Synthesis of amide isosteres of schweinfurthin-based stilbenes

Article abstract of DOI:10.1016/j.bmc.2017.08.016

The schweinfurthins are plant-derived stilbenes with an intriguing profile of anti-cancer activity. To obtain analogues of the schweinfurthins that might preserve the biological activity but have greater water solubility, a formal replacement of the central olefin with an amide has been explored. Two pairs of amides have been prepared, each containing the same hexahydroxanthene “left half” joined through an amide linkage to two different “right halves.” In each series, the amide has been inserted in both possible orientations, placing the carbonyl group on the tricyclic ABC ring system and the amine on the D-ring, or placing the amine on the hexahydroxanthene and the carbonyl group on the D-ring. The four new schweinfurthin analogues have been tested in the NCI 60 cell line screen, and in both cases the more active isomer carried the carbonyl group on the C-ring.

Full text of DOI:10.1016/j.bmc.2017.08.016

Accepted Manuscript
Synthesis of Amide Isosteres of Schweinfurthin-based Stilbenes
David P. Stockdale, John A. Beutler, David F. Wiemer
PII:
S0968-0896(17)31306-8
DOI:
http://dx.doi.org/10.1016/j.bmc.2017.08.016
BMC 13919
Reference:
Bioorganic & Medicinal Chemistry
To appear in:
Received Date:
Revised Date:
Accepted Date:
24 June 2017
3 August 2017
8 August 2017
Please cite this article as: Stockdale, D.P., Beutler, J.A., Wiemer, D.F., Synthesis of Amide Isosteres of
Schweinfurthin-based Stilbenes, Bioorganic & Medicinal Chemistry (2017), doi: http://dx.doi.org/10.1016/j.bmc.
2017.08.016
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Synthesis of Amide Isosteres of Schweinfurthin-
based Stilbenes
David P. Stockdale,a John A. Beutler,b and David F. Wiemera*
Department of Chemistry University of Iowa, Iowa City, Iowa 52242-1294, United States
bMolecular Targets Laboratory, Center for Cancer Research, NCI-Frederick,
Frederick, MD 21702
E-mail: david-wiemer@uiowa.edu
RECEIVED DATE:
KEYWORDS. Schweinfurthin, stilbene, amide isostere, cancer
Draft: August 2, 2017
1

Table of Contents Graphic.
OCH3
C
3
2
O
B
A
OH
HO
D
H
10 (3-Deoxyschweinfurthin B)
OH
OCH3
OCH3
O
O
H
O
N
OH
OH
HO
HO
N
H
H
H
O
OH
OH
11
12
Abstract.
The schweinfurthins are plant-derived stilbenes with an intriguing profile of anti-cancer
activity. To obtain analogues of the schweinfurthins that might preserve the biological activity
but have greater water solubility, a formal replacement of the central olefin with an amide has
been explored. Two pairs of amides have been prepared, each containing the same
hexahydroxanthene “left half” joined through an amide linkage to two different “right halves.”
In each series, the amide has been inserted in both possible orientations, placing the carbonyl
group on the tricyclic ABC ring system and the amine on the D-ring, or placing the amine on the
hexahydroxanthene and the carbonyl group on the D-ring. The four new schweinfurthin
analogues have been tested in the NCI 60 cell line screen, and in both cases the more active
isomer carried the carbonyl group on the C-ring.
2

Introduction.
The natural products commonly grouped as schweinfurthins include six compounds
isolated from the plant Macaranga schweinfurthii1-3 (A–D, 1–4, I and J), four isolated from the
plant Macaranga alnifolia4 (E–H, 5–8), and vedelianin (9) which was isolated much earlier from
Macaranga vedeliana.5 When tested in the National Cancer Institute screen of 60 human cancer
cell lines, those containing a hexahydroxanthene substructure as the ABC ring system showed an
intriguing pattern of biological activity. Their unique fingerprint of activity does not parallel that
of any chemotherapeutic agent in current clinical use, and approximates those of only a few, far
more complex natural products (notably cephalostatins,6 OSW-1,7 ritterazines,8 and stellettins9).
Mechanistic investigations from several groups have suggested that the schweinfurthins may
engage several different targets, including oxysterol binding proteins,10 trans-Golgi-network
trafficking,11 and cholesterol biosynthesis and its cellular export.12 The combination of a unique
profile of activity with the limited success of efforts to obtain more of the schweinfurthins by
isolation from the plant source, has led us to an extended effort to prepare these natural products
by chemical synthesis. Our efforts to date have afforded seven of the natural products
(schweinfurthins A,13 B,14 C,15 E,14 F,16 G16 and vedelianin17), as well as 3-deoxyschweinfurthin
B18 (10) which we have used as a lead for a number of structure-activity studies.19,20 All of the
optically active synthetic materials were prepared in high ee through reagent level control of
absolute stereochemistry via an enantioselective epoxidation followed by a cascade cyclization
to the tricyclic core. In fact, both enantiomers of schweinfurthin F were prepared,16 and the
significantly different selectivity of the two enantiomers in the 60 cell line screen was used to
assign the natural absolute stereochemistry as R, R, R and not S, S, S.
3

A possible drawback to the use of schweinfurthin-based drugs in chemotherapy is their
limited solubility in water. Based on the activity of various analogues we have prepared, it
appears that features essential for activity include a trans-fused A-B ring system, an oxygen
substituent at C-5 of the C-ring, at least one free phenol on the D-ring, and conjugation from the
C-ring to the D-ring as found in the trans (but not the cis19) olefin. On the other hand, the C-3
oxygen of schweinfurthin B is expendable without significant loss of activity and the 6´-position
in the D-ring can accommodate a wide variety of substituents. Thus we have come to view the
hexahydroxanthene found in the ABC ring system as the primary pharmacophore, although the D
ring substituents contribute to activity in a lesser way. These observations led us to examine
whether the central stilbene olefin could be replaced with a more polar group such as an amide to
maintain activity while improving water solubility. The restricted rotation around the amide
bond should favor a transoid structure, and may allow some communication of electronic effects
from the C-ring to the D-ring. As a test of that hypothesis, in this paper we report the
preparation of four new “schweinfurthin amides” as well as our initial studies on their biological
activity.
Figure 1. Some natural schweinfurthins (1-9) and a lead analogue (10).
4

OR
OH
5
3
HO
HO
O
HO
A
B
C
OH
OH
2
H
D
6'
H
2
3 Schweinfurthin C
1 R = H Schweinfurthin A
2 R = CH3 Schweinfurthin B
OH
OH
OCH3
O
OCH3
HO
HO
HO
O
O
OH
H
HO
H
OH
OH
8 Schweinfurthin H
OH
4 Schweinfurthin D
OH
OR
O
R'
5
6
R = CH3 R' = OH n = 1 Schweinfurthin E
R = CH3 R' = H n = 1 Schweinfurthin F
OH
HO
H
7
9
R = H R' = H n = 1 Schweinfurthin G
R = H R' = OH n = 1 Vedelianin
H
n
10 R = CH3 R' = H n = 1 3-Deoxyschweinfurthin B
OH
Results and Discussion.
From the outset of this effort, it was viewed as essential to prepare the new
schweinfurthin analogues as a matched pair (Scheme 1), that is, one analogue with the carbonyl
group on the tricyclic ABC ring system and the amide nitrogen on the D-ring (11), and a second
isomeric analogue where the substituents were reversed (12). The obvious disconnection at the
amide bond leads to the acids 13 and 16 and the amines 14 and 15. If some variation on the
Curtius or Hoffman reaction21 could be employed despite the presence of a variety of other
functional groups, it would be possible to derive the amine 14 from the acid 16 and the amine 15
from the acid 13. This would enhance the efficiency of the overall effort by the dual use of these
carboxylic acids. While the ether and acetal groups in compound 13 were viewed as relatively
stable to both acidic and basic conditions, the stability of the isoprenoid olefins in compounds of
the general structure 16 was of more concern. Nevertheless, given the possibility for use of
compound 16 in both target amides, the initial goal became preparation of a protected acid 16.
5

OCH3
OCH3
O
O
H
N
O
OH
OH
HO
HO
N
H
H
H
O
11
12
OH
OH
OCH3
OCH3
O
H2N
OR
O
HO2C
NH2
OR
RO
CO2H
RO
H
H
OR
OR
16
13
14
15
16
13
Scheme 1. Retrosynthesis of a representative schweinfurthin amide.
The synthetic sequence used to prepare the target “right half” acid began with
commercial 3,5-dihydroxybenzoic acid (17). Treatment of this resorcinol with bromine under
acidic conditions gave the para bromo derivative 18 in nearly quantitative yield.22 Treatment of
compound 18 with MOMCl and diisopropylethylamine resulted in smooth formation of the
triMOM derivative 19. While acyloxy esters commonly have been employed in prodrugs,23
application of the MOM group as a carboxylic acid protecting group in place of a methyl ester or
protected primary alcohol shortened the synthetic sequence significantly relative to our previous
efforts. The MOM ester 19 proved to be sufficiently stable to allow halogen-metal exchange and
alkylation with geranyl bromide to give the ester 20 in moderate yield.24
Selective hydrolysis of the MOM ester by treatment with LiOH gave the free carboxylic
acid 21, and set the stage for preparation of an aryl amine via C-C bond cleavage and a formal
insertion. One might consider either a Hoffmann or Curtius rearrangement to accomplish this
transformation, but the presence of the isoprenoid olefin led us to favor the Curtius strategy.
While there is precedent for conversion of an olefin to an aziridine via reaction with a
nitrene,25,26 the prevailing view is that the Curtius rearrangement is a concerted process rather
6

than one which involves discrete nitrene formation.21 In the event, reaction of the acid 21 with
diphenyl phosphoryl azide (DPPA) followed by treatment with LiOH, gave the desired amine 22
in moderate yield. The complementary carboxylic acid 24 could be prepared by simple
oxidation of the aldehyde 23, a hexahydroxanthene we have used in past syntheses of numerous
schweinfurthin analogues.14 An EDC-mediated condensation of the acid 24 and the amine 22
gave the expected amide 25, and a final acid-catalyzed hydrolysis of the MOM protecting groups
gave the target compound 11.
O
O
.
then GerBr
n-BuLi, CuBr DMS
MOMCl
DIPEA
HO2C
OH
X
MOMOC
OMOM
Br
ROC
OMOM
89%
60%
OH
OMOM
OMOM
17 X = H
18 X = Br
19
20 R = MOM
21 R = H
Br2, HCl
96%
LiOH, THF/H2O
81%
1) DPPA, NEt3
2) LiOH, THF/H2O
49%
EDC
DMAP
OCH3
OCH3
O
H2N
OMOM
O
H
N
X
54%
OR
MOMO
C
O
RO
H
H
OMOM
22
O
NaClO2, NaH2PO4
TsOH, CH3OH
52%
23 X = H
24 X = OH
25 R = MOM
11 R = H
OR
2-methyl-2-butene
53%
Scheme 2. Synthesis of the first amide analogue of a schweinfurthin.
After amide 11 was prepared, synthesis of amide 12 was relatively straightforward
because the second sequence could take advantage of some intermediates already in hand. As
shown in Scheme 3, the carboxylic acid 24 gave the desired amine 26 upon treatment with
DPPA. An EDC mediated condensation of acid 21 and amine 26 gave the desired amide
framework (27), and MOM hydrolysis gave the final target, amide 12, in reasonable yield.
7

1) DPPA, NEt3
OCH3
OCH3
2) LiOH, THF/H2O
O
O
54%
OH
MOMO
C
O
MOMO
NH2
H
H
24
26
21
EDC
DMAP
OCH3
51%
O
O
OR
RO
N
H
H
OR
TsOH, CH3OH
74%
27 R = MOM
12 R = H
Scheme 3. Synthesis of an isomeric schweinfurthin amide.
For a more robust comparison of the impact of formal replacement of the stilbene olefin
with an amide unit, a second pair of schweinfurthin amides was prepared. We recently reported
the synthesis and biological activity of some indole schweinfurthin analogues27,28 and used that
effort as an inspiration for this second pair. As shown in Scheme 4, the parent indole carboxylic
acid ester 28 was first dimethylated (29) to protect potentially sensitive functionality and to allow
direct comparison with the activity of an indole schweinfurthin previously prepared. After
hydrolysis of the methyl ester 29, the resulting carboxylic acid 30 was converted to the
corresponding amine 31 by reaction with DPPA. Formation of the amide 32 was accomplished
under standard conditions, as was final hydrolysis of the MOM protecting groups. The
“reversed” amide 34 was obtained upon condensation of the amine 26 with the carboxylic acid
30, and a final hydrolysis of the MOM groups gave the target amide 35.
8

O
O
1) DPPA, NEt3
H
CH3
CH3
NaH
then CH3I
H3COC
ROC
2) LiOH, THF/H2O H2N
N
N
N
93%
83%
OH
OCH3
OCH3
LiOH
THF, H2O
29 R = H3C
30 R = H
28
24
31
EDC
DMAP
95%
99%
OCH3
O
H
N
CH3
N
RO
H
O
OCH3
TsOH, CH3OH
65%
32 R = MOM
33 R = H
30
EDC
DMAP
OCH3
O
O
CH3
N
26
45%
RO
N
H
H
OCH3
TsOH, CH3OH
60%
34 R = MOM
35 R = H
Scheme 4. Synthesis of schweinfurthin-indole amides.
Once the four new schweinfurthin amides were in hand, each was tested in the NCI’s 60
cell line assay.29 These compounds showed schweinfurthin-like activity as measured by similar
patterns of selectivity, with Pearson correlation coefficients of 0.65 to 0.78 (Table 1), and with
the potency of compounds 11 and 33 comparable to the parent stilbenes. Both of the isomeric
amides 12 and 35 were less potent and demonstrated a lower differential activity across the 60
cell lines assayed. In terms of calculated logP, there is no difference in water solubility between
the two amide isomers in each pair, so the observed differences in biological activity must track
to other molecular properties.
9

Table 1. NCI 60 Data Summary
Compound
Mean GI50
(µM)
0.36
Differential at
Pearson Correlation
LogP
GI50 (log10)
3.11
Coefficient to 1 at GI50
(calculated)a
1.00
0.77
0.78
0.65
0.78
0.70
8.29
8.94
7.89
7.89
4.61
4.61
1
0.87
3.25
10
11
12
33
35
0.21
2.73
1.1
1.50
0.66
2.41
6.6
2.12
aValues were determined using the calculator at
http://www.molinspiration.com/services/properties.html
In conclusion, we have developed synthetic sequences that allow formal replacement of
the central stilbene olefin of the schweinfurthins with an amide linkage. This substitution
preserves the selectivity and potency of the parent schweinfurthins, and should increase the water
solubility of these analogues relative to the parent compounds as measured by calculated logP
values. In both series tested, the more active isomers 11 and 33 bore the carbonyl group on the
C-ring, and the amine on the D-ring, suggesting that electron donation to the D-ring is more
beneficial to activity than electron withdrawal. Further studies will be needed to determine if
this is a consistent trend, but these findings provide some guidance to the design of still more
pharmaceutically useful schweinfurthin analogues.
10

Experimental Section
General Experimental Procedures. Both tetrahydrofuran (THF) and diethyl ether
(Et2O) were freshly distilled from sodium and benzophenone, whereas methylene chloride
(CH2Cl2) was distilled from calcium hydride prior to use. The solutions of n–BuLi were
purchased from a commercial source and titrated with diphenylacetic acid prior to use. All other
reagents and solvents were purchased from commercial sources and used without further
purification. All reactions in nonaqueous solvents were conducted in flame-dried glassware
under a positive pressure of argon and with a magnetic stir bar. NMR spectra were obtained at
400 or 500 MHz for 1H, 101 or 126 MHz for 13C NMR, in CDCl3 with (CH3)4Si (1H, 0.00 ppm)
13
or CDCl3 (1H, 7.26 ppm; C NMR; 77.16 ppm) or CD3OD (1H, 3.31 ppm; 13C NMR; 49.00
ppm), as the internal standards. High-resolution mass spectra were obtained by GC-TOF. Silica
gel (60 Å, 0.040 – 0.063 mm) was used for flash column chromatography.
(2R,4aR,9aR)-N-(4-((E)-3,7-Dimethylocta-2,6-dienyl)-3,5-dihydroxyphenyl)-2-hydroxy-5-
methoxy-1,1,4a-trimethyl-2,3,4,4a,9,9a-hexahydro-1H-xanthene-7-carboxamide
(11).
NSC#791211. To a stirred solution of the acetal 25 (39 mg, 56 µmol) in MeOH (5.6 mL) was
added p-TsOH·H2O (61 mg, 0.32 mmol). The flask was sealed and stirred for 28 hours at rt.
Analysis by tlc suggested that the reaction was not complete so additional p-TsOH·H2O (15 mg,
79 µmol) was added and the solution was stirred for an additional 17 hours. The solution was
diluted with EtOAc and then washed with saturated aqueous NaHCO3. The layers were separated
and the aqueous layer was extracted with EtOAc (3x). The combined organic extracts were
washed with brine, dried over Na2SO4, and filtered, and the filtrate was concentrated in vacuo.
Final purification using an ISCO Combiflash Rf chromatography gradient (0 to 80% EtOAc in
11

hexanes) afforded amide 11 (16.3 mg, 52%) as an off-white solid: 1H NMR (400 MHz, CD3OD)
δ 7.33 (d, J = 1.9 Hz, 1H), 7.30 (d, J = 1.8 Hz, 1H), 6.71 (s, 2H), 5.29 – 5.21 (m, 1H), 5.12 –
5.05 (m, 1H), 3.85 (s, 3H), 3.38 – 3.32 (m, 1H), 3.28 (d, J = 7.4 Hz, 2H), 2.79 – 2.73 (m, 2H),
2.10 – 2.01 (m, 3H), 1.99 – 1.91 (m, 2H), 1.84 – 1.74 (m, 5H), 1.67 – 1.62 (m, 5H), 1.57 (s, 3H),
13
13
1.22 (s, 3H), 1.09 (s, 3H), 0.87 (s, 3H); C NMR (101 MHz, CD3OD) δ C NMR (101 MHz,
CD3OD) δ 168.6, 157.2 (2C), 149.9, 147.2, 138.0, 134.8, 132.0, 127.3, 125.6, 124.8, 123.8,
122.8, 113.1, 110.0, 101.4 (2C), 78.9, 78.6, 56.5, 48.2, 41.0, 39.5, 38.8, 28.9, 27.9, 27.8, 25.9,
24.1, 23.0, 20.3, 17.7, 16.3, 14.9; HRMS (TOF MS ES+) m/z calculated for C34H46NO6 (M +
H)+ 564.3325, found 564.3326.
4-((E)-3,7-Dimethylocta-2,6-dienyl)-3,5-dihydroxy-N-((2R,4aR,9aR)-2-hydroxy-5-methoxy-
1,1,4a-trimethyl-2,3,4,4a,9,9a-hexahydro-1H-xanthen-7-yl)benzamide (12), NSC#791210.
To a stirred solution of the acetal 27 (32 mg, 46 µmol) in MeOH (4.6 mL) was added p-
TsOH·H2O (50 mg, 0.26 mmol). The flask was sealed and stirred for 27 hours at rt. After tlc
analysis suggested that the reaction was not complete, additional p-TsOH·H2O (15 mg, 79 µmol)
was added and the solution was stirred for an additional 18 hours. The solution was diluted with
EtOAc and then washed with saturated aqueous NaHCO3. The layers were separated and the
aqueous layer was extracted with EtOAc (3x). The combined organic extracts were washed with
brine, dried over Na2SO4, and filtered, and the filtrate was concentrated in vacuo. Final
purification using an ISCO Combiflash Rf chromatography gradient (0 to 80% EtOAc in
hexanes) afforded amide 12 (19.2 mg, 74%) as an off-white solid: 1H NMR (400 MHz, CD3OD)
δ 7.13 (s, 1H), 6.95 (s, 1H), 6.80 (s, 2H), 5.25 (t, J = 7.1 Hz, 1H), 5.08 (t, J = 7.0 Hz, 1H), 3.80
(s, 3H), 3.35 (d, J = 7.2 Hz, 3H), 2.72 (s, 1H), 2.70 (s, 1H), 2.11 – 2.00 (m, 3H), 2.00 – 1.91 (m,
12

2H), 1.84 – 1.74 (m, 5H), 1.69 – 1.64 (m, 2H), 1.63 (s, 3H), 1.57 (s, 3H), 1.21 (s, 3H), 1.08 (s,
3H), 0.87 (s, 3H); 13C NMR (101 MHz, CD3OD) δ 169.4, 157.4 (2C), 149.7, 140.9, 135.5, 134.8,
132.0, 131.9, 125.5, 124.0, 123.8, 120.6, 115.6, 106.8 (2C), 105.6, 78.7, 77.9, 56.4, 48.5, 41.0,
39.5, 38.9, 29.0, 27.9, 27.8, 25.9, 24.3, 23.4, 20.1, 17.7, 16.3, 14.8. HRMS (TOF MS ES+) m/z
calculated for C34H46NO6 (M + H)+ 564.3325, found 564.3336.
Methoxymethyl 4-bromo-3,5-bis(methoxymethoxy)benzoate (19). To a stirred solution of 4-
bromo-3,5-dihydroxybenzoic acid (1.64 g, 7.0 mmol) and N,N-diisopropylethylamine (4.0 mL
o
23.2 mmol) in CH2Cl2 (24 mL) at 0 C was added chloromethyl methyl ether (2.14 mL, 28.2
mmol) dropwise via syringe. The solution was allowed to equilibrate to rt overnight and then
washed with saturated aqueous NH4Cl. The layers were separated and the aqueous layer was
extracted with CH2Cl2 (3x). The organic layers were combined and washed with brine, and then
dried over Na2SO4. The mixture was filtered and the filtrate was concentrated in vacuo. Final
purification using an ISCO Combiflash Rf chromatography gradient (0 to 30% EtOAc in
hexanes) afforded 19 (1.16 g, 89%) as an off-white solid: 1H NMR (500 MHz, CDCl3) δ 7.52 (s,
2H), 5.48 (s, 2H), 5.31 (s, 4H), 3.54 (s, 3H), 3.53 (s, 6H); 13C NMR (101 MHz, CDCl3) δ 165.4,
155.0 (2C), 130.2, 110.3 (2C), 110.1, 95.3 (2C), 91.4, 58.1, 56.7 (2C). HRMS (TOF MS ES+)
m/z calculated for C13H1779BrO7Na (M + Na)+ 387.0055, found 387.0060.
(E)-Methoxymethyl 4-(3,7-dimethylocta-2,6-dienyl)-3,5-bis(methoxymethoxy)benzoate (20).
An oven-dried flask was charged with ester 19 (0.5 g, 1.37 mmol) in anhydrous THF (10 mL) at
–78 oC. To this solution was added n-BuLi (2.5M in hexanes, 0.58 mL, 1.4 mmol) dropwise via
syringe. The resulting solution was stirred at –78 oC for 20 minutes and then CuBr·DMS (0.31 g,
13

o
1.5 mmol) was added. The solution was stirred an additional 20 minutes at –78 C and then
geranyl bromide (0.33 g, 1.5 mmol) was added dropwise via syringe. The solution was allowed
to equilibrate to rt overnight and then the reaction was quenched by the addition of saturated
aqueous NH4Cl. The layers were separated and the aqueous layer was extracted with EtOAc
(3x). The organic extracts were combined, washed with brine, and dried (Na2SO4). The mixture
was filtered and the filtrate was concentrated in vacuo. Final purification using an ISCO
Combiflash Rf chromatography gradient (0 to 30% EtOAc in hexanes) afforded compound 20
1
(0.34 g, 60%) as a yellow oil: H NMR (500 MHz, CDCl3) δ 7.47 (s, 2H), 5.46 (s, 2H), 5.24 (s,
4H), 5.20 – 5.15 (m, 1H), 5.05 (t, J = 6.9 Hz, 1H), 3.53 (s, 3H), 3.48 (s, 6H), 3.45 (d, J = 7.1 Hz,
2H), 2.03 (dd, J = 14.7, 6.9 Hz, 2H), 1.99 – 1.90 (m, 2H), 1.79 (s, 3H), 1.64 (s, 3H), 1.56 (s, 3H);
13C NMR (126 MHz, CDCl3) δ 166.0, 155.7 (2C), 135.6, 131.5, 128.7, 126.5, 124.4, 121.8,
109.4 (2C), 94.7 (2C), 91.0, 57.9, 56.3 (2C), 39.9, 26.9, 25.8, 23.2, 17.8, 16.3. HRMS (TOF MS
ES+) m/z calculated for C23H34O7Na (M + Na )+ 445.2202, found 445.2197.
(E)-4-(3,7-Dimethylocta-2,6-dienyl)-3,5-bis(methoxymethoxy)benzoic acid (21). To a stirred
solution of ester 20 (0.470 g, 1.11 mmol) in THF (5 mL) and H2O (5 mL) was added LiOH·H2O
(93 mg, 2.23 mmol). The flask was stirred at rt overnight and then the solution was acidified with
HCl. The layers were separated and the aqueous layer was extracted with EtOAc (3x). The
combined organic extracts were washed with brine, dried over Na2SO4 and filtered, and the
filtrate was concentrated in vacuo. Final purification using an ISCO Combiflash Rf
chromatography gradient (0 to 40% EtOAc in hexanes) afforded compound 21 (0.421 g, 81%) as
1
a white powder: H NMR (500 MHz, CDCl3) δ 7.51 (s, 2H), 5.25 (s, 4H), 5.21 – 5.16 (m, 1H),
5.05 (t, J = 6.8 Hz, 1H), 3.49 (s, 6H), 3.46 (d, J = 7.0 Hz, 2H), 2.07 – 2.00 (m, 2H), 1.99 – 1.93
14

13
(m, 2H), 1.79 (s, 3H), 1.64 (s, 3H), 1.56 (s, 3H); C NMR (126 MHz, CDCl3) δ 171.7, 155.7
(2C), 135.7, 131.5, 128.1, 126.9, 124.4, 121.7, 109.8 (2C), 94.7 (2C), 56.3 (2C), 39.9, 26.8, 25.8,
23.2, 17.8, 16.3. HRMS (TOF MS ES+) m/z calculated for C21H30O6Na (M + Na)+ 401.1940,
found 401.1946.
(E)-4-(3,7-Dimethylocta-2,6-dienyl)-3,5-bis(methoxymethoxy)aniline (22). An oven-dried
flask was charged with carboxylic acid 21 (100 mg, 0.26 mmol) in anhydrous benzene (26 mL).
To this stirred solution was added triethylamine (0.368 mL, 2.60 mmol) followed by the
dropwise addition of DPPA (0.569 mL, 2.60 mmol) via syringe. The solution was stirred at rt for
15 minutes, and then the flask was fitted with a reflux condenser and heated at reflux overnight.
The benzene was removed under reduced pressure and the residue was dissolved in THF (2.6
mL). To this solution was added aqueous 4N LiOH (1.3 mL, 5.30 mmol) and the resulting
mixture was stirred vigorously at rt for 1 hour. The mixture was diluted with H2O and the layers
were separated. The aqueous layer was extracted with EtOAc (3x) and the combined organic
extracts were washed with brine, and dried (Na2SO4). The mixture was filtered and the filtrate
was concentrated in vacuo. Final purification using an ISCO Combiflash Rf chromatography
gradient (0 to 40% EtOAc in hexanes) afforded amine 22 (45 mg, 49%) as a brown oil: 1H NMR
(400 MHz, CDCl3) δ 6.19 (s, 2H), 5.22 – 5.18 (m, 1H), 5.15 (s, 4H), 5.13 – 5.06 (m, 1H), 3.48 (s,
6H), 3.30 (d, J = 7.0 Hz, 2H), 2.10 – 2.01 (m, 2H), 2.00 – 1.92 (m, 2H), 1.78 (s, 3H), 1.67 (s,
3H), 1.59 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 156.6 (2C), 145.8, 134.0, 131.3, 124.6, 123.8,
110.7, 96.0 (2C), 94.6 (2C), 56.0 (2C), 40.0, 26.9, 25.8, 22.2, 17.8, 16.1. HRMS (TOF MS ES+)
m/z calculated for C20H32NO4 (M + H)+ 350.2331, found 350.2324.
15

(2R,4aR,9aR)-5-Methoxy-2-(methoxymethoxy)-1,1,4a-trimethyl-2,3,4,4a,9,9a-hexahydro-
1H-xanthene-7-carboxylic acid (24). To a stirred solution of aldehyde 23 (250 mg, 0.72 mmol)
and 2-methyl-2-butene (1.50 mL, 14.4 mmol) in t-BuOH (7 mL) was added NaH2PO4 (301 mg,
2.50 mmol) and NaClO2 (390 mg, 4.3 mmol) in H2O (2.4 mL) via syringe. The solution was
stirred vigorously at rt for 3.5 hours and then washed with saturated aqueous NH4Cl. The
mixture was extracted with EtOAc (3x) and the combined organic extracts were washed with
brine and dried (Na2SO4). The mixture was filtered and filtrate was concentrated in vacuo. Final
purification using an ISCO Combiflash Rf chromatography gradient (0 to 40% EtOAc in
1
hexanes) afforded carboxylic acid 24 (138 mg, 53%) as a white solid: H NMR (500 MHz,
CDCl3) δ 7.57 (s, 1H), 7.42 (s, 1H), 4.78 (d, J = 6.9 Hz, 1H), 4.65 (d, J = 6.9 Hz, 1H), 3.90 (s,
3H), 3.41 (s, 3H), 3.28 (dd, J = 11.6, 3.9 Hz, 1H), 2.80 – 2.69 (m, 2H), 2.16 (d, J = 12.8 Hz, 1H),
2.05 – 1.97 (m, 1H), 1.86 – 1.77 (m, 1H), 1.71 (dd, J = 11.5, 6.5 Hz, 1H), 1.65 – 1.54 (m, 1H),
1.27 (s, 3H), 1.10 (s, 3H), 0.91 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 172.0, 148.8, 148.0,
125.3, 122.5, 120.3, 110.5, 96.3, 84.1, 78.2, 56.2, 55.8, 47.0, 38.4, 37.6, 27.5, 25.4, 23.2, 20.1,
15.3. HRMS (TOF MS ES-) m/z calculated for C20H27O6 (M - H)- 363.1808, found 363.1798.
(2R,4aR,9aR)-N-(4-((E)-3,7-Dimethylocta-2,6-dienyl)-3,5-bis(methoxymethoxy)phenyl)-5-
methoxy-2-(methoxymethoxy)-1,1,4a-trimethyl-2,3,4,4a,9,9a-hexahydro-1H-xanthene-7-
carboxamide (25). To a stirred solution of carboxylic acid 24 (49 mg, 0.13 mmol) and amine 22
(39 mg, 0.11 mmol) in anhydrous CH2Cl2 (1 mL) was added EDC (64 mg, 0.34 mmol) and 4-
(dimethylamino)pyridine (2.7 mg, 22 µmol). The solution was stirred at rt for 19 hours and then
washed with saturated aqueous NH4Cl. The layers were separated and the aqueous layer was
extracted with CH2Cl2 (3x). The combined organic extracts were washed with brine, dried over
16

Na2SO4, and filtered, and the filtrate was concentrated in vacuo. Final purification using an ISCO
Combiflash Rf chromatography gradient (0 to 50% EtOAc in hexanes) afforded amide 25 (42
1
mg, 54%) as a yellow oil: H NMR (400 MHz, CDCl3) δ 7.89 (s, 1H), 7.31 (d, J = 1.9 Hz, 1H),
7.21 (d, J = 1.8 Hz, 1H), 7.18 (s, 2H), 5.23 – 5.16 (m, 5H), 5.11 – 5.04 (m, 1H), 4.76 (d, J = 6.9
Hz, 1H), 4.64 (d, J = 6.9 Hz, 1H), 3.87 (s, 3H), 3.50 – 3.46 (m, 6H), 3.40 (s, 3H), 3.37 (d, J = 7.1
Hz, 2H), 3.26 (dd, J = 11.5, 4.0 Hz, 1H), 2.76 – 2.68 (m, 2H), 2.15 – 2.10 (m, 1H), 2.08 – 1.99
(m, 3H), 1.98 – 1.93 (m, 3H), 1.85 – 1.79 (m, 1H), 1.78 (s, 3H), 1.69 – 1.66 (m, 1H), 1.65 (s,
3H), 1.61 – 1.52 (m, 4H), 1.24 (s, 3H), 1.08 (s, 3H), 0.89 (s, 3H); 13C NMR (101 MHz, CDCl3) δ
165.4, 155.9 (2C), 149.1, 146.1, 137.3, 134.6, 131.3, 126.1, 124.5, 122.9, 122.4, 120.4, 116.4,
108.7, 100.4 (2C), 96.3, 94.7 (2C), 84.0, 77.8, 56.2, 56.2 (2C), 55.7, 47.0, 39.9, 38.4, 37.5, 27.5,
26.9, 25.8, 25.4, 23.3, 22.5, 20.0, 17.7, 16.2, 15.2. HRMS (TOF MS ES+) m/z calculated for
C40H58NO9 (M + H)+ 696.4112, found 696.4116.
2R,4aR,9aR)-5-Methoxy-2-(methoxymethoxy)-1,1,4a-trimethyl-2,3,4,4a,9,9a-hexahydro-
1H-xanthen-7-amine (26). An oven-dried flask was charged with carboxylic acid 24 (75 mg,
0.21 mmol) in anhydrous benzene (21 mL). To this stirred solution was added triethylamine
(0.287 mL, 2.10 mmol) followed by the dropwise addition of DPPA (0.443 mL, 2.10 mmol) via
syringe. The resulting solution was stirred at rt for 15 minutes, and then the flask was fitted with
a reflux condenser and heated at reflux overnight. The benzene was removed under reduced
pressure and the residue was dissolved in THF (2.0 mL). To this solution was added aqueous 4N
LiOH (1.0 mL, 4.12 mmol) and the resulting mixture was stirred vigorously at rt for 1 hour. The
mixture was diluted with H2O and the layers were separated. The aqueous layer was extracted
with EtOAc (3x) and the combined organic extracts were washed with brine, and dried over
17

Na2SO4. The mixture was filtered and the filtrate was concentrated in vacuo. Final purification
using an ISCO Combiflash Rf chromatography gradient (20 to 60% EtOAc in hexanes) afforded
1
amine 26 (37 mg, 54%) as a brown oil: H NMR (400 MHz, CDCl3) δ 6.15 (d, J = 2.5 Hz, 1H),
6.06 (d, J = 2.4 Hz, 1H), 4.76 (d, J = 6.8 Hz, 1H), 4.64 (d, J = 6.8 Hz, 1H), 3.78 (s, 3H), 3.40 (s,
3H), 3.25 (dd, J = 11.6, 4.2 Hz, 1H), 2.61 (s, 1H), 2.59 (s, 1H), 2.08 (dt, J = 12.8, 3.4 Hz, 1H),
1.96 (ddd, J = 13.2, 7.6, 3.7 Hz, 1H), 1.77 (td, J = 13.4, 3.2 Hz, 1H), 1.69 (dd, J = 10.0, 8.1 Hz,
1H), 1.63 – 1.49 (m, 1H), 1.21 (s, 3H), 1.06 (s, 3H), 0.88 (s, 3H); 13C NMR (101 MHz, CDCl3) δ
149.4, 139.0, 135.7, 123.3, 107.4, 99.0, 96.3, 84.3, 76.1, 56.0, 55.7, 47.3, 38.3, 37.8, 27.5, 25.4,
23.4, 19.7, 15.2; HRMS (TOF MS ES+) m/z calculated for C19H30NO4 (M + H)+ 336.2175,
found 336.2182.
4-((E)-3,7-Dimethylocta-2,6-dienyl)-N-((2R,4aR,9aR)-5-methoxy-2-(methoxymethoxy)-
1,1,4a-trimethyl-2,3,4,4a,9,9a-hexahydro-1H-xanthen-7-yl)-3,5-
bis(methoxymethoxy)benzamide (27). To a stirred solution of carboxylic acid 21 (42 mg, 0.11
mmol) and amine 26 (31 mg, 92 µmol) in anhydrous CH2Cl2 (1 mL) was added EDC (53 mg,
0.28 mmol) and 4-(dimethylamino)pyridine (2.3 mg, 18 µmol). The solution was stirred at rt for
20 hours and then washed with saturated aqueous NH4Cl. The layers were separated and the
aqueous layer was extracted with CH2Cl2 (3x). The combined organic extracts were washed with
brine, dried over Na2SO4, and filtered, and the filtrate was concentrated in vacuo. Final
purification using an ISCO Combiflash Rf chromatography gradient (0 to 60% EtOAc in
hexanes) afforded amide 27 (32 mg, 51%) as a yellow oil: 1H NMR (400 MHz, CDCl3) δ 7.75 (s,
1H), 7.27 (s, 2H), 7.19 (d, J = 2.1 Hz, 1H), 6.91 (d, J = 2.2 Hz, 1H), 5.26 (s, 4H), 5.24 – 5.18 (m,
1H), 5.12 – 5.04 (m, 1H), 4.79 (d, J = 6.8 Hz, 1H), 4.66 (d, J = 6.8 Hz, 1H), 3.86 (s, 3H), 3.50 (s,
18

6H), 3.46 (d, J = 7.2 Hz, 2H), 3.43 (s, 3H), 3.28 (dd, J = 11.6, 4.1 Hz, 1H), 2.72 (s, 1H), 2.70 (s,
1H), 2.13 (dt, J = 12.7, 3.3 Hz, 1H), 2.09 – 2.03 (m, 2H), 2.01 – 1.95 (m, 3H), 1.85 – 1.77 (m,
4H), 1.73 (t, J = 9.1 Hz, 1H), 1.66 (s, 3H), 1.63 – 1.55 (m, 4H), 1.26 (s, 3H), 1.09 (s, 3H), 0.91
13
(s, 3H); C NMR (101 MHz, CDCl3) δ 165.5, 155.9 (2C), 148.9, 139.8, 135.5, 134.2, 131.5,
130.2, 127.2, 124.4, 122.8, 121.9, 113.4, 106.7 (2C), 103.4, 96.3, 94.7 (2C), 84.2, 76.8, 56.3
(2C), 56.2, 55.8, 47.2, 39.9, 38.4, 37.7, 27.5, 26.8, 25.8, 25.4, 23.4, 23.0, 19.8, 17.8, 16.3, 15.2.
HRMS (TOF MS ES+) m/z calculated for C40H58NO9 (M + H)+ 696.4112, found 696.4122.
Methyl 4-methoxy-1-methyl-1H-indole-6-carboxylate (29). An oven-dried flask was charged
with commercial methyl 4-hydroxyindole-6-carboxylate (50 mg, 0.26 mmol) in anhydrous DMF
(1 mL) at 0 oC. To this solution was added NaH (60% in mineral oil, 31 mg, 0.79 mmol) and the
solution was stirred for 30 minutes at 0 oC. After CH3I (40 µL, 0.63 mmol) was added dropwise
to the solution via syringe, the solution was allowed to equilibrate to rt overnight. The reaction
was quenched with the addition of H2O (3 mL) and the mixture was extracted with EtOAc (5x).
The organic extracts were combined, dried over Na2SO4, and filtered, and the filtrate was
concentrated under reduced pressure. Final purification using an ISCO Combiflash Rf
chromatography gradient (0 to 20% EtOAc in hexanes) afforded the dimethylated compound 29
(47.8 mg, 83%) as a yellow oil: 1H NMR (500 MHz, CDCl3) δ 7.78 (s, 1H), 7.20 (s, 1H), 7.11 (d,
J = 3.0 Hz, 1H), 6.61 (d, J = 2.7 Hz, 1H), 4.00 (s, 3H), 3.95 (s, 3H), 3.84 (s, 3H).30
4-Methoxy-1-methyl-1H-indole-6-carboxylic acid (30). To a stirred solution of indole 29 (47.8
mg, 0.22 mmol) in THF (1 mL) and H2O (1 mL) was added LiOH·H2O (18 mg, 0.44 mmol). The
19

flask was stirred at rt overnight and then the solution was washed with saturated aqueous NH4Cl.
The layers were separated and the aqueous layer was extracted with EtOAc (3x). The combined
organic extracts were washed with brine, dried over Na2SO4 and filtered, and the filtrate was
concentrated in vacuo. Final purification using an ISCO Combiflash Rf chromatography gradient
(0 to 40% EtOAc in hexanes) afforded the carboxylic acid 30 (42.4 mg, 95%) as a white powder:
1H NMR (500 MHz, CDCl3) δ 7.88 (s, 1H), 7.27 (s, 1H), 7.15 (d, J = 2.9 Hz, 1H), 6.64 (d, J =
2.9 Hz, 1H), 4.03 (s, 3H), 3.86 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 173.1, 153.1, 137.4,
131.0, 123.7, 123.3, 107.0, 100.2, 99.2, 55.7, 33.4. HRMS (TOF MS ES-) m/z calculated for
C11H10NO3 (M - H)- 204.0661, found 204.0669.
4-Methoxy-1-methyl-1H-indol-6-amine (31). An oven-dried flask was charged with carboxylic
acid 30 (31 mg, 0.15 mmol) in anhydrous benzene (15 mL). To this stirred solution was added
triethylamine (210 µL, 1.50 mmol) followed by the dropwise addition of DPPA (326 µL, 1.50
mmol) via syringe. The solution was stirred at rt for 15 minutes, and then the flask was fitted
with a reflux condenser and heated at reflux overnight. The benzene was removed under reduced
pressure and the residue was dissolved in THF (1.5 mL). To this solution was added aqueous 4N
LiOH (755 µL, 3.00 mmol) and the resulting mixture was stirred vigorously at rt for 2 hours.
After the mixture was diluted with H2O, the layers were separated. The aqueous layer was
extracted with EtOAc (3x) and the combined organic extracts were washed with brine, and dried
over Na2SO4. The mixture was filtered and the filtrate was concentrated in vacuo. Final
purification using an ISCO Combiflash Rf chromatography gradient (0 to 80% EtOAc in
1
hexanes) afforded amine 31 (24.7 mg, 93%) as a brown oil: H NMR (500 MHz, CDCl3) δ 6.75
(d, J = 3.1 Hz, 1H), 6.43 (d, J = 3.1 Hz, 1H), 6.24 (s, 1H), 6.01 (s, 1H), 3.90 (s, 3H), 3.63 (s,
20

13
3H); C NMR (126 MHz, CDCl3) δ 154.0, 143.1, 139.3, 125.4, 112.7, 98.3, 91.8, 88.2, 55.4,
33.0. HRMS (TOF MS ES+) m/z calculated for C10H13N2O (M + H)+ 177.1028, found 177.1033.
(2R,4aR,9aR)-5-Methoxy-N-(4-methoxy-1-methyl-1H-indol-6-yl)-2-(methoxymethoxy)-
1,1,4a-trimethyl-2,3,4,4a,9,9a-hexahydro-1H-xanthene-7-carboxamide (32). To a stirred
solution of carboxylic acid 24 (20 mg, 57 µmol) and amine 31 (12 mg, 68 µmol) in anhydrous
CH2Cl2 (1 mL) was added EDC (33 mg, 0.17 mmol) and 4-(dimethylamino)pyridine (1.4 mg, 11
µmol). The solution was stirred at rt for 24 hours and then washed with saturated aqueous
NH4Cl. The layers were separated and the aqueous layer was extracted with CH2Cl2 (3x). The
combined organic extracts were washed with brine, dried over Na2SO4 and filtered, and the
filtrate was concentrated in vacuo. Final purification using an ISCO Combiflash Rf
chromatography gradient (0 to 80% EtOAc in hexanes) afforded 32 (20.4 mg, 99%) as a yellow
1
oil: H NMR (500 MHz, CDCl3) δ 7.96 (s, 1H), 7.61 (s, 1H), 7.36 (d, J = 1.4 Hz, 1H), 7.25 (s,
1H), 6.93 (d, J = 3.1 Hz, 1H), 6.63 (s, 1H), 6.53 (d, J = 3.0 Hz, 1H), 4.77 (d, J = 6.9 Hz, 1H),
4.65 (d, J = 6.9 Hz, 1H), 3.94 (s, 3H), 3.90 (s, 3H), 3.74 (s, 3H), 3.41 (s, 3H), 3.27 (dd, J = 11.6,
4.1 Hz, 1H), 2.78 – 2.69 (m, 2H), 2.15 (dt, J = 12.7, 3.2 Hz, 1H), 2.03 – 1.97 (m, 1H), 1.81 (td, J
= 13.8, 3.2 Hz, 1H), 1.71 (dd, J = 11.1, 6.9 Hz, 1H), 1.59 (d, J = 14.0 Hz, 1H), 1.26 (s, 3H), 1.09
13
(s, 3H), 0.90 (s, 3H); C NMR (126 MHz, CDCl3) δ 165.6, 153.4, 149.3, 146.1, 138.2, 133.8,
127.6, 126.6, 122.5, 120.4, 116.3, 108.9, 98.5, 96.4, 95.0, 94.3, 84.1, 77.8, 56.4, 55.8, 55.6, 47.1,
38.4, 37.7, 33.2, 27.6, 25.4, 23.4, 20.0, 15.3. HRMS (TOF MS ES+) m/z calculated for
C30H39N2O6 (M + H)+ 523.2808, found 523.2812.
21

(2R,4aR,9aR)-2-Hydroxy-5-methoxy-N-(4-methoxy-1-methyl-1H-indol-6-yl)-1,1,4a-
trimethyl-2,3,4,4a,9,9a-hexahydro-1H-xanthene-7-carboxamide (33), NSC#795315. To a
stirred solution of amide 32 (15 mg, 29 µmol) in MeOH (3 mL) was added p-TsOH·H2O (11 mg,
29 µmol). The flask was sealed and stirred for 2 days at rt. The solution was diluted with EtOAc
and then washed with saturated aqueous NaHCO3. The layers were separated and the aqueous
layer was extracted with EtOAc (3x). The combined organic extracts were dried over Na2SO4
and filtered, and the filtrate was concentrated in vacuo. Final purification using an ISCO
Combiflash Rf chromatography gradient (0 to 80% EtOAc in hexanes) afforded 33 (9 mg, 65%)
as a clear oil: 1H NMR (400 MHz, CDCl3) δ 7.91 (s, 1H), 7.60 (s, 1H), 7.35 (s, 1H), 7.26 (s, 1H),
6.93 (d, J = 1.1 Hz, 1H), 6.62 (s, 1H), 6.53 (s, 1H), 3.95 (s, 3H), 3.91 (s, 3H), 3.74 (s, 3H), 3.43
(d, J = 8.8 Hz, 1H), 2.80 – 2.73 (m, 2H), 2.15 (d, J = 14.3 Hz, 1H), 1.93 – 1.82 (m, 2H), 1.73 –
1.66 (m, 1H), 1.64 – 1.56 (m, 2H), 1.26 (s, 3H), 1.11 (s, 3H), 0.89 (s, 3H); 13C NMR (101 MHz,
CDCl3) δ 164.6, 152.4, 148.3, 145.1, 137.2, 132.8, 126.6, 125.6, 121.5, 119.4, 115.3, 107.9, 97.5,
94.0, 93.3, 77.1, 76.9, 55.4, 54.6, 45.8, 37.6, 36.8, 32.3, 27.5, 26.5, 22.5, 19.1, 13.5. HRMS
(TOF MS ES+) m/z calculated for C28H35N2O5 (M + H)+ 479.2546, found 479.2541.
4-Methoxy-N-((2R,4aR,9aR)-5-methoxy-2-(methoxymethoxy)-1,1,4a-trimethyl-
2,3,4,4a,9,9a-hexahydro-1H-xanthen-7-yl)-1-methyl-1H-indole-6-carboxamide (34). To a
stirred solution of amine 26 (11.5 mg, 34 µmol) and carboxylic acid 30 (16.5 mg, 80 µmol) in
anhydrous CH2Cl2 (1 mL) was added EDC (26 mg, 0.14 mmol) and 4-(dimethylamino)pyridine
(1 mg, 7 µmol). The solution was stirred at rt for 24 hours and then washed with saturated
aqueous NH4Cl. The layers were separated and the aqueous layer was extracted with CH2Cl2
(3x). The combined organic extracts were washed with brine, dried over Na2SO4, and filtered,
22

and the filtrate was concentrated in vacuo. Final purification using an ISCO Combiflash Rf
chromatography gradient (0 to 100% EtOAc in hexanes) afforded amide 34 (8 mg, 45%) as a
1
yellow oil: H NMR (400 MHz, CDCl3) δ 7.77 (s, 1H), 7.51 (s, 1H), 7.23 (d, J = 2.3 Hz, 1H),
7.10 (d, J = 3.1 Hz, 1H), 6.99 (d, J = 1.0 Hz, 1H), 6.93 (d, J = 2.3 Hz, 1H), 6.62 (d, J = 2.6 Hz,
1H), 4.77 (d, J = 6.8 Hz, 1H), 4.65 (d, J = 6.8 Hz, 1H), 4.02 (s, 3H), 3.88 (s, 3H), 3.84 (s, 3H),
3.41 (s, 3H), 3.28 (dd, J = 11.5, 4.1 Hz, 1H), 2.71 (s, 1H), 2.68 (s, 1H), 2.13 (dt, J = 12.7, 3.3 Hz,
1H), 1.99 (ddd, J = 11.4, 7.5, 3.5 Hz, 1H), 1.80 (td, J = 13.8, 3.3 Hz, 1H), 1.64 – 1.57 (m, 1H),
1.26 (s, 3H), 1.08 (s, 3H), 0.90 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 166.9, 153.5, 149.0,
139.7, 137.6, 130.6, 130.1, 129.7, 122.9, 121.9, 113.3, 103.3, 102.7, 99.0, 98.1, 96.3, 84.2, 67.2,
56.2, 55.8, 55.7, 47.2, 38.4, 37.7, 33.4, 27.5, 25.5, 23.4, 19.9, 15.2. HRMS (TOF MS ES+) m/z
calculated for C30H39N2O6 (M + H)+ 523.2808, found 523.2818.
N-((2R,4aR,9aR)-2-Hydroxy-5-methoxy-1,1,4a-trimethyl-2,3,4,4a,9,9a-hexahydro-1H-
xanthen-7-yl)-4-methoxy-1-methyl-1H-indole-6-carboxamide (35), NSC#795316. To a stirred
solution of amide 34 (8.6 mg, 16 µmol) in MeOH (1.6 mL) was added p-TsOH·H2O (6 mg, 31
µmol). The flask was sealed and stirred for 2 days at rt. The solution was diluted with EtOAc and
then washed with saturated aqueous NaHCO3. The layers were separated and the aqueous layer
was extracted with EtOAc (3x). The combined organic extracts were dried over Na2SO4 and
filtered, and the filtrate was concentrated in vacuo. Final purification using an an ISCO
Combiflash Rf chromatography gradient (0 to 100% EtOAc in hexanes) afforded amide 35 (4.7
1
mg, 60%) as a yellow oil: H NMR (400 MHz, CDCl3) δ 7.82 (s, 1H), 7.52 (s, 1H), 7.23 (d, J =
2.1 Hz, 1H), 7.09 (d, J = 3.0 Hz, 1H), 7.00 (s, 1H), 6.94 (d, J = 2.0 Hz, 1H), 6.62 (d, J = 3.1 Hz,
1H), 4.02 (s, 3H), 3.87 (s, 3H), 3.83 (s, 3H), 3.42 (dd, J = 11.1, 2.8 Hz, 1H), 2.71 (s, 1H), 2.68 (s,
23

1H), 2.16 – 2.09 (m, 1H), 1.91 – 1.79 (m, 2H), 1.71 (t, J = 9.0 Hz, 1H), 1.65 – 1.56 (m, 2H), 1.25
13
(s, 3H), 1.09 (s, 3H), 0.88 (s, 3H); C NMR (101 MHz, CDCl3) δ 166.9, 153.5, 149.0, 139.7,
137.6, 130.7, 130.1, 129.8, 122.8, 122.0, 113.3, 103.5, 102.7, 99.0, 98.2, 78.2, 56.2, 55.7, 47.0,
38.5, 37.9, 33.4, 28.5, 27.5, 23.5, 19.9, 14.4. One carbon signal was obscured by the chloroform
resonance; when the spectrum was recorded in C6D6 this was observed at 76.4 ppm. HRMS
(ESI) m/z calcd for C28H35N2O5 (M + H)+ 479.2546, found 479.2540.
1
13
Supporting Information Available: The H and C NMR spectra of all new compounds, and
the full 60 cell assay data (including the GI50, TGI, and LC50 values for each cell line) for
compounds 11, 12, 33, and 35, can be found here. This material is available free of charge via
the Internet at
Acknowledgment. We thank the Center for Biocatalysis and Bioprocessing for a fellowship (to
D.P.S.) through the predoctoral Training Program in Biotechnology (T32 GM008365). Financial
support from the Roy J. Carver Charitable Trust (#01-224) through its Research Program of
Excellence (to D.F.W.) is greatly appreciated. This research was supported by the Intramural
Research Program of the NIH, National Cancer Institute, Center for Cancer Research (1ZIA-
BC01147005). We thank the Developmental Therapeutics Program of NCI for NCI 60 testing,
and Jason Evans for COMPARE analyses.
Competing financial interests. JAB and DFW are named inventors on several patents that
describe schweinfurthin analogues, held by the University of Iowa and/or NIH.
24

References
(1)
Beutler, J. A.; Shoemaker, R. H.; Johnson, T.; Boyd, M. R. J. Nat. Prod. 1998,
Beutler, J. A.; Jato, J.; Cragg, G. M.; Boyd, M. R. Natural Product Letters 2000,
Klausmeyer, P.; Van, Q. N.; Jato, J.; McCloud, T. G.; Beutler, J. A. J. Nat. Prod.
61, 1509-1512.
(2)
14, 399-404.
(3)
2010, 73, 479-481.
(4)
Yoder, B. J.; Cao, S.; Norris, A.; Miller, J. S.; Ratovoson, F.; Razafitsalama, J.;
Andriantsiferana, R.; Rasamison, V. E.; Kingston, D. G. I. J. Nat. Prod. 2007, 70, 342-346.
(5)
31, 1439-1442.
(6)
Thoison, O.; Hnawia, E.; Guerittevoegelein, F.; Sevenet, T. Phytochemistry 1992,
Pettit, G. R.; Inoue, M.; Kamano, Y.; Herald, D. L.; Arm, C.; Dufresne, C.;
Christie, N. D.; Schmidt, J. M.; Doubek, D. L.; Krupa, T. S. J. Am. Chem. Soc. 1988, 110, 2006-
2007.
(7)
Kubo, S.; Mimaki, Y.; Terao, M.; Sashida, Y.; Nikaido, T.; Ohmoto, T.
Phytochemistry 1992, 31, 3969-3973.
(8)
Komiya, T.; Fusetani, N.; Matsunaga, S.; Kubo, A.; Kaye, F. J.; Kelley, M. J.;
Tamura, K.; Yoshida, M.; Fukuoka, M.; Nakagawa, K. Cancer Chemother. Pharmacol. 2003,
51, 202-208.
25

(9)
Tasdemir, D.; Mangalindan, G. C.; Concepcion, G. P.; Verbitski, S. M.;
Rabindran, S.; Miranda, M.; Greenstein, M.; Hooper, J. N. A.; Harper, M. K.; Ireland, C. M. J.
Nat. Prod. 2002, 65, 210-214.
(10) Burgett, A. W. G.; Poulsen, T. B.; Wangkanont, K.; Anderson, D. R.; Kikuchi, C.;
Shimada, K.; Okubo, S.; Fortner, K. C.; Mimaki, Y.; Kuroda, M.; Murphy, J. P.; Schwalb, D. J.;
Petrella, E. C.; Cornella-Taracido, I.; Schirle, M.; Tallarico, J. A.; Shair, M. D. Nature Chemical
Biology 2011, 7, 639-647.
(11) Bao, X. F.; Zheng, W. J.; Sugi, N. H.; Agarwala, K. L.; Xu, Q. L.; Wang, Z. C.;
Tendyke, K.; Lee, W. N.; Parent, L.; Li, W.; Cheng, H. S.; Shen, Y. C.; Taylor, N.; Dezso, Z.;
Du, H.; Kotake, Y.; Zhao, N. D.; Wang, J.; Postema, M.; Woodall-Jappe, M.; Takase, Y.;
Uenaka, T.; Kingston, D. G. I.; Nomoto, K. Cancer Biology & Therapy 2015, 16, 589-601.
(12) Kuder, C. H.; Weivoda, M. M.; Zhang, Y.; Zhu, J.; Neighbors, J. D.; Wiemer, D.
F.; Hohl, R. J. Lipids 2015, 50, 1195-1207.
(13) Topczewski, J. J.; Kodet, J. G.; Wiemer, D. F. J. Org. Chem. 2011, 76, 909-919.
(14) Topczewski, J. J.; Neighbors, J. D.; Wiemer, D. F. J. Org. Chem. 2009, 74, 6965-
6972.
(15) Treadwell, E. M.; Cermak, S. C.; Wiemer, D. F. J. Org. Chem. 1999, 64, 8718-
8723.
(16) Mente, N. R.; Neighbors, J. D.; Wiemer, D. F. J. Org. Chem. 2008, 73, 7963-
7970.
(17) Topczewski, J. J.; Wiemer, D. F. Tetrahedron Lett. 2011, 52, 1628-1630.
(18) Neighbors, J. D.; Beutler, J. A.; Wiemer, D. F. J. Org. Chem. 2005, 70, 925-931.
26

(19) Ulrich, N. C.; Kodet, J. G.; Mente, N. R.; Kuder, C. H.; Beutler, J. A.; Hohl, R. J.;
Wiemer, D. F. Bioorg. Med. Chem. 2010, 18, 1676-1683.
(20) Topczewski, J. J.; Callahan, M. P.; Kodet, J. G.; Inbarasu, J. D.; Mente, N. R.;
Beutler, J. A.; Wiemer, D. F. Bioorg. Med. Chem. 2011, 19, 7570-7581.
(21) Aubé, J.; Fehl, C.; Liu, R.; McLeod, M. C.; Motiwala, H. F. In Comprehensive
Organic Synthesis: Second Edition 2014; Vol. 6, p 598-635.
(22) Hume, P. A.; Furkert, D. P.; Brimble, M. A. Organic Letters 2013, 15, 4588-
4591.
(23) Wiemer, A. J.; Wiemer, D. F. Top. Curr. Chem. 2015, 360, 115-160.
(24) Gardner, K. D.; Wiemer, D. F. J. Org. Chem. 2016, 81, 1585-1592.
(25) Jones, J. E.; Ruppel, J. V.; Gao, G.-Y.; Moore, T. M.; Zhang, X. P. J. Org. Chem.
2008, 73, 7260-7265.
(26) Gao, G.-Y.; Jones, J. E.; Vyas, R.; Harden, J. D.; Zhang, X. P. J. Org. Chem.
2006, 71, 6655-6658.
(27) Kodet, J. G.; Beutler, J. A.; Wiemer, D. F. Bioorg. Med. Chem. 2014, 22, 2542-
2552.
(28) Kodet, J. G.; Wiemer, D. F. J. Org. Chem. 2013, 78, 9291-9302.
(29) Monks, A.; Scudiero, D.; Skehan, P.; Shoemaker, R.; Paull, K.; Vistica, D.; Hose,
C.; Langley, J.; Cronise, P.; Vaigrowolff, A.; Graygoodrich, M.; Campbell, H.; Mayo, J.; Boyd,
M. J. Natl. Cancer Inst. 1991, 83, 757-766.
(30) Kim, M.; Vedejs, E. J. Org. Chem. 2004, 69, 6945-6948.
27