Synthesis of lomazarin and norlomazarin, pigments from Lomandra hastilis

Article abstract of DOI:10.1007/s10600-009-9193-5

5,8-Dihydroxy-2,3,6-trimethoxy-7-ethyl-1,4-naphthoquinone (1) was used to synthesize in high yield 5,8-dihydroxy-7(1′-hydroxyethyl)-2,3,6- trimethoxy-1,4-naphthoquinone (lomazarin, 3), a pigment from Lomandra hastilis. Alkaline hydrolysis of lomazarin produced mainly 5,6,8-trihydroxy-2,3-dimethoxy- 1,4-naphthoquinone (9) through a retro-aldol decomposition of the 6-keto-form of 5,6,8-trihydroxy-7(1′-hydroxyethyl)-2,3-dimethoxy-1,4-naphthoquinone (13b) formed during the reaction. 2,5,8-Trihydroxy-7(1′-hydroxyethyl)-3,6- dimethoxy-1,4-naphthoquinone (norlomazarin, 4a), a pigment of L. hastilis, and its 3,5,8-trihydroxy-7(1′-hydroxyethyl)-2,6-dimethoxy isomer 4b were formed as a difficultly separable mixture in addition to quinone 9.

Full text of DOI:10.1007/s10600-009-9193-5

Chemistry of Natural Compounds, Vol. 44, No. 6, 2008
SYNTHESIS OF LOMAZARIN AND NORLOMAZARIN,
PIGMENTS FROM Lomandra hastilis
D. N. Pelageev,1* M. N. Panchenko, N. D. Pokhilo,
2
1
UDC 547.655.6
1
1
V. A. Denisenko, and V. F. Anufriev
5
5
,8-Dihydroxy-2,3,6-trimethoxy-7-ethyl-1,4-naphthoquinone (1) was used to synthesize in high yield
,8-dihydroxy-7(1′-hydroxyethyl)-2,3,6-trimethoxy-1,4-naphthoquinone (lomazarin, 3), a pigment from
Lomandra hastilis. Alkaline hydrolysis of lomazarin produced mainly 5,6,8-trihydroxy-2,3-dimethoxy-1,4-
naphthoquinone (9) through a retro-aldol decomposition of the 6-keto-form of 5,6,8-trihydroxy-7(1′-
hydroxyethyl)-2,3-dimethoxy-1,4-naphthoquinone (13b) formed during the reaction. 2,5,8-Trihydroxy-7(1′-
hydroxyethyl)-3,6-dimethoxy-1,4-naphthoquinone (norlomazarin, 4a), a pigment of L. hastilis, and its
3
,5,8-trihydroxy-7(1′-hydroxyethyl)-2,6-dimethoxy isomer 4b were formed as a difficultly separable mixture
in addition to quinone 9.
Key words: echinochrome trimethyl ether, lomazarin, norlomazarin, Lomandra hastilis, retro-aldol reaction,
spinochrome D dimethyl ether, Echinotrix calamaris, tricrozarin B, Tritonia crocosmaeflora.
The chemistry of polymethoxylated derivatives of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) (Structures of
naphthazarin derivatives are given, unless specifically noted, as only one of the possible tautomers) is practically unstudied
because oftheir poor availability[1]. Wepreviouslydevelopedconvenient methods for synthesizing these compounds [2], which
made them convenient starting materials for the synthesis of several natural products and their analogs [3-5]. One of these
promising derivatives is the trimethyl ether of echinochrome (1, TMEE) [2, 6]. Thus, hydrolysis of TMEE formed
echinochrome (2) [7], a metabolite of the sea urchin Scaphechinus mirabilis [3], that is used as a cardioprotector and
ophthalmological drug [8].
OH
OR
O
OH
O
OH
O
1'
RO
RO
MeO
MeO
7
MeO
RO
1
4
*
6
OR
OMe
O
OH
O
OH
3, 10
O
OH
1
, 2
7, 8
−
HO
1, 7, 10: R = Me; 2, 3, 8: R = H
7
8
In continuation of these studies, we investigated the transformation of TMEE into lomazarin (3) [3, 9] and
norlomazarin (4a) [4], metabolites (Compounds 3 and 4 contain asymmetric C-1′; however, it was not reported [4, 9] if they
were optically active or a mixture of isomers.) that were previously isolated from roots of Lomandra hastilis. The biological
activity of pigments from L. hastilis has not been studied because of their low content. Therefore, synthesis is the only reliable
source of these compounds in amounts sufficient for studying their biological properties. A question arose during structure
determinations about the mutual location of the β-hydroxyls and methoxyls (They could also be adjacent in one ring [4]) of
1
) Pacific Institute of Bioorganic Chemistry, Far-East Branch, Russian Academy of Sciences, Russian Federation,
6
90022, Vladivostok, prosp. 100-Letiya Vladivostoka, 159, fax: (4232) 31 40 50, e-mail: pelageev@piboc.dvo.ru; 2) Institute
of Chemistryand Applied Ecology, Far-East State University, Russian Federation, 690600, Vladivostok, ul. Oktyabr′skaya, 27,
fax: (4232) 25 76 09. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 581-584, November-December, 2008.
Original article submitted September 2, 2008.
©
0
009-3130/08/4406-0719 2008 Springer Science+Business Media, Inc.
719

norlomazarin (4) relative to its backbone. Therefore, the goal of our work was to resolve the question of which actual isomer
corresponds to the resonances observed in the PMR spectra [4]. Compound (3) was synthesized by the following scheme:
O
OH
O
OH Br
O
OH OH
MeO
MeO
MeO
MeO
MeO
MeO
Br
CCl
2
1. KOAc
. CF COOH
4
2
OMe
OMe
3
OMe
O
OH
O
OH
O
OH
1
5
3
Free-radical bromination of 1 in CCl gave 1′-bromo derivative 5 in practicallyquantitative yield (98%). The halogen
4
atom in 5 was readily replaced byacetoxyusing KOAc in HOAc. This produced 1′-acetate 6 (72%). Hydrolysis of intermediate
6
in MeOH—CF COOH gave 3 also in practically quantitative yield (97%). As expected, the physicochemical properties of
3
the synthetic product were completely identical to lomazarin (3) [3, 9].
2
,3-Dimethoxy-1,4-naphthoquinonesarebytheir natureanalogsofvinyl ethersofcarboxylicacids, which isresponsible
for their sensitivity to bases. This property, which was used earlier for selective conversion of the dimethyl ether of
methylspinazarin (7) into its monomethyl ether 8 [10], was used to hydrolyze lomazarin (3).
Heating lomazarin in NaOH solution (1%) gave several products. Two of them were isolated as a mixture (∼1:1) that
consisted according to PMR of norlomazarin (4) [4] and its isomer. The mixture was chromatographed over a silica-gel column
with elution by hexane:acetone (20:1) to isolate two fractions that were mixtures of these compounds in 2:1 and 1:2 ratios,
13
respectively. This made it possible to assign reliablyresonances of each of them in the PMR and C NMR spectra. Resonances
of protons in the PMR spectra and C atoms in the 13C NMR spectra of the product mixtures were assigned based on HMBC
experiments (Table 1).
The spectral data were used to refine the structure of norlomazarin and ascribe it structure 4a; its isomer, 4b. Thus,
in contrast with the hydrolysis of 7 [10], this reaction with lomazarin occurred nonselectively.
O
OH OH
O
OH
R O
1
MeO
R O
2
OMe
MeO
OH
O
OH
a, b
a: R = H, R = Me; 4b: R = Me, R = H
O
OH
4
9
4
1
2
1
2
However, the main product formed by reacting 3 with dilute NaOH solution was the dimethyl ether of spinochrome
D (9, 50%) [1], a pigment of the sea urchin Echinotrix calamaris [3], and also the main product obtained from base hydrolysis
of 5, 6, and the methyl ether of lomazarin (10) [11]. Its structure was proved unambiguously by spectroscopic methods and a
series ofchemical transformations. Thus, selective methylation of9 byCH N gave tricrozarin B(11), a pigment isolated earlier
2
2
from bulbs of Tritonia crocosmaeflora [12]. Free-radical C-ethylation of 9 by propionylperoxide gave the dimethyl ether of
echinochrome (12), which gave 1 after treatment with CH N .
2
2
O
O
OH
OH
O
O
OH
OH
O
O
OH
OH
O
O
OH
OH
MeO
MeO
MeO
MeO
MeO
MeO
MeO
MeO
CH N
(EtCOO)2
OH
CH N
2 2
2
2
OMe
OH
OMe
1
1
9
12
1
Dimethylether 9 appears as a subgroup in the structure of several natural biologicallyactive products [3-5]. Therefore,
it could become a convenient intermediate for their synthesis.
Dimethylether 9 was formed through a retro-aldol decomposition ofdimethylether 13, which was formed byhydrolysis
of 3. The keto-form 13b was involved in the reaction. Evidently equilibrium was wholly shifted toward hydroxynaphthazarin
(
9) in this instance. Therefore, 13 was not observed among the products from base hydrolysis.
7
20

1
13
1
TABLE 1. Through-Space H− C Correlations in 2D HMBC Experiment and H Chemical Shifts (δ , ppm, CDCl , TMS,
H
3
3
0°C) of 4a and 4b
13C correlations
H atom
norlomazarin (4a)
δH (ppm, m, J/Hz)
isomer of norlomazarin (4b)
δC
δH (ppm, m, J/Hz)
δC
2
′-CH3
1.57 (d, J = 6.5)
5.27 (q, J = 6.5)
-
7
1.58 (d, J = 6.5)
5.27 (q, J = 6.5)
4.20 s
7
1
′-CH
2
3
-OMe
-OMe
-
2
-
4.17 s
13.01 s
4.14 s
3
3*, 4a, 5, 6, 7, 6-OMe*
6
-
5-OH
12.04 s
4.10 s
3*, 4a, 5, 6, 7, 6-OMe*
6
-OMe
6
8-OH
12.39 s
1, 2*, 7, 8, 8a
13.35 s
1, 2*, 7, 8, 8a
_
*
_____
Correlations observed in experiment optimized for 2 Hz.
OH
O
OH
OH
OH
O
O
OH
H
MeO
MeO
MeO
MeO
−
HO
H O
OH
O
2
OH
O
1
3a
13b
OH
O
O
O
O−
O
O
H
H
MeO
MeO
O
H O
2
_
H
O
+ H
−
OH
O
HO
OH
O
9
Thus, the promise of using polymethoxynaphthazarins to synthesize natural metabolites and their analogs was
demonstrated using the conversion of the trimethyl ether of echinochrome (1) into lomazarin (3) and its derivatives as an
example. The retro-aldol decomposition of 5,6,8-trihydroxy-7(1′-hydroxyethyl)-2,3-dimethoxy-1,4-naphthoquinone (13)
observed by us was of definite interest. This reaction led to dimethylether of spinochrome D (9), a convenient substrate for
synthesizing several natural biologically active compounds.
EXPERIMENTAL
Melting points were determined on a Boetius heating stage and are uncorrected. PMR and 13C NMR spectra in CDCl3
were recorded on Bruker DRX-500 (500.13 and 125 MHz) and Bruker Avance-300 (300 and 75 MHz) spectrometers. Chemical
shifts are given on the δ scale relative to Me Si. 2D heteronuclear correlation (HMBC) spectra were obtained by standard
4
n
n
methods. HMBC experiments were optimized for J = 2 and J = 10 Hz. IR spectra in CHCl solution were recorded on
HC
HC
3
a Bruker Vector 22 spectrophotometer. Mass spectra (EI) were obtained on an LKB-9000S instrument with direct introduction
with ionizing-electron energy70 eV. Pure compounds were isolated bypreparative TLC on plates (20 × 20 cm) with an unfixed
+
+
silica-gel layer (H -form, 5-40 µm) or column chromatography over a column of silica gel (L 40/100 µm, H -form) [13]. The
purity of compounds was monitored using TLC on Sorbfil plates (Russia) using hexane:acetone (3:1). Elemental analysis was
performed on a Flash EA1112 C, H, N analyzer. Elemental analyses of all compounds agreed with those calculated.
7
(1′-Bromoethyl)-5,8-dihydroxy-2,3,6-trimethoxy-1,4-naphthoquinone (5). Asolution of1(1g)in commercial CCl4
(
400 mL) was treated dropwise with Br (0.2 mL) and stirred in light at room temperature for 4 h (TLC monitoring). Solvent
2
was removed in vacuo. The solid was chromatographed over a column with elution by hexane:acetone (20:1) to afford 5
(1.23 g, 98%), mp 83-89°C (acetone).
721

PMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 2.09 (3H, d, J = 7.1, CH ), 4.09 (3H, s, OCH ), 4.14 (3H, s, OCH ),
3
3
3
3
4
.20 (3H, s, OCH ), 5.75 (1H, q, J = 7.1, CH), 12.87 (1H, s, α-OH), 13.38 (1H, s, α-OH).
3
1
3
C NMR spectrum (75 MHz, CDCl , δ, ppm): 180.0, 179.6, 162.5, 157.6, 156.2, 148.8, 147.3, 133.9, 110.2, 108.3,
3
6
1.7 (two OMe on C-6 and C-7), 61.5, 37.0, 23.7.
+
Mass spectrum (EI, 70 eV, m/z, I , %): 386/388 (5) [M] , 307 (100), 291 (48), 275 (17), 263 (21).
rel
7
(1′-Acetoxyethyl)-5,8-dihydroxy-2,3,6-trimethoxy-1,4-naphthoquinone (6). A mixture of 5 (0.5 g) and AcOK
(
0.63 g) in AcOH (20 mL) and CHCl (3:1) was refluxed for 2 h and evaporated at reduced pressure. The solid was dissolved
3
in water (100 mL) and extracted with AcOEt. The extract was dried over anhydr. Na SO . Solvent was evaporated at reduced
2
4
pressure. The solid was chromatographed over a silica-gel column with elution by hexane:acetone (20:1) to afford 6 (0.34 g,
−
1
7
4
1
2%), mp 103-105°C (acetone). IR spectrum (ν, cm ): 1603 (C=O), 1744 (CH C=O).
3
PMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 1.63 (3H, d, J = 6.8, CH ), 2.07 (3H, s, OAc), 4.08 (3H, s, OCH ),
.13 (6H, s, OCH ), 6.27 (1H, q, J = 6.8, CH), 12.88 (1H, s, α-OH), 13.23 (1H, s, α-OH).
3
3
3
3
1
3
C NMR spectrum (75 MHz, CDCl , δ, ppm): 180.8, 179.4, 170.4, 162.1, 157.0, 156.0, 148.8, 147.3, 131.5, 110.2,
3
06.5, 65.1, 61.6, 61.5, 21.1, 18.7.
+
Mass spectrum (EI, 70 eV, m/z, I , %): 366 (21) [M] , 306 (100), 291 (100), 273 (22), 263 (59).
rel
5
,8-Dihydroxy-7(1′-hydroxyethyl)-2,3,6-trimethoxy-1,4-naphthoquinone (lomazarin, 3). Asolution of6(105 mg)
in MeOH—F COOH (2:1, 9 mL) was refluxed for 10 h (TLC monitoring) and evaporated at reduced pressure. The solid was
3
chromatographed over a silica-gel column with elution by hexane:acetone (20:1) to afford 3 (90 mg, 97%), mp 97-100°C
−
1
(
acetone) (lit. [9] mp 100-101°C) (petroleum ether). IR spectrum (ν, cm ): 1602 (C=O), 3589, 3554 (OH).
PMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 1.57 (3H, d, J = 6.8, CH ), 4.10 (3H, s, OCH ), 4.13 (6H, s, OCH ),
3
3
3
3
5
.26 (1H, q, J = 6.8, CH), 12.89 (1H, s, α-OH), 13.28 (1H, s, α-OH).
1
3
C NMR spectrum (75 MHz, CDCl , δ, ppm): 178.9, 177.9, 163.7, 158.6, 154.3, 148.4, 147.4, 134.7, 109.5, 106.5,
3
6
4.3, 61.7, 61.6, 23.3.
+
Mass spectrum (EI, 70 eV, m/z, I , %): 324 (66) [M] , 309 (73), 306 (50), 291 (100), 263 (33).
rel
Base Hydrolysis of 3 and Its Derivatives 5, 6, and 10. Compounds 3, 5, 6, and 10 (0.27 mmol) in aqueous NaOH
(
1%, 10 mL) were refluxed for 3 h, cooled, neutralized with conc. HCl, and extracted with AcOEt. The extract was dried over
anhydr. Na SO . Solvent was evaporated at reduced pressure. The solid was chromatographed over a silica-gel column with
2
4
elution by hexane:acetone (10:1) to afford 9 (50-55%) and a mixture (1:1, PMR) of 4a and 4b (20-25%). The mixture of 4a
and 4b (50 mg) was chromatographed over a silica-gel column (d = 15 mm, h = 60 cm) with elution by hexane:acetone (20:1).
Two bands were isolated and contained mixtures of 4a and 4b in 2:1 and 1:2 ratios, respectively.
5
,6,8-Trihydroxy-2,3-dimethoxy-1,4-naphthoquinone (9), mp 195-197°C (acetone) (lit. [1] mp 194-196°C).
−
1
IR spectrum (ν, cm ): 1601 (C=O), 3408 (OH), 3520 (OH).
PMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 4.06 (3H, s, OCH ), 4.16 (3H, s, OCH ), 6.46 (1H, s, H-3), 7.08 (1H,
3
3
3
br.s, OH-2), 12.27 (1H, s, α-OH), 13.12 (1H, s, α-OH).
1
3
C NMR spectrum (75 MHz, CDCl , δ, ppm): 177.5, 167.8, 167.0, 165.1, 156.4, 150.5, 146.1, 110.4, 108.0, 106.0,
3
6
1.7, 61.6
+
Mass spectrum (EI, 70 eV, m/z, I , %): 266 (100) [M] , 251 (79), 237 (25), 223 (26), 205 (26).
rel
2
,5,8-Trihydroxy-7(1′-hydroxyethyl)-3,6-dimethoxy-1,4-naphthoquinone (norlomazarin, 4a). PMR spectrum
(
500 MHz, CDCl , δ, ppm, J/Hz): 1.57 (3H, d, J = 6.8, CH ), 4.14 (s, 3H, OCH ), 4.18 (s, 6H, OCH ), 5.27 (1H, q, J = 6.8, CH),
3
3
3
3
7
.00 (1H, br.s, OH-2), 12.39 (1H, s, α-OH), 13.01 (1H, s, α-OH).
1
3
C NMR spectrum (75 MHz, CDCl , δ, ppm): 183.7 (C-4), 180.9 (C-1), 158.1 (C-8), 155.2 (C-6), 153.8 (C-5), 143.8
3
(C-2), 140.6 (C-3), 133.8 (C-7), 108.9 (C-4a), 105.3 (C-8a), 64.2 (C-1′), 61.9 (6-OMe), 60.8 (3-OMe), 23.3 (C-2′).
3
,5,8-Trihydroxy-7(1′-hydroxyethyl)-2,6-dimethoxy-1,4-naphthoquinone (4b). PMRspectrum (500MHz, CDCl3,
δ, ppm, J/Hz): 1.58 (3H, d, J = 6.8, CH ), 4.10 (3H, s, OCH ), 4.20 (6H, s, OCH ), 5.27 (1H, q, J = 6.8, CH), 7.00 (1H, br.s,
3
3
3
OH-2), 12.04 (1H, s, α-OH), 13.35 (1H, s, α-OH).
1
3
C NMR spectrum (75 MHz, CDCl , δ, ppm): 182.8 (C-1), 182.1 (C-4), 158.7 (C-8), 153.0 (C-5), 153.0 (C-6), 143.0
3
(
C-3), 141.1 (C-2), 136.0 (C-7), 108.4 (C-4a), 105.7 (C-8a), 64.4 (C-1′), 61.7 (6-OMe), 60.9 (2-OMe), 23.3 (C-2′).
,6,8-Trihydroxy-2,3-dimethoxy-7-ethyl-1,4-naphthoquinone (12). A boiling solution of 9 (100 mg) in t-BuOH
15 mL) was treated dropwise with an ether solution of propionyl peroxide [14] (TLC monitoring). The reaction was stopped
5
(
at about 50% conversion. Solvent was evaporated. Chromatography (PTLC) using hexane:acetone (3:1) isolated 9 (50 mg,
7
22

−
1
5
3
0%) and 12 (28 mg, 24%), mp 150-152°C (acetone) (lit. [1] mp 153-154°C). IR spectrum (ν, cm ): 1597 (C=O), 3412 (OH),
522 (OH).
PMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 1.15 (3H, t, J = 7.4, CH ), 2.62 (2H, q, J = 7.4, CH ), 4.05 (3H, s,
3
3
2
OCH ), 4.13 (3H, s, OCH ), 7.21 (1H, br.s, OH-2), 12.14 (1H, s, α-OH), 13.49 (1H, s, α-OH).
3
3
1
3
C NMR spectrum (75 MHz, CDCl , δ, ppm): 183.1, 175.2, 159.6, 158.8, 153.3, 150.2, 146.1, 126.6, 106.6, 106.5,
3
6
1.63, 61.58, 16.3, 12.6.
5
,8-Dihydroxy-2,3,6-trimethoxy-1,4-naphthoquinone (tricrozarin B, 11). A solution of 9 (50 mg) in diethylether
(
(
10 mL) was stirred, treated dropwise with diazomethane in diethylether [15] (TLC monitoring), and evaporated to afford 11
52 mg, 100%), mp 169-173°C (acetone) (lit. [11] mp 176-177°C) (methanol).
PMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 3.96 (3H, s, OCH ), 4.07 (3H, s, OCH ), 4.16 (3H, s, OCH ), 6.41
3
3
3
3
(
1H, s, H-3), 12.93 (1H, s, α-OH), 13.04 (1H, s, α-OH).
1
3
C NMR spectrum (75 MHz, CDCl , δ, ppm): 174.6, 172.2, 170.1, 161.4, 159.2, 150.2, 149.5, 146.9, 109.4, 107.5,
3
1
05.0, 61.62, 61.56, 56.7.
,8-Dihydroxy-2,3,6-trimethoxy-7-ethyl-1,4-naphthoquinone (TMEE, 1). A solution of 12 (25 mg) in diethylether
5
(
(
10 mL) was stirred, treated dropwise with diazomethane in diethylether [15] (TLC monitoring), and evaporated to afford 1
26 mg, 100%).
ACKNOWLEDGMENT
The work was financially supported partially by a grant of the RAS Presidium (Molecular and Cellular Biology
Program), the interdisciplinary integrated project of the Far-East and Siberian Branches of the RAS (No. 07-II-CO-05-020),
a grant of the RFBR No. 06-04-96974, and State Contract No. 02.522.11.2013.
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723