Efficient total synthesis of lycophyll (ψ,ψ-carotene-16,16′- diol)

Article abstract of DOI:10.1021/op050137f

A practical procedure is described for the total synthesis of lycophyll (16,16′-dihydroxy-lycopene; ψ,ψ-carotene-16,16′-diol), based on a C10 + C20 + C10 synthetic methodology using the commercially available materials geraniol (C10) and crocetin-dialdehyde (C20). A late-stage double Wittig olefination on crocetindialdehyde was used to form the desired lycophyll scaffold in eight linear synthetic steps, while generating a mixture of polyenic geometric isomers that could be effectively separated using HPLC. All-trans lycophyll was subsequently separated to >95% purity by semipreparative chromatography using a C30 carotenoid column.

Full text of DOI:10.1021/op050137f

Organic Process Research & Development 2005, 9, 830−836
Efficient Total Synthesis of Lycophyll (ψ,ψ-Carotene-16,16′-diol)
Henry L. Jackson, Geoffry T. Nadolski, Cristi Braun, and Samuel F. Lockwood*
Hawaii Biotech, Inc., 99-193 Aiea Heights DriVe, Suite 200, Aiea, Hawaii 96701, U.S.A.
Abstract:
A practical procedure is described for the total synthesis of
lycophyll (16,16′-dihydroxy-lycopene; ψ,ψ-carotene-16,16′-diol),
based on a C10 + C20 + C10 synthetic methodology using the
commercially available materials geraniol (C10) and crocetin-
dialdehyde (C20). A late-stage double Wittig olefination on
crocetindialdehyde was used to form the desired lycophyll
scaffold in eight linear synthetic steps, while generating a
mixture of polyenic geometric isomers that could be effectively
separated using HPLC. All-trans lycophyll was subsequently
separated to >95% purity by semipreparative chromatography
using a C30 carotenoid column.
Figure 1. Chemical structures of lycopene, lycoxanthin, and
lycophyll.
Introduction
Studies in cultured human cells1-3 have shown that
lycopene (ψ,ψ-Carotene; Figure 1), the primary carotenoid
in tomatoes, can be growth inhibitory against transformed
cells as well as normal prostatic epithelium, alone and/or in
combination with other antioxidants (e.g., vitamin E). In
animal studies, the results regarding protection against
proliferation of transformed cells induced with various
carcinogenic agents have been mixed;4-6 in the ferret, the
most representative model in terms of absorption-distribu-
tion-metabolism-excretion (ADME) for humans, lycopene
was in fact protective against cigarette-smoke-induced lung
pathology.7 Epidemiological studies in humans clearly sup-
port an association between dietary consumption of lycopene-
containing food products and a lower risk of prostate cancer.8
Prospective, randomized clinical trials in humans also
demonstrate improved indices of proliferation and oxidative
stress across a range of oral doses in cancer patients (e.g., 2
mg/day to 30 mg/day).9-11 Whether lycopene itself, or
another phytochemical in tomato-based products, provides
the efficacy suggested by epidemiological studies is currently
unknown. Delivery of a highly potent radical scavenger to
prostatic tissue, to restore or augment endogenous antioxidant
levels, should be a promising area of current prostate cancer
research.12,13
Lycoxanthin (ψ,ψ-Caroten-16-ol) and lycophyll (ψ,ψ-
Carotene-16,16′-diol) (Figure 1), isolated from the red berries
of Solanum dulcamara, are C40 lycopene xanthophylls
functionalized with primary hydroxyl groups. The carote-
noids of the berries were first investigated by Zechmeister
and Cholnoky in 1936.14 The originally proposed chemical
structures of the xanthophylls, however, lacked complete
assignment and required further studies that were realized
in the early 1970s. Utilizing high-resolution mass spectros-
copy and NMR, the regiochemistry of the hydroxyl groups
was characterized.15,16 Absolute confirmation of both struc-
tures was obtained approximately one year later, with the
total syntheses of lycoxanthin and lycophyll reported by
Kjøsen and Liaaen-Jensen in 1972.17 The original total
synthesis was based on a C10 + C20 + C10 synthetic
paradigm, in part due to the commercial availability of C20
* Corresponding author. E-mail: slockwood@hibiotech.com. Telephone:
(808) 220-9168. Fax: (808) 792-1343.
(1) Pastori, M.; Pfander, H.; Boscoboinik, D.; Azzi, A. Biochem. Biophys. Res.
Commun. 1998, 250, 582.
(2) Kim, L.; Rao, A. V.; Rao, L. G. J. Med. Food 2002, 5, 181.
(3) Obermuller-Jevic, U. C.; Olano-Martin, E.; Corbacho, A. M.; Eiserich, J.
P.; van der Vliet, A.; Valacchi, G.; Cross, C. E.; Packer, L. J. Nutr. 2003,
133, 3356.
(4) Guttenplan, J. B.; Chen, M.; Kosinska, W.; Thompson, S.; Zhao, Z.; Cohen,
L. A. Cancer Lett. 2001, 164, 1.
(5) Imaida, K.; Tamano, S.; Kato, K.; Ikeda, Y.; Asamoto, M.; Takahashi, S.;
Nir, Z.; Murakoshi, M.; Nishino, H.; Shirai, T. Carcinogenesis 2001, 22,
467.
(6) Boileau, T. W.; Liao, Z.; Kim, S.; Lemeshow, S.; Erdman, J. W., Jr.;
Clinton, S. K. J. Natl. Cancer Inst. 2003, 95, 1578.
(7) Liu, C.; Lian, F.; Smith, D. E.; Russell, R. M.; Wang, X. D. Cancer Res.
2003, 63, 3138.
(8) Giovannucci, E. J. Natl. Cancer Inst. 1999, 91, 317.
(9) Kucuk, O.; Sarkar, F. H.; Sakr, W.; Djuric, Z.; Pollak, M. N.; Khachik, F.;
Li, Y. W.; Banerjee, M.; Grignon, D.; Bertram, J. S.; Crissman, J. D.;
Pontes, E. J.; Wood, D. P., Jr. Cancer Epidemiol. Biomarkers PreV. 2001,
10, 861.
(10) Bowen, P.; Chen, L.; Stacewicz-Sapuntzakis, M.; Duncan, C.; Sharifi, R.;
Ghosh, L.; Kim, H. S.; Christov-Tzelkov, K.; van Breemen, R. Exp. Biol.
Med. (Maywood) 2002, 227, 886.
(11) Ansari, M. S.; Gupta, N. P. BJU Int. 2003, 92, 375.
(12) Li, H.; Kantoff, P. W.; Giovannucci, E.; Leitzmann, M. F.; Gaziano, J.
M.; Stampfer, M. J.; Ma, J. Cancer Res. 2005, 65, 2498.
(13) Petros, J. A.; Baumann, A. K.; Ruiz-Pesini, E.; Amin, M. B.; Sun, C. Q.;
Hall, J.; Lim, S.; Issa, M. M.; Flanders, W. D.; Hosseini, S. H.; Marshall,
F. F.; Wallace, D. C. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 719.
(14) Cholnoky, L.; Szabolcs, J.; Waight, E. S. Tetrahedron Lett. 1968, 16, 1931.
(15) Markham, M. C.; Liaaen-Jensen, S. Phytochemistry 1968, 7, 839.
(16) Kelly, M.; Andresen, S. A.; Liaaen-Jensen, S. Acta Chem. Scand., Ser. A
1971, 25, 1607.
(17) Kjosen, H.; Liaaen-Jensen, S. Acta Chem. Scand., Ser. A 1972, 26, 4121.
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10.1021/op050137f CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/08/2005

Scheme 1a
a (a) SeO2, 95% EtOH, reflux; (b) NaClO2, NaH2PO4, Me2CdCHMe, t-BuOH/H2O; (c) K2CO3, MeOH/H2O; (d) CH3I, K2CO3, DMF/H2O; (e) CBr4/Ph3P, THF,
0 °C; (f) Ph3P, EtOAc.
Scheme 2 a
beneficial effects as direct aqueous radical scavengers;21,24,25
as myocardial salvage agents in experimental infarction
models;26-29 and as cancer chemopreventive agents.30-33 The
derivatives have shown increased utility as parenteral agents
in these settings, as well as improved oral bioavailability in
model animal studies.34 Acquisition of lycophyll through total
synthesis (Schemes 1 and 2) should facilitate the generation
of water-dispersible lycophyll salts. Such derivatives will
likely find application in those indications in which parenteral
delivery of highly potent radical scavengers possessing the
lycopene scaffold is necessary to achieve their intended
purpose. Specifically, these compounds will be evaluated for
efficacy in contemporary in Vitro and in ViVo cancer
chemoprevention models.
Experimental Procedures
Synthesis of Lycophyll, General. Crocetindialdehyde (8)
was obtained from SynChem, Inc. (Des Plaines, IL) as a
brick-red solid and was used without further purification.
Acetic acid 3,7-dimethyl-8-oxo-octa-2,6-dienyl ester (2)35
was synthesized by literature procedures from commercially
available geranyl acetate (1). All other reagents and solvents
used were purchased from Acros Organics (Morris Plains,
NJ) and Sigma-Aldrich (St. Louis, MO) and were used
without further purification. All reactions were performed
a (a) LiOMe in MeOH, toluene, reflux; (b) DIBAL, THF, 0 °C.
dialdehyde (crocetindialdehyde). Up to the present, little
additional chemical or biological information has accumu-
lated in the primary literature for either compound.18
In the current study, the original synthetic design by
Kjøsen and Liaaen-Jensen was used as a guide to generate
lycophyll by total synthesis. Retrosynthetic analysis of the
target xanthophyll revealed an efficient methodology utilizing
the commercially available materials geranyl acetate, a
protected form of geraniol (C10), and crocetindialdehyde
(C20). The concise total synthesis of lycophyll was realized
in eight synthetic steps (Schemes 1 and 2). Synthetic high-
lights include an endgame double-Wittig olefination that
successfully formed the target C40 scaffold while generating
a mixture of geometric isomers (Scheme 2). The isomeric
mixture was then effectively deconvoluted to yield one
primary target, all-trans lycophyll.
(21) Jackson, H. L.; Cardounel, A. J.; Zweier, J. L.; Lockwood, S. F. Bioorg.
Med. Chem. Lett. 2004, 14, 3985.
(22) Zsila, F.; Fitos, I.; Bika´di, Z.; Simonyi, M.; Jackson, H. L.; Lockwood, S.
F. Bioorg. Med. Chem. Lett. 2004, 14, 5357.
(23) Foss, B. J.; Sliwka, H. R.; Partali, V.; Naess, S. N.; Elgsaeter, A.; Melø,
T. B.; Naqvi, K. R.; O’Malley, S.; Lockwood, S. F. Chem. Phys. Lipids
2005, 135, 157.
(24) Cardounel, A. J.; Dumitrescu, C.; Zweier, J. L.; Lockwood, S. F. Biochem.
Biophys. Res. Commun. 2003, 307, 704.
(25) Foss, B. J.; Sliwka, H. R.; Partali, V.; Cardounel, A. J.; Zweier, J. L.;
Lockwood, S. F. Bioorg. Med. Chem. Lett. 2004, 14, 2807.
(26) Gross, G. J.; Lockwood, S. F. Life Sci. 2004, 75, 215.
(27) Gross, G. J.; Lockwood, S. F. Mol. Cell. Biochem. 2005, 272, 221.
(28) Lauver, D. A.; Lockwood, S. F.; Lucchesi, B. R. J. Pharmacol. Exp. Ther.
2005, 314, 686.
(29) Lockwood, S. F.; Gross, G. J. CardioVasc. Drug ReV. 2005, 23, 199.
(30) Hix, L. M.; Lockwood, S. F.; Bertram, J. S. Cancer Lett. 2004, 211, 25.
(31) Hix, L. M.; Lockwood, S. F.; Bertram, J. S. Redox Rep. 2004, 9, 181.
(32) Hix, L. M.; Vine, A. L.; Lockwood, S. F.; Bertram, J. S. Carotenoids and
Retinoids: Molecular Aspects and Health Issues; Packer, L., Obermueller-
Jevic, U., Kraemer, K., Sies, H., Eds.; AOCS Press: Champaign, IL, 2005;
Chapter 11, p 182.
Previous work by us and collaborators have shown that
targeted derivatization of carotenoids can successfully in-
crease the aqueous dispersibility of the highly lipophilic
natural scaffolds.19-23 These compounds have demonstrated
(18) Britton, G.; Liaaen-Jensen, S.; Pfander, H.; Mercadante, A. Z.; Egeland,
E. S. Carotenoids Handbook; Birkha¨user: Basel, 2004.
(19) Lockwood, S. F.; O’Malley, S.; Mosher, G. L. J. Pharm. Sci. 2003, 92,
922.
(20) Frey, D. A.; Kataisto, E. W.; Ekmanis, J. L.; O’Malley, S.; Lockwood, S.
F. Org. Process Res. DeV. 2004, 8, 796
(33) Hix, L. M.; Frey, D. A.; McLaws, M. D.; Østerlie, M.; Lockwood, S. F.;
Bertram, J. S. Carcinogenesis 2005, 26, 1634.
(34) Showalter, L. A.; Weinman, S. A.; Osterlie, M.; Lockwood, S. F. Comp.
Biochem. Physiol., C. 2004, 137, 227.
(35) Liu, X. H.; Prestwich, G. D. J. Am. Chem. Soc. 2002, 124, 20.
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under a nitrogen atmosphere. All flash chromatographic
purifications were performed on Natland International Cor-
poration 230-400 mesh silica gel using indicated solvents.
LC/MS (APCI and ESI + modes) data were recorded on an
Agilent 1100 LC/MSD VL system; column, Zorbax Eclipse
XDB-C18 Rapid Resolution (4.6 mm × 75 mm, 3.5 µm);
temperature, 25 °C; flow rate, 1.0 mL/min; mobile phase
(A ) 0.025% TFA in H2O, B ) 0.025% TFA in acetonitrile).
Gradient program (for intermediates 2-7): 70% A/30% B
(start), step gradient to 50% B over 5 min, step gradient to
100% B over 1.3 min, hold at 100% B over 4.9 min. Gradient
program (for intermediates 9, 10): 70% A/30% B (start),
step gradient to 50% B over 5 min, step gradient to 98% B
over 3.3 min, hold at 98% B over 16.9 min. All-trans
lycophyll was obtained from crude material using a Waters
996 Photodiode Array detector, Millipore 600E System
Controller, and Waters 717 Autosampler; column, YMC C30
Carotenoid S-5 (10 mm × 250 mm, 5 µm column);
temperature, 25 °C; flow rate, 4.7 mL/min; mobile phase
(A ) methanol (MeOH), B ) methyl-tert-butyl ether
(MTBE)). Gradient program: 60% A/40% B (start), step
gradient to 80% A over 1 min, hold at 80% A over 119
min. Fractions were collected from 55 to 66 min. Fraction
analysis was performed on a YMC C30 Carotenoid S-5 (4.6
mm × 250 mm, 5 µm column). Nuclear magnetic resonance
(NMR) spectra were obtained on a Varian Unity INOVA
500 spectrometer operating at 500 MHz (megahertz) for
proton NMR (1H NMR) and 125 MHz for carbon NMR (13C
NMR). Chemical shifts are given in ppm (δ), and coupling
constants, J, are reported in hertz (Hz). Electronic absorption
spectra were recorded on a Cary 50 Bio UV-visible
spectrophotometer.
carbonate (K2CO3) (24.4 g, 177 mmol) in 100 mL of water.
The resulting mixture was vigorously stirred overnight at
room temperature. The reaction was cooled to 0 °C,
methylene chloride (DCM) (200 mL) was added, and the
aqueous layer was acidified to pH 3 with 1 M HCl. The
organic layer was separated, and the aqueous layer was
extracted with DCM (2 × 200 mL). The combined organic
extracts were washed with brine, dried over MgSO4, and
reduced to dryness in vacuo. The crude product (9.65 g, 52.4
mmol, 59% yield) was used in the next step without further
purification: 1H NMR (CDCl3) δ: 6.86 (t of q, J ) 7.25
Hz, J ) 1.50 Hz, 1H, dCH), 5.43 (t of q, J ) 7.00 Hz, J )
1.50 Hz, 1H, dCH), 4.16 (d, J ) 7.00 Hz, 2H, sCH2Os),
2.33 (q, J ) 7.50 Hz, 2H, sCH2s), 2.16 (t, J ) 7.50 Hz,
2H, sCH2s), 1.83 (s, 3H, sCH3), 1.68 (s, 3H, sCH3). 13
C
NMR (CDCl3) δ: 173, 144, 138, 127, 124, 59.2, 37.8, 27.0,
16.2, 12.0. LC/MS (ESI): m/z 207 [M + Na]+.
8-Hydroxy-2,6-dimethyl-octa-2,6-dienoic Acid Methyl
Ester (5). To a solution of acid 4 (20.1 g, 109 mmol) in 400
mL of dimethylformamide (DMF) was added a solution of
K2CO3 (16.6 g, 120 mmol) in 80 mL of water. The resulting
mixture was vigorously stirred for several minutes. To the
mixture was added iodomethane (CH3I) (7.50 mL, 120
mmol) via syringe. The resulting mixture was vigorously
stirred overnight at room temperature. Water (400 mL) and
EtOAc (400 mL) were added, and the aqueous layer was
acidified to pH 3 by addition of 1 M HCl. The organic layer
was separated, and the aqueous layer was extracted with
EtOAc (3 × 200 mL). The combined organic extracts were
washed with water (3 × 500 mL), saturated aqueous sodium
bicarbonate (NaHCO3), and brine and dried over MgSO4.
The solvent was removed under reduced pressure, and the
crude product was purified by flash chromatography (MeOH/
CH2Cl2, 1:49) to afford methyl ester 5 as a clear oil (19.4 g,
90% yield): 1H NMR (CDCl3) δ: 6.72 (t of q, J ) 7.50
Hz, J ) 1.50 Hz, 1H, dCH), 5.43 (t of q, J ) 6.75 Hz, J )
1.50 Hz, 1H, dCH), 4.16 (d, J ) 7.00 Hz, 2H, sCH2Os),
3.73 (s, 3H, sCH3), 2.31 (q, J ) 7.50 Hz, 2H, sCH2s),
2.15 (t, J ) 7.50 Hz, 2H, sCH2s), 1.83 (s, 3H, sCH3),
1.69 (s, 3H, sCH3). 13C NMR (CDCl3) δ: 169, 142, 138,
128, 124, 59.3, 51.7, 38.0, 26.8, 16.2, 12.4. LC/MS (ESI):
m/z 221 [M + Na]+.
8-Bromo-2,6-dimethyl-octa-2,6-dienoic Acid Methyl
Ester (6). To a 0 °C solution of alcohol 5 (12.9 g, 64.9
mmol) in 250 mL of anhydrous THF was added carbon
tetrabromide (CBr4) (23.8 g, 71.4 mmol) in several portions.
The mixture was stirred for a few minutes, and then
triphenylphosphine (Ph3P) (18.7 g, 71.4 mmol) was added
and the mixture was allowed to warm to room temperature
and stirred overnight. The solvent was removed under
reduced pressure, and the resulting residue was suspended
in diethyl ether (Et2O). The suspension was filtered through
a pad of Celite. After solvent removal under reduced
pressure, the resulting crude product (contaminated with
triphenylphosphine oxide (Ph3PO)) was used directly in the
next step: 1H NMR (CDCl3) δ: 6.61 (t of q, J ) 7.50 Hz,
J ) 1.50 Hz, 1H, dCH), 5 47 (t of q, J ) 8.00 Hz, J ) 1.50
Hz, 1H, dCH), 3.92 (d, J ) 8.50 Hz, 2H, sCH2Br), 3.63
8-Acetoxy-2,6-dimethyl-octa-2,6-dienoic Acid (3). To
a solution of aldehyde 2 (19.5 g, 92.7 mmol) in 300 mL of
tert-butyl alcohol was added 2-methyl-2-butene (98.0 mL,
925 mmol). To this was added a solution of sodium
dihydrogen phosphate (NaH2PO4) (44.5 g, 371 mmol) in 300
mL of water. Sodium chlorite (NaClO2) (33.6 g, 371 mmol)
was added in several portions. The resulting mixture was
rapidly stirred overnight at room temperature. Ethyl acetate
(EtOAc) was added, and the aqueous layer was acidified to
pH 3 by addition of 1 M HCl. The organic layer was
separated, and the aqueous layer was extracted with EtOAc
(3 × 200 mL). The combined organic extracts were washed
with brine, dried over magnesium sulfate (MgSO4), and
reduced to dryness in vacuo. The crude product (27.4 g, 121
mmol, >100% yield) was used in the next step without
1
further purification: H NMR (CDCl3) δ: 6.84 (t of q, J )
7.25 Hz, J ) 1.50 Hz, 1H, dCH), 5.34 (t of q, J ) 7.00 Hz,
J ) 1.50 Hz, 1H, dCH), 4.56 (d, J ) 7.00 Hz, 2H,
sCH2Os), 2.31 (q, J ) 7.50 Hz, 2H, sCH2s), 2.15 (t,
J ) 7.50 Hz, 2H, sCH2s), 2.03 (s, 3H, sCH3), 1.81 (s,
3H, sCH3), 1.70 (s, 3H, sCH3). 13C NMR (CDCl3) δ: 173,
171, 144, 141, 127, 119, 61.1, 37.8, 26.9, 20.9, 16.3, 11.9.
LC/MS (ESI): m/z 249 [M + Na]+.
8-Hydroxy-2,6-dimethyl-octa-2,6-dienoic Acid (4). To
a solution of acid 3 (20.0 g, 88.4 mmol) in 400 mL of
methanol (MeOH) was added a solution of potassium
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Figure 2. Chromatogram of “crude” lycophyll (10) obtained using a C18 reversed-phase HPLC column (see text). Total lycophyll
content (including cis and trans geometric isomers) >90% (as AUC).
Figure 3. Chromatogram of “crude” lycophyll (10) obtained using a C30 carotenoid column (see text). Total lycophyll content
(including cis and trans geometric isomers) >90% as AUC. All-trans lycophyll, which elutes at 21.139 min (23.6% AUC), was
further purified by semipreparative chromatography and its absolute configuration was confirmed by NMR (Figure 5).
(s, 3H, sCH3), 2.22 (q, J ) 8.00 Hz, 2H, sCH2s), 2.10 (t,
J ) 8.00 Hz, 2H, sCH2s), 1.75 (d, J ) 1.00 Hz, 3H, s
CH3), 1.66 (d, J ) 1.00 Hz, 3H, sCH3). 13C NMR (CDCl3)
δ: 168, 142, 141, 128, 121, 51.4, 37.7, 28.8, 26.4, 15.7, 12.2.
(2,6-Dimethyl-8-octa-2,6-dienoic acid methyl ester)-
triphenylphosphonium Bromide (7). To a solution of
bromide 6 (9.20 g, 35.2 mmol) in EtOAc (200 mL) was
added Ph3P (10.2 g, 38.8 mmol). The resulting mixture was
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833

Dimethyl ψ,ψ-Carotene-16,16′-dioate (9). To a solution
of crocetindialdehyde (8) (0.810 g, 2.74 mmol) and 7 (4.30
g, 8.21 mmol) in toluene (100 mL) was added 1 M lithium
methoxide (LiOMe) in MeOH (7.67 mL, 7.67 mmol) via
syringe. The resulting mixture was refluxed for 24 h and
cooled to room temperature, and then water (100 mL) was
added. The organic phase was collected, extracted with water
twice, and then dried over anhydrous Na2SO4. After filtration
and removal of the solvent in vacuo, the resulting residue
was purified by flash chromatography (EtOAc/toluene, 1:99)
to afford dimethyl ester 9 as a red solid (1.15 g, 67% yield,
as a mixture of geometric isomers). LC/MS (APCI): m/z
625 [M + H]+.
ψ,ψ-Carotene-16,16′-diol (Lycophyll) (10). To a solution
of dimethyl ester 9 (1.14 g, 1.83 mmol) in anhydrous THF
(100 mL) at 0 °C was added diisobutylaluminum hydride
(DIBAL) (20% by wt. in toluene) (9.13 mL, 11.0 mmol)
via syringe. The mixture was warmed to room temperature
and stirred for 1 h. The reaction was quenched by the
sequential addition of water (440 µL), 15% aqueous NaOH
(440 µL), and water (1.10 mL). The resulting mixture was
stirred for 30 min and then dried over anhydrous MgSO4.
The resulting slurry was filtered, and the solvent was
removed in vacuo to afford the diol 10 as a red solid (1.01
g, 97% yield, as a mixture of geometric isomers). 1H NMR
(CDCl3) δ: 6.63 (m, 4H), 6.48 (d of d, J ) 15.0 Hz, J )
11.0 Hz, 2H), 6.36 (d, J ) 15.0 Hz, 2H), 6.26 (m, 4H), 6.19
(d, J ) 11.5 Hz, 2H), 5.95 (d, J ) 11.0 Hz, 2H), 5.40 (brt,
J ) 6.90 Hz, 2H), 4.00 (s, 4H), 2.19 (m, 4H), 2.16 (m, 4H),
Figure 4. Through-space connectivities of 10 as measured by
1D NOE difference experiments. Each double-headed arrow
represents a medium to strong NOE interaction and hence a
corresponding though-space contact revealing the close spatial
proximity of the two protons or groups of protons.
vigorously stirred for a few minutes, at which time an
insoluble material began to oil out from the solution, adhering
to the sides of the flask. The reaction solution was then
decanted into a clean reaction vessel. This procedure was
repeated every 5 to 10 min until no more oily insoluble
residue was noted, at which time a white solid started to
precipitate from the solution. The cloudy mixture was then
stirred overnight at room temperature. The mixture was
filtered, and the filter cake was rinsed with EtOAc and dried
in vacuo to afford phosphonium salt 7 as a white solid (9.60
g, 52% yield). 1H NMR (CDCl3) δ: 7.88-7.84 (m, 6 arom.
H), 7.79-7.75 (m, 3 arom. H), 7.68-7.64 (m, 6 arom. H),
6.51 (t of q, J ) 5.00 Hz, J ) 1.00 Hz, 1H, dCH), 5.10 (q,
J ) 7.00 Hz, 1H, dCH), 4.70 (d of d, J ) 15.0, J ) 8.00
Hz, 2H, sCH2PPh3Br), 3.67 (s, 3H, sCH3), 2.16 (q, J )
7.00 Hz, 2H, sCH2s), 2.08 (t, J ) 6.00 Hz, 2H, sCH2s),
1.70 (s, 3H, sCH3), 1.35 (d, J ) 4.00 Hz, 3H, sCH3). 13
C
NMR (CDCl3) δ: 168, 146, 141, 135, 134, 130, 128, 118,
109, 51.7, 38.2, 26.2, 24.5, 17.2, 12.4. LC/MS (ESI): m/z
443 [M]+.
1
Figure 5. Olefinic region of the H NMR spectrum of all-trans lycophyll.
834
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Table 1. 1H NMR Data of Lycopene37 and Lycophyll
lycophyll
1.97 (s, 12H), 1.82 (s, 6H), 1.68 (s, 6H). LC/MS (APCI):
m/z 569 [M + H]+.
lycopene
5.11
2.11
2.11
5.95
6.49
6.25
6.18
6.64
6.35
6.25
6.62
1.69
H-C(2)
H-C(2′)
2 H-C(3)
2 H-C(3′)
2 H-C(4)
2 H-C(4′)
H-C(6)
5.40
2.19
2.16
5.95
6.48
6.25
6.19
6.63
6.36
6.26
6.63
Results and Discussion
Following the original synthetic route utilized by Kjøsen
and Liaaen-Jensen,17 our synthetic strategy was likewise
based on the availability of crocetindialdehyde 8. The original
synthesis utilized an endgame Wittig olefination using 2
molar equiv of C10 phosphonium salt for 1 equiv of C20
dialdehyde to form lycophyll’s C40 scaffold. Significant
synthetic effort involved the preparation of the required C10
head pieces. Kjøsen and Liaaen-Jensen’s route toward the
C10 fragment began with a three-carbon synthon involving
nine synthetic steps that included two Wittig olefination
coupling reactions. This methodology successfully produced
the desired head piece in fair yield while also introducing
significant amounts of cis-olefin contamination. Using the
original route as a template, our efforts toward a concise
and efficient preparation of lycophyll involved three key
goals: (1) the development of a highly convergent synthesis
of the target scaffold, (2) the preparation of an all-trans C10
headpiece, and (3) the optimization of synthetic manipula-
tions needed to access multiple gram amounts of generated
intermediates and the final target.
Geraniol, an abundantly available and naturally occurring
C10 allylic alcohol, proved to be an appropriate starting
synthon in preparing the synthetic intermediate phosphonium
salt 7 (Scheme 1). Specifically, geranyl acetate 1 underwent
regioselective oxidation using selenium dioxide to afford
known aldehyde 2.35 The aldehyde was then cleanly oxidized
to carboxylic acid 3 with NaClO2 in the presence of
2-methyl-2-butene. Chromium-based oxidants such as pyr-
idinium dichromate and Jones’ reagent were screened,
yielding a complex mixture largely contaminated with
chromium-containing byproducts that proved difficult to
remove. The acetate of 3 was saponified using K2CO3 in
MeOH/H2O to form the free allylic alcohol 4. Treatment of
4 with CH3I converted the carboxylic acid to its correspond-
ing methyl ester. Initially, the allylic alcohol of 5 was
converted directly to the phosphonium salt using Ph3P‚HBr,
however, in poor yield and with unacceptable amounts of
cis-olefin contamination. A more mild, two-step protocol was
adopted, such that the phosphonium salt was accessed
through the preceding halide. Specifically, addition of CBr4
and Ph3P to alcohol 5 afforded bromide 6. The crude bromide
was then treated with Ph3P to provide the all-trans phos-
phonium salt 7 in good yield. NOE difference36 experiments
were utilized to confirm the trans-olefin geometry about
bonds 2 and 6 of phosphonium salt 7. The Wittig condensa-
tion (Scheme 2) of phosphonium salt 7 with crocetindial-
dehyde 8 yielded dimethyl ester 9. Reduction of diester 9
with DIBAL provided lycophyll 10 (Figure 2) as a complex
mixture of geometric isomers. Subsequent purification of the
all-trans fraction (Figure 3) from the complex mixture was
afforded by HPLC chromatography, yielding all-trans lyco-
phyll at >95% purity (as area under the curve; AUC).
H-C(6′)
H-C(7)
H-C(7′)
H-C(8)
H-C(8′)
H-C(10)
H-C(10′)
H-C(11)
H-C(11′)
H-C(12)
H-C(12′)
H-C(14)
H-C(14′)
H-C(15)
H-C(15′)
Me(16)
Me(16′)
2 H-C(16)
2 H-C(16′)
Me(17)
Me(17′)
Me(18)
Me(18′)
Me(19)
Me(19′)
Me(20)
4.00
1.68
1.82
1.97
1.97
1.61
1.82
1.97
1.97
Me(20′)
Lycophyll (as both the mixture of geometric isomers as well
as the purified all-trans form) has been subsequently utilized
in in Vitro and in ViVo biological experiments
The all-trans configuration of the polyene chromophore
and the regiochemistry of the primary hydroxyl groups of
the purified material were subsequently confirmed by 2D
COSY, 1D TOCSY, and NOE analysis. The connectivity of
most of the coupled protons was deduced by a 2D COSY
experiment. Using one-dimensional NOE difference experi-
ments, through-space couplings confirmed the expected
trans-orientation of selected polyenic protons (Figure 4). The
chemical shifts and coupling constants of two sets of two
overlapping olefinic protons (Figure 5) were revealed by a
series of 1D TOCSY experiments. A comparison of polyenic
1H NMR data of all-trans lycopene37 with purified, synthetic
all-trans lycophyll showed a near complete matching of
peaks, specifically in ppm value, multiplicity, and integration
(Table 1). As seen in Figure 6, the electronic absorption of
lycophyll (as a mixture of cis/trans isomers) in various
solvents displays the characteristic overall shape and fine
structure expected of the lycopene chromophore. The posi-
tions of peaks I, II, and III in acetone (444, 469, and 499
nm) are slightly blue-shifted from those reported by Britton
et al. (446 nm, 475 nm, 505 nm)18 for all-trans lycophyll
(36) Stotta, K.; Keelera, J.; Vanb, Q. N.; Shakab, A. J. J. Magn. Reson. 1997,
125, 302.
(37) Hengartner, U.; Bernhard, K.; Meyer, K.; Englert, G.; Glinz, E. HelV. Chim.
Acta 1992, 75, 1848.
Vol. 9, No. 6, 2005 / Organic Process Research & Development
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835

Figure 6. UV/vis spectral evaluation of lycophyll (as mixture of geometric isomers) in four solvents of differing polarities: hexanes,
acetone, ethanol (EtOH), and tetrahydrofuran (THF). Concentration of lycophyll standardized to 1 µg/mL in each solvent. Ethanol
and hexanes solvents included 0.5% THF. The absorbance in acetone is reported above 300 nm due to interference from absorbance
of the solvent itself between 200 and 300 nm.
and is likely due to the presence of cis isomers in this spectral
sample. As expected, as solvent polarizability increases, red-
shifting of the absorbance spectrum is seen, nearly 8 nm for
peak II between hexanes and THF.
find application in those therapeutic areas in which lycopene-
like compounds have previously shown efficacy, such as
prostate cancer.
Acknowledgment
The authors would like to thank Anthony Mehok of
Hawaii Biotech, Inc. for analytical chemistry assistance and
Wesley Yoshida of the University of Hawaii in Manoa for
experimental assistance with the collection and interpretation
of NMR data.
Conclusion
In summary, we report the improved total synthesis of
the rare xanthophyll lycophyll at gram scale, with methods
for purification to desired geometric isomers using semi-
preparative chromatography. The natural tissue tropism of
these compounds can now be exploited to introduce potent
radical scavenging activity through additional methods of
drug administration. As such, these compounds will likely
Received for review August 8, 2005.
OP050137F
836
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Vol. 9, No. 6, 2005 / Organic Process Research & Development