Self gelating isoracemosol A, new racemosaceramide A, and racemosol E from Barringtonia racemosa

Article abstract of DOI:10.1080/14786419.2016.1212033

Phytochemical investigation into the CHCl₃extract of the fruits of Barringtonia racemosa resulted in the isolation of two new metabolites along with isoracemosol A and betulinic acid as known metabolites. The new compounds were characterised as phytosphingosine-type ceramide [(2S,3S,4R)-2-[(2R)-2-hydroxyhexadecanoyl amino]-hexacos-8(E)-ene-1,3,4-triol, 1] and racemosol E [21β-acetoxy-22α-(2-methylbutyroxy)-olean-12-ene-3β,16α,28-triol, 2] on the basis of extensive spectroscopic data analysis and chemical modifications. In addition, the self-gelating property of isoracemosol A (3) was investigated for the first time, which leads to the unexpected agglomerated porous-like morphology.

Full text of DOI:10.1080/14786419.2016.1212033

Natural Product Research
Formerly Natural Product Letters
ISSN: 1478-6419 (Print) 1478-6427 (Online) Journal homepage: http://www.tandfonline.com/loi/gnpl20
Self gelating isoracemosol A, new
racemosaceramide A, and racemosol E from
Barringtonia racemosa
Mangala Gowri Ponnapalli, Nalini Dangeti, Madhu Babu Sura, Haribabu
Kothapalli, V. S. Sarma Akella & Jeelani Basha Shaik
To cite this article: Mangala Gowri Ponnapalli, Nalini Dangeti, Madhu Babu Sura, Haribabu
Kothapalli, V. S. Sarma Akella & Jeelani Basha Shaik (2017) Self gelating isoracemosol A, new
racemosaceramide A, and racemosol E from Barringtonia racemosa, Natural Product Research,
31:1, 63-69, DOI: 10.1080/14786419.2016.1212033
To link to this article: http://dx.doi.org/10.1080/14786419.2016.1212033
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Date: 18 November 2016, At: 07:27

Natural Product research, 2017
Vol. 31, No. 1, 63–69
http://dx.doi.org/10.1080/14786419.2016.1212033
Self gelating isoracemosol A, new racemosaceramide A, and
racemosol E from Barringtonia racemosa
Mangala Gowri Ponnapallia, Nalini Dangetia, Madhu Babu Suraa, Haribabu Kothapallia,
V. S. Sarma Akellab and Jeelani Basha Shaikb
aNatural Products chemistry division, Indian Institute of chemical technology, hyderabad, India; bNMr
division, Indian Institute of chemical technology, hyderabad, India
ABSTRACT
ARTICLE HISTORY
received 9 February 2016
accepted 6 June 2016
Phytochemical investigation of the CHCl3 extract of the fruits of
Barringtonia racemosa resulted in the isolation of two new metabolites
along with isoracemosol A and betulinic acid as known metabolites.
The new compounds were characterized as phytosphingosine-
type ceramide [(2S,3S,4R)-2-[(2R)-2-hydroxyhexadecanoyl amino]-
hexacos-8(E)-ene-1,3,4-triol, 1] and racemosol E [21β-acetoxy-22α-
(2-methylbutyroxy)-olean-12-ene-3β,16α,28-triol, 2] on the basis of
extensive spectroscopic data analysis and chemical modifications.
In addition, the self gelating property of isoracemosol A (3) was
investigated for the first time, which leads to the unexpected
agglomerated porous like morphology.
KEYWORDS
Barringtonia racemosa;
racemosaceramide a;
racemosol e; isoracemosol
a; morphology and gelating
property
1. Introduction
Recently, pentacylic triterpenoids of lupane (Braga Gopal & Shib Shankar 2011) and oleanane
(Braga Gopal et al. 2006) triterpenoids (O’Neill et al. 2005) have been emerged as supramo-
lecular architectures. Nature continues to offer enormous synthetic challenges, of which
acylated polyhydroxy triterpenoids are rather unusual and difficult to manipulate synthet-
ically. Plants belonging to the Barringtonia, (Clive et al. 2005; Consolacion et al. 2012) and
Foetidia (Marie-Laure et al. 2002) genera of Lecythidaceae family were found to be a rich
source of acylated triterpenoids. As part of our ongoing program on isolation of bioactive
metabolites from Indian mangrove flora (Gowri et al. 2009; Ponnapalli et al. 2012; Annam
CONTACT Mangala Gowri Ponnapalli
mangala@iict.res.in
supplemental data for this article can be accessed here at http://dx.doi.org/10.1080/14786419.2016.1212033.
© 2016 Informa uK limited, trading as taylor & Francis Group

64
M. G. PONNAPALLI ET AL.
et al. 2015; Sura et al. 2015), we have investigated metabolites from Barringtonia racemosa.
It grows on the west coast of India and has been used as a folk medicine for several ailments
ranging from stomach complaints to fever, rheumatoidal arthritis (Jayaweera 1981) and
cancer (Deraniyagala et al. 2003). Herein, we report the isolation and structure elucidation
of a ceramide termed as racemosaceramide A (1) and racemosol E (2) along with two known
compounds isoracemosol A (3) and betulinic acid (4) (Yang et al. 2006). In addition, the
gelating behaviour of isoracemosol A was investigated for the first time, which leads to the
unexpected agglomerated porous like morphology that brings accessibility for designing
new functional materials.
2. Results and discussion
Racemosaceramide A (1) was obtained as an amorphous powder with optical rotation,
[ꢀ]2D7 +20.2 (c 0.3, Py). Its molecular formula was determined as C42H83NO5 on the basis of
pseudomolecular ion peak at m/z 704.6174 [M + Na]+ in HR-ESIMS and FAB MS. Its IR spectrum
demonstrated absorption bands for hydroxy, olefinic and amide groups.
The 1D NMR data (Table S1) of 1 indicated the presence of an amide proton doublet at
δH [8.57 (1H, d, J = 8.8 Hz); δC 174.9], two olefinic proton signals at δ 5.50 (2H, m), and protons
of two different long methylene chains at δ1.28 with terminal methyl groups at [δH 0.88 (6H,
t, J = 7.9 Hz) δC 14.0] indicating a phytosphingosine-type ceramide (Takahiro et al. 2006).
The characteristic resonances of 2-amino-1,3,4-triol of the sphingosine unit were observed
at [δH 4.49 (1H, dd J = 4.9, 3.8 Hz); δC 61.7], δH [4.40 (1H, dd, J = 4.9, 10.8 Hz); δC 76.5], δH [4.32
(1H, m); δC 72.6], δH 4.27 (1H, m); δC 72.2].
Methanolysis of 1 afforded a fatty acid methyl ester (FAME), and a long-chain base. The
FAME was identified as methyl-2-hydroxyhexadeconoate ([M+] 286) by means of GCMS anal-
ysis and the absolute configuration at C-2 was determined to be R from the specific rotation
(Shibuya et al. 1990) and also the negative Cotton effect at 215 nm in its CD spectrum (Craig
& Lee 1977). The presence of a hydroxy group in the α-position was ascertained by compar-
ison of spectral data with reported data (Shibuya et al. 1990). The presence of a 1,3,4-trihy-
1
droxy unsaturated long-chain base was deduced from the H–1H COSY spectrum. The
position of the double bond in the long chain base was established by the characteristic
fragment ions at m/z 403, 459 in FAB-MS due to allylic cleavage (Figure S3) and also by EIMS
analysis of the corresponding dimethyl sulphide derivative of compound 1 (Stothers 1972).
The characteristic fragment ion at m/z 299, indicated the double bond was located at C-8.
The chemical shifts of the allylic methylene carbons in 1 were assigned at δC 33.5 (C-7 or
C-10) and 33.1 (C-7 or C-10) based on the clearly observed HMBC correlations from olefinic
protons to C-7 and C-10. The geometry of the double bond was ascertained to be trans
according to the chemical shifts of the allylic carbons (Stothers 1972). The sequence of C-1
to C-5 moiety in 1, which includes 3 hydroxyls and an amide group (Figure 1) was established
by a DQF-COSY experiment (Table S2 and Figure S2) which correlated all the corresponding
protons, including the NH signal. Analysis of the 1H–1H COSY, HSQC, and HMBC spectra (Table
S2 and Figure S1) led to the assignment of all the corresponding proton and carbon signals
for 1. The correlations from δH 8.57 (NH) to δC 174.9 (C-1′, s), 72.2 (C-2′, d), 61.7 (C-1, t). 52.7
(C-2, d), and 76.5 (C-3, d) were observed in the HMBC spectrum of 1. These correlations
established the location of the amide group in compound 1

NATuRAL PRODuCT RESEARCH
65
30O
29
O
21
O
16'
3'
5
19
13
O
1'
H
CH3
22
28 O
( )12
N
17
OH
11
25
26
1
OH
9
(
1
)
26
16
OH
8
4
15
HO
CH3
10
2
8
OH
3
27
OH
7
R
5
HO
23
24
2
3
R = H
1
R = OH
O
OH
HO
4
Figure 1. compounds isolated from the fruits of Barringtonia racemosa.
The chemical shifts of H-2 (δ 5.10, 1H, m), H-3 (δ 4.32, 1H, m), and H-4 (δ 4.27, 1H, m) in
C5D5N were in good agreement with those of known synthetic ceramide (2S,3S,4R)-2-[(2R)-
2-hydroxytetracosanoylamino]-hexadecane-1,3,4-triol and natural ceramide gracilamide B
(Yi et al. 2006). The absolute stereochemistry of the ceramide moiety was presumed to be
2S, 3S, 4R, 2R by comparison of specific rotation with asteriaceramide A (Takahiro et al. 2006).
Thus, the structure of compound 1 was unequivocally established as (2S,3S,4R)-2-[(2R)-2-
hydroxyhexadecanoyl amino]-hexacos-8(E)-ene-1,3,4-triol.
Racemosol E (2) was obtained as an amorphous solid,[ꢀ]2D7 +2.5 (c 0.006, Py). Its HR-ESIMS
showed a pseudo molecular ion peak at m/z 639.4259 [M + Na]+ (Calcd 639.4231, which
corresponded to a molecular formula C37H60O7 with 8° of unsaturation. Its IR spectrum
revealed absorption bands for hydroxy, an ester carbonyl, and olefinic functionalities. The
1H NMR spectrum (Table S1) revealed the presence of seven tertiary methyl groups, one
trisubstituted olefinic proton at δ 5.44 (1H, t, J = 3.3 Hz). Furthermore, four oxymethines, an
oxymethylene, an acetyl and 2-methylbutyryl groups were evident from its 1H NMR spectrum.
The 13C NMR spectrum (Table S1) displayed 37 carbon resonances, which were analysed as
10 methyls, 9 methylenes, 9 methines and 9 quaternary carbon atoms from its DEPT and
1
HSQC spectra. A preliminary analysis of the H and 13C NMR data (Table S1) revealed that
two possess an acylated olean-12-ene structural framework. The 1H–1H COSY (Table S2 and
Figure S1) correlations from H-1 to H-2 and H-5 to H-6 were suggestive to determine the
sequence of C1-C5 moiety in 2. Moreover, the presence of 2-methyl butanoyl moiety was
confirmed based on observed 2′-H to 3′-H, 4′-H, 5′-H COSY correlations. The HMBC (Table S2
and Figure S1) correlations from H-21 to the acetyl carbonyl carbon and from H-22 to C-1′
confirmed the location of an acetyl and a 2-methyl butanoyl groups in the pentacarbocyclic
architecture of olean-12-ene. upon alkaline hydrolysis, compound 2 formed barringtogenol
C, which was identified by spectroscopic data as well as by comparison with authentic sample
and reported data (Crublet et al. 2002). Compound 2 was characterized as an acyl derivative
of baringtogenol C. The location of the hydroxyls at C-3, C-16, C-28 was further confirmed
by HMBC correlations of H-3/C-23, C-24; H-16/C-14, C-18; and H2-28/C-17, C-18, C-22
respectively.

66
M. G. PONNAPALLI ET AL.
The relative configuration of two was determined by NOESY correlations (Table S2, Figure
S2) and also by coupling constant. The NOESY spectrum of 1 showed cross-peaks of H-3/
H3-23; H-21/H3-30; H-22/H3-29, H-16/H3-26, 28-Ha. These were used to postulate the relative
configuration of stereogenic centres in 2. Consequently, the structure of compound 2 was
determined as 21β-acetoxy-22α-(2-methylbutyroxy)-olean-12-ene-3β,16α,28-triol (2).
2.1. Gelation behaviour
We have studied the gelation property of isoracemosol A in a wide range of aliphatic (acyclic
and cyclic) and aromatic organic solvents (See Supporting Information). The gelating behav-
iour of compound 3 is summarised in Table (See Supporting Information). Isoracemosol A,
a naturally occurring diacylated polyhydroxy triterpenoid possesses weak amphiphilic char-
acter to induce self assembly in CCl4. However, at higher concentrations it was possible to
get strong gel upon slight warming (at 60 °C) in CCl4 after keeping the solution at room
temperature for 30 min. Moreover, we have extended the gelation efficiency of compound
3 in mixture of n-hexane and acetone (See Supporting Information) and the results are
depicted in Table (See Supporting Information).
2.2. Thermal stability of the gel
The thermal stability of the organogel of 3 was checked in a mixture of solvents by the
‘inverted test tube method’ (Babu & Maitra 2005). Compound (3) showed thermal stability
(0.2 w/v%) in mixture of n-hexane and acetone 88:12. The Tgel vs. concentration plots (See
Supporting Information) indicated that for the same concentration range, the thermal sta-
bilities were, 88:12 > 86:14 > 90:10 proportions of n-hexane and acetone.
2.3. Morphology
The morphology of bare compound and gel derived from isoracemosol A was investigated
by Scanning Electron Microscopy (SEM) (Figure S3). The SEM micrograph did not reveal any
regular fibrous structures. Bare compound 3 only showed stone-like morphology, while its
gel exhibited agglomerated porous-like structure, which is rather unusual. It can be sug-
gested that hydrogen bonding interactions may be responsible for the agglomerated porous
formation, as the molecules contain hydroxy groups.
3. Experimental
3.1. General experimental procedures
Optical rotations were measured on a Horiba SEPA-300 high sensitive Polarimeter. IR spectra
1
were recorded on a Thermo Nicolet Nexus 670 spectrometer with K Br pellets. H NMR
(600 MHz) and 13C NMR (150 MHz) spectra were recorded with a Bruker Avance II spectrom-
eter in C5D5N with TMS as an internal standard. Coupling constants (J) were given in Hz. The
ESIMS data were recorded on an Agilent 1100 MSD with an ESI SL trap. The HR-ESIMS data
were acquired on an Agilent 6510 Q-TOF and ESI probe. Column chromatography was per-
formed with silica gel (100–200, 230–400 mesh, Sigma). Silica gel F254 (0.25 mm, Merck) was

NATuRAL PRODuCT RESEARCH
67
used for analytical TLC. Field Emission Scanning electron microscopy experiments were car-
ried out using Zeiss ultra Plus scanning electron microscope.
3.2. Plant material
Fruits of B. racemosa Roxb. were purchased from a local market in Trivandrum in March 2011
from Kerala, India, and authenticated by Prof B. Kondala Rao, Department of Marine Living
Sources, Andhra university, Visakhapatnam. A voucher specimen (#IIC-MG-116) has been
deposited in the Herbarium of Natural Products Chemistry, IICT, Hyderabad, India.
3.3. Isolation and identification
The fruits of (2.0 kg) B. racemosa were ground to a fine powder and extracted with CHCl3
(10 L) in a Soxhlet apparatus for 18 h. After filtration, the filtrate was concentrated under
reduced pressure to yield a pale yellow residue (26.7 g). A part of this residue (25 g) was
subjected to silica gel (230–400 mesh, Merck) VLC and eluted with n-hexane:acetone mix-
tures of increasing polarity, resulted in 12 main fractions of 800 mL each. Fraction-6 was
subjected to Si gel CC afforded racemosaceramide A (1, 10 mg). Fraction-8 was submitted
to silica gel CC eluted with n-hexane–acetone (8:2) resulted in the isolation of racemosol E
(2, 9 mg), isoracemosol A (3, 300 mg). Fraction 12 was repeatedly purified by silica gel CC
using n-hexane–acetone (6:4) to obtain pure betulinic acid, 4 (20 mg).
3.3.1. Racemosaceramide A (1)
C H NO ; white amorphous powder; [ꢀ]D27 +20.2 (c 0.3, pyridine); IR (KBr) vmax 3390 and
42 83
5
1070 cm−1 (hydroxy); 1633 cm−1 (amide); and 2917, 2849, 1470 cm−1 (aliphatic) functionalities;
HR-ESIMS m/z [M + Na]+ 704.6174 (Calcd mass for C42H83NO5 681.62712), and FAB MS m/z
705 [M+ + Na + H]; 1H NMR (600 MHz, C5D5N), δ: 8.57 (1H, d, J = 8.8 Hz, N–H), 1.28 (aliphatic
C chain), 4.49 (1H, dd, J = 4.9, 3.8 Hz, H-1α), 4.40 (1H, dd, J = 4.9, 10.8 Hz, H-1), 5.10 (1H, m,
H-2), 4.32 (1H, m, H-3), 4.27 (1H, m, H-4), 5.50 (2H, m, H-8/9), 4.61 (1H, dd, J = 3.6, 7.5 Hz, H-2′),
1.98 (5H, m, H-5β, H-4′α, H-8β, H-9β, H-3′β), 0.88 (6H, J = 7.9, H-18, H-24′); 13C (150 MHz,
C5D5N), δ: 174.9 (C-1′), 72.2 (C-2′), 35.4 (C-3′), 25.6 (C-4′), 61.7 (C-1), 52.7 (C-2), 76.5 (C-3), 72.6
(C-4), 33.6 (C-5), 26.5 (C-6), 33.1 (C-7), 130.6 (C-8), 130.4 (C-9), 32.7 (C-10) and 2D NMR data
(Table S2 and Figures S1–S2).
3.3.2. Racemosol E (2)
C H O ; white amorphous solid;[ꢀ]2D7 +2.5 (c 0.06, pyridine); IR (KBr) vmax 3452, 2942, 2853,
37 60
7
1732, 1648, 1463, 1377, 1245, 1086 cm−1; HR-ESIMS m/z [M + Na]+ 639.4259 (Calcd mass for
C37H60O7, 639.4231); 1H NMR (600 MHz, C5D5N), δ: 1.58 (1H, m, H-1α), 1.03 (1H, m, H-1β), 1.87
(1H, m, H-2α), 3.47 (1H, dd, J = 5.1, 11.0 Hz, H-3), 0.88 (1H, d, J = 7.0 Hz, H-5), 1.57 (1H, m,
H-6α), 1.39 (1H, m, H-6β), 1.62 (1H, m, H-7α), 1.33 (1H, m, H-7β), 1.78 (1H, m, H-9), 1.93 (1H,
m, H-11α), 1.85 (1H, m, H-11β), 5.44 (1H, t, J = 3.3 Hz, H-12), 2.02 (1H, m, H-15α), 1.64 (1H, m,
H-15β), 4.48 (1H, br s, H-16), 3.08 (1H, m, H-18), 3.08 (1H, m, H-19α), 1.41 (1H, m, H-19β), 6.54
(1H, d, J = 10.1, H-21), 6.28 (1H, d, J = 10.1, H-22), 1.25 (3H, s, H-23), 0.92 (3H, s, H-24), 0.91
(3H, s, H-25), 1.05 (3H, s, H-26), 1.81 (3H, s, H-27), 3.68 (1H, d, J = 10.5, H-28a), 3.42 (1H, d,
J = 10.5, H-28b), 1.06 (3H, s, H-29), 1.28 (3H, s, H-30), 2.10 (3H, s, H-21-COCH3), 2.27 (1H, sext,
J = 7.0 Hz, H-2′), 1.72 (1H, m, H-3′b), 0.79 (3H, t, J = 7.4 Hz, H-4′) 1.12 (3H, d, J = 7.0 Hz, H-5′);

68
M. G. PONNAPALLI ET AL.
13C (150 MHz, C5D5N), δ: 39.1 (C-1), 28.1 (C-2), 78.0 (C-3), 40.1 (C-4), 55.8 (C-5), 18.8 (C-6), 33.2
(C-7), 39.4 (C-8), 47.1 (C-9), 37.2 (C-10), 23.9 (C-11), 123.0 (C-12), 142.9 (C-13), 41.7 (C-14), 34.8
(C-15), 68.3 (C-16), 48.2 (C-17), 40.1 (C-18), 47.2 (C-19), 36.3 (C-20), 79.3 (C-21), 73.5 (C-22),
28.7 (C-23), 16.9 (C-24), 16.6 (C-25), 16.9 (C-26), 27.4 (C-27), 63.6 (C-28), 29.4 (C-29), 20.1 (C-30),
170.8 (C-21-CO-CH3), 21.2 (C-21-CO-CH3), 176.7 (C-1′), 41.7 (C-2′), 26.9 (C-3′), 11.9 (C-4′), 15.8
(C-5′) and 2D NMR data (Tables S1–S2 and Figures S1–S2).
3.4. DMDS Derivative of (1)
Compound 1 (0.5 mg) was dissolved in CS2 (0.2 mL) with the addition of dimethyl disulfide
(DMDS) (0.2 mL) and 20 μL of iodine solution (60 mg of I2 IN 1 mL of diethyl ether). After
stirring for 48 h at 60 °C in a 10 mL tube sealed with a Teflon-lined cap, the reaction mixture
was diluted with 0.2 mL of Na2S2O3 solution (5% in distilled water). The organic phase was
refluxed and the aqueous phase was extracted twice with 0.2 mL of n-hexane. The organic
extracts were concentrated, and the DMDS derivative was analysed by EIMS, which showed
molecular ion peak at m/z 775.
4. Conclusion
This is the first report of occurrence of ceramide from Lecythidaceae family. In addition, the
self gelating property of isoracemosol A was investigated for the first time, which leads to
the unexpected agglomerated porous like morphology.
Supplementary material
Supplementary material relating to this article is available online, alongside Figures S1–S2 and Tables
S1–S2.
Acknowledgement
We thank Dr S. Chandrasekhar, director, I.I.C.T. for constant support and encouragement.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the Department of Science and Technology, New Delhi, India [grant
number SR/S1/OC-33/2011].
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