This Issue is Dedicated to the Memory of Professor Ivano Morelli

1102 Natural Product Communications Vol. 1 (12) 2006 Simões-Pires et al.
B
100
Relative Abundance
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
517.1 [M+H] +
mAU
2500 1
2000
1500
1000
500
0
250 300 350 400 450
nm
518.1
519.1
500.1 488.2
520.1
467.4
222.7 280.2 337.9 356.8 572.7
604.1
790.3
167.1 673.7 693.0
717.3
650 700 750
200 250 300 350 400 450 500 550 600 m/z
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Relative Abundance
531.0 [M+H] +
mAU
1200 2
1000
800
600
400
200
0
250 300 350 400 450
nm
532.1
513.1
533.0
534.0
572.6
308.1326.0 475.3488.0
245.9263.1 351.0 369.1 647.9
184.9 412.8 691.7
708.8
200 400 700 750 250 300 350 450 500 550 600 650 800
m/z
A
0.6
0.5
0.4
0.3
0.2
0.1
UV 254 nm
0
0 2 4 6 8 10 12 14 16 18 20
Time (min)
Figure 1: (A) LC-UV-APCI/MS analysis of the alkaloid extract of the aerial parts of Psychotria myriantha. (B) UV and mass spectra of compounds 1 and 2.
(LC/UV/MS conditions: see Experimental section).
1 was identified as strictosidinic acid by comparing
its data with those of published values [6].
Compound 2 was isolated as an amorphous solid. The
high-resolution electrospray mass spectrum
(HRESI/MS) showed a [M+H] + peak at an exact
mass of m/z 531.2344 corresponding to the formula
C 27 H 35 N 2 O 9 , suggesting the presence of an additional
methyl group when compared to compound 1. A
careful analysis of 1 H, 13 C and 2D NMR data
indicated the presence of an open secologanin unit.
As observed for compound 1, the 1 H NMR spectrum
showed the presence of four signals at δ H 8.17 (H-9,
J = 7.81 Hz), 7.20 (H-10, J = 7.33 and 7.81 Hz), 7.50
(H-11, 7.33 and 7.81 Hz), 7.56 (H-12, J = 7.82 Hz),
attributed to the aromatic protons of the indole
moiety. However, the presence of two doublets at δ H
7.93 (H-6, J = 4.8 Hz) and 8.23 (H-5, J = 4.8 Hz)
indicated the presence of a double bond between the
carbons H-6 and H-5. Analysis of the COSY and the
HMBC spectra for the remainder of the molecule
suggested the presence of a secologanin unit. All the
same, careful analysis of these data revealed some
differences when compared with 1. The HMBC
spectrum showed correlations between the signal at
δ H 1.00 and δ C 119 (C-18), 135 (C-19) and 96 (C-21)
suggesting the presence of a methyl group in position
C-20. These data indicated that the ring of the
secologanin was open. The attachment of the open
secologanin unit to the β-carboline skeleton was
ascertained from the HMBC spectrum. The
correlations between the methine proton at C-3
(δ H 3.11), and the carbon at C-15 (δ C 30.5) suggested
the attachment of the unit at C-3. These data led to
the structure of compound 2. The HMBC spectrum of
compound 2 showed correlations between the
anomeric proton at δ H 4.50 and the carbon at δ C 95.4,
suggesting the presence of a sugar moiety attached to
C-21. The 2D NMR experiments (COSY, HMBC
and HSQC) allowed the identification of the sugar as
β-glucose. Acid and enzymatic hydrolysis confirmed
the presence of β-D-glucose. These results pointed to
a new natural product named myrianthosine.
12
12
9
N
H
9
N
H
14
HOOC
14
6
3
HOOC
6
3
NH
NH
18
19
20 HO
21 O
1'
O
16
17
O
16
17
1
18
19
20
HO
21 O
2
1'
O
O
OH
OH
Figure 2: Structures of compounds 1 and 2.
OH
OH
OH
OH