2532
Short Reports
Table 1. 1H and a3C chemical shifts (ppm) of flavonoid glucoside malonates and acetates in DMSO-d6 at room temperature
Malonyl
CH_2
Malony]
Acetyl
Glucosyl carbon
Compound
CH_3CO HOO_C _CH2 COOR CH3 _COOR
1
2
3
4
5
6
KGMal (1)
KGAc
QGMal (2)
QGAc
3.04
3.11
167.6
167.5
41.1 166.4
......
40.9 166.3
.......
20.0 169.6
....
101A
100.9
101.0
100.8
73.8 76.0 69.4 73.8 63.4
73.7 76.0 69.7 73.9 62.6
73.9 76.1 69.5 73.9 63.5
73.8 76.1 69.7 73.8 62.6
1.74
1.69
20.0 169.7
169.3
170.0
--
63.6
7Z9 76.0 69.6 73.8
62.6
AGMal (3)
AGAc
3.32
.....
*
br
........
99.4
99.4
2.00
20.4 169.9
72.9 76.0 69.6 73.7 63.2
Abbreviations: KGMal=kaempferol 3-fl-D-glucoside 6"-malonate; KGAc=kaempferol 3-fl-D-glucoside 6"-acetate; QGMal
=quercetin 3-fl-D-glucoside 6"-malonate; QGAc=quercet!n 3-fl-o-glucoside 6"-acetate; AGMal=apigenin 7-fl-o-glucoside 6"-
malonate; AGAc=apigenin 7-/~-D-glucoside 6"-acetate; R=glucosylflavonoid.
*Resonance overlapped by solvent signals.
of acetates and malonates it is conceivable that in some
instances the acetates will have arisen as artifacts during
the work-up procedures.
solvent the protons of the malonyl methylene group,
which is relatively acidic because of its situation between
carbonyl groups, exchange with deuterium, even at room
temperature.* In one experiment a sample of quercetin 3-
fl-D-glucoside 6"-malonate (2) in DMSO-d 6 D20 (93:7)
was kept at room temperature while its proton spectrum
was being observed. After 30 min the methylene signal
had decreased to about half and after 60 min to about a
quarter of its original height. (As expected, the methylene
signal began to show splitting as the exchange pro-
ceeded.) The sample was kept for an additional 4 hr,
following which the 13C spectrum was determined. This
was essentially identical to that of the original compound
except for the absence of the methylene peak at 640.9.
Similar results were obtained with kaempferol 3-fl-D-
glucoside 6"-malonate (1), though here the exchange was
more rapid [about 90% exchanged in 35 min in DMSO-
d6-D20 (24: 1)]; the addition of a drop of water to the
NMR tube caused partial restoration of the methylene
proton peak at 63.04. When the deuterated form of
compound 1 was heated at 95° it lost CO 2 and yielded
6,8-dideuteriokaempferol 3-fl-D-glucoside 6"-trideuter-
ioacetate as indicated by NMR and mass spectral data.
Proton-deuterium exchange in aromatic systems con-
taining meta-hydroxy groups has been observed pre-
viously [4].
EXPERIMENTAL
NMR spectra were determined at 60, 100 or 270MHz.
FABMS were determined in the positive ion mode using a
glycerol matrix and xenon as the fast atom beam {20 mA at 7 or
8 kV). Compounds 1-3 were isolated earlier from flowers of
Gerberajamesonii [5]. The potassium salt of 2 was isolated from
flowers of Heavenly Blue morning glory (lpomoea tricolor) (S.
Asen, unpublished data). FABMS: 589 [M + K] ~, 503 [M + K
-malonyl] +, 303 [quercetin + H] ~. 6,8-Dideuteriokaempferol
3-3-D-glucoside 6"-trideuterioacetate was isolated from
the exchange/decarboxylation reaction by evaporating
the solvent in a stream of N,. FABMS: 496 [M + HI ~
289 [dideuteriokaempferol +]-I]
Acknowledgement We thank Stephen Poling for the mass spec-
tral data.
REFERENCES
1. Markham, K. and Chari, V. M. (1982) in The Flavonoids:
Advances in Research (Harborne, J. B. and Mabry, T. J., eds),
p. 19. Chapman & Hall, London.
2. Cornuz, G., Wyler, H. and Lauterwein, J. (1981) Phytochem-
istry 20, 1461.
3. Feeny, P., Sachdev, K., Rosenberry, L. and Carter, M. (1988)
Phytochemistry 27, 3439.
4. Hand, E. S. and Horowitz, R. M. (1964) 3. Am. Chem. Soc. 86,
The experiments described here suggest that malonyl
derivatives require some care in handling. NMR spectral
measurements of newly isolated glycosides should be
carried out initially at room temperature and in the
absence of D20, methanol-d4 or other solvents contain-
ing exchangeable deuterium. The appearance of an acetyl
methyl signal as the compound is being heated is con-
firmation that the precursor is a malonyl derivative. If
plant extracts are found that contain corresponding pairs
2084.
5. Asen, S. (19841 Phytochemistry 23, 2523.
*The exchange has been observed earlier in pelargonidin 3-
malonylsophoroside dissolvedin D20/DCI [2] and in luteolin 7-
O-(6"-O-matonyl)-fl-D-glucopyranoside dissolved in pyridine-
d5/D20 [3].