Synthesis of salvinorin A analogues as opioid receptor probes

Article abstract of DOI:10.1021/np060094b

Several neoclerodanes, such as salvinorin A (1) and herkinorin (3), have recently been shown to possess opioid receptor activity in vitro and in vivo. To explore the structure-affinity relationships of this interesting class of compounds, we have synthesi

Full text of DOI:10.1021/np060094b

914
J. Nat. Prod. 2006, 69, 914-918
Synthesis of Salvinorin A Analogues as Opioid Receptor Probes
Kevin Tidgewell,† Wayne W. Harding,† Anthony Lozama,† Howard Cobb,† Kushal Shah,† Pavitra Kannan,†
Christina M. Dersch,‡ Damon Parrish,§ Jeffrey R. Deschamps,§ Richard B. Rothman,‡ and Thomas E. Prisinzano*,†
DiVision of Medicinal & Natural Products Chemistry, College of Pharmacy, The UniVersity of Iowa, Iowa City, Iowa 52242,
Clinical Psychopharmacology Section, IRP, NIDA, NIH, DHHS, Baltimore, Maryland 21224, and NaVal Research Laboratory,
4555 OVerlook AVenue, SW, Washington, D.C. 20735
ReceiVed March 3, 2006
Several neoclerodanes, such as salvinorin A (1) and herkinorin (3), have recently been shown to possess opioid receptor
activity in vitro and in vivo. To explore the structure-affinity relationships of this interesting class of compounds, we
have synthesized a series of analogues from 1 isolated from SalVia diVinorum. Here, we report the semisynthesis of
neoclerodane diterpenes and their structure-affinity relationships at opioid receptors. This work will allow the further
development of novel opioid receptor ligands.
SalVia diVinorum is a plant from the mint family that has been
used in the traditional spiritual practices by the Mazatec Indians of
Oaxaca, Mexico. Chewing fresh leaves or smoking dried leaves
will produce hallucinogenic-like experiences.1 These experiences
last for up to an hour and are reported to be potent and intense.2-5
These effects, however, appear to be different than other hal-
lucinogenic substances such as LSD or DOB. Recreational use of
S. diVinourm is increasing in part due to its availability for purchase
through the Internet.6
The main active constituent isolated from the leaves of S.
diVinorum is salvinorin A (1), a neoclerodane diterpene.7,8 Com-
pound 1 was found to be a potent and selective κ opioid receptor
(κOR) agonist.9-11 Interestingly, the pharmacology of 1 appears to
be different than other κ agonists.12 Recent work has shown that 1
decreases dopamine levels in the caudate putamen of mice and that
this effect is blocked by the κOR antagonist nor-binaltorphimine.13
A study has also shown that 1 dose dependently increases
immobility in the forced swim test, indicating that 1 has depressive-
like effects.14 Furthermore, 1 disrupts climbing behavior on an
inverted screen task.15 This study showed that there are differences
in the susceptibility of 1 and the standard κOR agonist U69,593 to
antagonism by nor-binaltorphimine. This finding also indicates that
1 may bind in a manner that is qualitatively different than traditional
κOR ligands.
Recently, we described the synthesis of several analogues of 1
that were found to be opioid receptor ligands.11 Among these
compounds described were analogues 2-4. Propionate 2 was found
to have approximately the same affinity for the κOR as 1 but was
less potent as an agonist. This work also identified herkinorin (3),
the first neoclerodane diterpene with µ opioid receptor affinity, and
WH-1-32 (4), an analogue slightly more potent than 1 as a κOR
agonist.11 Recently, methoxymethyl analogue 516 and carbamate
617 were identified as having affinity for κORs similar to 1.
Interestingly, 5 was found to be a full agonist more potent than 1,
and 6 is a partial agonist at κORs. These observations illustrate
that substitution at the C-2 position can have profound effects on
opioid receptor affinity and activity.
Recently, a model was proposed for the binding of 1 to the
κOR.18 This model was developed through the use of molecular
modeling and mutagenesis studies. However, the binding pocket
of salvinorin A will not be known until the structure of a κOR-1
complex is solved. Given the lack of these studies, other methods
are needed to elucidate the mode of binding. Here, we describe
our additional efforts to more fully understand the manner of the
high affinity of 1 for opioid receptors through structure-affinity
studies.
Results and Discussion
Synthesis. The synthesis of the salvinorin A analogues is outlined
in Scheme 1. Salvinorin B (7) was prepared from 1 that was isolated
from S. diVinorum and subjected to methanolysis under basic
conditions as described previously.19 The reaction of 7 with the
appropriate alkanoyl chloride and a catalytic amount of DMAP in
CH2Cl2 gave analogues 8a-8c in 68-74% yield.17 The coupling
of 7 with N-Boc glycine using a mixture of (benzotriazol-1-yloxy)-
tris(dimethylamino)phosphonium hexafluorophosphate (BOP), N-(3-
dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI),
and 1-hydroxybenzotriazole hydrate (HOBT) afforded ester 8d in
58% yield. Treatment of 7 with phenylacetyl chloride and hydro-
* To whom correspondence should be addressed. E-mail: thomas-
prisinzano@uiowa.edu. Tel: (319) 335-6920. Fax: (319) 335-8766.
† University of Iowa.
‡ IRP, NIDA, NIH, DHHS.
§ Naval Research Laboratory.
10.1021/np060094b CCC: $33.50
© 2006 American Chemical Society and American Society of Pharmacognosy
Published on Web 05/26/2006

Synthesis of SalVinorin A Analogues
Journal of Natural Products, 2006, Vol. 69, No. 6 915
Scheme 1a
a Reagents and conditions: (a) appropriate alkanoyl chloride, DMAP, CH2Cl2; (b) appropriate alkanoyl chloride, DMAP, CH2Cl2 or N-Boc glycine, BOP, EDCI,
HOBT, pyridine, CH2Cl2; (c) appropriate aroyl chloride, DMAP, CH2Cl2; (d) appropriate benzenesulfonyl chloride, DMAP, CH2Cl2.
cinnamoyl chloride afforded 9a and 9b, respectively. The reaction
Table 1. Binding Affinities of Salvinorin A Analogues at
Opioid Receptors Using [125I]IOXY as Radioligand23,24
of 7 with 2-bromo and 3-bromobenzoyl chloride afforded analogues
10a and 10b in 60 and 70% yield, respectively. Compound 10c
was synthesized as described previously.20 Similar conditions using
2-thiophenecarbonyl chloride afforded 10d in 60% yield. Finally,
the reaction of 7 with benzenesulfonyl chloride and 4-methylben-
zenesulfonyl chloride afforded 11a and 11b in 76 and 86% yield,
respectively.
Ki ( SD, nM
selectivity
µ/κ δ/κ
compound
µ
δ
κ
1a
>1000b
>1000b
12 ( 1
5790 ( 980
6690 ( 870
1170 ( 60
1.9 ( 0.2 >530 3050
1.8 ( 0.1 >560 2730
2a
3a
90 ( 2
0.13
12
4a
6820 ( 660 >10 000
2.3 ( 0.1 2750
>4000
1010
265
61
>100
>30
52
>100
>100
2
Biological Results. Analogues 8-11 were then evaluated for
affinity at opioid receptors using methodology previously described
(Table 1).21 As shown previously, 1 and 2 have approximately the
same affinity and selectivity for κ receptors.11 This indicated that
perhaps chain length might not play an important role. To further
explore the role of chain length, we synthesized chain-extended
analogues 8a-8c. Increasing the chain length by one carbon (8a)
had little effect on affinity for κORs compared to 2 (Ki ) 4 nM vs
Ki ) 1.8 nM). This modification also had little effect on affinity
for δORs (Ki ) 6690 nM vs Ki ) 4030 nM). However, affinity for
µORs was increased (Ki ) 520 nM vs Ki > 1000 nM). The further
extension of the carbon chain, 8b and 8c, generally decreased
affinity for κORs compared to 8a (Ki ) 15 nM and Ki ) 70 nM vs
Ki ) 4 nM). The additional chain length had little effect on affinity
for µ and δORs compared to 8a. The replacement of the acetoxy
group in 1 with a 2-tert-butoxycarbonylaminoacetoxy group (8d)
resulted in reduced affinity at κORs compared to 1 (Ki ) 90 nM
vs Ki ) 1.9 nM). This is interesting given the observation that
replacement of the acetoxy group in 1 with an 2-acetylaminoacetoxy
8a
8b
8c
8d
9a
9b
10a
10b
10c
10d
11a
11b
520 ( 50
310 ( 50
520 ( 80
4030 ( 250
3970 ( 270
4240 ( 290
4 ( 1
130
21
7
63
4
15 ( 2
70 ( 4
90 ( 10
290 ( 40
5660 ( 250 >10 000
1090 ( 90
280 ( 40
110 ( 10
110 ( 10
10 ( 1
10 ( 2
>10 000
220 ( 20
>10 000
9330 ( 1010 180 ( 10
2
>10 000
>10 000
90 ( 7
70 ( 7
1.2
1.6
1410 ( 80
1380 ( 130
>10 000
740 ( 40 0.01
260 ( 20 0.04
60 ( 6
50 ( 5
5
>150 >150
4 74
3720 ( 400
a Data from ref 11. b Partial inhibitor.
group abolishes affinity for κORs (Ki > 10 000 nM).17 This
difference is likely due to the different radioligands used ([3H]-
diprenorphine vs [125I]IOXY) or the additional steric bulk of the
tert-butoxycarbonyl moiety compared to the acetyl group.
Given the clear effects of chain length in the C-2 position on
affinity for opioid receptors, we synthesized 9a and 9b, analogues

916 Journal of Natural Products, 2006, Vol. 69, No. 6
Tidgewell et al.
affinity at κORs and enhanced affinity at µORs compared to 4. As
expected, this structural change reduced affinity at κORs compared
to 4 (Ki ) 60 nM vs Ki ) 2.3 nM). To our surprise, 11a had no
affinity for µORs (Ki > 10 000 nM). In addition, introduction of a
4-methyl group to 11a (11b) had no effect on κOR affinity (Ki )
50 nM vs Ki ) 60 nM) and increased affinity for δORs (Ki ) 3720
nM vs Ki > 10 000 nM) compared to 11a. This change, however,
increased affinity for µORs compared to 11a (Ki ) 220 nM vs Ki
> 10 000 nM). These changes, however, are not parallel to the
ester series. This indicates that the previous structure-activity
relationships (SAR) may not be applicable to the sulfonate series.
It also suggests that these two series are not binding in an identical
manner at either the µOR or κOR.
In conclusion, we have synthesized a series of neoclerodane
diterpenes (8-11) from 1 isolated from S. diVinorum. We have
shown that chain length in the C-2 position generally decreases
affinity for κORs and increases affinity to µORs. Substitution in
the 4-position of the benzene ring in 3 is best tolerated. Furthermore,
3 and mesylate 4 appear to bind in a different manner at both the
κOR and the µOR.
Experimental Section
General Experimental Procedures. Unless otherwise indicated, all
reagents were purchased from commercial suppliers and were used
without further purification. All melting points were determined on a
Thomas-Hoover capillary melting apparatus and are uncorrected. The
1H NMR and 13C NMR spectra were recorded at 300 MHz on a Bruker
Avance-300 spectrometer or on a Bruker AMX-600 spectrometer using
CDCl3 as solvent, δ values in ppm (TMS as internal standard), and J
(Hz) assignments of 1H resonance coupling. Thin-layer chromatography
(TLC) was performed on 0.25 mm Analtech GHLF silica gel plates.
Spots on TLC were visualized with vanillin/H2SO4 in EtOH. Column
chromatography was performed with silica gel (32-63 µm particle size)
from Bodman Industries (Atlanta, GA). Elemental analyses were
performed by Atlantic Microlabs, Norcross, GA. The systematic name
for salvinorin A (1) is (2S,4aR,6aR,7R,9S,10aS,10bR)-9-(acetyloxy)-
2-(furan-3-yl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho-
[2,1-c]pyran-7-carboxylic acid methyl ester.
Figure 1. Results from the X-ray analysis on 10c drawn from the
experimentally determined coordinates with thermal parameters at
20% probability.
of herkinorin 3. The introduction of a one carbon spacer between
the carbonyl and phenyl ring (9a) led to a decrease in affinity at
κORs compared to 3 (Ki ) 290 nM vs Ki ) 90 nM). This change
also resulted in a 90-fold decrease in affinity for µORs (Ki ) 1090
nM vs Ki ) 12 nM). The addition of a second methylene unit (9b)
increased affinity for µORs 4-fold compared to 9a (Ki ) 280 nM
vs Ki ) 1090 nM). This modification also increased affinity for
κORs (Ki ) 180 nM vs Ki ) 290 nM). Generally, however,
increasing the spacer between the carbonyl and phenyl ring
decreased affinity approximately 10-fold for δORs compared to 3.
After probing the spacer between the carbonyl and phenyl ring
in 3, we sought to explore the role of ring substitution on affinity
and selectivity for opioid receptors. Introduction of a bromo group
in the 2-position of the benzene ring in 3 (10a) had no effect on
κOR affinity (Ki ) 90 nM vs Ki ) 90 nM). The 2-bromo group,
however, decreased affinity for µORs 9-fold (Ki ) 110 nM vs Ki
) 12 nM). This modification decreased affinity for δORs compared
to 3 (Ki > 10 000 nM vs Ki ) 1170 nM) and thereby increased
selectivity for µ and κ receptors over δ receptors. Parallel effects
were seen at all three opioid receptors with 3-bromo analogue 10b.
The presence of a 4-bromo group (10c) decreased affinity for κORs
8-fold compared to 3 (Ki ) 740 nM vs Ki ) 90 nM). To our delight,
this modification had no effect on µ or δOR affinity (Ki ) 10 nM
vs Ki ) 12 nM and Ki ) 1410 nM vs Ki ) 1170 nM, respectively).
This result however is in contrast to previous reports. A previous
report indicated that 10c had no affinity (Ki > 10 000 nM) for any
opioid receptor.20 Given the large difference seen in our assay, we
sought to further confirm the absolute configuration of 10c using
a single-crystal X-ray diffraction study. Structural analysis was
carried out and the absolute stereochemistry of 10c was determined
using the Flack parameter22 and is as shown (Figure 1). Finally,
the bioisosteric replacement of the benzene ring with a 2-thiophene
(10d) was explored. Diterpene 10d reduced affinity for κORs 3-fold
compared to 3 (Ki ) 260 nM vs Ki ) 90 nM). This change,
however, had no effect on affinity for µ or δORs (Ki ) 10 nM vs
Ki ) 12 nM and Ki ) 1,380 nM vs Ki ) 1170 nM, respectively).
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(Butyryloxy)-2-(3-furanyl)-
dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho[2,1-c]pyran-
7-carboxylic Acid Methyl Ester (8a). A solution of 7 (60 mg, 0.15
mmol), butyryl chloride (75 µL, 0.72 mmol), and a catalytic amount
of DMAP in CH2Cl2 (40 mL) was stirred at room temperature for 12
h. The mixture was washed with 2 N HCl (2 × 30 mL), saturated
NaHCO3 (2 × 20 mL), and saturated NaCl (30 mL). The organic extract
was dried (Na2SO4) and filtered and the solvent removed in vacuo to
give the crude product as a pale yellow oil. The crude product was
purified by flash column chromatography (30-40% ethyl acetate/
hexanes) to afford 48 mg (68%) of 8a as a white solid: mp 158-160
°C; 1H NMR (CDCl3) δ 1.00 (3H, t, J ) 7.5); 1.14 (3H, s); 1.47 (3H,
s); 1.52-1.66 (3H, m); 1.68-1.76 (2H, m); 1.81 (1H, m); 2.10 (1H,
dd, J ) 2.7, 11.1); 2.16 (1H, m); 2.19 (1H, s); 2.27-2.34 (2H, m);
2.38-2.46 (2H, ddd, J ) 5.7, 7.5, 7.5); 2.52 (1H, dd, J ) 5.1, 13.5);
2.77 (1H, dd, J ) 9.3, 9.3); 3.74 (3H, s); 5.17 (1H, dd, J ) 10.2, 10.2);
5.54 (1H, dd, J ) 4.8, 11.4); 6.40 (1H, dd, J ) 0.9, 1.2), 7.40 (1H, m);
7.43 (1H, m); 13C NMR (CDCl3) δ 13.9, 15.4, 16.6, 18.4, 18.6, 31.1,
35.7, 36.0, 38.4, 42.3, 43.6, 51.6, 52.1, 53.8, 64.3, 72.2, 75.0, 108.6,
125.4, 139.7, 143.9, 171.3, 171.8, 172.8, 202.2; anal. C 64.94%, H
7.02%, O 27.63%, calcd for C25H32O8, C 65.20%, H 7.00%, O 27.79%.
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(Pentanoyloxy)-2-(3-furanyl)-
dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho[2,1-c]pyran-
7-carboxylic Acid Methyl Ester (8b). 8b was synthesized as described
for 8a from 7 using valeroyl chloride to afford 52 mg (74%) of 8b as
1
a white solid: mp 159-161 °C; H NMR (CDCl3) 0.94 (3H, t, J )
7.2); 1.13 (3H, s); 1.39 (3H, m); 1.46 (3H, s); 1.54-1.72 (7H, m);
1.80 (1H, 3.0, 9.9); 2.09 (1H, dd, J ) 2.7, 11.4); 2.14-2.21 (2H, m);
2.27-2.34 (2H, m); 2.44 (2H, dt, J ) 4.8, 7.4); 2.52 (1H, dd, J ) 4.8,
13.4); 2.77 (1H, t, J ) 8.4); 5.16 (1H, dd, J ) 10.2, 10.2); 5.53 (1H,
dd, J ) 5.1, 11.7); 6.39 (1H, dd, J ) 0.9, 1.8); 7.40 (1H, dd, J ) 1.8,
1.8); 7.42 (1H, dd, J ) 0.9, 1.8). 13C NMR (CDCl3) δ 13.9, 15.4, 16.6,
18.4, 22.4, 27.1, 31.1, 33.8, 35.7, 38.4, 42.3, 43.5, 51.6, 52.2, 53.8,
Given our previous finding that introduction of an aromatic group
to the C-2 position increased affinity for µ receptors,11 we
synthesized compounds 11a and 11b, analogues of WH-1-32 (4).
It was envisoned that replacement of the mesylate in 4 with a
benzenesulfonate (11a) would result in a compound with reduced

Synthesis of SalVinorin A Analogues
Journal of Natural Products, 2006, Vol. 69, No. 6 917
64.2, 72.2, 75.0, 108.6, 125.4, 139.7, 143.9, 171.4, 171.8, 173.0, 202.2;
anal. C 65.58%, H 7.27%, O 27.21%, calcd for C26H34O8, C 65.81%,
H 7.22%, O 26.97%.
ran-7-carboxylic Acid Methyl Ester (10a). 10a was synthesized as
described for 8a from 7 using 2-bromobenzoyl chloride to afforded 70
mg (60%) of 10a as a white solid: mp 189-191 °C; 1H NMR (CDCl3)
δ 1.15 (3H, s); 1.45 (3H, s); 1.59-1.67 (3H, m); 1.82 (1H, m); 2.11-
2.16 (2H, m); 2.35 (1H, s); 2.40-2.51 (3H, m); 2.86 (1H, dd, J ) 8.4,
8.4); 3.73 (3H, s); 5.40-5.50 (2H, m); 6.39 (1H, m); 7.34-7.42 (4H,
m); 7.69 (1H, dd, J ) 1.8, 7.4); 7.97 (1H, dd, J ) 2.4, 7.4); 13C NMR
(CDCl3) δ 15.4, 16.7, 18.4, 25.7, 31.0, 38.4, 42.4, 43.6, 51.6, 52.2,
53.8, 64.3, 72.3, 76.1, 108.6, 122.2, 125.4, 127.5, 131.1, 132.1, 133.3,
134.7, 139.7, 143.9, 165.1, 171.3, 171.7, 201.8; anal. C 58.46%, H
5.16%, O 22.07%, calcd for C28H29BrO8, C, 58.65%, H, 5.10%, O,
22.32%.
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(3-Bromobenzoyloxy)-2-(3-fura-
nyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho[2,1-c]py-
ran-7-carboxylic Acid Methyl Ester (10b). 10b was synthesized as
described for 8a from 7 using 3-bromobenzoyl chloride to afford 75
mg (70%) of 10b as a white solid: mp 195-199 °C; 1H NMR (CDCl3)
δ 1.17 (3H, s); 1.45 (3H, s); 1.28-1.69 (3H, m); 1.82 (1H, m); 2.10
(1H, dd, J ) 2.4, 11.1); 2.18 (1H, m); 2.29 (1H, s); 2.42-2.54 (3H,
m); 2.83 (1H, dd, J ) 6.3, 10.5); 3.75 (3H, s); 5.39 (1H, dd, J ) 9.0,
9.0); 5.52 (1H, dd, J ) 5.1, 11.7); 6.38 (1H, m); 7.32-7.42 (3H, m);
7.72 (1H, ddd, J ) 1.2, 1.8, 7.8); 8.01 (1H, ddd, J ) 1.2, 1.2, 7.8);
8.21 (1H, dd, J ) 1.8, 1.8); 13C NMR (CDCl3) δ 15.4, 16.7, 18.4,
31.1, 35.7, 38.4, 42.5, 43.7, 51.6, 52.3, 53.8, 64.4, 72.3, 76.0, 108.6,
122.8, 125.4, 128.7, 130.3, 131.2, 133.1, 136.7, 139.7, 143.9, 164.4,
171.3, 171.7, 201.7; anal. C 58.54%, H 5.18%, O 22.15%, calcd for
C28H29BrO8, C, 58.65%, H, 5.10%, O, 22.32%.
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(Hexanoyloxy)-2-(3-furanyl)-
dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho[2,1-c]pyran-
7-carboxylic Acid Methyl Ester (8c). 8c was synthesized as described
for 8a from 7 using hexanoyl chloride to afford 53 mg (70%) of 8c as
1
a white solid: mp 82-85 °C; H NMR (CDCl3) δ 0.91 (3H, t, J )
6.9); 1.14 (3H, s); 1.30-1.41 (4H, m) 1.47 (3H, s); 1.55-1.73 (6H,
m); 1.81 (1H, dd, J ) 3.0, 9.9); 2.10 (1H, dd, J ) 3.0, 11.4); 2.19 (1H,
s); 2.26-2.37 (2H, m); 2.44 (2H, dt, J ) 5.5, 7.8); 2.53 (1H, dd, J )
5.1, 13.2); 2.77 (1H, dd, J ) 8.7, 8.7); 3.74 (3H, s); 5.16 (1H, dd, J )
10.5, 10.5); 5.54 (1H, dd, J ) 5.1, 11.7); 6.39 (1H, dd, J ) 0.9, 1.8);
7.40 (1H, dd, J ) 1.8, 1.8); 7.43 (1H, dd, J ) 0.9, 1.8); 13C NMR
(CDCl3) δ 14.1, 15.4, 16.6, 18.4, 22.5, 24.7, 31.1, 31.5, 34.1, 35.7,
38.4, 42.3, 43.6, 51.6, 52.2, 53.8, 64.3, 72.2, 75.0, 108.6, 125.4, 139.7,
143.9, 171.3, 171.8, 173.0, 202.2; anal. C 65.46%, H 7.50%, O 26.91%,
calcd for C27H36O8•0.25H2O, C 65.76%, H 7.46%, O 26.77%.
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(2-tert-Butoxycarbonylaminoacety-
loxy)-2-(3-furanyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-
naphtho[2,1-c]pyran-7-carboxylic Acid Methyl Ester (8d). (Benzo-
triazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate
(BOP) (244 mg, 0.55 mmol), N-Boc glycine (146 mg, 0.83 mmol),
N-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI)
(160 mg, 0.83 mmol), 1-hydroxybenzotriazole hydrate (HOBT) (112.5
mg, 0.83 mmol), and pyridine (0.23 mL, 2.74 mmol) were added to a
solution of 7 (120 mg, 0.31 mmol) in CH2Cl2 (30 mL), and the mixture
was stirred for 4 days at room temperature. The mixture was diluted
with CH2Cl2 (80 mL) and was washed sequentially with 2 N HCl (2 ×
80 mL), 2 N NaOH (2 × 50 mL), and water (2 × 50 mL). The organic
extract was dried (Na2SO4), filtered, and concentrated to give a yellow-
brown oil. The crude product was purified by flash column chroma-
tography (30% acetone/hexanes) to give 98 mg (58%) of 8d as a white
foam: mp 124-127 °C; 1H NMR (CDCl3) δ 1.13 (3H, s); 1.46 (12 H,
br s); 1.50-1.70 (3H, m); 1.83 (1H, d, J ) 2.1 Hz); 2.11 (1H, d, J )
10.5); 2.19 (2H, m); 2.30 (1H, d, J ) 4.8); 2.36 (1H, d, J ) 9.6); 2.49
(1H, dd, J ) 5.4, 13.5); 2.76 (1H, dd, J ) 9.3, 9.3); 3.75 (3H, s); 3.99
(1H, dd, J ) 5.1, 13.2); 4.13 (1H, dd, J ) 6.3, 18.3); 4.99 (1H, br s);
5.20 (1H, dd, J ) 10.2, 10.2); 5.53 (1H, dd, J ) 5.1, 11.4); 6.39 (1H,
br s); 7.42 (2H, m); 13C NMR (CDCl3) δ 15.4, 16.7, 18.4, 28.5(3),
30.9, 35.7(2), 38.4, 42.4, 43.6, 51.6, 52.3, 53.7, 64.3, 72.2, 75.9, 77.4,
108.6, 125.4, 139.6, 144.0, 156.2, 171.2, 171.6(2), 201.6; anal. C
61.36%, H 6.86%, O 29.27%, calcd for C28H37NO10, C 61.41%, H
6.81%, O 29.22%.
Thiophene-2-carboxylic Acid (2S,4aR,6aR,7R,9S,10aS,10bR)-7-
Carbomethoxy-2-(3-furanyl)dodecahydro-6a,10b-dimethyl-4,10-di-
oxo-2H-naphtho[2,1-c]pyran-9-yl Ester (10d). A solution of 7 (80
mg, 0.21 mmol), 2-thiophene carbonyl chloride (0.11 mL, 2.73 mmol),
Et3N (0.38 mL, 2.73 mmol), pyridine (0.22 mL, 2.73 mmol), and a
catalytic amount of DMAP in CH2Cl2 (40 mL) was stirred at room
temperature overnight. The mixture was diluted with CH2Cl2 (30 mL)
and washed with 2 N HCl (2 × 30 mL), saturated NaHCO3 (2 × 30
mL), and water (40 mL). The organic extract was then dried (Na2-
SO4), filtered, and concentrated to give an oil, which was purified by
flash column chromatography (30-40% ethyl acetate/hexanes) to give
1
63 mg (60%) of 10d as a white solid: mp 143-145 °C; H NMR
(CDCl3) δ 1.18 (3H, s); 1.48 (3H, s); 1.54-1.77 (3H, m); 1.84 (1H,
dd, J ) 3.0, 10.2); 2.12 (1H, dd, J ) 2.2, 11.1); 2.19 (1H, m); 2.26
(1H, s); 2.47 (2H, m); 2.56 (1H, dd, J ) 5.3, 13.4); 2.83 (1H, dd, J )
7.2, 9.6); 3.76 (3H, s); 5.36 (1H, dd, J ) 9.9, 9.9); 5.53 (1H, dd, J )
5.4, 11.7); 6.40 (1H, dd, J ) 1.2, 1.8); 7.15 (1H, dd, J ) 3.8, 5.1);
7.42 (2H, m); 7.63 (1H, dd, J ) 1.3, 5.1); 7.89 (1H, dd, J ) 1.3, 3.8);
13C NMR (CDCl3) δ 15.4, 16.7, 18.4, 31.1, 35.7, 38.4, 42.4, 43.6, 51.7,
52.2, 53.9, 64.3, 72.3, 75.7, 108.6, 125.4, 128.1, 132.6, 133.5, 134.5,
139.7, 143.9, 161.3, 171.3, 171.8, 201.8; anal. C 62.66%, H 5.84%, O
25.67%, calcd for C26H28O8S, C 62.39%, H 5.64%, O 25.57%.
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(Benzenesulfonyloxy)-2-(3-fura-
nyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho[2,1-c]py-
ran-7-carboxylic Acid Methyl Ester (11a). A solution of 7 (100 mg,
0.26 mmol), benzenesulfonyl chloride (66 µL, 0.51 mmol), pyridine
(0.23 mL, 2.74 mmol), and a catalytic amount of DMAP in CH2Cl2
(30 mL) was stirred at room temperature overnight. The mixture was
diluted with CH2Cl2 (40 mL) and washed sequentially with 2 N HCl
(2 × 30 mL), saturated NaHCO3 (2 × 30 mL), and water (40 mL).
The organic extract was dried (Na2SO4), filtered, and concentrated to
an oil, which was purified by flash column chromatography (40% ethyl
acetate/hexanes) to give 103 mg (76%) of 11a as a white solid: mp
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(Phenylacetyloxy)-2-(3-furanyl)-
dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho[2,1-c]pyran-
7-carboxylic Acid Methyl Ester (9a). 9a was synthesized from 7 using
phenylacetyl chloride as described for 8a to afford 70 mg (54%) of 9a
1
as a white solid: mp 111-114 °C; H NMR (CDCl3) δ 1.10 (3H, s);
1.40 (3H, s); 1.41-1.52 (2 H, m); 1.61 (1H, m); 1.73 (1H, m); 1.87
(1H, dd, J ) 3.0, 11.4); 2.10 (1H, dd, J ) 3.0, 13.2); 2.22 (1H, s);
2.31 (2H, m); 2.72 (1H, m); 3.72 (3H, s); 3.75 (2H, s); 5.17 (1H, dd,
J ) 9.3, 9.3); 5.37 (1H, dd, J ) 4.8, 11.7); 6.36 (1H, dd, J ) 0.9, 1.5);
7.27-7.36 (6 H, m); 7.38-7.42 (2H, m); 13C NMR (CDCl3) δ 15.3,
16.6, 18.2, 30.9, 35.5, 38.2, 40.8, 42.1, 42.9, 51.3, 52.1, 53.6, 63.8,
72.0, 75.6, 108.8, 125.2, 127.4, 128.8(2), 129.6(2), 133.7, 139.9, 143.8,
171.0, 171.3, 171.8, 202.0; anal. C 68.74%, H 6.36%, O 24.93%, calcd
for C29H32O8, C 68.49%, H 6.34%, O 25.17%.
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(3-Phenylpropionyl)-2-(3-fura-
nyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho[2,1-c]py-
ran-7-carboxylic Acid Methyl Ester (9b). 9b was synthesized from
7 as described for 8a using hydrocinnamoyl chloride to afford 69 mg
1
157-159 °C (dec); H NMR (CDCl3) δ 1.10 (3H, s); 1.44 (3H, s);
1.47-1.71 (4H, m); 1.82 (1H, m); 2.06 (1H, dd, J ) 3.0, 12.0), 2.10
(1H, s); 2.19 (1H, m); 2.26-2.46 (3H, m); 2.72 (1H, dd, J ) 4.2, 12.3);
3.73 (3H, s); 5.00 (1H, dd, J ) 8.1, 11.7); 5.53 (1H, dd, J ) 5.0, 11.6);
6.40 (1H, m); 7.44 (2H, m); 7.58 (2H, m); 7.67 (1H, m). 8.01 (1H, m);
13C NMR (CDCl3) δ 15.3, 16.6, 18.3, 32.4, 35.7, 38.3, 42.2, 43.5, 51.5,
52.3, 53.7, 64.6, 72.1, 80.0, 108.6, 125.4, 126.6, 128.0, 128.1, 129.4-
(2), 134.2, 139.6, 144.0, 171.1, 171.2, 200.0; anal. C 61.16%, H 5.85%,
O 27.06%, calcd for C27H30O9S, C 61.62%, H 5.70%, O 27.14%.
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(4-Methylbenzenesulfonyloxy)-
2-(3-furanyl)-dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho-
[2,1-c]pyran-7-carboxylic Acid Methyl Ester (11b). 11b was syn-
thesized as described for 11a from 7 using 4-methylbenzenesulfonyl
chloride to afforded 10 mg (0.22 mmol, 86%) of 11b as a white solid:
mp 163-165 °C (dec); 1H NMR (CDCl3) δ 1.10 (3H, s); 1.44 (3H, s);
1
(63%) of 9b as a white solid: mp 155-158 °C; H NMR (CDCl3) δ
1.14 (3H, s); 1.47 (3H, s); 1.52-1.74 (3H, m); 1.81 (1H, m); 2.09
(1H, dd, J ) 3.0, 11.1); 2.17 (1H, m); 2.19 (1H, s); 2.25-2.34 (2H,
m); 2.53 (1H, dd, J ) 5.3, 13.7); 2.71-2.76 (1H, m); 2.79 (2H, t, J )
7.5), 3.01 (2H, t, J ) 7.5); 3.74 (3H, s); 5.17 (1H, dd, J ) 10.1, 10.1);
5.55 (1H, dd, J ) 4.8, 11.7); 6.40, (1H, dd, J ) 0.9, 1.8), 7.20-7.26
(3H, m); 7.32 (2H, m); 7.43 (2H, m); 13C NMR (CDCl3) 15.4, 16.6,
18.4, 31.0, 35.6, 35.7, 38.4, 42.3, 43.6, 51.6, 52.2, 53.8, 64.3, 72.2,
75.2, 77.4, 108.6, 125.4, 126.6, 128.5(2), 128.7(2), 139.7, 140.4, 143.9,
171.3, 171.7, 172.1, 202.1; anal. C 69.23%, H 6.59%, O 24.23%, calcd
for C30H34O8, C 68.95%, H 6.56%, O 24.49%.
(2S,4aS,6aR,7R,9S,10aS,10bR)-9-(2-Bromobenzoyloxy)-2-(3-fura-
nyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho[2,1-c]py-

918 Journal of Natural Products, 2006, Vol. 69, No. 6
Tidgewell et al.
(3) Siebert, D. J. J. Ethnopharmacol. 1994, 43, 53-56.
1.47-1.67 (4H, m); 1.81 (1H, dd, J ) 2.7, 9.9); 2.05-2.08 (1H, dd,
obscured); 2.08 (1H, s); 2.17 (1H, dd, J ) 3.0, 10.2); 2.32-2.44 (2H,
m); 2.41 (3H, s); 2.72 (1H, dd, J ) 4.2, 12.3); 3.73 (3H, s); 4.96 (1H,
dd, J ) 7.5, 11.7); 5.53 (1H, dd, J ) 5.1, 11.7); 6.40 (1H, dd, J ) 1.2,
1.2); 7.34 (2H, d, J ) 7.8); 7.43 (2H, m); 7.84 (2H, d, J ) 7.8); 13C
NMR (CDCl3) δ 15.3, 16.6, 18.3, 21.8, 32.5, 35.7, 38.3, 42.2, 43.5,
51.6, 52.3, 53.7, 64.6, 72.1, 77.4, 79.8, 108.6, 125.4, 128.1(2), 130.0(2),
139.7, 144.0, 145.4, 171.1, 171.2, 200.1; anal. C 61.17%, H 5.84%, O
27.07%, calcd for C28H32O9S‚0.25H2O, C 61.24%, H 5.97%, O 26.95%.
X-ray Crystal Structure of (2S,4aS,6aR,7R,9S,10aS,10bR)-9-(4-
Bromobenzoyloxy)-2-(3-furanyl)dodecahydro-6a,10b-dimethyl-4,-
10-dioxo-2H-naphtho[2,1-c]pyran-7-carboxylic Acid Methyl Ester
(10c). Single-crystal X-ray diffraction data on compound 10c were
collected at 93 K using Mo KR radiation and a Bruker SMART 1000
CCD area detector. A 0.32 × 0.04 × 0.02 mm3 crystal was prepared
for data collection coating with high-viscosity microscope oil (Paratone-
N, Hampton Research). The oil-coated crystal was mounted on a glass
rod and transferred immediately to the cold stream (93 K) on the
diffractometer. The crystal was orthorhombic in space group P212121
with unit cell dimensions a ) 6.382(2) Å, b ) 10.008(7) Å, and c )
20.534(8) Å. Corrections were applied for Lorentz, polarization, and
absorption effects. Data were 99.9% complete to 25.33° θ (ap-
proximately 0.83 Å) with an average redundancy of 5.3. The structure
was solved by direct methods and refined by full-matrix least squares
on F2 values using the programs found in the SHELXTL suite (Bruker,
SHELXTL v6.14, Bruker AXS Inc., Madison, WI, 2000). Parameters
refined included atomic coordinates and anisotropic thermal parameters
for all non-hydrogen atoms. Hydrogen atoms on carbons were included
using a riding model [coordinate shifts of C applied to H atoms] with
C-H distance set at 0.98 Å. The absolute configuration was determined
from the X-ray data (Flack parameter ) 0.025(17)). Atomic coordinates
for compound 10c have been deposited with the Cambridge Crystal-
lographic Data Centre (deposition number 299266). Copies of the data
can be obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK [fax: +44(0)-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk].
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Acknowledgment. This work was supported by the National
Institutes of Health, National Institute on Drug Abuse Grant DA18151
(to T.E.P.), and in part by the Office of Naval Research and the
Intramural Research Program of the NIH, NIDA.
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Supporting Information Available: CIF file of X-ray data for
compound 10c. This material is available free of charge via the Internet
at http://pubs.acs.org.
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References and Notes
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7, 287-312.
(2) Valdes, L. J., III. J. Psychoact. Drugs 1994, 26, 277-283.
NP060094B