Salvinorin C, a New Neoclerodane
Diterpene from a Bioactive Fraction of
the Hallucinogenic Mexican Mint Salvia
divinorum
Leander J. Valde´s III,*,?* Hui-Ming Chang,? Daniel C. Visger,§ and
Masato Koreeda*,§,^
UniVersity of Michigan Hospital, Pharmacy SerVices, Ann Arbor, Michigan 48109,
School of Pharmacy, Northeast Louisiana UniVersity, Monroe, Louisiana 71209,
and Departments of Chemistry and Medicinal Chemistry, UniVersity of Michigan,
Ann Arbor, Michigan 48109
[email protected]
Received September 26, 2001
ABSTRACT
Salvinorin C (1), a minor component from a biologically active TLC fraction, was isolated from the leaves of the Mexican mint Salvia divinorum.
Its structure was elucidated on the basis of extensive proton and C-13 NMR experiments, as well as by comparison of the NMR data with
those of the mono- and diacetate derivatives 5-7 of the major NaBH4-reduction product of salvinorin A (2).
As part of our continuing investigations1-6 of the psychotropic
Mexican labiate SalVia diVinorum (Epling & Jativa´-
M.), we report the isolation and structure of a new transneoclerodane
diterpene, salvinorin C (1). Previous studies
of the mint led to the isolation of salvinorins (divinorins) A
(2) and B (3),2,7 as well as the unambiguous determination
of their absolute stereochemistry6 by the use of the exciton
chirality circular dichroism method.8 Salvinorin A exhibits
activity paralleling that of mescaline, the prototype hallucinogen,
in the modified open field bioassay.2,5,9 Research
in humans has shown that, although essentially inactive when
taken orally, vaporizing and inhaling 200-500 ?g of
salvinorin A induces profound hallucinations.10 Salvinorin
A is the first diterpene to be identified as a hallucinogen in
humans and is one of the most potent naturally occurring
compounds thus far isolated.11 We have discussed the effects
of S. diVinorum and salvinorin A in animals and humans
?* University of Michigan Hospital.
? Northeast Louisiana University.
§ Department of Chemistry, University of Michigan.
^ Department of Medicinal Chemistry, University of Michigan.
(1) Valde´s, L. J., III; Dı´az, J. L.; Paul, A. G. J. Ethnopharmacol. 1983,
27, 287-312.
(2) Valde´s, L. J., III; Butler, W. M.; Hatfield, G. M.; Paul, A. G.;
Koreeda, M. J. Org. Chem. 1984, 49, 4716-4720.
(3) Valde´s, L. J., III. J. Nat. Prod. 1986, 49, 171.
(4) Valde´s, L. J., III; Hatfield, G. M.; Koreeda, M.; Paul, A. G. Econ.
Bot. 1987, 41, 283-291.
(5) Valde´s, L. J., III. J. PsychoactiVe Drugs 1994, 26, 277-283.
(6) Koreeda, M.; Brown, L.; Valdes, L. J., III. Chem Lett. 1990, 2015-
2018.
(7) Ortega, A.; Blount, J. F.; Marchand, P. S. J. Chem. Soc., Perkin Trans.
1 1982, 2505-2508.
(8) Harada, N.; Nakanishi, K. Circular Dichroic Spectroscopy-Exciton
Coupling in Organic Stereochemistry; University Science Books: Mill
Valley, CA, 1983.
(9) Valde´s, L. J., III. Ph.D. Dissertation, University of Michigan, Ann
Arbor, Michigan, 1983. See also: Brimblecombe, R. W.; Green, A. L.
Nature (London) 1962, 45, 983.
(10) Siebert, D. J. J. Ethnopharmacol. 1994, 43, 53-56.
(11) Schultes, R. E.; Hofmann, A. The Botany and Chemistry of
Hallucinogens; Charles, C., Ed.; Thomas Publisher: Springfield, IL, 1980.
ORGANIC
LETTERS
2001
Vol. 3, No. 24
3935-3937
10.1021/ol016820d CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/03/2001
and warned of their potential to become drugs of abuse.5
During our research on S. diVinorum, salvinorin A was first
isolated from a single pharmacologically active TLC band
using a solvent system of 100/10/1 CHCl3/MeOH/H2O.
Differences in potency between the purified diterpene and
the original TLC fraction led us to surmise that the latter
contained other strongly bioactive compounds that cochromatographed
with salvinorin A during the chromatographic
separation. Upon changing the solvent system to 1/1
hexanes/EtOAc, the minor component became separated
from salvinorin A. Even though it is estimated that salvinorin
C comprises only about 10% of the pharmacologically active
TLC fraction, the rest being salvinorin A, the fraction was
significantly more potent than an equivalent amount of
salvinorin A alone. This seems to indicate that the new
diterpene may also have strong psychotropic activity.
Air-dried, pulverized leaves (0.49 kg) of S. diVinorum were
extracted as before2 with ether, and salvinorins were isolated
by repeated flash column chromatography. Final purification
of salvinorin C was achieved by HPLC.12 Repeated recrystallization
from hexanes/EtOAc provided pure salvinorin C
(1)13 (38.5 mg): mp 196-198 °C, [R]22
D +49.3 (c 0.61,
CHCl3).
Salvinorin C (1) has the molecular formula C25H30O9, and
its IR spectrum suggests the presence of an R,??-unsaturated
ester (1715 cm-1), as well as another ester and a ?-lactone
(1755 and 1735 cm-1, respectively). Its complete structure
was elucidated by the use of 1H and 13C NMR spectroscopy.
NMR data were compared with those of salvinorin A (2)
and the acetate derivatives of the major product obtained by
the NaBH4-reduction of salvinorin A. Partial structures
deduced by the analysis of NMR data are indicated in
connecting thick lines (Figure 1). Although no splitting was
visible between H-1 and H-10 in the 1H NMR spectrum of
salvinorin C (J1,10 < 0.8 Hz), irradiation of the H-1 peaks
sharpened the H-10 singlet. In addition, at the same time
the H-3 peaks collapsed into a doublet, confirming the
presence of the W-shape coupling between H-1 and H-3 (J
) 1.4 Hz). The connectivity between the C-12 and the furan
group was established by the detection of the weak coupling
between H-12 and H-16 (4J12,16 ) 0.8 Hz).
In an effort to further ascertain the structure of salvinorin
C, salvinorin A (2) was reduced with NaBH4 in isopropyl
alcohol (35 °C, 2.5 h). As we reported earlier,2 the reaction
produced a 2.3:1 mixture of cis-diol 4 and its C-8 epimer14
in 87% combined yield. Attempts at directly forming the
1,2-diacetate from diol 4 proved virtually impossible with
Ac2O/pyridine, even at elevated temperatures, presumably
as a result of the severe steric hindrance of the 1R-OH
imposed by the two 1,3-diaxially juxtaposed methyl groups.
Instead, the formation of 2-monoacetate 62 was observed.
Therefore, in analogy to a similar situation encountered in
our study on forskolin,15 diol 4 was first treated with trimethyl
orthoacetate at 100 °C in the presence of a catalytic amount
of acetic acid. Immediate acid-catalyzed hydrolysis of the
resulting 1,2-cyclic orthoacetate provided 1-monoaceate 516
in 83% yield, consistent with the general observation on the
selective formation of the axial monoester of diols obtainable
upon acid hydrolysis of their cyclic ortho ester derivatives.17
Acetylation of 5 under standard conditions then afforded the
desired 1,2-diacetate 718 in 94% yield.
Comparison of the 13C NMR chemical shifts of salvinorin
C (1), monoacetates 5 and 6, and diacetate 7 (Table 1) gave
(12) A 10-?m Radial Pak Microporasil silica gel column (10 cm 8
mm id) eluted with an isocratic solvent mixture of 10% acetonitrile, 30%
methyl-tert-butyl ether, and 60% hexanes with a flow rate of 1.5 mL/min.
(13) Salvinorin C (1): IR (KBr) 3150, 2950, 2920, 2850, 1755, 1735,
1715, 1635, 1430, 1370, 1310, 1225, 1140, 1070, 1035, 955, 905, 870,
785, 765 cm-1; HRMS (EI) m/z calcd for C25H30O9 474.1890, found
474.1865.
(14) Data for the 8-epimer of diol 4: mp 234-235 °C (EtOH); [R]22
D
+8.8 (c 0.24, MeOH); 1H NMR (400 MHz, acetone-d6) ? 0.97 (d, 1H, J
) 1.1 Hz), 1.33 (s, 3H), 1.43 (ddd, 1H, J ) 13.7, 4.5, 3.9 Hz), 1.60 (ddd,
1H, J ) 13.7, 13.6, 5.0 Hz), 1.58-1.68 (m, 1H), 1.70 (s, 3H), 1.82 (dd,
1H, J ) 12.1, 11.6 Hz), 1.91 (dddd, 1H, J ) 13.6, 13.3, 4.7, 3.9 Hz), 2.03
(dddd, 1H, J ) 13.3, 5.0, 4.5, 1.9 Hz), 2.14 (dd, 1H, J ) 11.6, 1.9 Hz),
2.16 (dd, 1H, J ) 9.7, 1.9 Hz), 2.17 (ddd, 1H, J ) 12.0, 11.5, 9.7 Hz),
2.60 (dd, 1H, J ) 4.7, 1.9 Hz), 2.86 (s, 1H, 1-OH), 2.89 (s, 1H, 2-OH),
3.60 (ddd, 1H, J ) 11.5, 4.5, 2.3 Hz), 3.62 (s, 3H), 4.09 (dd, 1H, J ) 2.3,
1.1 Hz), 5.49 (ddd, 1H, J ) 12.1, 1.9, 1.2 Hz), 6.58 (dd, 1H, J ) 1.8, 0.7
Hz), 7.57 (dd, 1H, J ) 1.8, 1.7 Hz), 7.66 (ddd, 1H, J ) 1.7, 1.2, 0.7 Hz);
13C NMR (75 MHz, acetone-d6) ? 17.36 (q), 18.91 (t), 26.59 (q), 29.77 (t),
37.43 (s), 37.51 (s), 37.85 (t), 46.85 (d), 49.67 (t), 51.15 (q), 55.38 (d),
55.48 (d), 70.08 (d), 70.21 (d), 71.93 (d), 109.66 (d), 125.90 (s), 140.80
(s), 144.38 (d), 173.75 (s), 174.31 (s). Anal. Calcd for C21H28O7: C, 64.60;
H, 7.23. Found: C, 64.14; H, 7.18.
(15) Valdes, L. J., III.; Koreeda, M. J. Org. Chem. 1991, 56, 844-846.
Figure 1. Partial structures and their connectivity (bold lines)
established by 1H and 13C NMR spectroscopy.
3936 Org. Lett., Vol. 3, No. 24, 2001
further credence to the proposed structure of salvinorin C.
In addition, examination of the 1H NMR spectra of salvinorin
C (1) and diacetate 7 was informative in deducing the A-ring
stereochemistry of both compounds. A long-range W-type
coupling (1.2 Hz) was observed between the two equatorial
Hs at C-1 and C-3 in diacetate 7 as in the case of salvinorin
C (vide ante).
These salvinorin compounds from S. diVinorum closely
resemble a large number of neoclerodane diterpenes isolated
from Latin American SalVia plants.19 It would be interesting
to examine if any of those compounds also exhibit psychotropic
activity.
Acknowledgment. This work was supported in part by
research grants from the NIH (to M.K.) and the University
of Michigan College of Pharmacy (to L.J.V.).
OL016820D
(16) Data for 5: mp 206-209 °C (hexanes/EtOAc); [R]22
D +7.1 (c 0.70,
CHCl3); 1H NMR (400 MHz, CDCl3) ? 1.16 (s, 3H), 1.36 (s, 3H), 1.42
(ddd, 1H, J ) 13.9, 13.0, 3.6 Hz), 1.47 (d, 1H, J ) 1.7 Hz), 1.60 (dddd,
1H, J ) 14.1, 13.9, 12.1, 2.9 Hz), 1.62 (d, 1H, J ) 1.7 Hz), 1.72 (ddd, 1H,
J ) 13.0, 3.5, 2.9 Hz), 1.73 (dddd, 1H, J ) 13.0, 4.9, 2.8, 1.0 Hz), 1.90
(dd, 1H, J ) 13.2, 11.7 Hz), 2.00 (dddd, 1H, J ) 14.1, 3.6, 3.5, 3.2 Hz),
2.07 (s, 3H), 2.11 (ddd, 1H, J ) 13.2, 13.0, 12.1 Hz), 2.32 (dd, 1H, J )
13.2, 2.8 Hz), 2.35 (dd, 1H, J ) 12.1, 3.2 Hz), 2.48 (dd, 1H, J ) 13.2, 5.4
Hz), 3.64 (s, 1H, OH), 3.65 (s, 3H), 3.68 (ddd, 1H, J ) 12.1, 4.9, 1.7 Hz),
5.54 (dd, 1H, J ) 11.7, 5.4 Hz), 5.60 (ddd, 1H, J ) 1.7, 1.7, 1.0 Hz), 6.59
(dd, 1H, J ) 1.8, 0.8 Hz), 7.57 (dd, 1H, J ) 1.8, 1.5 Hz), 7.68 (ddd, 1H,
J ) 1.5, 0.8, 0.8 Hz). Anal. Calcd for C23H30O8: C, 63.58; H, 6.96.
Found: C, 63.42; H, 7.00.
(17) King, J. F.; Allbutt, A. D. Can. J. Chem. 1970, 48, 1754-1769.
(18) Data for 7: mp 211-214 °C (hexanes/EtOAc); [R]22
D -7.5 (c 0.81,
CHCl3); 1H NMR (400 MHz, acetone-d6) ? 1.16 (s, 3H), 1.38 (s, 3H), 1.50
(dddd, 1H, J ) 14.0, 12.8, 12.2, 2.6 Hz), 1.62 (d, 1H, J ) 1.7 Hz), 1.63
(ddd, 1H, J ) 13.0, 12.8, 3.2 Hz), 1.76 (dddd, 1H, J ) 12.9, 4.8, 2.8, 1.2
Hz), 1.78 (ddd, 1H, J ) 13.0, 3.2, 3.0 Hz), 1.90 (s, 3H), 1.94 (dd, 1H, J )
13.2, 11.7 Hz), 2.02 (dddd, 1H, J ) 14.0, 3.3, 3.2, 3.0 Hz), 2.14 (s, 3H),
2.23 (ddd, 1H, J ) 13.2, 12.9, 12.4 Hz), 2.32 (dd, 1H, J ) 13.2, 5.5 Hz),
2.40 (dd, 1H, J ) 12.2, 3.3 Hz), 2.45 (dd, 1H, J ) 13.2, 2.8 Hz), 3.67 (s,
3H), 4.81 (ddd, 1H, J ) 12.4, 4.8, 3.4 Hz), 5.56 (dd, 1H, J ) 11.7, 5.5
Hz), 5.68 (ddd, 1H, J ) 3.4, 1.7, 1.2 Hz), 6.58 (dd, 1H, J ) 1.8, 0.8 Hz),
7.56 (dd, 1H, J ) 1.8, 1.5 Hz), 7.66 (ddd, 1H, J ) 1.5, 0.8, 0.8 Hz). Anal.
Calcd for C25H32O9: C, 63.01; H, 6.77. Found: C, 62.87; H, 6.71.
(19) Rodriguez-Hahn, L.; Alvarado, G.; Ca´rdenas, J.; Esquivel, B.;
Gavin?o, R. Phytochemistry 1994, 35, 447-450 and references therein.
Table 1. NMR Data for 1 and 5-7 in CDCl3
a
salvinorin C (1)
?¸ ?C
1-OAc
5 ?C
2-OAc
6 ?C
diacetate
7 ?C
Divinorin A, a Psychotropic Terpenoid, and
Divinorin B f r o m the Hallucinogenic Mexican
Mint Salvia divinorum
Leander J. Valdes, III,*t William M. Butler,'
George M. Hatfield,' Ara G. Paul,' and Masato Koreeda**J
School of Pharmacy and Department of Chemistry, The
University of Michigan, Ann Arbor, Michigan 48109
Received January 31, 1983
While nonalkaloidal constituents have been implicated
as being at least partially responsible for the biological
School of Pharmacy.
t Department of Chemistry.
0022-326318411949-4716$01.50/0
activity of several hallucinogenic plants,2 little has been
reported on the structures of such possible hallucinogens.
The Mexican labiate Salvia divinorum (Epling and Jati-
va-M.) is used in divinatory rites by the Mazatec Indians
of Oaxaca, Mexico. An infusion prepared from the crushed
fresh leaves of this plant (known locally as sku Maria
Pastora) is used to induce "visions" and its psychotropic
effects have been verified by a number of researcher^.^
(1) Address correspondence to this author at the Department of
Chemistry.
(2) (a) Shultes, R. E.; Hofmann, A. "The Botany and Chemistry of
Hallucinogens"; Charles C. Thomas Publisher: Springfbld, IL, 1980; !2nd
ed. (b) Lewis, W. H.; Elvin-Lewis, M. P. F. In 'Medical Botany"; Wiley:
New York, 1977; Chapter 18. (c) Dim, J. L. Ann. Reu. Pharmacol.
Toxicol. 1977, 17, 647.
0 1984 American Chemical Society
Notes
(A) 6375 7.389
(dd, 092, 1.83) (dd, l.53.183)
- 2
I Y?.?.
J. Org. Chem., Vol. 49, No. 24, 1984 4717
(B)
C H j
20.53
'171.57
Figure 1. Divinorin A (1): (A) 360-MHz 'H NMR data in CDCl,, 6 values from (CHdSi [multiplicity and J values (in Hz) in parentheses];
(B) 90.56-MHz 13C NMR data in CDC13, S values from (CH3),S1; assignments are based on off-resonance, selective, and gated-selective
decoupling experiments and chemical shift comparisons with compounds 2-4 and model compounds.
Furthermore, upon administration of large doses of the
plant extract in animals, one observes behavioral patterns
that resemble the "intoxication" the infusion produces in
human beings. Despite previous investigations, the prin-
ciple(s) responsible for this biological activity has never
been identified.4 We now report the isolation and the
structures of the new neoclerodane diterpenes, divinorins
A and B from S. divinorum. Divinorin A, the first clearly
documented psychotropic terpenoid: exerts a sedative
effect on mice when tested in a bioassay based on a
modification of Hall's open field.6
Lyophilized, pulverized leaves (5.35 kg) of S. divinorum
were extracted with ether. The nonpolar components were
removed from the concentrated extract through partition
between hexanes and 90% aqueous methanol. The dried
methanolic fraction was crudely purified by silica gel flash
column chromatography' (hexanes-ethyl acetate, 2/ 1).
Further purification of the combined biologically active
fractions by additional silica gel flash column chroma-
tography (methylene chloride-methanol, 20/1) followed
by repeated recrystallization yielded pure divinorins A (1)
(1.2 g) and B (3) (50 mg).8
(3) (a) Wasson, R. G. Bot. Mus. Lea& Haruard Uniu. 1962,20,77.
(b) Hofmann, A. 'LSD: My Problem Child"; McGraw-Hill: New York,
1980, pp 127-144. (c) Valdes, L. J.; Dim, J. L.; Paul, A. G. J. Ethano-
pharmacol. 1983, 7, 287.
(4) (a) Hofmann, A. PZanta Medica 1964,12,341. (b) Diaz, J. L. In
'Etnofarmacologia de Plantas Alucinogenas Latinoamericanas"; Diaz, J.
L., Ed.; Centro Mexican0 de Estudioe en Farmaco-dependencia: Mexico
City, 1975; pp 149-152. Although it was reported that active fractions
reacted with Ludy Tenger reagent (a m d e d Dragendorffs reagent) and
possibly alkaloids, extensive work in our laboratory has shown that the
pharmacologically active extracts from S. diuinorum do not contain al-
kaloids, nor were we able to isolate any alkaloids from the plant itself.
(5) Infusions and tinctures of the green matter from Lagochilua in-
ebriana Bge. are described as having pharmacological activity exhibited
by hemostatic and sedative properties of a general nature that are in part
attributed to the spiro ether-containing labdane, lagochilin, which has
been ieoleted from the plant. However, details regarding activities of the
preparations and the diterpene itself are not available: (a) Abramov, M.
M.; Yaparova, S. A. J. Appl. Chem., USSR 1963,36,2471. (b) Chizhov,
0. S.; Kessenikh, A. V.; Yakolev, I. P.; Zolatorev, B. M.; Petukhov, V. A.
Tetrahedron Lett. 1969, 1361.
(6) Brimblecombe, R. W.; Green, A. L. Nature (London) 1962, 194,
983. The following is a summary of our modified bioassay: Mice were
dosed with various fractions of the extract and the ani" activities were
observed in the field, which consisted of a 3-ft. circle divided into squares.
Parameters measured were the numbers of squares entered (lines
crossed), rearing8 on the hind legs, and time spent immobile. Divinorin
A reduced all three measures of activity, resembling that of S. diuinorum
in human beings."
(7) Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923.
Divinorin A (l), mp 242-244 OC, [a]22D -45.3' (c 8.530,
CHC13), had the molecular formula Cz3HZ8o8. The UV
spectrum [211 nm ( E 5260)] was indicative of the presence
of the furan moiety. This was further corroborated by the
products from the hydrogenation reaction of divinorin A
which was accompanied by hydrogenolysis at C-12. Thus,
catalytic hydrogenation of divinorin A in methanol over
5% Pd/C provided quantitatively a stereoisomeric mixture
(at C-13) of hexahydro derivatives 4. Although it was
difficult to determine the presence of a ketone group from
the IR spectrum of divinorin A alone, as its carbonyl region
is strongly absorbed due to three other carbonyl func-
tionalities, the presence of a highly hindered ketone group
in divinorin A became evident from the results of its so-
dium borohydride reduction. The sodium borohydride
reduction of divinorin A was found to be extremely sluggish
at room temperature, presumably owing to the severe steric
crowding near the ketone located at C-1. However, re-
duction at higher temperatures produced the mixture of
2 (40%) and its stereoisomeric diol (40%). The latter
appears to be stereoisomeric at C-8 and/or C-9, which
evidently had resulted from its "base-promoted" C-8/C-9
cleavage followed by reclosure prior to the reduction. The
stereochemistry of the diol 2 was secured as identical with
that of divinorin A by its conversion to the latter via
acetylation with acetic anhydride/pyridine, at room tem-
perature, followed by oxidation with pyridinium chloro-
chromate. In contrast, the same sequence of the reactions
of the other diol gave a thus far undetermined stereoisomer
of divinorin A.
Both lH and 13C NMR spectra were particularly in-
formative since all lH and 13C signals could be observed
and assigned through extensive proton decoupling, off-
resonance decoupling, and selective decoupling experi-
ments. These provided partial structures which are in-
dicated in connecting thick lines and by solid blocks de-
noting quaternary carbons in Figure 1A. The linkage
between C-1 and C-10 was ascertained from the lH NMR
spectrum in acetone-d, of the diol 2, mp 218-220 "C, ob-
(8) Purified, recrystallized divinorin A has activity slightly stronger
than the original plant extract, whereas divinorin B was inactive in this
bioassay (this does not preclude the possibility of a different psychotropic
activity in the latter). The mother liquor from recrystallization contains
at least two more terpenoids in addition to these two divinorins. This
mixture shows substantially stronger activity, thus suggesting the pres-
ence of a minor component(s) that either synergistically enhances the
activity of divinorin A or has strong sedative properties in itself. Isolation
of these minor components and identifying their activities is currently
being pursued.
4718 J. Org. Chem., Vol. 49, No. 24, 1984 Notes
CH,OO~ CH3OOC
4 2 R I = H I R2=OH -
3 R I , R2.0
(divinorin B)
tained in 40% yield from divinorin A with sodium boro-
hydride in isopropyl alcohol at 35 "C for 2.5 h. Thus,
inspection of the coupling constants involving protons a t
C-10, C-1, and C-4 (Jlop,lp = 2.0 Hz, Jls,2a = 2.1 Hz, Jzp,ap
Hz) led t o the proposed structure 1 for divinorin A.
This structure was finally confirmed by a single-crystal
X-ray diffraction experiment. A perspective drawing of
the final X-ray model, less hydrogen atoms, is shown in
Figure 2. Details of the X-ray analysis are given in the
Experimental Section and bond lengths, angles, other
crystallographic parameters are provided as supplementary
information.
-3.39O (c 0.441,
EtOH), was found to be desacetyldivinorin A, which was
verified by its conversion into divinorin A via acetylation
with acetic anhydride in pyridine. The absolute configu-
rations are proposed based on the CD spectra (MeOH) of
divinorins A (1) (At294 -2.63) and B (3) -1.41) and
hexahydrodivinorin A (4) -1.67). While the absolute
configurations shown appear to be corroborated by the
negative n - T* Cotton effect of isofructicolone: the un-
ambiguous assignment of the absolute configurations of
the divinorins is yet t o be made.
Experimental Section
Microanalysis was performed by Spang Microanalytical Lab-
oratory, Eagle Harbor, MI. Melting points were taken on a Fisher
Johns melting point apparatus and are uncorrected. The ultra-
violet spectrum was determined on a Hewlett-Packard 8450A
UV/vis spectrophotometer. Infrared spectra were recorded on
a Perkin-Elmer Model 281 spectrometer as potassium bromide
(KBr) disks. Mass spectra were taken with a Finnigan Model
4023 GC/MS spectrometer. Nuclear magnetic resonance spectra
were obtained on a Bruker WM360 spectrometer (360 MHz for
'H and 90.56 MHz for 13C) in CDC1, unless otherwise stated and
all chemical shifts are reported in parts per million relative to
internal tetramethylsilane. Optical rotations were determined
on a Perkin-Elmer 241 polarimeter using a quartz cell of 10-cm
length and 1-mL volume. Circular dichroism spectra were re-
corded on a JASCO J-40A automatic recording spectropolarimeter
using a quartz cell of 20-mm length and 3.5-mL volume.
Collection, Extraction, and Isolation. Live specimens of
S. divinorum were collected at Cerro Quemado (Sept 3,1979) and
Cerro Rabon (March 7, 1980) in Oaxaca, Mexico. The plants were
cultivated at the Matthaei Botanical Gardens, The University
of Michigan, in order to provide material for research.
Fresh Salvia leaves (5.350 kg) were lyophilized and forced
through 7- and 16-mesh screens yielding 674.1 g of powdered dry
material. The powder was extracted in 30-40-g lots for 24 h with
ethyl ether (1 L/lot) using a Soxhlet apparatus and dried in vacuo,
giving a total of 27.51 g of ether extract. The extract was par-
titioned between hexanes (600 mL) and 90% aqueous methanol
(600 mL) for 48 h using a liquid/liquid extractor and yielded, after
= 4.9 Hz, J2p,3a = 11.4 Hz, J3p,4p = 2.1 Hz, and J3a,4p = 13.2
Divinorin B (3), mp 213-216 O C ,
Figure 2. Computer-generated perspective drawing of divinorin
A (1) with crystallographic numbering scheme.
removal of the solvent in vacuo, a 7.41-g methanol fraction. The
hexane fraction was repartitioned as above and the combined
concentrated methanol fractions (9.36 g) were subjected to further
purification by flash column chromatography.
In a typical experiment, a Fischer Porter 2.5 X 25 cm column
containing 55 g of silica gel (70-230 mesh), which had been treated
with 2.75 mL of water, was equilibrated with the eluting solvent,
hexanes/ethyl acetate (2/ 1). Fivehundred milligrams of the
methanolic fraction was adsorbed on 5 g of silica gel and carefully
poured on the preequilibrated column. The eluting solvent was
then forced (using nitrogen pressure) through the column at the
flow rate of 25-35 mL/min and 100-mL fractions were collected.
Each fraction was followed by bioassay, and fractions 4-9 were
determined to be active. The 9.36 g of methanolic fraction yielded
2.349 g of desired crude material. The material recovered was
further purified by using another flash column chromatography.
Fivehundred milligrams of the crudely purified methanol fraction,
adsorbed on 5 g of silica gel, was added to the top of the 2.5 X
25 cm Fischer Porter column containing 55 g of silica gel which
had been treated with 2.75 mL of water and preequilibrated with
the eluting solvent, methylene chloride/methanl (20/ 1). The
column was eluted at a rate of 25-35 mL/min with the aid of 5
psi of nitrogen pressure, and 25-mL fractions were collected. The
biologically active fractions (fractions 3-5) were combined. The
2.349 g of starting material gave 1.515 g of impure diterpene
mixture from which pure divinorin A (893 mg) was obtained after
two recrystallizations from absolute ethanol. The combined
mother liquors were subjected to preparative TLC purification
(Merck GF-254, 15 X 1 mm plate, 20 X 20 cm, developed with
CHCl3/MeOH/HZ0, 100/10/1), which gave more divinorin A (305
mg; R, 0.63) and crude divinorin B. The crude divinorin B was
further purified by two recrystallizations from methanol, yielding
50 mg of divinorin B (Rf 0.48). Divinorin A (1): mp 242-244
"C; [alZzD -45.3" (c 8.530, CHC1,); UV (MeOH) 211 nm ( e 5260);
IR (KBr) 3220, 1745, 1735, 1240, 875 cm-'; NMR (lH and 13C)
see Figure 1; mass spectrum (EI; 70 eV), m / z 432 (M', 1.5), 273
(6.5), 166 (8.6), 121 (13.0), 108 (8.0), 107 (9.7), 95 (17.9), 94 (loo),
93 (9.9), 91 (6.9), 81 (11.2), 79 (5.5), 55 (13.7); CD (MeOH)
-2.63. Anal. Calcd for C23Hz8O8: C, 63.89; H, 6.48; 0, 29.63.
Found C, 63.44; H, 6.61; 0,30.14. Divinorin B (3): mp 213-216
"C; [ C Y ] ~ D -3.39" (c 0.441, EtOH); IR (KBr) 3495,3140,1735,1715,
1250,860 cm-'; 'H NMR (360 MHz) 6 1.101 (s, 3 H, 19-H), 1.484
(s, 3 H, 20-H), 1.50-1.65 (m, 3 H, 7-Hs and 11/3-H), 1.797 (ddd,
1 H, J = 2.7, 3.1, 12.9 Hz, 6a-H), 2.020 (ddd, 1 H, J = 11.4, 13.5,
13.6 Hz, ~ c Y - H ) , 2.074 (dd, 1 H, J = 2.0, 11.7 Hz, 8-H), 2.169 (9,
1 H, 10-H), 2.17 (m, 1 H, 68-H), 2.480 (ddd, 1 H, J = 3.1,7.7, 13.6
(9) Mhinez-Ripoll, M.; Fayos, J.; Rodriguez, B,; Garcia-Alvarez, M. Hz, 3b-H), 2.548 (dd, H, = 5*27 13.4 Hz, 2'709 (dd,
C.; Savona, G.; Piozzi, F.; Paternostro, M.; Hanson, J. R. J. Chem. SOC.,
Perkin Trans. 1 1981, 1186.
1 H, J = 3.1, 13.5, 4-H), 3.599 (d, 1 H, J = 3.3 Hz, OH), 3.717 (s,
3 H, COOMe), 4.080 (ddd, 1 H, J = 3.3, 7.7, 11.4 Hz, 2-H), 5.567
Notes J . Org. Chem., Vol. 49, No. 24, 1984 4719
dried over sodium sulfate, and evaporated in vacuo. The crude
mixture (35 mg) was purified via flash column chromatography
(50 g of 230-400 mesh silica gel; eluted with hexanes/ethyl acetate
(1/1)), providing 21 mg of diol 3 2-monoacetate along with 2 mg
of the starting diol 3. Diol 3 2-monoacetate: IR (KBr) 3600,
1740,1735,1240 cm-'; 'H NMR (360 MHz) 6 1.002 (s, 1 H, lO-H),
1.390 (s, 3 H), 1.458 (s, 3 H), 2.096 (s, 3 H, OAc), 3.677 (s, 3 H,
COOMe), 4.292 (br s, 1 H, 1-H), 4.696 (ddd, 1 H, J = 3.2,4.6,11.7
Hz, 3-H); 13C NMR (90.56 MHz) 6 16.81, 17.90,18.72, 21.07, 24.90,
36.96, 37.87, 40.66, 51.43, 52.58, 55.00, 55.88, 67.36, 71.75, 74.60,
108.47, 125.91, 139.39, 143.78, 169.61, 171.68, 172.44.
The diol 3 2-monoacetate (19 mg), dissolved in 5 mL of
methylene chloride, was placed in a 25-mL round bottomed flask
and treated with 53 mg of PCC in 5 mL of methylene chloride
at room temperature. After 30 h, the reaction mixture was diluted
with 50 mL of ether. The ether layer was recovered by decantation
and the dark residue was extracted with 10 mL of ether. The
combined ether layers were dried over sodium sulfate and the
organic solvents removed in vacuo. The crude reaction products
(20 mg) were purified via flash column chromatography (55 g of
Merck silica gel, 230-400 mesh; eluted with hexane/EtOAc (3/2)
which yielded 10 mg of divinorin A (1) and 5 mg of diol 3 2-
monoacetate.
Acetylation of Divinorin B (2). Divinorin B (10 mg) dis-
solved in 5 mL of dry pyridine and placed in a 10-mL round
bottomed flask, was treated with 0.5 mL of acetic anhydride at
room temperature. The mixture was stirred for 6 h at that
temperature. The reaction was terminated by addition of 1 mL
of methanol and the mixture poured into ice water (50 mL). The
resulting precipitates were collected by filtration, washed thor-
oughly with water, and dried in vacuo. The crude product was
recrystallized from absolute ethanol and found identical with
divinorin A.
X-ray Crystallographic Analysis of Divinorin A (1).
Crystals of divinorin A were obtained by slow cooling of a satu-
rated ethanolic solution. A crystal of dimensions 0.078 X 0.269
x 0.418 mm was mounted on a Syntex P2, diffractometer and
found to have the space group P2,2,2, with a = 6.369 (2) A, b =
11.366 (4) A, and c = 30.747 (12) A. The density was calculated
to be 1.29 g/cc for 2 = 4. Intensity data were obtained using Mo
Ka radiation monochromatized by means of a graphite crystal
whose diffraction vedor was perpendicular to the diffraction vector
of the sample. A total of 2494 reflections with 20 < 50" were
measured, of which 1376 were considered observed [ I > 3u(I)].
The data were reduced by procedures previously used.l0 The
structure was solved using MULTAN~E. Hydrogen atomic positions
were calculated and added to the structure. They were given
isotropic temperature factors one unit greater than the atom to
which they are attached and their positions were not refined.
Standard techniques were used to refine the structure to R1 =
0.087 and R2 = 0.092.
Note Added in Proof. After the original submission of
the manuscript, we learned that Ortega et al. reported the
structure of salvinorin which is identical with that of di-
vinorin A described herein (Ortega, A.; Blount, J. F.;
Manchand, P. S. J. Chem. SOC., Perkin Trans. 1 1982,
2505). Therefore, divinorins A and B should be called
salvinorins A and B, respectively.
Acknowledgment. We are greateful t o the National
Science Foundation and the University of Michigan for
their contributions to the purchase of a Bruker 360-MHz
NMR and Finnigan 4023 GC/MS spectrometer. L.J.V.
is grateful for a Lilly Endowment Fellowship in Pharmacy
during the course of this work.
Registry No. 1, 83729-01-5; 2, 92545-29-4; 3, 92545-30-7; 4,
Supplementary Material Available: Final positional pa-
rameters with estimated standard derivations are shown in Table
I; anisotropic thermal parameters with their standard deviations
92545-31-8.
(dd, 1 H, J = 5.1, 11.7 Hz, 12-H), 6.376 (dd, 1 H, J = 0.92, 1.8
Hz, 14-H), 7.399 (dd, 1 H, J = 1.5, 1.8 Hz, 15-H), 7.416 (dd, 1 H,
J L- 0.92, 1.5 Hz, 16-H); 13C NMR (C&,N; 90.56 MHz) 6 15.35
(q), 16.49 (q), 18.89 (t), 35.82 (t), 38.31 (s), 42.44 (s), 43.53 (t), 51.22
(d), 51.51 (q), 53.62 (d), 63.18 (d), 71.99 (d), 75.27 (d), 109.31 (d),
126.64 (s), 140.26 (d), 144.15 (d), 171.38 (s), 172.59 (s), 209.79 (s)
ppm; CD (MeOH) Aczw -1.41.
Hexahydrodivinorin A (4). A mixture of 150 mg of divinorin
A (1) in 100 mL of methanol and 162 mg of 5% palladium on
charcoal in a 125-mL round bottomed flask was hydrogenated
at room temperature under a slightly positive pressure for 24 h.
The catalyst was removed by filtration and the solvent removed
in vacuo. The residual oil was dissolved in 25 mL of methylene
chloride and extracted 3 times with 5mL portions of 1% NaHC03
in HzO. The combined aqueous layers were acidified to pH 1.0
with concentrated HC1 and extracted 3 times with 5-mL portions
of methylene chloride. The organic fraction was taken to dryness
in vacuo and the crude oily product was recrystallized from
ethanol-water to provide pure hexahydrodivinorin A (4) (143 mg):
mp 196-198 "C; IR (KBr) 3100,1755,1735,1725,1225 cm-'; 'H
NMR (360 MHz) b 1.033 (8, 3 H), 1.340 and 1.345 (both s, total
3 H), 2.137 and 2.139 (both s, total 3 H), 3.686 (8, 3 H); 13C NMR
(90.56 MHz) 6 15.99 (q), 19.71/19.74* (q), 20.48 (q), 21.26 (t),
27.19/27.27* (t), 31.33 (t), 32.10/32.22* (t), 38.10 and 38.29
(multiplicities not certain due to overlap), 38.19 (s), 38.37 (t),
39.56/39.63* (d), 42.91*/42.92 (e), 49.05*/49.08 (d), 51.71 (q),
54.02*/54.15 (d), 58.67*/58.79 (d), 67.84 (t), 73.31*/73.37 (t),
75.44*/75.45 (d), 169.61 (s), 171.65 (s), 177.26*/177.49 (s),
202.08/202.10* (s) (the paired chemical shifts represent those of
spectroscopically resolved diastereomers, and the ones with as-
terisks indicate the more intense 13C peaks between the two
paired); mass spectrum (CI; CH,), m/z (relative intensity) 467
(12), 440 (22), 439 (M + H+; 100); 437 (ll), 422 (15), 421 (681,167
(6), 104 (17), 99 (8),97 (61, 95 (7),85 (9); CD (MeOH) Aem6 -1.67.
Sodium Borohydride Reduction of Divinorin A. Divinorin
A (1; 260 mg) was dissolved in 120 mL of isopropyl alcohol in a
200-mL round bottomed flask and was treated with 14 mg of
sodium borohydride. The mixture was warmed up to 33-35 "C
and was kept at that temperature for 2.5 h. The reaction was
terminated by addition of 3 mL of methanol. The solvent was
removed under vacuum and the dried crude products were re-
dissolved in 50 mL of chloroform and washed with 50 mL of 1 %
HC1 and twice with 50-mL portions of water. The organic fraction
was dried over sodium sulfate and taken to dryness (255 mg). The
crude mixture was p d i e d through flash column chromatography
on silica gel (230-400 mesh; 30 g) using hexanes/ethyl acetate
(1/2) as the eluting solvents. The more polar diol (2; 124 mg)
was recovered along with the less polar, thus far unidentified
stereoisomeric diol (120 mg; mp 234-235 "C). Diol 2 mp 218-220
"C; [aIBD +1.16" (c 1.55, EtOH); IR (KBr) 3505,1725,1705 cm-';
'H NMR (acetone-&; 360 MHz) 6 1.163 (s, 1 H, 10-H), 1.375 (s,
3 H), 1.438 (s, 3 H), 1.56-1.62 (m, 4 H, 3@H, 6-H's and 7a-H),
1.799 (dd, 1 H, J = 11.9, 13.2 Hz, llP-H), 1.964 (dddd, 1 H, J =
3.3,3.3,3.5, 13.8 Hz, 7@-H), 2.109 (ddd, 1 H, J = 11.4, 12.7, 13.2
Hz, 3a-H), 2.203 (dd, 1 H, J = 2.1,13.2 Hz, 4-H), 2.294 (dd, 1 H,
J = 3.3, 12.3 Hz, 8-H), 2.494 (dd, 1 H, J = 5.6,13.2 Hz, lla-H),
3.358 (br s, 1 H, 1-OH), 3.553 (dddd, 1 H, J = 2.0,4.9, 5.4, 11.4
Hz, 2-H), 3.623 (s, 3 H, COOMe), 4.027 (d, 1 H , J = 5.4 Hz, 2-OH),
4.207 (br s, 1 H, 1-H), 5.594 (dd, 1 H, J = 5.6, 11.9 Hz, 12-H),
1.8 Hz, 15-H), 7.650 (dd, 1 H, J = 0.7, 1.6 Hz, 16-H); 13C NMR
(acetone-d6; 90.56 MHz) 6 17.02 (q), 18.07 (q), 19.71 (t), 29.39 (t),
37.39 (s), 38.50 (s), 41.22 (t), 44.75 (t), 51.24 (q), 52.79 (a), 55.81
(d), 56.05 (d), 69.69 (d), 72.12 (d), 72.33 (d), 109.70 (d), 127.74
(s), 140.62 (d), 144.52 (d), 172.12 (s), 173.75 (s); mass spectrum
(CI; CH4), m/z (relative intensity) 421 (7), 394 (21), 393 (M +
H', loo), 375 (74), 357 (78), 343 (87).
Conversion of Diol 3 to Divinorin A (1). The diol 3 (25 mg)
was dissolved in 7 mL of dry pyridine, placed in a 25-mL round
bottomed flask, and treated with 1 mL of acetic anhydride. After
being stirred at room temperature for 5 h, the reaction was ter-
minated by addition of 1 mL of methanol. The mixture was
poured into ice water (50 mL), its pH was adjusted to -10 by
addition of aqueous NH40H and it was extracted twice with
60-mL portions of chloroform. The combined organic layers were
washed with 25 mL of 10% aqueous HCl and then 25 mL of water,
6.593 (dd, 1 H, J = 0.7, 1.8 Hz, 14-H), 7.556 (dd, 1 H, J = 1.6,
(IO) Butler, W. M.; Tanaka, Y.; Koreeda, M. J. Org. Chem. 1981,46,
4620.
4720 J. Org. Chem. 1984,49, 4720-4721
are listed in Table 11; Table I11 lists the crystallographically
determined bond distances and angles (Tables 1-11) (listings of
observed and calculated structure factors amplitudes are available
from the authors); a figure which shows a computer-generated
stereodrawing with anisotropic thermal ellipsoids of the compound
(5 pages). Ordering information is given on any current masthead
page.
Preparation of cy-Fluoro Enolates and Their Use
in the Directed Aldol Reaction
John T. Welch,* Karl Seper, Seetha Eswarakrishnan, and
Janet Samartino
Department of Chemistry, State University of New York at
Albany, Albany, New York 12222
Received April 4, 1984
Although the directed aldol reaction has been the subject
of much investigation,l surprisingly little has been reported
about the stereochemistry of a-heteroatom substituted
enolates and their utilization in directed aldol reactions.
The stereoselective formation of olefins by the aldol
products of silyl-substituted enolates2 on warming has
engendered speculation that formation of the aldol product
is itself diastereoselective.2d Stereoselectively formed
a-amino en~latesl*,~ may react with high diastereoselec-
t i ~ i t y . ~ In contrast, neither the stereochemistry of mo-
nohalogenated enolates6 nor their diastereoselectivity in
aldol reactions has been reported.
Results and Discussion
We have found that the lithium enolate of ethyl fluor-
oacetate may be readily prepared and efficiently utilized
in the directed aldol reaction6 (Table I). The utility of
the fluoroacetate residue in compounds such as y-fluoro-
glutamic acid or fluorocitric acid in discerning biochemical
pathways has been limited by the difficulty of constructing
the fluorinated molecules. We are currently exploring the
use of this anion in the stereoselective synthesis of such
specifically fluorinated natural products, where substitu-
tion by fluorine has a little steric effect but a pronounced
electronic effect on the properties of the molecule. Much
early work has been reported on the use of ethyl fluoro-
acetate in synthesis but with no indication of stereochem-
istry and often under conditions where the fluorohydrin
would not survive.' Previously ethyl bromofluoroacetate,
(1) (a) Evans, D. A; Nelson, J. V.; Taber, T. R. Top. Stereochem. 1982,
13,l-115. (b) Mukaiyama, T. Org. React. (N.Y.) 1982,28,203-331. (c)
Mukaiyama, T. Pure Appl. Chem. 1983,55,1749-1758. (d) Heathcock,
C. H. In "Comprehensive Carbanion Chemistry"; Buncel, E., Durst, T.,
Eds.; Elsevier: Amsterdam, 1984; Part B, Chapter 4.
(2) (a) Shimoji, K.; Taguchi, H.; Oshima, K.; Yamamoto, H.; Nozaki,
H. J. Am. Chem. SOC. 1974,96,1620-1621. (b) Hartzell, S. L.; Rathke,
M. W. Tetrahedron. Lett. 1976,2757-2760. (c) Larson, G. L.; Quiroz, F.;
Suarez, J. Synth. Commun. 1983, 13, 833-844. (d) Larcheeveque, M.;
Debal, A. J. Chem. SOC., Chem. Commun. 1981, 877-879.
(3) Garst, M. E.; Bonfiglio, J. N.; Grudoski, D. A.; Marks, J. J . Org.
Chem. 1980,45, 2307-2315.
(4) Shanzer, A.; Somekh, L. Butina, D. J . Org. Chem. 1979, 44,
(5) (a) House, H. 0.; Fischer, W. F.; Gd, M.; McLaughlin, T. E.; Peet,
N. P. J. Org. Chem. 1971,36,3429-3437. (b) Kowalski, C.; Creary, X.;
Rollin, A. J.; Burke, M. C. J. Org. Chem. 1978,43, 2601-2608.
(6) Ethyl fluoroacetate is extremely poisonous, causing convulsions,
and ventricular fibrillation. It was only handled by using syringe tech-
niques in an efficient fume hood.
(7) (a) Bergmann, E. D.; Cohen, S.; Shahak, I. J. Chem. SOC. 1955,
2190-2193. (b) Bergmann, E. D.; Cohen, S.; Shahak, I. J. Chem. SOC.
1959,3278-3285. (c) Bergmann, E. D.; Schwarcz, J. J. Chem. SOC. 1956,
1524-1527. (d) Bergmann, E. D.; Szinai, S. J. Chem. SOC. 1956,
1521-1524. (e) Bergmann, E. D.; Cohen, S.; Shahak, I. J. Chem. SOC.
1959, 3286-3289. (0 Bergmann, E. D.; Chun-Hsu, L. Synthesis 1973,
44-56. (9) Bergmann, E. D.; Cohen, S. J. Chem. SOC. 1961, 3537-3538.
(h) Kent, P. W.; Barnett, J. E. G. J. Chem. SOC. 1964, 2497-2500.
3967-3969.
Scheme I
0
1
0
EtO; b H 3
Scheme I1
E
LiO-F
EtOAH
_c
F
2
in a Reformatsky reaction, and the lithium enolate of
tert-butyl fluoroacetate were used in the preparation of
fluorocitrate8 and fluorohomocitric acid: respectively. In
both reports, difficulty in the preparation of the lithium
enolate of ethyl fluoroacetate or very low yields in the
attempted directed aldol reaction of the lithium enolate
were described. For the introduction of the fluoroacetate
residue, commercially available ethyl fluoroacetate where
the ester function can be easily manipulated further is the
reagent of choice.
In contrast to the low yields of aldol product reported
upon enolate formation with lithium diisopropylamide
(LDA) at -78 "C in the presence of 1 equiv of hexa-
methylphosphoric triamide (HMPA), generation of the
enolate with lithium hexamethyldisilazide (LHMDS) at
-78 "C resulted in consistently higher yields of aldol
products (eq 1 and 2). Furthermore it was observed that
CH2FC02CH2CH3 + LHMDS - LiCHFC02CH2CH3
(1)
RR'COHCHFCO2CH2CH3 (2)
LiCHFC02CH2CH3 + RR'CO -
generation of the base with methyllithium-lithium brom-
ide complex in diethyl ether resulted in higher yields than
when the base was isolated in the conventional manner.'O
Success in the generation of the enolate with LHMDS led
to our reexamination of the reaction with LDA. Compa-
rable yields of aldol products were isolated when the
enolate was formed with LDA at -105 "C in the presence
of HMPA. The enolate may be trapped with chlorotri-
methylsilane to form the corresponding silyl enol ether (eq
3). The ratio of the E:Z enolate was found to be 1:l by
LiCHFCO2CH2CH3 + (CH3)3SiC1 - CHF=C(OCH,CH,)(OSi(CH,),) (3)
'H NMR spectroscopy.l' Not unexpectedly, the enol silyl
ether-fluoroketene acetal was observed to decompose
(8) Brandiilnge, S.; Dahlman, 0.; Morch, L. J. Am. Chem. Soc. 1981,
(9) Molines, H.; Massoudi, M. H.; Cantacuzene, D.; Wakselman, C.
(10) Rathke, M. W. J. Am. Chem. SOC. 1970,92, 3222-3223.
(11) Chemical shifts are reported in ppm from Me,Si in carbon tet-
103, 4452-4458.
Synthesis 1983, 322-324.
rachloride solution: 6.2, JH,F = 77 Hz; 6.32, JH,F = 74 Hz.
0022-3263/84/1949-4720$01.50/0 0 1984 American Chemical Society