Polyketides from Eleutherine bulbosa

Article abstract of DOI:10.1080/14786419.2010.500007

Four new polyketides, (R)-4-hydroxyeleutherin, eleuthone, eleutherinol-8-O - D-glucoside and isoeleuthoside C (dihydroisoeleutherin-5-O -β- D-gentiobioside) were isolated from the bulbs of Eleutherine bulbosa, to join eleutherin, isoeleutherin, eleutherin

Full text of DOI:10.1080/14786419.2010.500007

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Polyketides from Eleutherine bulbosa
Francesca R. Gallo a , Giovanna Palazzino a , Elena Federici a ,
Raffaella Iurilli a , Corrado Galeffi a , Kusamba Chifundera b &
Marcello Nicoletti c
a Dipartimento del Farmaco , Istituto Superiore di Sanità , V. le
Regina Elena 299, I-00161 Rome, Italy
b Institut Supérieur d’Ecologie pour la Conservation de la Nature,
Lwiro , P.O. Box 293 Cyangugu, Rwanda
c Dipartimento di Biologia Vegetale , Università degli Studi
‘Sapienza’ , P.le Aldo Moro 5, I-00185 Rome, Italy
Published online: 09 Sep 2010.
To cite this article: Francesca R. Gallo , Giovanna Palazzino , Elena Federici , Raffaella Iurilli ,
Corrado Galeffi , Kusamba Chifundera & Marcello Nicoletti (2010) Polyketides from Eleutherine
bulbosa , Natural Product Research: Formerly Natural Product Letters, 24:16, 1578-1586, DOI:
10.1080/14786419.2010.500007
To link to this article: http://dx.doi.org/10.1080/14786419.2010.500007
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Natural Product Research
Vol. 24, No. 16, 10 October 2010, 1578–1586
Polyketides from Eleutherine bulbosay
a
a
a
a
*
Francesca R. Gallo , Giovanna Palazzino , Elena Federici , Raffaella Iurilli ,
Corrado Galeffia, Kusamba Chifunderab and Marcello Nicolettic
a
`
Dipartimento del Farmaco, Istituto Superiore di Sanita, V. le Regina Elena 299, I-00161
Rome, Italy; Institut Superieur d’Ecologie pour la Conservation de la Nature, Lwiro,
b
´
c
`
P.O. Box 293 Cyangugu, Rwanda; Dipartimento di Biologia Vegetale, Universita degli
Studi ‘Sapienza’, P.le Aldo Moro 5, I-00185 Rome, Italy
(Received 10 February 2009; final version received 7 June 2010)
Four new polyketides, (R)-4-hydroxyeleutherin, eleuthone, eleutherinol-
8-O-ꢀ-D-glucoside and isoeleuthoside C (dihydroisoeleutherin-5-O-ꢀ-D-
gentiobioside) were isolated from the bulbs of Eleutherine bulbosa, to join
eleutherin, isoeleutherin, eleutherinol, eleutherol, eleuthoside B (eleutherol-
4-O-ꢀ-D-gentiobioside), eleuthoside C (dihydroeleutherin-5-O-ꢀ-D-gentio-
bioside), hongconin (4-oxodihydroisoeleutherin) and elecanacin, which
have already been isolated from the same plant. The structures of the new
polyketides, based on oxydated cyclic systems, have been elucidated by
chemical and spectroscopic methods.
Keywords: Eleutherine
bulbosa;
Iridaceae;
polyketides;
(R)-4-
Hydroxyeleutherin; eleuthone; eleutherinol-8-O-ꢀ-D-glucoside; isoeleutho-
side C (dihydroisoeleutherin-5-O-ꢀ-D-gentiobioside)
1. Introduction
The bulbs of Eleutherine bulbosa [Mill.] Urban (¼Eleutherine americana Merr. ex
Heyne ¼ Eleutherine palmifolia (L.) Merr., Iridaceae) are used in folk medicine in
several countries: in Haiti as an abortifacient and emmenagogue (Weniger, Haag-
Berrurier, & Anton, 1982), in Eastern Asia to treat heart failure (Ding & Huang,
1982) and in Indonesia as an anticancer drug (Shibuya et al., 1997). Extracts are also
used and have been patented as skin lighteners (Tanaka, Yokogawa, Yagi, Shibata,
& Naganuma, 1997) on account of the melanogenesis-suppressing and tyrosinase-
inhibiting activities of its naphthopyranes. Several cyclic polyketides have been
isolated, including naphthopyranes (Ebnother, Meijer, & Schmid, 1952), naphtho-
¨
furans (Alves, Kloos, & Zani 2003) and tetracyclic compounds (Bianchi &
Ceriotti, 1975).
As part of our continued study of the constituents of African medicinal plants
(Gallo et al., 2006), we now report the isolation of four new polyketide constituents
from the bulbs of E. bulbosa from Eastern Congo, where among the Zulu the plant is
*Corresponding author. Email: francesca.gallo@iss.it
yPresented at 23rd IUPAC – 2002, International Symposium on the Chemistry of Natural
Products, Firenze, Italy, 28 July–2 August 2002.
ISSN 1478–6419 print/ISSN 1029–2349 online
ß 2010 Taylor & Francis
DOI: 10.1080/14786419.2010.500007
http://www.informaworld.com

Natural Product Research
1579
Figure 1. Chemical structures of compounds 1–4.
named ‘ababomvu’ or ‘abanqonqosi’ (Hutchings, 1996), and its red bulbs are used as
an antidiarrhoeal agent (Lin, Puckree & Mvelase, 2002) and for food colouring
(Chifundera, 2002). The new compounds are (R)-4-hydroxyeleutherin (1), eleuthone
(2), eleutherinol-8-O-ꢀ-D-glucoside (3) and isoeleuthoside C (dihydroisoeleutherin-5-
O-ꢀ-D-gentiobioside) (4), which join eleutherin (5) (Schmid, Ebnother, & Meijer,
¨
1950a), isoeleutherin (6) (Schmid & Ebnother, 1951), eleutherinol (7) (Ebnother
¨
et al., 1952; Harris & Wittek, 1975), eleutherol (8) (Haber, Ebnother, & Schimd 1956;
¨
¨
Schmid, Meijer, & Ebnother 1950b), eleuthoside B (eleutherol-4-O-ꢀ-D-gentiobio-
¨
side) (9) (Shibuya et al., 1997), eleuthoside C (dihydroeleutherin-5-O-ꢀ-D-gentiobio-
side) (10) (Shibuya et al., 1997), hongconin (4-oxodihydroisoeleutherin) (11) (Chen
et al., 1986) and elecanacin (12) (Hara et al., 1997), which have all already been
isolated from the same plant (Figure 1).
2. Results and discussion
The structure of (R)-4-hydroxyeleutherin was assigned to 1, C16H16O5 (EIMS, [M]þ
at m/z 288), by analysis of NMR data (Table 1) and the assignments based on the
5-methoxynaphthoquinone skeleton, common to other substances already isolated in
the same plant, and confirmed by HETCOR, long range HETCOR and selective
INEPT experiments. A linear, fused dihydropyrane ring was present, with two
secondary methyl groups in positions 1 and 3, as in eleutherin, 5, and isoeleutherin,

1580
F.R. Gallo et al.
Table 1. NMR data (in CDCl3) for compound 1.
Position
ꢁC
ꢁH (mult, J in Hz)
LR HETCOR
Me-1
INEPT
1
3
4
4a
5
5a
6
7
8
9
9a
10
10a
Me-1
Me-3
OMe
OH
67.4
67.1
67.6
4.94 (dq, J ¼ 6.9, 1.3)
3.89 (dq, J ¼ 8.1, 6.5)
4.46 (dt, J ¼ 8.1, 1.3)
C (10a), C (4a), C (3), Me-1
C (4)
C (4a), C (10a), Me-3
138.7
182.7
133.8
119.1
135.1
118.2
159.7
119.5
186.2
149.1
19.0
7.74 (dd, J ¼ 7.2, 1.2)
7.68 (t, J ¼ 7.2)
H-8
C (9a), C (8)
C (5a), C (8), C (9)
C (6), C (7), C (9a)
7.31 (dd, J ¼ 7.2, 1.2)
H-6
OMe
Me-1
1.59 (d, J ¼ 6.9)
1.41 (d, J ¼ 6.5)
4.01 (s)
C (1), C (10), C (10a), Me-3
C (3), C (4)
C (9)
18.6
56.5
3.84 (bs)
6; the only difference being the presence of a secondary hydroxy group in position 4
(H-4, 4.46, dt, J ¼ 8.1, 1.3 Hz). The enantiomeric relationship between 5 and 6
concerns the position of the stereogenic centre at position 3 (Hugo, Oosthuizen, &
Green, 2000). Assuming a hemichair-like conformation for the dihydropyrane ring, a
trans diaxial relationship was assigned between H-3 (ꢁH 3.89) and H-4, on the basis
of J ¼ 8.1 Hz and in accordance with the reciprocal enhancements of Me-3 (ꢁH 1.41)
and H-4 signals, observed by irradiation in nuclear overhauser experiments (NOE).
The NOE interaction between Me-1 (ꢁH 1.59) and H-4 accounted for the cis
relationship between the two ꢀ-methyl groups, as stated in the structure of 5
(Chen et al., 1986).
Compound 2, named eleuthone, is an isomer of 1, C16H16O5 (FABMS, [M þ 1]þ
at m/z 289), again showing the 5-methoxynaphthoquinone moiety, but with two
additional short chains, 1-hydroxyethyl and 2-oxopropyl, derived by hydrolytic
opening of the dihydropyrane ring in 1 and subsequent dehydration (NMR data
in Section 3.3.1).
The third polyketide, 3, C21H22O9 (ICRMS, [M þ 1]þ at m/z 419.13345, Calcd
419.13366), positive to Folin–Ciocalteu spray reagent, is a glucoside as evidenced by
the enzymatic hydrolysis with ꢀ-glucosidase, giving glucose and the aforementioned
eleutherinol, 7 (Table 2). The glucose unit was found to be linked to the OH-8 of 7, as
evidenced by the enhancement of H-9 and H-7 after irradiation of the anomeric H-10
in NOEs. As confirmation in the 1H NMR spectrum of the penta-acetyl derivative of
3, 13, one Ac group was assigned to position 10 owing to its deshielded value
(ꢁH 2.45), as a result of the effects of the coplanar aromatic system and
steric hindrance.
FABMS data of the fourth substance, 4, C28H38O14, besides the [M þ 1]þ at m/z
599 as the parent peak (ICRMS, m/z [M þ 1 þ Na]þ found 621.21359, Calcd
621.17884), showed at m/z 437 (77%) and 274 (100%) peaks due to the loss of two

Natural Product Research
1581

1582
F.R. Gallo et al.
Table 3. NMR data (in CD3OD) for compounds 4 and 6.
ꢁC
Position of 4
ꢁH of 4
(mult, J in Hz)
LR HETCOR ꢁC
of 4
ꢁH of 6
(mult, J in Hz)
of 6
1
3
4
70.0 5.22 (q, J ¼ 6.5)
64.3 3.99 (m, ov)
32.6 2.42 (dd, J ¼ 16.8; 10.5)
3.06 (ov)
127.8
142.3
130.6
117.5 8.00 (d, J ¼ 8.3)
126.3 7.28 (dd, J ¼ 8.3, 7.6)
105.1a 6.85 (d, J ¼ 7.6)
157.6
118.5
147.3
67.4 5.01 (dq, J ¼ 6.9, 1.8)
62.4 3.99 (m)
29.5 2.70 (dd, J ¼ 18.9, 3.6) 2.24
(ddd, J ¼ 18.9, 10.1, 1.8)
4a
5
5a
6
7
8
139.4
184.2
OMe
134.1
119.1 7.76 (dd, J ¼ 7.2, 1.2)
134.7 7.66 (t, J ¼ 7.2)
117.8 7.29 (dd, J ¼ 7.2, 1.2)
9
159.7
118.6
182.7
148.1
9a
10
10a
10
121.5
H-4
105.5a 4.80 (d, J ¼ 6.6)
104.4 4.08 (d, J ¼ 6.6)
75.9 3.4–4.1
1000
2
2000
3
75.0 3.4–4.1
77.8 3.4–4.1
77.9 3.4–4.1
71.8 3.4–4.1
300
40
4000
71.5 3.4–4.1
77.8 3.4–4.1
77.1 3.4–4.1
69.6 3.63 (dd, J ¼ 12.1, 4.0)
4.01 (dd, J ¼ 12.1 2.4)
63.0 3.56 (dd, J ¼ 12.1, 4.0)
3.80 (dd, J ¼ 12.1, 2.4)
19.6 1.60 (d, J ¼ 6.5)
22.4 1.32 (d, J ¼ 6.1)
56.8 4.05 (s)
5
500
60
600
Me-1
Me-3
OMe
OH
19.7 1.59 (d, J ¼ 6.9)
21.5 1.41 (d, J ¼ 6.5)
56.4 4.01 (s)
4.60 (bs)
a
Note: The values with the same letter are interchangeable.
hexose moieties, which by the analysis of the 13C NMR data (Table 3) were assigned to
a gentiobioside unit, the same that also occurs in 10, eleuthoside C (dihydroeleutherin-
5-O-ꢀ-D-gentiobioside). The two substances actually had the same raw formula and
similar NMR data, but the enzymatic hydrolysis of 4 with cellulase gave, besides
glucose, 6, an aglycone identified by comparison with the published physico-chemical
1
and H NMR data (Schimd et al., 1950b) and by the analysis of 13C NMR spectra
(Table 3). The naphthoquinone form in 6 is the result of the oxidation of the parent
hydroquinonic moiety of 4. The observed long-range correlations of H-6 with C-5 and
the anomeric H-10, as well as the value of the last proton (ꢁH 5.22), accounted for
position 5 for the linkage of the glycosidic moiety. Furthermore, the hydrolysis of 4
with ꢀ-glucosidase again gave glucose and 6, and the coupling constant value of H-10
(6.6 Hz) assigned a ꢀ-orientation to the glycosidic linkage.
Among the previously reported compounds, 5 showed an inhibitory effect on
DNA topoisomerase II, a target for anticancer agents (Krishnan & Bastow, 2000),

Natural Product Research
1583
while 6 showed an interesting activity against HIV replication (Hara et al., 1997).
Furthermore, a mixture of 5, 6 and 8 isolated from the bulbs of E. americana was
found to be effective for the treatment of angina pectoris in clinical trials (Ding &
Huang, 1982). 11 was reported to have cardioprotective activity (Kraus, Li, Gordon,
& Jensen, 1994).
3. Experimental
3.1. General experimental procedures
A Craig-Post apparatus (200 stages, 10 : 10 mL, upper and lower phase) was used for
the separation, which was performed by counter-current distribution (CCD).
CC : silica gel 60 (0.063–0.200 mm; 70–230 mesh, Merck), cyclohexane : EtOAc
(system a). The separations were monitored by TLC on silica gel 60 F254 aluminium
sheets (Merck) and developed in the solvent system a or with the upper phase
(system b) of solvent mixture n-BuOH : HOAc : H2O (4 : 1 : 5). Detection was by
fluorescence quenching and/or by anisaldehyde : HOAc : H2SO4 (0.5 : 50 : 1). All
solvents for the chromatographic separation were of analytical grade from Carlo
Erba (Rodano, Italy). Melting points were determined on a Reichert melting point
apparatus and are uncorrected. The ꢂD and UV data were registered on a Perkin
Elmer polarimeter 141 and on a UNICAM UV530 UV-vis spectrophotometer,
respectively. Ion cyclotron resonance mass spectra (ICRMS) were obtained by
electrospray ionisation with an APEX II 4.7 instrument (Bruker Daltonics, MA,
USA), while FABMS and HREIMS were obtained with a VG 7070 EQ-HF
1
instrument using m-nitrobenzyl alcohol as matrix. H and 13C NMR spectra were
1
recorded on a Varian Gemini 300 NMR spectrometer observing H and 13C at 300
1
and 75 MHz, respectively. The H and 13C chemical shifts are given in parts per
million relative to TMS (internal standard).
3.2. Plant material
The bulbs of E. bulbosa [Mill.] Urban were collected by Dr Chifundera Kusamba
in 1993 from Itebero (Kivu Province, Eastern Democratic Republic of Congo) at an
´
altitude of 600 m and identified at the Institut Superieur d’Ecologie pour la
Conservation de la Nature, Lwiro (Cyangugu, Rwanda), where a voucher specimen
is preserved (CKL 649).
3.3. Extraction and separation
The powdered air-dried red bulbs (360 g) were extracted three times with MeOH.
The residue (51 g) obtained from the evaporation of the solvent was dissolved in H2O
(350 mL) and extracted with EtOAc (2 mL ꢀ 200 mL) and then with n-BuOH
(3 mL ꢀ 150 mL). The residues from the organic EtOAc and n-BuOH phases
amounted to 6.4 and 29 g, respectively. The former was submitted to CCD with the
biphase system H2O : acetone : EtOH : EtOAc : cyclohexane (7 : 5 : 3 : 3 : 9; TLC,
system a, 1 : 1) and five fractions, A–E, were obtained. Fraction B, CC, system a,
9 : 1, gave oleic acid. Fraction C, CC, system a, 85 : 15, was a 1 : 1 mixture of
stigmasterol and ꢀ-sitosterol. Fraction D, repeated CC, system a, 8 : 2, resulted in a

1584
F.R. Gallo et al.
mixture of 1, 5, 6, 8, 11 and 12. From fraction D, CC, system a, 7 : 3, compounds 2
and 7 were purified. The n-butanolic extract, combined with fraction E, was
submitted to CCD in portions of 6 g with biphase mixture H2O : EtOAc : n-PrOH
(system c), changing the ratio from 10 : 9 : 1 to 10 : 7 : 3. Five fractions, A–E, were
collected (TLC, system b). Fraction B, CCD, system c, 10 : 9 : 1, gave 3 (0.54 g).
Fraction D, CCD with recycling, system c, 10 : 8 : 2, gave 4 (0.34 g) and 10 (0.22 g).
Fraction E, CCD, system c, 10 : 7 : 3, gave 9 (0.39 g). Oleic acid, stigmasterol and
ꢀ-sitosterol (in mixture) as well as all known compounds were identified by
comparison of their physico-chemical and spectroscopic data.
3.3.1. (R)-4-hydroxyeleutherin (1)
20
Crystals from n-hexane, m.p. 113–115ꢁC; ½ꢂꢂD ¼ ꢃ118.7 (c 0.19, CHCl3); UV (EtOH)
ꢃmax (nm) (log "): 250 sh (4.l8), 260 (4.22), 316 (3.33), 406 (3.62); HREIMS, m/z:
288.1345 (Calcd for C16H16O5, 288.0997); EIMS, m/z (relative intensities): 288(2),
1
273(6), 255(9), 244(100), 229(34), 216(65), 201(54), 173 (35); H and 13C NMR data
in Table 1.
3.3.2. Eleuthone (2)
20
Crystals from n-hexane, m.p. 166–168ꢁC; ½ꢂꢂD ¼ þ18.3 (c 0.11, CHCl3); UV (EtOH)
ꢃ
max (nm) (log "): 226(4.07), 274(4.05), 374(3.49); FABMS, m/z: 289 [M þ 1]þ (Calcd
for C16H17O5, 289.0997); 1H NMR spectral data (CDCl3): ꢁ 7.81 (1H, bd, J ¼ 7.3 Hz,
H-6), 7.71 (1H, bt, J ¼ 7.3 Hz, H-7), 7.25 (1H, bd, J ¼ 7.3 Hz, H-8), 5.21 (1H, q,
J ¼ 6.4 Hz, H-1), 4.03 (3H, s, OMe), 2.86 (2H, AB system, 2 H-4), 1.96 (3H, s, Me-3),
1.28 (3H, d, J ¼ 6.9 Hz, Me-1); 13C NMR spectral data (CDCl3): ꢁ 205.5 (C-3), 184.5
(C-5), 179.6 (C-10), 160.1 (C-9), 147.7 (C-10a), 137.9 (C-4a), 136.5 (C-7), 135.0 (C-
5a), 119.8 (C-6), 118.7 (C-8), 117.6 (C-9a), 69.5 (C-1), 56.5 (OMe), 29.5 (C-4), 21.3
(Me-3), 20.1 (Me-1).
3.3.3. Eleutherinol-8-O-ꢀ-D-glucoside (3)
20
Pale yellow amorphous powder; ½ꢂꢂD ¼ ꢃ8.5 (c 0.42, MeOH); UV (MeOH) ꢃmax
(nm) (log "): 236 (4.34), 270 (4.20), 359 (3.68); ICRMS, m/z: 419.13345 [M þ 1]þ
1
(Calcd for C21H23O9, 419.13366); H and 13C NMR data in Table 2.
3.3.4. Enzymatic hydrolysis of eleutherinol-8-O-ꢀ-D-glucoside (3)
ꢀ-glucosidase (10 mg) was added to a solution of 3 (55 mg) in acetate buffer, pH 5.5
(20 mL). The solution was allowed to stand at 36ꢁC, monitored by TLC with solvent
system b. After 2 days, a few drops of HOAc were added to the solution and it was
extracted with EtOAc. The residue of the organic phase was submitted to CCD with
biphase solvent system H2O : EtOH : EtOAc : cyclohexane (10 : 4 : 3 : 11). The aglu-
cone thus obtained was identified as eleutherinol, 7, by direct comparison and
analysis of physico-chemical data in comparison with those in the literature: m.p.
1
310ꢁC; C H O EIMS: 256 (100), 216 (68) (Ebnother et al., 1952). H and 13C
¨
15 12
4
NMR data given in Table 2. The aqueous phase, after the evaporation of EtOAc,
was percolated through a column of Dowex 50 W (Hþ). In the residue D-glucose was
identified by TLC.

Natural Product Research
3.3.5. Pentaacetyleutherinol-8-O-ꢀ-D-glucoside (13)
1585
Compound 3 was acetylated with a mixture of anhydrous pyridine and (Ac)2O. After
the evaporation of the reagents, the residue was crystallised from cyclohexane and
1
formed 13, m.p. 221ꢁC; ½ꢂꢂD ¼ ꢃ34.4 (c 0.35, CHCl3); H and 13C NMR data given
20
in Table 2.
3.3.6. Isoeleuthoside C (dihydroisoeleutherin-5-O-ꢀ-D-gentiobioside) (4)
20
Pale yellow amorphous powder; ½ꢂꢂD ¼ þ 4.63 (c 0.32, MeOH); UV (MeOH) ꢃmax
(nm) (log "): 235 (4.06), 324 (3.86), 339 (3.88); ICRMS, m/z: 597.21621 [M þ 1]þ
(Calcd for C28H39O14, 599.19705), 621.21359 [M þ 1 þ Na]þ (Calcd for C28H39
O14Na, 621.17884); FABMS, m/z (relative intensities): 599 (100) [M þ 1]þ, 437 (77)
[M þ 1 ꢃ gluc]þ, 274 (100) [M ꢃ 2 gluc]þ; NMR data given in Table 3.
3.3.7. Enzymatic hydrolysis of isoeleuthoside C (dihydroisoeleutherin-
5-O-ꢀ-D-gentiobioside) (4)
Cellulase (60 mg) was added to a solution of 4 (65 mg) in an acetate buffer, pH 4.5
(20 mL). The solution was allowed to stand at 36ꢁC, monitored by TLC (system b).
After 2 days, a few drops of HOAc were added to the solution and it was extracted
with EtOAc. The residue of the organic phase was submitted to CC with system a,
7 : 3. The substance thus obtained was identified as isoeleutherin, 6, by the direct
comparison and analysis of physico-chemical data in comparison with those in the
literature (Chen et al., 1986). 13C NMR data are shown in Table 3. The aqueous
phase, after the evaporation of EtOAc, was percolated through a column of Dowex
50 W (Hþ). In the residue, glucose was identified by TLC. The same hydrolysis
occurs with ꢀ-glucosidase (enzyme : substance, 1 : 10, buffer pH 5.5) with the
intermediate formation of the monoglucoside that is not isolated here.
Acknowledgements
The authors thank Prof. Franco Delle Monache (CNR, Centro Chimica dei Recettori,
Universita Cattolica S. Cuore, Rome, Italy) for his NMR support.
References
Alves, T.M.A., Kloos, H., & Zani, C.L. (2003). Eleutherinone, a novel fungitoxic
naphtoquinone from Eleutherine bulbosa (Iridaceae). Memorias Do Instituto Oswaldo
Cruz, 98(5), 709–712.
Bianchi, C., & Ceriotti, G. (1975). Chemical and pharmacological investigation of constituents
of Eleutherine bulbosa (Miller) Urb. (Iridaceae). Journal of Pharmaceutical Sciences,
64(8), 1305–1308.
Chen, Z., Huang, H., Wang, C., Li, Y., Ding, J., Ushio, S., . . . Yoichi, I. (1986). Hongconin,
a new naphthalene derivative from Hong-Cong, the rhizome of Eleutherine
americana Merr. et Heyne (Iridaceae). Chemical & Pharmaceutical Bulletin, 34(7),
2743–2746.

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F.R. Gallo et al.
Chifundera, K. (2002). New tricyclic poliketide metabolites from Eleutherine bulbosa. Paper
presented at the International Symposium on the Chemistry of Natural Products,
Florence, Italy, 28 July–2 August.
Ding, J., & Huang, H. (1982). Preparation of Hong Cong Su tablet. Zhongcaoyao, 13,
499–501.
Ebnother, A., Meijer, Th.M., & Schmid, H. (1952). Eleutherinol, a natural naphtopyrone.
¨
VI. Constituents of Eleutherine bulbosa. Helvetica Chimica Acta, 35(III), 910–928.
Gallo, F.R., Palazzino, G., Federici, E., Iurilli, R., Delle Monache, F., Chifundera, K., &
Galeffi, C. (2006). Oligomeric secoiridoids from Jasminum abyssinicum. Phytochemistry,
67(5), 504–510.
Haber, R.G., Ebnother, A., & Schimd, H. (1956). Constituents of Eleutherine bulbosa. VII.
¨
The synthesis of (ꢄ) elutherol. Helvetica Chimica Acta, 39, 1529–1537.
Hara, H., Maruyama, N., Yamashita, S., Hayashi, Y., Lee, K.-H., Bastow, K.F., . . .
Imakura, Y. (1997). Elecanacin, a novel new naphthoquinone from the bulb of
Eleutherine americana. Chemical & Pharmaceutical Bulletin, 45(10), 1714–1716.
Harris, T.M., & Wittek, P.J. (1975). Biogenetic-type syntheses of polycyclic polyketide
metabolites using partially protected beta-hexa and beta-heptaketones: 6-hydroxymu-
sizin, barakol, emodin, and eleutherinol. Journal of the American Chemical Society,
97(11), 3270–3271.
Hugo, V.I., Oosthuizen, F.J., & Green, I.R. (2000). Reaction of aluminium chloride with
benzo[c]- and naphto[2,3-c]pyrans. Synthetic Communication, 30(6), 1035–1044.
Hutchings, A. (1996). Zulu medicinal plants: An inventory. Scottsville, South Africa: University
of Natal Press.
Kraus, G.A., Li, J., Gordon, M., & Jensen, J.H. (1994). Regiocontrol by remote substituents.
A direct total synthesis of racemic hongconin. Journal of Organic Chemistry, 59(8),
2219–2222.
Krishnan, P., & Bastow, K.F. (2000). Novel mechanisms of DNA topoisomerase II inhibition
by pyranonaphthoquinone derivatives—eleutherin, ꢂ-lapachone, and ꢀ-lapachone.
Biochemical Pharmacology, 60, 1367–1379.
Lin, J., Puckree, T., & Mvelase, T.P. (2002). Anti-diarrhoeal evaluation of some medicinal
plants used by Zulu traditional healers. Journal of Ethnopharmacology, 79, 53–56.
Schmid, H., & Ebnother, A. (1951). Constituents of Eleutherine bulbosa. IV. Isolation and
¨
constitution of isoeleutherin. Allo and allo-isoeleutherin. Helvetica Chimica Acta, 34,
561–576.
Schmid, H., Ebnother, A., & Meijer, Th.M. (1950a). Substance from Eleutherine bulbosa. III.
¨
The constitution of elutherin. Helvetica Chimica Acta, 33, 1751–1770.
Schmid, H., Meijer, Th.M., & Ebnother, A. (1950b). The constitution of eleutherol. I.
¨
Helvetica Chimica Acta, 33, 595–608.
Shibuya, H., Fukushima, T., Ohashi, K., Nakamura, A., Riswan, S., & Kitagawa, I. (1997).
Indonesian medicinal plants. XX. Chemical structures of eleuthosides A, B, and C, three
new aromatic glucosides from the bulbs of Eleutherine palmifolia (Iridaceae). Chemical
& Pharmaceutical Bulletin, 45(7), 1130–1134.
Tanaka, N., Yokogawa, Y., Yagi, E., Shibata, Y., & Naganuma, M. (1997). Skin-lightening
cosmetics containing Eleutherin or Iris extracts. Kokai Tokkyo Koho (Japanese Patent)
JP 09030954 A2 19970204.
Weniger, B., Haag-Berrurier, M., & Anton, R. (1982). Plants of Haiti used as antifertility
agents. Journal of Ethnopharmacology, 6(1), 67–84.