Ethylenediamine: An effective reagent for deacetylation of natural products

Article abstract of DOI:10.1080/10286020.2010.507545

The use of ethylenediamine in methanol is described for the selective cleavage of the acetate group in nimbin (1) to 6-deacetyl nimbin (1a) under microwave irradiation. This method enables to deacetylate without affecting other functional groups such as ,α,β-unsaturated ketone, ester, ether, etc. in certain tetranortriterpenoids and other acetate-containing natural compounds.

Full text of DOI:10.1080/10286020.2010.507545

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Ethylenediamine: an effective reagent
for deacetylation of natural products
Ramasamy Mohankumar a , Kaliappan Ilango b , Vichangal Pridiuldi
Santhanakrishnan a , Viswanathan Radhakrishnan a & Srinivasan
Narasimhan a
a Asthagiri Herbal Research Foundation, 14/1 Second Main Road,
Jaya Nagar, Tambaram Sanatorium, Chennai, 600 047, Tamilnadu,
India
b Department of Pharmaceutical Chemistry, SRM College of
Pharmacy, Kattankulathur, Kancheepuram, 603 203, Tamilnadu,
India
Version of record first published: 28 Sep 2010.
To cite this article: Ramasamy Mohankumar , Kaliappan Ilango , Vichangal Pridiuldi
Santhanakrishnan , Viswanathan Radhakrishnan & Srinivasan Narasimhan (2010): Ethylenediamine:
an effective reagent for deacetylation of natural products, Journal of Asian Natural Products
Research, 12:10, 851-858
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Journal of Asian Natural Products Research
Vol. 12, No. 10, October 2010, 851–858
ORIGINAL ARTICLE
Ethylenediamine: an effective reagent for deacetylation
of natural products
Ramasamy Mohankumara, Kaliappan Ilangob, Vichangal Pridiuldi Santhanakrishnana,
Viswanathan Radhakrishnana and Srinivasan Narasimhana*
aAsthagiri Herbal Research Foundation, 14/1 Second Main Road, Jaya Nagar, Tambaram
Sanatorium, Chennai 600 047, Tamilnadu, India; bDepartment of Pharmaceutical Chemistry, SRM
College of Pharmacy, Kattankulathur, Kancheepuram 603 203, Tamilnadu, India
(Received 7 January 2010; final version received 8 July 2010)
The use of ethylenediamine in methanol is described for the selective cleavage of the
acetate group in nimbin (1) to 6-deacetyl nimbin (1a) under microwave irradiation.
This method enables to deacetylate without affecting other functional groups such as
a,b-unsaturated ketone, ester, ether, etc. in certain tetranortriterpenoids and other
acetate-containing natural compounds.
Keywords: forskolin; ethylenediamine; nimbin; microwave
1. Introduction
resonance at 170 ppm (acetate carbonyl),
indicating hydrolysis of a 7b-acetoxy
moiety. The carbonyl resonance at
203 ppm confirmed the presence of C-11
carbonyl in concurrence with the above-
mentioned observation. This prompted us
to evaluate the use of ethylenediamine to
produce deacetyl products from polyfunc-
tional natural products. The available
agents such as NaOH and Na2CO3 in
alcohol resulted in the formation of de-
esterified products along with the deace-
tylated product in nimbin. The Lewis acids
would cleave the epoxide moiety [2] and
the use of the other reagents like hydrazine
hydrate may result in the cleavage of a,b-
epoxy ketones [3]. Ethylenediamine seems
to be a superior reagent for deacetylation
in comparison with NH3 in MeOH [4],
exclusively yielding one product irrespec-
tive of the quantity of amine used. Hence,
an attempt has been made to deacetylate
Semi-synthetic modification of natural
products has gathered momentum in recent
times owing to its potential in generating
molecules with promising biological
activity. Modification of a given structural
entity is best achieved by functional group
transformation or by introduction of moi-
eties, whichcanenhance oralterthe activity.
2. Results and discussion
During our ongoing investigations to
prepare nitrogen analogs of some selected
diterpenes and tetranortriterpenoids, we
employed ethylenediamine in methanol to
produce an imino product with forskolin
[1], a compound known to exhibit
excellent vasodilating and cardio-stimulat-
ing properties.
The NMR spectrum of the product
revealed the disappearance of the CvO
*Corresponding author. Email: asthagiri.herbal@gmail.com
ISSN 1028-6020 print/ISSN 1477-2213 online
q 2010 Taylor & Francis
DOI: 10.1080/10286020.2010.507545
http://www.informaworld.com

852
R. Mohankumar et al.
23
23
22
22
12
18
12
O
18
H3COOC
O
H3COOC
11
30
11
30
O
19
13
O
19
13
21
20
21
20
1
14
9
1
14
9
17
16
17
16
2
MeOH/EDA
MWI, 7min
2
10
8
8
10
15
4
6
3
15
O
4
6
3
O
5
7
5
7
H3COOC
H3COOC
OCOCH3
28
OH
29
28
29
1
1a
Scheme 1. Conversion of nimbin (1) to deacetyl nimbin (1a).
nimbin using ethylenediamine resulting in
deacetyl nimbin (Scheme 1) in 75% yield
within 7 min under microwave [5,6]
irradiation condition without any side
products. The compound was then purified
by column chromatography.
view of the usefulness of ethylenediamine
[12,13] in organic synthesis.
3. Experimental
3.1 Procedure
Various tetranortriterpenoids such as nim-
bin, salannin, azadiradione, nimonol, etc.
were obtained in the pure form after being
subjected to repeated purification by
column chromatography from the oil,
fruit coat, and leaves of Azadirachta
indica. Similarly, forskolin was obtained
from Coleus forskohlii and cedrelone from
the barks of Toona ciliata. The b-amyrin
and pregnenolone were obtained from SD
Fine Chemicals, Worli, Mumbai, India.
NMR spectra were recorded on a
Bruker 200 MHz instrument using TMS
It has been observed that this reagent is
mild and selectively cleaves the acetate
group amid other functional groups. We
have demonstrated (Table 1) the selective
cleavage of acetate in certain tetranortri-
terpenoids such as nimbin [7,8], nimonol,
salannin, and azadiradione [9–11] with
multiple functional groups, and therefore
this method has advantages over other
methods.
The basicity of ethylenediamine is
exploited in deacetylation without affect-
1
ing other functional groups. The H and
1
as the internal reference for both H and
13C NMR spectra of this compound
showed a similar characteristic to that of
nimbin, except for the acetate group at
C-7. It was clearly evident from the
disappearance of the carbonyl group of
acetate at 170.3 ppm and the methyl group
signal at 20.8 ppm. The formation of the
hydroxyl group at C-7 was confirmed by
the appearance of the signal at 86.9 ppm,
which in turn showed the connectivity to
the proton at 3.76 ppm. The assigned
structure for the product obtained is
6-deacetyl nimbin, which is in agreement
with the mass 498 [M]þ.
13C NMR experiments. CDCl3 was used as
the solvent. Chemical shifts are given in
terms of parts per million (d scale). MS
analyses were recorded on a Shimadzu QP
5000 instrument. IR spectra (cm21) were
recorded on a Perkin-Elmer RX1 FT-IR
spectrophotometer. Precoated thin layer
chromatography plates (E-Merck, Darm-
stadt, Germany; Kieselgel 60 F254,
0.2 mm thickness, coated on aluminum
sheets) were used. Column chromatog-
raphy was performed using silica gel (60–
120 mesh and 230–400 mesh).
In summary, we have developed a
simple, selective, and mild procedure for
the cleavage of the acetate group in natural
products, which will have a wide scope in
3.2 Deacetylation of nimbin
Nimbin (108 mg, 5 mmol) was added to a
solution of ethylenediamine (2 ml in 2 ml

Journal of Asian Natural Products Research
853
Table 1. Deacetylation of natural products with ethylenediamine under modified microwave
irradiation.
Time Isolated
(min) yield (%)
Entry
Substrate
Product
COOCH3
COOCH3
O
O
O
O
1
7
75
O
O
CH3OOC
CH3OOC
OAc
OH
Deacetyl nimbin (1a)
Nimbin (1)
O
O
2
3
4
5
6
88
O
O
OAc
OH
OH
OH
Nimonol
Deacetyl nimonol
MeO2C
Otig
O
O
MeO2C
Otig
12
10
5
76
78
82
O
O
AcO
HO
H
O
H
O
Salannin
Deacetyl salannin
O
O
O
O
O
O
OH
Deacetyl azadiradione
OAc
Azadiradione
O
O
O
O
O
O
OCOCH3
O
O
OH
Cedrelone acetate
Cedrelone

854
R. Mohankumar et al.
Table 1 – continued
Time Isolated
(min) yield (%)
Entry
Substrate
Product
CH3
O
CH3
O
O
OH
OH
CH2
CH2
CH3
CH3
O
CH3
CH3
O
6
5
80
OH
OH
O
CH3
OH
H
H
CH3
CH3
H3C
H3C
HO
HO
OH
OH
Deacetyl forskolin
Forskolin
O
O
7
4
90
H3COCO
Pregnenolone
Pregnenolone acetate
8
4
94
AcO
Amyrin
Amyrin acetate
Note: Yields were calculated after purification by column chromatography.
of methanol) and irradiated under micro-
wave with stirring for 7 min. The reaction
was monitored by TLC (70:30; ethyl
acetate–hexane). The solvent was
removed under reduced pressure. The
reaction mixture was poured into ice-cold
water and extracted with ethyl acetate to
afford a white powder. The yield obtained
after purification by column chromatog-
raphy was 81 mg (75%). A series of
deacetyl products are given in Table 1.
3.2.1 Deacetyl nimbin
C28H34O8; mp 2088C; UV lmax (MeOH):
209 nm; IR (KBr) nmax: 3574, 3640, 2940,
2855, 1455, 1390, 1370, 1355, 1275, 1250,
1140, 1112, 1090, 1060, 1028, 878, 783,
744 cm21
;
1H NMR (d, ppm): 7.32
(m, 1H), 7.24 (m, 1H), 6.41 (d, 1H,
J ¼ 10.1 Hz), 6.33 (m, 1H), 5.84 (d, 1H,
J ¼ 10.1 Hz), 5.55 (m, 1H), 4.01 (d,
1H, J ¼ 3.3 Hz), 3.91 (dd, 1H, J ¼ 11.4,
3.3 Hz), 3.70 (s, 3H), 3.65 (s, 3H), 3.60 (m,
1H), 3.40 (d, 1H, J ¼ 11.7 Hz), 2.92
(m, 1H), 2.77 (m, 1H), 2.25 (m, 1H),
2.20 (m, 1H), 2.06 (m, 1H), 1.21–1.69
1
The selected H and 13C NMR spectral
data of both the starting material and the
product are shown in Tables 2–6.

Journal of Asian Natural Products Research
855
1
Table 2. The selected H and 13C NMR spectral data of nimbin (1) and 6-deacetyl nimbin (1a).
13C NMR
(d ppm)
1H NMR (d ppm)
Carbon no.
1
1a
1
1a
5
6
7
8
9
10
3.70 (m, 1H)
5.25 (dd, 1H, J ¼ 12.3, 3.0 Hz)
3.40 (d, 1H, J ¼ 11.7 Hz)
41.5
68.6
84.5
47.1
38.5
47.9
43.6
66.1
86.9
47.3
39.0
47.4
3.91 (dd, 1H, J ¼ 11.7, 3.3 Hz)
4.05 (d, 1H, J ¼ 3.0 Hz)
4.01 (d, 1H, J ¼ 3.3 Hz)
–
–
2.77 (m, 1H)
–
2.85 (dd, 1H, J ¼ 5.5, 3.0 Hz)
–
Table 3. The selected 1H and 13C NMR spectral data of nimonol (2) and 7-deacetyl nimonol (2a).
1H NMR (d ppm) 13C NMR (d ppm)
Carbon no.
2
2a
2
2a
5
6
7
8
9
10
2.23 (m, 1H)
4.37 (m, 1H)
5.37 (m, 1H)
–
2.44 (m, 1H)
–
2.45 (m, 1H)
4.22 (m, 1H)
3.49 (m, 1H)
–
2.87 (m, 1H)
–
49.9
68.1
79.1
45.5
36.9
43.3
47.2
68.4
75.9
44.4
35.6
45.6
Table 4. The selected 1H and 13C NMR spectral data of salannin (3) and 3-deacetyl salannin (3a).
13C NMR
(d ppm)
1H NMR (d ppm)
Carbon no.
3
3a
3
3a
1
2
3
4
5
6
4.78 (t, 1H, J ¼ 2.7 Hz)
2.04–2.37 (m, 2H)
4.96 (t, 1H, J ¼ 2.8 Hz)
–
5.30 (m, 1H)
2.05–2.35 (m, 2H)
3.87 (m, 1H)
71.3
27.5
71.3
42.6
40.5
72.5
72.8
30.5
70.8
44.2
38.8
72.4
–
2.81 (d, 1H, J ¼ 12.5 Hz)
2.63 (d, 1H, J ¼ 12.3 Hz)
4.01 (dd, 1H, J ¼ 12.5, 3.3 Hz)
4.08 (dd, 1H, J ¼ 12.3, 3.3 Hz)
Table 5. The selected 1H and 13C NMR spectral data of azadiradione (4) and 7-deacetyl
azadiradione (4a).
13C NMR
(d ppm)
1H NMR (d ppm)
Carbon no.
4
4a
4
4a
5
6
7
8
9
10
2.20 (dd, 1H, J ¼ 3.7, 11.6 Hz)
2.50 (dd, 1H, J ¼ 12.8 Hz)
46.1
23.3
73.8
44.4
38.1
39.9
36.5
27.1
71.7
44.2
44.5
40.1
1.88 (m, 2H)
1.88 (m, 2H)
3.99 (m, 1H)
5.32 (t, 1H, J ¼ 2.7 Hz)
–
2.50 (m, 1H)
–
–
2.55 (m, 1H)
–

856
R. Mohankumar et al.
Table 6. The selected 1H and 13C NMR spectral data of forskolin (6) and 7-deacetyl forskolin (6a).
1H NMR (d ppm) 13C NMR (d ppm)
Carbon no.
6
6a
6
6a
5
6
7
8
9
10
1.05 (m, 1H)
4.57 (m, 1H)
1.07 (m, 1H)
4.48 (m, 1H)
4.62 (m, 1H)
41.8
74.0
73.2
68.8
80.3
41.7
42.9
70.5
74.7
82.2
82.2
42.7
5.48 (d, 1H, J ¼ 4.3 Hz)
–
–
–
–
–
–
(br s, 4 £ CH3); 13C NMR (d, ppm): 202.9,
175.5, 173.7, 148.1, 146.9, 143.0, 139.0,
134.9, 126.8, 126.4, 110.4, 87.4, 86.9,
66.2, 53.0, 51.6, 49.6, 47.8, 47.5, 43.6,
47.3, 41.4, 39.0, 34.4. MS m/z: 498 [M]þ.
(m, 1H), 3.50 (s, 1H), 2.55 (m, 1H), 2.50
(dd, 1H, J ¼ 12.8 Hz), 2.08 (m, 1H), 2.04
(m, 1H), 1.88 (m, 2H), 1.86 (m, 1H), 1.84
(m, 1H), 1.42 (s, 3H), 1.27 (s, 3H), 1.12 (s,
3H), 1.12 (s, 3H), 0.96 (s, 3H); 13C NMR
(d, ppm): 204.6, 201.8, 193.7, 157.1,
142.8, 141.7, 125.9, 123.4, 118.4, 111.1,
71.7, 60.9, 48.3, 44.6, 44.2, 40.2, 36.6,
30.5, 27.1, 26.4, 26.0, 25.4, 21.44, 19.1,
15.7. MS m/z: 408 [M]þ.
3.2.2 Deacetyl salannin
C32H42O8; mp 213–2168C; UV lmax
(MeOH): 210 nm; IR (KBr) cm21: 3430,
2993, 1698, 1662, 1593, 1460, 1387, 1151,
1
1030, 752, 602; H NMR (d, ppm): 7.31
3.2.4 Deacetyl nimonol
(m, 1H), 7.25 (m, 1H), 6.92 (m, 1H), 6.27
(m, 1H), 5.38 (m, 1H), 5.30 (m, 1H), 4.18
(d, 1H, J ¼ 3.3 Hz), 4.08 (dd, 1H,
J ¼ 12.3, 3.3 Hz), 3.87 (m, 1H), 3.87 (m,
1H), 3.62 (m, 1H), 3.62 (m, 1H), 3.19 (s,
3H), 2.67 (m, 1H), 2.50–2.75 (d, 1H,
J ¼ 4.5 Hz), 2.05–2.35 (m, 2H), 2.05–
2.35 (m, 1H), 2.05–2.35 (m, 1H), 2.05–
2.35 (m, 2H), 1.85 (s, 3H), 0.96–1.69 (br s,
4 £ CH3); 13C NMR (d, ppm): 172.6,
166.3, 146.4, 142.8, 138.7, 138.1, 134.9,
128.6, 127.1, 110.6, 87.8, 85.8, 77.8, 72.8,
72.4, 70.8, 51.4, 49.3, 48.9, 44.2, 41.2,
40.9, 39.4, 38.8, 30.5, 30.5, 19.8, 16.8,
15.1, 14.5, 13.1, 12.1. MS m/z: 554 [M]þ.
C26H34O4; mp 194–1988C; UV lmax
:
(MeOH): 223 nm; IR nmax (MeOH) cm21
3500, 2900, 2875, 1658, 1460, 1382, 1224,
1
1157, 1103, 1028, 931, 794, 597, 466; H
NMR (d, ppm): 7.38 (m, 1H), 7.25 (m, 1H),
7.07 (d, 1H, J ¼ 10.2 Hz), 6.29 (m,
1H), 5.86 (d, 1H, J ¼ 10.2Hz), 5.58 (d,
1H, J ¼ 10.2Hz), 4.22 (m, 1H), 3.49 (m,
1H), 2.87 (m, 1H), 2.45 (m, 1H), 2.45
(m, 1H), 2.16–2.37 (m, 2H), 2.16–2.37 (m,
2H), 1.95 (m, 2H), 1.11–1.42 (s, 3H),
1.11–1.42 (s, 3H), 1.11–1.42 (s, 3H),
1.11–1.42 (s, 3H); 13C NMR (d, ppm):
206.1, 161.0, 157.3, 142.7, 139.8, 126.2,
124.2, 120.0, 111.0, 76.0, 68.4, 51.6, 49.5,
47.2, 45.6, 44.4, 40.8, 35.6, 34.4, 32.3, 29.7,
26.9, 20.6, 20.3, 16.2. MS m/z: 410 [M]þ.
3.2.3 Deacetyl azadiradione
C26H32O4; mp 2088C; UV lmax (MeOH)
237 nm; IR (KBr) cm21: 3409, 2923,
2826, 1728, 1649, 1435, 1387, 1259, 1155,
3.2.5 Cedrelone
1
1037, 983, 786, 732, 599; H NMR (d,
C26H32O4; mp 2088C; UV lmax (MeOH):
237 nm; IR (KBr) cm21: 3392, 3118,
3033, 2933, 2866, 1676, 1618, 1448, 1384,
1340, 1251, 1153, 1060, 1031, 981, 947,
ppm): 7.43 (m, 1H), 7.34 (m, 1H), 7.10
(d, 1H, J ¼ 10.2 Hz), 6.10 (s, 1H), 6.06
(m, 1H), 5.89 (d, 1H, J ¼ 10.2 Hz), 3.99

Journal of Asian Natural Products Research
857
918, 877, 813, 779, 752, 715, 669, 634,
596; 1H NMR (d, ppm): 7.37 (m, 1H), 7.15
(m, 1H), 6.90 (d, 1H, J ¼ 9.7 Hz), 6.44 (bs,
D2O exchangeable), 6.18 (m, 1H), 5.89 (d,
1H, J ¼ 9.7 Hz), 3.80 (s, 1H), 2.30 (m,
1H), 2.75 (m, 1H), 2.67 (m, 1H), 2.07 (m,
1H), 1.94 (m, 1H), 1.85 (m, 1H), 1.69 (m,
1H), 0.75–1.57 (br s, £ CH3); 13C NMR
(d, ppm): 203.7, 197.9, 152.4, 143.0,
141.1, 139.3, 134.8, 127.2, 123.1, 110.6,
69.8, 55.0, 46.8, 48.5, 43.1, 42.1, 42.0,
41.7, 40.2, 35.1, 26.7, 23.9, 23.0, 21.1,
20.2, 19.4. MS m/z: 422 [M]þ.
38.8, 36.4, 36.5, 31.8, 31.7, 31.6, 31.5, 24.5,
22.8, 21.1, 19.4, 13.2. MS m/z: 316 [M]þ.
3.2.8 b-Amyrin
C30H50O; mp 196–1988C; UV lmax
(MeOH): 206 nm; IR (KBr) cm21: 3316,
2854, 1643, 1456, 1360, 1195, 1036, 988,
881, 824, 660; 1H NMR (d, ppm): 4.62 (m,
1H), 3.21 (m, 1H), 1.92–2.10 (m, 2H),
1.65–1.85 (4H, m), 1.40–1.55 (m, 12H),
0.90–1.10 (m, 4H), 1.03 (s, 3H), 0.99 (s,
3H), 0.96 (s, 2H), 0.94 (s, 3H), 0.91 (s, 3H),
0.82 (s, 3H), 0.79 (s, 3H), 0.76 (s, 3H); 13
C
NMR (d, ppm): 150.1, 124.4, 79.0, 55.2,
48.0, 48.0, 46.9, 41.5, 40.0, 38.7, 38.7,
37.1, 34.2, 33.3, 32.9, 32.6, 31.3, 28.1,
28.4, 28.0, 27.4, 26.1, 25.1, 23.5, 23.5,
18.9, 16.1, 15.7, 15.4. MS m/z: 426 [M]þ.
3.2.6 Deacetyl forskolin
C20H32O6; mp: 163–1668C; UV lmax
(MeOH): 210 nm; IR (KBr) cm21: 3419,
2939, 1716, 1562, 1402, 1247, 1103, 1060;
1H NMR (d, ppm): 6.12 (dd, 1H, J ¼ 17.4,
10.7 Hz), 5.19 (d, 1H, J ¼ 17.3 Hz), 4.98
(d, 1H, J ¼ 10.8 Hz), 4.63 (m, 1H), 4.48
(m, 1H), 4.13 (m, 1H), 3.18 (d, 1H,
J ¼ 17.2 Hz), 2.50 (d, 1H, J ¼ 17.2 Hz),
2.35 (m, 1H), 2.20 (m, 1H), 2.09 (m, 1H),
1.75 (m, 1H), 1.65 (s, 3H), 1.43 (s, 3H),
Acknowledgements
R.M.K. thanks DBT, V.P.S. and V.R.K. thank
CSIR for the financial support and Spic Science
Foundation for the Analytical Center Facility.
Supporting Information
1.41 (s, 3H), 1.27 (s, 3H), 1.06 (s, 3H); 13
C
Supporting information is available online.
NMR (d, ppm): 205.8, 146.5, 110.5, 82.3,
82.2, 75.2, 74.8, 74.7, 70.5, 48.8, 48.8,
43.0, 42.8, 36.1, 34.3, 33.0, 30.8, 24.2,
23.4, 20.0. MS m/z: 368 [M]þ.
References
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3352, 3028, 2933, 2835, 1683, 1461, 1433,
1357, 1292, 1224, 1191, 1168, 1134, 1097,
1053, 985, 950, 914, 840, 800, 596, 468;
1H NMR (d, ppm): 5.36 (m, 1H), 3.53 (m,
1H), 2.54 (t, 1H, J ¼ 9.0 Hz), 2.20–2.35
(m, 2H), 2.20–2.35 (m, 2H), 2.13 (s, 3H),
2.06 (m, 1H), 2.04 (m, 2H), 1.40–1.75 (m,
2H), 1.40–1.75 (m, 2H), 1.40–1.75 (m,
1H), 1.40–1.75 (m, 1H), 1.40–1.75 (m,
2H), 1.40–1.75 (m, 1H), 1.00–1.30 (m,
2H), 1.0–1.30 (m, 2H), 1.01 (s, 3H), 0.63
(s, 3H); 13C NMR (d, ppm): 209.6, 140.8,
121.3, 71.6, 63.7, 56.9, 50.0, 44.0, 42.2,

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