Iotrochotamides I and II: New ceramides from the Indonesian sponge Iotrochota purpurea

Article abstract of DOI:10.1080/14786410701877971

Our search for biologically active marine natural products led to the isolation of two new ceramides, iotrochotamide I (1) and iotrochotamide II (2), together with three known 6-bromoindole alkaloids (6-bromo-1H-indole-3-carbaldehyde (3), 6-bromo-1H-indole-3-carboxylic acid methyl ester (4), and 6-bromo-1H-indole-3-carboxylic acid ethyl ester (5)) from the sponge Iotrochota purpurea collected in Indonesia. The structure elucidation of these compounds was secured by spectroscopic methods (1H, 13C, DEPT, COSY, HMQC and HMBC), accurate mass measurements (ESI, EI and GS-MS) as well as comparison with known compounds.

Full text of DOI:10.1080/14786410701877971

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Iotrochotamides I and II: New
ceramides from the Indonesian sponge
Iotrochota purpurea
Sabrin R.M. Ibrahim a , Gamal A. Mohamed b , Mostafa A. Fouad c ,
Ehab S. El-Khayat b & Peter Proksch d
a Faculty of Pharmacy, Pharmacognosy Department , Assiut
University , Assiut, Egypt
b Faculty of Pharmacy, Pharmacognosy Department , Al-Azhar
University , Assiut, Egypt
c Faculty of Pharmacy, Pharmacognosy Department , Minia
University , Minia, Egypt
d Institute Für Pharmazeutische Biologe , Heinrich-Heine-
Univeristät Düsseldorf , Universitätsstrasse 1, Geb. 26.23,
Düsseldorf, Germany
Published online: 29 Oct 2009.
To cite this article: Sabrin R.M. Ibrahim , Gamal A. Mohamed , Mostafa A. Fouad , Ehab S. El-
Khayat & Peter Proksch (2009) Iotrochotamides I and II: New ceramides from the Indonesian sponge
Iotrochota purpurea , Natural Product Research: Formerly Natural Product Letters, 23:1, 86-92,
DOI: 10.1080/14786410701877971
To link to this article: http://dx.doi.org/10.1080/14786410701877971
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Natural Product Research
Vol. 23, No. 1, 10 January 2009, 86–92
Iotrochotamides I and II: New ceramides from the Indonesian sponge
Iotrochota purpurea
a
b
c
*
Sabrin R.M. Ibrahim , Gamal A. Mohamed , Mostafa A. Fouad ,
Ehab S. El-Khayatb and Peter Prokschd
b
aFaculty of Pharmacy, Pharmacognosy Department, Assiut University, Assiut, Egypt; Faculty of
Pharmacy, Pharmacognosy Department, Al-Azhar University, Assiut, Egypt; Faculty of
c
d
Pharmacy, Pharmacognosy Department, Minia University, Minia, Egypt; Institute Fur
¨
Pharmazeutische Biologe, Heinrich-Heine-Univeristat Dusseldorf, Universitatsstrasse 1, Geb. 26.23,
¨
¨
¨
Dusseldorf, Germany
¨
(Received 27 May 2007; final version received 1 February 2008)
Our search for biologically active marine natural products led to the isolation of
two new ceramides, iotrochotamide I (1) and iotrochotamide II (2), together with
three known 6-bromoindole alkaloids (6-bromo-1H-indole-3-carbaldehyde (3), 6-
bromo-1H-indole-3-carboxylic acid methyl ester (4), and 6-bromo-1H-indole-3-
carboxylic acid ethyl ester (5)) from the sponge Iotrochota purpurea collected in
Indonesia. The structure elucidation of these compounds was secured by
spectroscopic methods (1H, 13C, DEPT, COSY, HMQC and HMBC), accurate
mass measurements (ESI, EI and GS-MS) as well as comparison with known
compounds.
Keywords: Iotrochota purpurea; iotrochotamide; ceramides; bromoindole
alkaloids
1. Introduction
Sponges have long been recognised as a rich source of structurally novel lipids including
unique sterols, fatty acids, phospholipids and triglycerides (Naglc, McClatchey, & Gerwick,
1992). Sphingolipids, e.g. ceramides, cerebrosides, glycosphingolipids (GSL), sphingomy-
lein and sphingosine derivatives or analogs are important constituents of cell membranes of
eukaryotic cells and are assumed to play important roles in antigen antibody reactions and
the transmission of biological information (Gao, Yang, Wang, & Liu, 2001; Qu, Zhang, &
Liu, 2004). Recently, some sphingolipids have been reported to exhibit anti-ulcergenic,
anti-hepatotoxic, anti-tumour, immunostimulatory, antiviral, antifungal, cytotoxic and
Caþ-ATPase activities (Gao et al., 2001; Muralidhar, Kumar, Krishna, Rao, & Rao, 2005;
Qu et al., 2004). Because of their promising biological activities, they have aroused
increasing research interest. Previous studies on the sponges belonging to Iotrochota sp.
have revealed bioactive metabolites including 6-bromoindole alkaloids (Carletti,
Banaigs, & Amade, 2000; Guella, Mancini, Duhet, Richer de Froges, & Pietra, 1989),
*Corresponding author. Email: sabrins2002@yahoo.com
ISSN 1478–6419 print/ISSN 1029–2349 online
ß 2009 Taylor & Francis
DOI: 10.1080/14786410701877971
http://www.informaworld.com

Natural Product Research
87
sphingolipids, a toxin, ecdysteroids, and tyrosine derivatives (Blunt, Copp, Munro,
Northcete, & Prinsep, 2003; Muralidhar, Krishna, Kumar, Rao, & Rao, 2003). In
continuation of our investigation of the chemical constituents from Indonesian marine
sponges, we describe herein the isolation and structural elucidation of two new ceramides,
iotrochotamide I (1) and iotrochotamide II (2), together with three known 6-bromoindole
alkaloids (6-bromoin-1H-indole-3-carbaldehyde (3), 6-bromo-1H-indole-3-carboxylic acid
methyl ester (4), and 6-bromo-1H-indole-3-carboxylic acid ethyl ester (5)). 6-Bromo-1H-
indole-3-carboxylic acid methyl ester (4) and 6-bromo-1H-indole-3-carboxylic acid ethyl
ester (5) are known sponge metabolites previous reported for the first time by Segraves &
Crews (Segraves & Crews, 2005) from Semenospongia sp. and Guella et al. (Guella et al.,
1989) from Iotrochota birotulata, respectively.
2. Experimental
2.1. General experimental procedures
1
Optical rotations were measured on a Perkin–Elmer-241 MC polarimeter. H NMR and
13C NMR spectra were measured on a Bruker DRX 500 spectrometer (1H: 500 MHz and
13C: 125 MHz). The UV spectra were carried out in methanol using a Perkin–Elmer
Lambda 25 UV/VIS spectrophotometer. Electron impact mass spectra (EI-MS) were
recorded on a Finnigan MAT TSQ 7000 mass spectrometer. Positive-ion electrospray
ionisation mass spectra (ESI-MS) were performed on a Thermofinnigan LCQ DECA mass
spectrometer coupled to an Agilent 1100 high performance liquid chromatography
(HPLC) system equipped with a photodiode-array detector. Vacuum liquid chromato-
graphy (VLC) was carried out on silica gel 60(0.040–0.063 mm, Merck). Column
chromatographic separations were performed over silica gel 60 (0.040–0.063 mm,
Merck) and Lichroprep RP-18 (Merck). TLC analysis was carried out on aluminum
sheets precoated with silica gel 60 F254S (Merck, Darmstadt, Germany). TLC visualisation
was by UV absorption at ꢀ 254 and 336 nm followed by spraying with anisaldehyde/H2SO4
reagent and heating at 110ꢀC for 2 min. All solvents were distilled prior to use. Spectral
grade solvents were utilised for chromatographic analysis.
2.2. Animal material
The sponges were collected by diving at a depth of 8 m from Pulau Baranglompo Island
(south) in Indonesia in July 1997. The animals were deep frozen after collection and then
freeze-dried prior to extraction. Taxonomic identification was carried out by Dr. Rob W.
M. van Soest (Zoological Museum, University of Amsterdam).
2.3. Extraction and isolation
The freeze-dried sponge (150 g) was extracted with methanol six times at room
temperature at 48 h intervals. The combined alcoholic extracts were concentrated under
reduced pressure. The concentrated extract was diluted with water and sequentially
extracted with ethyl acetate and n-butanol. The ethyl acetate fraction was concentrated
under vacuum to yield brown coloured gummy residue (1.8 g), which was subjected
to VLC on silica gel using eluants with increasing polarity starting from n-hexane
through ethyl acetate to methanol. Six fractions were collected and monitored through

88
S.R.M. Ibrahim et al.
silica gel TLC. Fraction 4 on further column chromatography over silica gel column using
n-hexane-ethyl acetate gradient elution yielded compounds 1 (15 mg) and 2 (8 mg)
(Figure 1). Fraction 7 was subjected to RP-18 column using H2O–MeOH (1 : 1) to give
compounds 3 (5 mg), 4 (4 mg) and 5 (5 mg).
25
Iotrochotamide I (1). Colourless amorphous powder 25 ½ꢁꢁD ꢂ8.3ꢀ (c 0.1, CHCl3). EI–MS:
m/z (rel. int.%) 663 Mþ (30.7), 365 (17.9), 281 (3.5), 97 (37.9), 57 (84.9), 43 (100). IR (KBr)
1
ꢂ
max: 3550, 3360, 1650, 2930, 2850, 1395 cmꢂ1. For H and 13C NMR data, see Table 1.
25
Iotrochotamide II (2). Colourless amorphous powder ½ꢁꢁD ꢂ10.5ꢀ (c 0.1, CHCl3).
ESI–LC/MS: m/z 720.3 M þ Hþ. IR (KBr) ꢂmax: 3560, 3380, 1662, 2927, 2856, 1386 cmꢂ1
.
1
For H and 13C NMR data, see Table 1.
6-Bromo-1H-indole-3-carbaldehyde (3). Colourless needles; UVꢀmax (MeOH) nm: 222.0,
247.3, 265.0 and 305. EI-MS: m/z (rel. int.%) 225/223 [M]þ (100), 224/222 [M-H]þ (82.8),
196/194 [M-CHO]þ (12), 144 [M-Br]þ (20.6), 115 [M-(CHO þ Br)]þ (30.5). 1H NMR
(CD3OD, 500 MHz): 9.91 (1H, s, H-8), 8.13 (1H, s, H-2), 8.10 (1H, d, 8.5 Hz, H-4), 7.67
(1H, d, 1.6 Hz, H-7), 7.35 (1H, dd, 8.5, 1.6 Hz, H-5).
6-Bromo-1H-indole-3-carboxylic acid methyl ester (4). Yellow solid; UV ꢀmax (MeOH) nm:
219.3, 250.4 and 279.9. EI-MS: m/z (rel. int.%) 253/255 [M]þ (92), 224/222 [M–CH3O]þ
(100),
196/194
[M–CH3OCO]þ
(11),
144
[M–(CH3O þ Br)]þ
(10),
115
[M–(CH3OCO þ Br)]þ (29). 1H NMR (CDCl3, 500 MHz): 8.56 (1H, br s, NH), 8.06
(1H, d, 8.5 Hz, H-4), 7.89 (1H, d, 3.1 Hz, H-2), 7.58 (1H, d, 1.6 Hz, H-7), 7.39 (1H, dd, 8.5,
1.6 Hz, H-5), 3.95 (3H, s, OCH3).
6-Bromo-1H-indole-3-carboxylic acid ethyl ester (5). Greenish white needles; UV ꢀmax
(MeOH) nm: 219.6, 250.5 and 280.0. EI-MS: m/z (rel. int.%) 269/267 [M]þ (91), 293/241
[M–C2H5]þ (22), 224/222 [M–C2H5O]þ (100), 196/194 (12), 144 (10), 115 (33.8). 1H NMR
(CDCl3, 500 MHz): 8.55 (1H, br s, NH), 8.05 (1H, d, 8.5 Hz, H-4), 7.89 (1H, d, 2.9 Hz,
H-2), 7.59 (1H, d, 1.6 Hz, H-7), 7.37 (1H, dd, 8.5, 1.6 Hz, H-5), 4.39 (2H, q, 6.9 Hz,
–OCH2–),1.42 (3H, t, 6.9 Hz, –CH3).
Methanolysis (Muralidhar et al., 2003). Compound 1 and 2 (6 mg) were separately treated
with 3 mL of 1N HCl in MeOH at 90ꢀC for 15 h. Cold water (10 mL) was poured to the
reaction mixture. The reaction mixture in each case was extracted with n-hexane
(15 ꢃ 3 mL) to give a corresponding fatty acid methyl ester. The combined organic layer
O
3′
2′
HN
17
6
HO
n
7
OH
n = 10
n = 14
1
2
Figure 1. Structures of componds 1 and 2.

Natural Product Research
89

90
S.R.M. Ibrahim et al.
was concentrated under reduced pressure to yield colourless residue. The residue was
1
analysed by GC-, EI-MS and H NMR.
n-Docosanoic acid methyl ester (2 mg) from compound 1 and 2: 1H NMR (CDCl3, 500 MHz)
ꢃH: 0.85 (3H, t, J ¼ 6.3 Hz), 1.25–1.32 (br s, –CH2–groups), 1.65 (2H, m, H-3), 2.30 (2H, t,
J ¼ 7.8 Hz, H-2), 3.67 (3H, s, OCH3). GC- and EI-MS m/z: 354 [M]þ. The MeOH/H2O
phase was evaporated and gave a long chain base. The long chain bases were subjected to
1
EI-MS and H NMR.
(E)-2-Amino-19-methylicos-4-ene-1,3-diol (2 mg) from compound 1: 1H NMR (CDCl3,
500 MHz) ꢃH: 0.85 (6H, d, J ¼ 6.3 Hz), 1.20–1.32 (br s –CH2–groups), 1.56 (1H, m), 2.09
(2H, m), 3.72 (1H, dd, J ¼ 3.3, 11 Hz, H-1B), 3.97 (1H, dd, J ¼ 3.5, 11.0 Hz, H-1A), 3.94
(1H, m, H-2), 4.31 (1H, t, J ¼ 5.2 Hz, H-3), 5.50 (1H, dd, J ¼ 6.5, 15.4 Hz, H-4), 5.75
(1H, dd, J ¼ 6.7, 15.4 Hz, H-5). EI-MS m/z: 341 [M]þ.
(E)-2-Amino-23-methyltetracos-4-ene-1,3-diol (0.5 mg) from compound 2: EI-MS
m/z: 397 [M]þ.
3. Results and discussion
25
Compound 1 was obtained as colourless amorphous powder, with an ½ꢁꢁD of – 8.3 (c 0.1,
CHCl3). EI-MS showed the characteristic molecular ion peak at m/z 663 [M]þ, which, in
conjunction with 1D and 2D NMR, was compatible with the molecular formula
C43H85NO3. The IR spectrum showed absorption bands at 3550 cmꢂ1 (hydroxyl); 3360,
1650 cmꢂ1 (amide); and 2930, 2850 and 1395 cmꢂ1 (aliphatic). The structural elucidation
1
and complete H and 13C assignments were achieved by 2D NMR techniques (1H–1H
COSY and HMQC) and chemical methods. A large methylene envelope at ꢃH 1.20–1.35 in
1H NMR and ꢃC 29.1–29.9 ppm in 13C NMR suggested the existence of two long aliphatic
chains (Qu et al., 2004). The presence of a sphingosine moiety was indicated by signals for
non-equivalent methylene proton signals at ꢃH 3.70 (1H, dd, J ¼ 3.2, 11.0 Hz, H-1B) and
3.95 (1H, dd, J ¼ 3.7, 11.0 Hz, H-1A), and two methine proton signals at ꢃH 3.92 (1H, m, H-
2) and 4.30 (1H, t, J ¼ 5.0 Hz, H-3). A characteristic amide NH signal was seen at ꢃH 6.25
(1H, d, J ¼ 7.3 Hz), exchangeable with D2O, which was also confirmed by the downfield
signals at ꢃC 174.0 (C-10) and 54.5 (C-2) in 13C NMR. In addition, the 1H NMR revealed the
presence of two olefinic proton signals at ꢃH 5.52 (1H, dd, J ¼ 6.3, 15.4 Hz, H-4) and 5.76
(1H, dt, J ¼ 6.6, 15.4 Hz, H-5), which were also confirmed by the signals at ꢃC 128.7 (C-4)
and 134.4 (C-5) in its 13C NMR spectrum (Table 1). The geometry of the double bond at C-4
was deduced to be E from the 1H–1H coupling constant (J ¼ 15.4 Hz) between H-4 and H-5
(Hattori, Adachi, & Shizuri 1998). The presence of a triplet signal at ꢃH 2.23 (2H, t,
J ¼ 8.2 Hz) due to the methylene protons connected to amide carbonyl indicated that the
1
N-acyl moiety in 1 was a non-hydroxy fatty acid (Gao et al., 2001). In H–1H COSY
(Figure 2), two spin systems were observed, the first spin system assigned to the sphingosine
base. The H-1A and H-1B correlated with H-2, assumed to be geminal with the nitrogen of
the secondary amide group correlated with H-3. H-3 correlated with the olefinic methine
proton H-4 and this further correlated with H-5. H-5 also correlated with H2-6 (ꢃH 2.07).
H2-6 gave a cross peak with H2-7 (ꢃH 1.37). H2-7 showed a cross peak with multiple proton
signal at ꢃH 1.20–1.35, which showed correlation with a methine proton at ꢃH 1.52 (septet,
J ¼ 6.9 Hz), which also correlated with two terminal methyls at ꢃH 0.86 (6H, d, J ¼ 6.6 Hz).
Thus the connectivity –O–CH2–CH(NH–)CH(O–)–CH¼CH–CH2–CH2–(CH2)n–CH

Natural Product Research
91
(CH3)2 was established. The second spin system corresponding to the saturated fatty acyl
1
moiety was evident from H–1H COSY spectrum. H2-20 correlated with H2-30, and this
further correlated with multiple proton signal at ꢃH 1.20–1.35, which showed correlation
with methyl proton signal at ꢃH 0.88 (t, J ¼ 6.5 Hz). The length and branching pattern of the
long chain base and fatty acid were determined on the basis of the results of its methanolysis
followed by EI-, GC-MS and 1H NMR analyses of the methanolysis products. The MeOH
layer provided a C21 sphingosine with an isopropyl terminus at ꢃH 0.86 (6H, d, J ¼ 6.6 Hz)
identified by 1H NMR spectral features and further confirmed by the presence of fragment
ion peaks at m/z 341 [M]þ and m/z 43 [M-C18H36NO2]þ due to loss of the terminal isopropyl
group in EI-MS. The n-hexane layer afforded a fatty acid methyl ester that showed a
molecular ion peak at m/z 354 [M]þ upon GC- and EI-MS spectral analyses, suggesting the
methyl ester of n-docosanoic acid. EI-MS spectrum of 1 confirmed the n-docosanoyl moiety
by the presence of significant fragment ion peaks at m/z 365 (a) and 281 (b) (Figure 3)
(Yaoita, Kohata, Kakuda, Machida, & Kikuchi, 2002). The relative stereochemistry of 1
1
at C-2 and C-3 was determined to be D-erythro (2S, 3R), since H NMR spectral data of
1 [H-1A at ꢃH 3.95 (dd, J ¼ 3.7, 11.0 Hz, H-1B at ꢃH 3.70 (dd, J ¼ 3.2, 11.0 Hz), H-2 at
ꢃH 3.92 (m) and H-3 at ꢃH 4.30 (t, J ¼ 5.0 Hz)] were in a good agreement with that of
N-docosanoyl-D-erythro-(2S,3R)-16-methyl-heptadecasphing-4(E)-enine isolated from
marine sponge Haliclona koremella [H-1A at ꢃH 3.94 (dd, J ¼ 3.8, 11.0 Hz), H-1B at ꢃH
3.68 (dd, J ¼ 3.0, 11.0 Hz), H-2 at ꢃH 3.89 (m) and H-3 at ꢃH 4.30 (dd, J ¼ 3.4, 6.6 Hz)]
(Hattori et al., 1998). The stereochemistry of 1 at C-2 and C-3 was further
confirmed to be 2S, 3R configuration by comparing the optical rotation values of 1
25
(½ꢁꢁD – 8.3ꢀ) and N-docosanoyl-D-erythro-(2S,3R)-16-methyl-heptadecasphing-4(E)-enine
([ꢁ]D – 6.0ꢀ). On the basis of this evidence, the structure of 1 was determined to be
(2S,3R,4E)-N-docosanoyl-2-amino-19- methyl-icosa-4-ene-1,3-diol, and was named iotro-
chotamide I.
Compound 2 was obtained as a colourless amorphous powder. ESI-LC/MS displayed a
pseudomolecular ion peak at m/z 720.3 [MþH]þ, thus differing from compound 1 by
56 mass units, suggested the presence of four additional methylene groups. The 1H and 13
C
O
HN
17
HO
n
OH
1
Figure 2. Some key H-1H COSY correlations of compound 1.
O
HN
17
m/z 365 (a)
HO
n
OH
m/z 281 (b)
Figure 3. Characteristic fragmentation pattern of compound 1.

92
S.R.M. Ibrahim et al.
NMR spectra of 2 closely resembled those of 1 except for the integration of the aliphatic
methylene protons at ꢃH 1.20–1.35. The lengths of LCB and fatty acid were determined by
1
methanolysis followed GC-, EI-MS and H NMR analyses of the methanolysis products.
GC- and EI-MS spectra of FAM showed a molecular ion peak at m/z 354 [M]þ, indicating
that the FAM was the same as that of 1 n-docosanoic acid methyl ester, and the LCB
had to be (E)-2-amino-23-methyl-tetracos-4-ene-1,3-diol. This was supported by EI-MS
of LCB, which gave a molecular ion peak at m/z 397 [M]þ. The optical rotation value of 2
25
(½ꢁꢁD ꢂ 10.5ꢀ) in comparison with 1 ([ꢁ]D ꢂ 8.3ꢀ) showed that 2 has the same absolute
configuration as that of 1 for C-2 and C-3 parts. Based on this evidence, the structure of 2
was unambiguously determined to be (2S,3R,4E)-N-docosanoyl-2-amino-23-methyl-
tetracos-4-ene-1,3-diol, and the name iotrochotamide II was given to this new natural
product. This is the first isolation of ceramide from the sponge Iotrochota purpurea.
The structures of compounds (3) (Rasmussen, Jensen, Anthoni, Christophersen, &
Nielsen, 1993), (4) Segraves & Crews. (2005), and (5) Guella et al. (1989) were determined
by interpretation of 1D and 2D NMR spectral data and confirmed by comparison with the
reported values.
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