 9.0, 1H), 2.17 (d,
J ) 9.4, 1H), 2.40 (dd, J ) 16.6, 5.5, 1H), 4.01 (m, 1H), 4.24, (m,
1H), 5.50 (s, 1H), 5.54 (dd, J ) 15.4, 9.4, 1H), 6.16 (m, 5H), 6.26
(d, 2H), 6.36 (m, 2H), 6.63 (m, 4H). 13C NMR (100 MHz, CDCl3):
δ 12.8, 13.1, 21.6, 22.6, 27.0, 28.7, 29.3, 30.3, 34.8, 37.1, 41.0,
42.5, 48.4, 55.0, 65.1, 66.8, 124.4, 124.8, 125.6, 126.2, 129.8, 130.1,
130.8, 131.3, 132.5, 132.6, 135.3, 135.7,136.5, 136.7, 137.5, 137.6,
137.7, 138.5. UV-vis λmax ) 446 nm (ethanol). HRMS (ESI+)
calcd for C40H56O2 568.42748, found 568.41731, and [(M - H2O)
+ H]+ 551.41869. CD: 328 nm (-2.08 mdeg), 266 nm (-5.03
mdeg), 238 nm (-5.78 mdeg).
Following the above procedure, (3R,3′S,6′S)-lutein (2, 82%, dr
99:1), (3R,3′S,6′R)-lutein or 3′-epilutein (3, 85%, dr 96:4), and
(3R,3′R,6′S)-lutein (4, 80%, 94% de) were similarly prepared.
(3R,3′R,6′R)-Lutein (1). Mp 132-134 °C. 1H NMR (400 MHz,
CDCl3): δ 0.86 (s, 3H), 1.01 (s, 3H), 1.08 (s, 6H), 1.37 (dd, J )
13.1, 6.7, 1H), 1.49 (t, J ) 12.3, 1H), 1.63 (s, 3H), 1.74 (s, 3H),
1.78 (dd, J ) 12.3, 2.8, 1H), 1.85 (dd, J ) 13.1, 5.8, 1H), 1.92 (s,
3H), 1.97 (s, 9H), 2.05 (d, J ) 16.3, 9.7, 1H), 2.40 (dd, J ) 16.3,
6.7, 1H), 2.41 (d, J ) 9.9, 1H), 4.01 (m, 1H), 4.26 (s, 1H), 5.44
(dd, J ) 15.5, 9.9, 1H), 5.55 (s, 1H), 6.12 (m, 2H), 6.17 (m, 3H),
6.26 (m, 2H), 6.37 (m, 2H), 6.63 (m, 4H). 13C NMR (100 MHz,
CDCl3): δ 12.8, 13.1, 21.6, 22.9, 24.3, 28.7, 29.5, 30.3, 34.0, 37.1,
42.6, 44.6, 48.4, 54.9, 65.1, 65.9, 124.5, 124.8, 124.9, 125.6, 126.2,
128.7, 130.0, 130.1, 130.8, 131.3, 132.6, 135.1, 135.7, 136.5, 137.6,
137.7, 138.0, 138.5. UV-vis λmax ) 444 nm (ethanol). HRMS
(ESI+) calcd for C40H56O2 568.42748, found 568.41896, and [(M
- H2O) + H]+ 551.41697. CD: 284 nm (-1.26 mdeg), 246 nm
(+2.67 mdeg), 212 nm (+3.75 mdeg). The CD spectra of 1 was
identical with that of the naturally occurring (3R,3′R,6′R)-lutein
isolated from a saponified extracts of marigold flowers.
Acknowledgment. The authors thank the Joint Institute for
Food Safety and Applied Nutrition (JIFSAN), University of
Maryland-Food and Drug Administration (UM-FDA) for fi-
nancial support.
Supporting Information Available: One-pot reduction of
23a to hydroxyaldehydes 15-18 and reduction of 23a to
hydroxynitriles 19- 22 with (R)-2-methyl-CBS-oxazaborolidine.
1
Copies of H and 13C NMR spectra of compounds 1-4, 6-9,
15-28, and (3R,3′R,6′R)-lutein diacetate. Copies of CD spectra
of naturally occurring (3R,3′R,6′R)-lutein and compounds 1-4,
6-9, and 15-18. Table 1S: detailed reduction of ketonitrile
23a to hydroxynitriles 19-22. Table 2S: details of HPLC (chiral,
normal phase) separations and copies of HPLC traces for
relevant compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
(3R,3′S,6′S)-Lutein (2). Mp 128-130 °C. 1H NMR (400 MHz,
CDCl3): δ 0.86 (s, 3H), 1.01 (s, 3H), 1.08 (s, 6H), 1.37 (dd, J )
JO900432R
J. Org. Chem. Vol. 74, No. 10, 2009 3885