Synthesis of 4- epi-Parviflorons A, C, and E: Structure-Activity Relationship Study of Antiproliferative Abietane Derivatives

Article abstract of DOI:10.1021/acs.joc.8b02832

The first syntheses of 4-epi-parviflorons A, C, and E (4-epi-1-3) were achieved in 12-13 steps from commercially available (-)-abietic acid (5). All synthesized compounds, including intermediates and derivatives, were evaluated for antiproliferative activity against five human tumor cell lines. A structure-activity relationship study revealed no significant difference between Pf E and 4-epi-Pf E, the importance of two oxygen functional groups at C-11 and C-12 for antiproliferative activity, as well as a combination of carbomethoxy at C-4 and a benzoyl ester with electron-drawing group at C-12 or hydroxymethyl at C-4 and an appropriate oxidation state of ring-B/C for triple-negative breast cancer cell selectivity.

Full text of DOI:10.1021/acs.joc.8b02832

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Article
Synthesis of 4-epi-Parviflorons A, C and E: Structure-Activity
Relationship Study of Antiproliferative Abietane Derivatives
Yui Miyajima, Yohei Saito, Munehisa Takeya, Masuo Goto, and Kyoko Nakagawa-Goto
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b02832 • Publication Date (Web): 22 Feb 2019
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Synthesis of 4-epi-Parviflorons A, C and E: Structure-Activity Relationship
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Study of Antiproliferative Abietane Derivatives
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Yui Miyajima,† Yohei Saito,† Munehisa Takeya,† Masuo Goto,‡ Kyoko Nakagawa-Goto†,‡,*
†
School of Pharmaceutical Sciences, College of Medical, Pharmaceutical and Health Sciences,
Kanazawa University, Kanazawa, 920-1192, Japan
‡ Chemical Biology and Medicinal Chemistry, Eshelman School of Pharmacy, University of North
Carolina, Chapel Hill, North Carolina 27599-7568, Unite States
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ABSTRACT
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The first syntheses of 4-epi-parviflorons A, C, and E (4-epi-1–3) were achieved in 12–13 steps
from commercially available (−)-abietic acid (5). All synthesized compounds, including
intermediates and derivatives, were evaluated for antiproliferative activity against five human
tumor cell lines. A structure-activity relationship study revealed no significant difference between
Pf E and 4-epi-Pf E, the importance of two oxygen functional groups at C-11 and C-12 for
antiproliferative activity, as well as a combination of carbomethoxy at C-4 and a benzoyl ester
with electron-drawing group at C-12 or hydroxymethyl at C-4 and an appropriate oxidation state
of ring-B/C for triple-negative breast cancer cell selectivity.
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INTRODUCTION
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Parviflorons (Pfs) are abietane diterpenes isolated from only the genus Plectranthus in the family
Lamiaceae. These compounds were first isolated by Eugster et al., Pfs A–F from P. parviflorus in
19781 and Pfs G and H from P. strigosus in 1984.2 Pfs feature a conjugated o-hydroxy-p-quinone
methide with an isopropyl group at C-13 and an oxygenated functional group on ring-A. They can
be classified into three groups based on the position of the oxygenation, C-4 for Pfs AC and E,
(1–4, Figure 1), C-2 for Pfs D, F and G and C-2/-4 for Pf H. Among the eight compounds, we
found that PFs C, E and F3 displayed potent antiproliferative activities with IC50 values of 2.5–7.3
µM against several human tumor cell lines (HTCLs) including a multidrug resistant cell line
(Figure 1).
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O
12
HO 11
1
13
: R =
Parvifloron A
C
1
2
3
4
B
: R = 4-OH-Ph, Parvifloron C
: R = 3,4-diOH-Ph, Parvifloron E
: R = 4-OH-3-OMe-Ph, Parvifloron B
A
4
7
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O
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19
R
O
Compound
Cell line/IC50 (µM)a
A549
3.1
KB
3.1
4.8
KB-VIN MDA-MB-231 MCF-7
Parvifloron C (2)
Parvifloron E (3)
3.4
7.2
3.4
5.0
3.7
4.8
5.1
Figure 1. The structures of parviflorons A–C and E (1–4) and antiproliferative activities of 2 and 3
aA549 (lung carcinoma), KB (identical to cervical carcinoma HeLa derivative AV-3), KB-VIN (P-gp-overexpressing
MDR subline of KB), MDA-MB-231 (triple-negative breast cancer), MCF-7 (estrogen receptor-positive & HER2-
negative breast cancer). Antiproliferative activity expressed as IC50 values for each cell line, the concentration of
compound that caused 50% reduction relative to untreated cells determined by the SRB assay.
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We recently reported the first total synthesis of Pf F.3 During this study, several derivatives
showed selective activity against the MDA-MB-231 triple-negative breast cancer (TNBC) cell line.
These results implied the possibility of developing more selective and potent anti-TNBC agents
from Pf derivatives. TNBC, which accounts for 10–20% of all invasive breast cancers,4 cannot be
treated with standard hormonal or targeted therapies, due to the lack of estrogen/progesterone
receptors (ER/PR) or HER2 overexpression. Thus, TNBC is associated with a poor prognosis and
30% of patients develop distant metastasis. More effective treatment depends urgently on the
discovery of TNBC selective antitumor agents. To obtain more potent compounds and structure-
activity relationship (SAR) information including the effects of substituents and stereocenter at C-
4, we accomplished the syntheses of PFs with oxygenated functional groups at C-4, namely 4-epi-
Pfs A, C and E, together with the related derivatives. All synthesized compounds were evaluated
for antiproliferative activity against five human tumor cell lines (HTCLs), MDA-MB-231
(TNBC), MCF-7 (estrogen receptor-positive and HER2-negative breast cancer), A549 (lung
carcinoma), KB (originally isolated from epidermoid carcinoma of the nasopharynx, while
identical to cervical carcinoma HeLa derivative AV-3), and KB-VIN (a KB-subline exhibiting
MDR phenotype with overexpression of P-gp).
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RESULTS AND DISCUSSION
Our retrosynthetic analysis is outlined in Scheme 1. We selected commercially available (−)-
abietic acid (5) as the starting material to maintain the chiral tricyclic framework, conceivably an
important core structure for the biological activity. We planned to assay all synthetic intermediates
to obtain important SAR, including the effect of the C-4 stereocenter on the cytotoxic activity as
the 4-epimers of natural Pfs will be generated from 5 through our proposed reaction sequence.
However, if necessary, we could invert the stereochemistry at C-4 via a reported method at the
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early stage.5 Our synthetic strategy involved a final esterification of the hydroxymethyl group in
6, prepared from catechol 7 through repeated oxidation and isomerization reactions (Scheme 1).
We planned to obtain catechol 7 from phenol 8 by Tada’s method using m-chlorobenzoyl peroxide
(mCBPO).6 Phenol 8 would be synthesized from (−)-abietic acid (5) through allylic oxidation to 9
followed by aromatization.
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O
OH
HO
HO
1 3
epi-Parviflorons –
CH2OH
CH2OH
6
7
OH
OH
COOMe
COOMe
COOH
5:
8
9
(-)-Abietic acid
Scheme 1. Retrosynthetic analysis of 4-epi-parviflorons A, C, and E
Using a known method,7 we initially produced mono-acetate 12 by methylation of (−)-abietic
acid (5), selective dihydroxylation at the 13,14 double bond with osmium (VIII) oxide, followed
by acetylation of the secondary alcohol (Scheme 2). The treatment of 12 with thionyl chloride
unexpectedly provided 9 with a hydroxyl rather than chloro group at C-12, even though water was
strictly excluded from the reaction. Although the mechanism of this reaction has been obscure,
12-chloroabietate B would be formed through SN2’ reaction from 14-acetoxy intermediate A.
SN2 reaction of a resultant acetate anion to C-12 on 12-chloroabietate B would provide 12-
acetoxyabietate C, which could be easily hydrolyzed to produce 9 (Scheme 3). Because the
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dihydroxylation step proceeded slowly and the overall yield of 9 was low, we attempted to insert
a hydroxyl group directly at the C-12 position of 10 using various allylic oxidation conditions. The
use of an iron carbonyl complex to achieve allylic oxidation was reported in 1988.8 In a model
reaction, in which the carbomethoxy moiety at C-4 was first converted to methyl group, the desired
allylic alcohol was obtained successfully via oxidative de-complexation of an iron carbonyl
complex with I2 in the presence of water. However, the same procedure with 10 did not produce
the desired compound 9. Other allylic oxidation conditions with different combinations of oxidants
(TBHP or O2) and metals [CuI, Pd(OH)2/C, RuCl3, Fe(acac)3, etc] resulted in complex mixtures.
However, under Wohl-Ziegler conditions, the desired 12-hydroxylated compound (9), rather than
the 12-brominated compound, was obtained in 19% yield. The direct allylic oxidation from 10 and
the three-step conversion from 6 produced 9 in similar overall yields. The resulting allylic alcohol
9 was then oxidized with pyridinium dichromate (PDC) and isomerized with sulfuric acid in acetic
acid at reflux temperature to provide phenol 8 together with its acetate 14, which was hydrolyzed
readily to 8. The ortho-oxidation of phenol 8 with m-chlorobenzoyl peroxide (mCBPO)6 produced
mainly 11-hydroxy-12-m-chlorobenzoyloxy 15 through an intramolecular ester exchange of 12-
hydroxy-11-m-chlorobenzoyloxy E, derived by a [3.3]sigmatropic shift from 12-m-
chlorobenzoperoxoate D (Scheme 4). The chemical structure of 15 was identified by HMBC,
particularly from the correlation between the hydroxyl proton with C-11 and C-10. The treatment
of 15 with 10 eq. mol of LiAlH4 in THF at reflux temperature for 7 h generated alcohol 7, while
the reduction with 5.5 eq. mol of reagent and a shorter reaction time gave methyl ester 16 in good
yield. Oxidation of 7 with Ag2O, followed by heating in toluene produced ortho-hydroxy quinone
methide 18, which was isomerized to 19 by heating.7 Further oxidation and isomerization of 19
produced 6, the common intermediate to 4-epi-Pfs.
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OH
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OH
OR
f
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COOR
COOMe
COOMe
COOMe
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5:
10:
R = H
R = Me
11:
12:
R = H
R = Ac
9
13
a
c
OR
OR
OH
O
12
HO 11
HO
R
O
j
k
l
i
COOMe
COOMe
R = m-chlorobenzoyl
CH2OH
15:
7:
16:
R = CH2OH
R = CO2Me
8:
14:
R = H
R = Ac
17
h
O
OH
HO
O
O
O
HO
HO
o
n
m
CH2OH
CH2OH
CH2OH
CH2OH
20
6
18
19
Scheme 2. Preparation of common intermediate 6
Reagents and conditions: (a) MeI, K2CO3, acetone, reflux, 22 h, 87%; (b) OsO4, py, CH3NO, H2O,
tBuOH, reflux, 66 h, 57%; (c) Ac2O, py, rt, 3 h, 92%; (d) SOCl2, Et3N, CH2Cl2, −78°C, 20 min,
56%; (e) NBS, AIBN, CCl4, rt, 27 h, 19%; (f) PDC, py, MS4Å, CH2Cl2, rt, 1 h, 60%; (g) cH2SO4,
HOAc, reflux, 3 h, 42% for 8, 39% for 14; (h) NaHCO3, H2O, MeOH, rt, 12.5 h, 95%; (i) mCPBO,
CH2Cl2, rt, 23 h, 69%; (j) LiAlH4 (10 eq. mol), THF, reflux, 4 h, 90% for 7, LiAlH4 (5.5 eq. mol),
THF, reflux, 1 h, 69% for 16; (k) Ag2O, CH2Cl2, rt, 2 h, 86%; (l) toluene, reflux, 2 h, 96%; (m)
neat, 115 °C, 3 h; (n) Ag2O, CH2Cl2, rt, 1 h, 62% for 2 steps; (o) toluene, reflux, 5 h, 60%.
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Cl
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OAc
OAc
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OAc
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COOMe
COOMe
COOMe
A
B
C
Scheme 3. A possible mechanism from 12 to 9
Cl
HMBC
H O
O
O
O
O
Cl
OH
Cl
O
O
O
8
COOMe
COOMe
COOMe
15
E
D
Scheme 4. The reaction pathway from phenol 8 to benzoate 15
Because compound 6 is unstable and acid sensitive,9 no acidic conditions could be applied
during subsequent esterification and deprotection steps. Only Shiina reagent proved successful for
the esterification of 6, although other condensation reagents, such as DCC, EDCI, and the use of
pentafluorophenyl ester, did not produce the desired ester. The treatment of 6 with 3-
methylcrotonic acid in the presence of Shiina reagent provided 4-epi-PF A (4-epi-1) in 11% yield
along with 22 in 4% yield (Scheme 5). The target compound 4-epi-Pf C (4-epi-2) was prepared by
reaction of 6 with benzoyl protected 4-hydroxybenzoic acid followed by deprotection of the
benzoyl group (Table 1, entry 2). Various methods were investigated to protect/deprotect the
catechol moiety of protocatechuic acid (Table 1, entries 3–6). While methyl and ethyl orthoesters
(24a,b) gave reasonable yields in the esterification of 6, the deprotection was inefficient under
slightly acidic or even neutral conditions (Table 1, entries 3–4).10 Esterification of 6 with
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protocatechuic acid protected as a silyl ether (24c) failed to give the desired product 26c, instead
giving only the ortho-quinone 20 (Table 1, entry 5). While the dibenzoyl protecting groups on the
desired esterified 26d were removed easily to give 4-epi-Pf E (4-epi-3) in good yield under basic
conditions using nBuNH2,11 the initial esterification of 6 not only gave 26d in low yield (16%) but
unexpectedly also produced 27 as well as 20 in lower (17%) and higher (56%) yields, respectively
(Table 1, entry 6). Compound 27 was produced by a reaction with benzoyl protection moiety on
24d rather than Shiina mixed anhydride.
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O
O
HO
HO
1) MNBA*, DMAP
Et3N, CH2Cl2
2) Deprotection
6
+
+
HOOC
Table 1
O
O
21
O
O
*MNBA:2-Methyl-6-nitrobenzoic anhydride
22
1
4-epi-Pf-A (4-epi- )
O
O
HO
1) MNBA, DMAP
Et3N, CH2Cl2
HO
HOOC
R
2) Deprotection
6
+
Table 1
R
R
R'
O
O
23:
24a
24b:
24c:
24d:
R = H, R' = OBz
: R, R' = OCH(OEt)
R, R' = OCH(OMe)
R = R' = OTBS
R = R' = OBz
OH
R'
O
O
25:
26a
26b:
26c:
26d:
R = H, R' = OBz
: R, R' = OCH(OEt)
R, R' = OCH(OMe)
R = R' = OTBS
R = R' = OBz
2
3
4-epi-Pf-C (4-epi- ), R = H
4-epi-Pf-E (4-epi- ), R = OH
27:
R = R' = H
Scheme 5. Total synthesis of 4-epi-Pfs (4-epi-1–3) from 6
Table 1. Reaction and yield of 4-epi-Pfs (4-epi-1–3)
Entry Acids Yields of ester products
Deprotection conditions
Yields of desired compounds
4-epi-1 (11%), 22 (4%), 20 (38%)
4-epi-2 (29%), 25 (4%)
1
2
3
21
23
24a
-
-
25 (45%), 20
26a (59%), 20 (16%)
n-BuNH2, PhH, rt, 7 h
PPTS, dioxane, H2O, rt, 4 d
4-epi-3 (8%), 26a (79%)
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24b
26b (38%), 20 (13%)
26c (0%), 20 (84%)
Amberlyst 15, K2HPO4,
KH2PO4, MeOH, THF, 45 °C
-
4-epi-3 (0%)
5
6
24c
24d
-
26d (16%), 27 (17%), 20 (56%) n-BuNH2, PhH, rt, 1 h
4-epi-3 (77%)
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As shown in Table 2, Pf E (3) and its epimer (4-epi-3) showed comparable potency against
the tested tumor cell lines; thus, the stereochemistry at C-4 did not affect the antiproliferative
activity. Accordingly, we felt that the additional stereo inversion step at C-4 was unnecessary to
our current study. In addition, we found that intermediate 15 with a m-chlorobenzoyloxy group on
C-12 exhibited selective inhibition of TNBC cell proliferation. This interesting finding led us to
synthesize related derivatives (30–40) with various aryloxy groups on C-12 (Scheme 6).
Furthermore, because catechol 16 showed broad antiproliferative activity against all tested tumor
cell lines, quinone methide 29 was also prepared to determine the effect of the oxidation state in
ring B/C.
O
O
O
HO
a
b
16
COOMe
COOMe
c
29
28
O
Ar
Ar
Ar
Ar
HO
O
12
39
40
2-naphthyl
3-Ph-Ph
30
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32
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36
37
38
3-F-Ph
3-Br-Ph
3-I-Ph
3-NO2-Ph
3,5-di-Cl-Ph
4-Cl-Ph
3-H-Ph
3-OMe-Ph
4-OMe-Ph
COOMe
Scheme 6. Preparation of abietane derivatives 30–40
Reagents and conditions: (a) Ag2O, CH2Cl2, rt, 40 min, 99%; (b) toluene, reflux, 8 h, 89%; (c)
ArCOOH, EDCI, DMAP, CH2Cl2, 0 C, 18–62%.
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According to the antiproliferative activity profiles against five HTCLs (Table 2), the compounds
were divided into three categories based on their biological profiles, (I) selectively active against
the TNBC cell line, (II) active (IC50 < 5 M) against all tested HTCLs, including MDR, and (III)
inactive against all tested HTCLs. The compounds belonging to group-I included 15, 18, 19, and
30–35. These compounds were four to five times more potent against MDA-MB-231 compared
with the remaining four cell lines. The synthesized 4-epi-3 and the intermediates 6, 7, 16, 17, 26a,
26d and 27 were classified as group-II. These eight compounds significantly inhibited the cell
growth of all tested HTCLs (although the actual active compound might be 6, which could be
produced by de-esterification of 4-epi-3 in the cell). Among them, compound 16 showed the most
potent cell growth inhibitory effects (IC50 < 3 M) against breast cancer cell lines, MDA-MB-231
and MCF-7, regardless of the hormonal receptor status. The remaining tested compounds were in
group-III and generally did not display significant cell growth inhibition. From these observations,
we determined the following SAR correlations, 1) two adjacent oxygenated functional groups at
C-11 and -12 are potentially required for increased antiproliferative activity [early intermediate
compounds 913 were weakly active or inactive, while 20 (11, 12-diketone) was an exception, 2)
when a carbomethoxy group is present at C-4, TNBC selectivity was induced by a benzoyl ester
substituted with an electronegative moiety at C-12 (compare 15 and 3035 with 16 and 3640), 3)
when a hydroxymethyl group is present at C-4, TNBC selectivity was dependent on the oxidation
state in ring-B/C (compare 6, 7, 17 and 20 with 18, 19 and 29). When 3-H-Ph (36) was substituted
by 3-F-Ph (30), TNBC selectivity was significantly increased. This observation suggests that 3-H-
Ph may be a target of oxidative detoxification by ubiquitously expressing enzyme, and the
halogens as well as nitrogen dioxide may be resistant (NO2, F > Br > I) against detoxifying enzyme
selectively expressed in MDA-MB-231. Overall, we demonstrates that TNBC selectivity can be
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inducible by moiety modified at C-12, while chirality at C-4 may not be responsible for the TNBC
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selectivity.
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Table 2. Antiproliferative Data of Synthesized Compounds
Cell lines / IC50 (M)a
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Compound A549
KB
KB-VIN MDA-MB-231 MCF-7
3 (Pf E)
5.1
5.3
4.8
7.2
9.5
5.0
5.5
6.1
6.4
4-epi-3
4.8
6
7
5.2
4.6
5.2
5.0
5.8
5.8
4.9
6.0
4.5
6.0
8
13.6
>40
>40
>40
>40
>40
20.1
5.0
3.9
3.7
18.6
>40
>40
>40
>40
>40
5.6
5.9
9
34.9
39.7
>40
>40
29.2
32.3
5.2
35.7
35.3
>40
>40
16.8
>40
6.1
>40
>40
>40
>40
39.0
20.4
2.8
10
11
12
13
15
16
2.7
17
6.9
5.0
6.5
4.8
6.4
18
17.9
18.5
>40
5.0
6.5
17.2
18.4
>40
5.5
4.9
7.1
19
17.2
>40
4.8
6.7
17.6
>40
4.4
20
36.4
4.1
26a
26d
27
7.0
13.5
4.9
21.6
5.2
6.3
8.1
4.9
5.0
5.2
29
21.8
29.4
>40
>40
24.3
19.2
23.4
39.2
33.7
22.0
29.5
>40
5.4
22.2
29.9
>40
>40
26.2
21.4
28.7
31.0
29.8
16.8
26.6
>40
6.3
23.7
32.9
>40
>40
33.9
34.6
35.9
33.6
30.1
17.1
23.9
>40
2352.8
11.6
5.2
17.1
17.9
22.9
27.2
20.9
17.0
19.1
26.3
21.9
24.1
34.2
29.4
10.9
30
31
8.4
32
11.5
5.1
33
34
3.9
35
4.0
36
21.4
11.0
23.4
17.9
19.6
8.7
37
38
39
40
PXLb(nM)
Class-(I) selectively active against the TNBC cell line; Class-(II) active (IC50 < 5 M) against all tested human tumor
cell lines (HTCLs); Class-(III) inactive against all tested HTCLs
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aAntiproliferative activity defined as IC50 value (M) for each cell line, the concentration of
compound that caused 50% reduction relative to untreated cells using the sulforhodamine B assay.
b Paclitaxel
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Because compounds that impact the cell cycle should inhibit cell growth in all tested tumor cell
lines, we postulated that the TNBC-selective compounds do not affect the cell cycle progression.
Thus, three group-I TNBC-selective compounds, 30, 31, and 33, with an electron-withdrawing
group at the m-position of the C-12 benzoyl ester, together with one less selective group-III
compound, 37, with an electron-donating group at the same position were assessed in a cell cycle
progression assay in MDA-MB-231 using flow cytometry (Figure 2). As we expected, none of the
four tested compounds displayed a significant effect on cell cycle progression or sub-G1 induction.
These results support our hypothesis that our selective compounds target a protein required for cell
growth expressed specifically in MDA-MB-231 cells but do not affect the proteins responsible for
the S- and G2/M-phase progression, as well as apoptotic induction. We are now conducting studies
to identify the target.
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Figure 2. Effects of compounds on cell cycle progression.
Triple-negative breast cancer MDA-MB-231 cells were treated with compound for 24 h at concentration of
1× IC50 or 3× IC50 as indicated. DMSO was used as a vehicle control (CTRL). 25 µM (1× IC50) 5-
fluorouracil (5-FU) or 0.1 µM (3× IC50) combretastatin A-4 (CA-4) was used for DNA replication (S-phase)
or mitotic inhibitor, respectively. Cell cycle distributions of treated cells were analyzed by flow cytometry
(LSRFortessa operated by FACS Diva software, BD Bioscience) after staining with propidium iodide (PI)
in the presence of RNase.
In conclusion, we achieved the first total synthesis of 4-epi-Pfs with ester functional groups
at C-4, including 4-epi-Pfs A, C and E, from (−)-abietic acid in 12–13 steps in 0.15% overall yield.
The synthesized compounds, including intermediates and derivatives, were evaluated for
antiproliferative activity against five HTCLs. We observed no significant difference of
antiproliferative activity between Pf E and its 4-epimer. The SAR study suggested the importance
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of two oxygenated functional groups at C-11 and C-12. Furthermore, the TNBC selective
compounds required one of two conditions, a carbomethoxy group at C4 combined with a benzoyl
ester substituted with an electron-drawing group or a hydroxymethyl group at C4 combined with
an appropriate oxidation state of ring-B/C.
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EXPERIMENTAL SECTION
General Procedures.
All chemicals and solvents were used as purchased. 1H and 13C{1H} NMR spectra were recorded
on a JEOL JMN-ECA600 or JMN-ECS400 spectrometers with tetramethylsilane (TMS) as an
internal standard. All chemical shifts are described as  values in ppm, apparent scalar coupling
constants J in Hz. Mass spectroscopic data were obtained on a JMS-700 MStation (FAB) mass
spectrometer with TOF analyzer. Analytical and preparative TLC was carried out on precoated
silica gel 60F254 and RP-18F254 plates (0.25 or 0.50 mm thickness; Merck).
General synthetic procedures for esterification:
Methyl 12-(3-chlorobenzoyloxy)-11-hydroxyabieta-8,11,13-trien-18-oate (15). mCBPO (161.7
mg, 0.52 mmol) was added to a solution of 8 (122.4 mg, 0.37 mmol) in anhyd CH2Cl2 (10.0 ml).
After stirring at rt for 23 h under Ar, the reaction was quenched with aqueous 20% Na2S2O3 (10.0
ml). The mixture was extracted three times with CH2Cl2. The combined organic layers were
washed with brine, dried over Na2SO4, and concentrated. The residue was purified by silica gel
column chromatography with hexane–CH2Cl2 (2 : 1) to afford 15 (114.7 mg, 0.24 mmol, 64%).
1H NMR (400 MHz, CDCl3) δ: 1.16 (d, J = 6.8 Hz, 3H), 1.19 (d, J = 6.8 Hz, 3H), 1.23–1.26 (m,
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1H), 1.29 (s, 3H), 1.31–1.33 (m, 1H), 1.38 (s, 3H), 1.40–1.47 (m, 2H), 1.59–1.64 (m, 1H), 1.71–
1.80 (m, 3H), 2.24–2.31 (m, 1H), 2.78–2.98 (m, 4H), 3.12–3.17 (m, 1H), 3.69 (s, 3H), 5.09 (s,
1H), 6.61 (s, 1H), 7.50 (t, J = 8.0 Hz, 1H), 7.64–7.67 (m, 1H), 8.12 (br d, J = 7.6 Hz, 1H), 8.21 (t,
J = 1.6 Hz, 1H); 13C{1H} NMR (150 MHz, CDCl3) δ: 16.9, 18.6, 20.3, 22.1, 22.9, 23.1, 27.6, 32.2,
35.7, 36.5, 38.9, 46.8, 48.4, 51.9, 118.8, 128.5, 130.2, 130.4, 134.1, 134.2, 134.6, 135.1, 135.7,
137.6, 145.5, 163.9, 179.3; HRMS (FAB-TOF) m/z: [M]+ calcd for C28H33ClO5, 484.2017; found,
484.2010.
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11,12-Dihydroxydehydroabietinol (7). 1M LAH in THF (1.60 ml, 1.60 mmol) was added to a
solution of 15 (110.4 mg, 0.23 mmol) in anhyd THF (3.0 ml) at 0 C. After refluxing for 4 h under
Ar, the reaction was quenched with 1N HCl (3.0 ml) at 0 C. The mixture was extracted three
times with EtOAc. The combined organic layers were washed with brine, dried over Na2SO4, and
concentrated. The residue was purified by silica gel column chromatography with hexane–acetone
(7 : 1) to afford 7 (65.8 mg, 0.21 mmol, 90%). 1H NMR (400 MHz, CDCl3) δ: 0.88 (s, 3H), 1.23
(d, J = 6.8 Hz, 3H), 1.25 (d, J = 6.8 Hz, 3H), 1.27–1.30 (m, 1H), 1.33–1.36 (m, 1H), 1.38 (s, 3H),
1.44–1.53 (m, 2H), 1.57–1.65 (m, 3H), 1.67–1.81 (m, 2H), 2.78–2.83 (m, 2H), 2.97 (sept, J = 7.2
Hz, 1H), 3.07–3.12 (m, 1H), 3.21 (dd, J = 6.4, 11.2 Hz, 1H), 3.50 (dd, J = 6.0, 10.4 Hz, 1H), 4.52
(s, 1H), 5.68 (s, 1H), 6.43 (s, 1H); HRMS (FAB-TOF) m/z: [M]+ calcd for C20H30O3, 318.2195;
found, 318.2194.
Methyl 11,12-dihydroxydehydroabietate (16). 1M LAH in THF (0.36 ml, 0.36 mmol) was added
to a solution of 15 (175.8 mg, 0.36 mmol) in anhyd THF (3.0 ml) at −78 C. After stirring at −78
C for 40 min under Ar, the reaction was quenched with 1N HCl (2.0 ml). The mixture was
extracted three times with EtOAc. The combined organic layers were washed with brine, dried
over Na2SO4, and concentrated. The residue was purified by silica gel column chromatography
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with EtOAc–hexane (1 : 20) to afford 16 (107.7 mg, 0.31 mmol, 86%). H NMR (400 MHz,
CDCl3) δ: 1.23 (d, J = 7.2 Hz, 3H), 1.25 (d, J = 7.2 Hz, 3H), 1.28 (s, 3H), 1.29–1.31 (m, 1H), 1.36
(s, 3H), 1.39–1.46 (m, 1H), 1.61–1.80 (m, 5H), 2.22 (d, J = 12.0 Hz, 1H), 2.73 (dd, J = 5.2, 16.0
Hz, 1H), 2.82–3.02 (m, 2H), 3.13 (br d, J = 12.4 Hz, 1H), 4.49 (s, 1H), 5.71 (s, 1H), 6.42 (s, 1H);
HRMS (FAB-TOF) m/z: [M]+ calcd for C21H30O4, 346.2144; found, 346.2144.
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(4bS,8R)-8-(Hydroxymethyl)-2-isopropyl-4b,8-dimethyl-4b,5,6,7,8,8a,9,10-
octahydrophenanthrene-3,4-dione (17). Ag2O (50.1 mg, 0.22 mmol) was added to a solution of 7
(37.5 mg, 0.12 mmol) in anhyd CH2Cl2 (3.0 ml). After stirring at rt for 40 min under Ar, the
mixture was filtered through celite with CH2Cl2 and the filtrate was concentrated. The residue was
purified by silica gel column chromatography with EtOAc–hexane (1 : 5) to afford 17 (27.3 mg,
0.086 mmol, 72%). 1H NMR (400 MHz, CDCl3) δ: 0.83 (s, 3H), 1.08 (br s, 3H), 1.10 (br s, 3H),
1.27 (s, 3H), 1.31–1.34 (m, 2H), 1.39–1.51 (m, 3H), 1.56–1.62 (m, 1H), 1.65–1.83 (m, 2H), 2.44–
2.46 (m, 2H), 2.71–2.76 (m, 1H), 2.86–2.93 (m, 1H), 3.16 (dd, J = 5.6, 10.4 Hz, 1H), 3.47 (dd, J
= 6.4, 11.2 Hz, 1H), 6.39 (s, 1H); 13C{1H} NMR (150 MHz, CDCl3) δ: 17.6, 17.7, 18.1, 20.3, 21.4,
21.4, 26.8, 33.4, 34.9, 35.5, 37.6, 37.8, 44.4, 71.8, 137.8, 144.7, 146.7, 148.0, 180.1, 181.1; HRMS
(FAB-TOF) m/z: [M]+ calcd for C20H28O3, 316.2038; found, 316.2040.
(4bS,8R)-4-Hydroxy-8-(hydroxymethyl)-2-isopropyl-4b,8-dimethyl-5,6,7,8,8a,9-
hexahydrophenanthren-3(4bH)-one (18). 17 (25.9 mg, 0.082 mmol) was dissolved in anhyd
toluene (2.0 ml). After refluxing for 2 h under Ar, the solution was concentrated. The residue was
purified by silica gel column chromatography with EtOAc–hexane (1 : 10) to afford 18 (25.0 mg,
0.079 mmol, 96%). 1H NMR (400 MHz, CDCl3) δ: 0.93 (s, 3H), 1.13 (d, J = 6.8 Hz, 3H), 1.15 (d,
J = 6.8 Hz, 3H), 1.22 (s, 3H), 1.30–1.35 (m, 2H), 1.48–1.60 (m, 2H), 1.66–1.78 (m, 2H), 1.93 (dd,
J = 4.0, 12.0 Hz, 1H), 2.36–2.45 (m, 1H), 2.51–2.59 (m, 1H), 3.00–3.10 (m, 2H), 3.19 (dd, J = 6.0,
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10.8 Hz, 1H), 3.19 (dd, J = 6.0, 10.8 Hz, 1H), 6.78–6.80 (m, 2H), 7.48 (s, 1H); 13C{1H} NMR (150
MHz, CDCl3) δ: 18.0, 18.2, 18.9, 21.5, 21.8, 25.6, 26.6, 35.1, 36.3, 38.0, 38.4, 44.1, 71.9, 127.0,
131.6, 136.2, 140.5, 143.8, 148.6, 181.4; HRMS (FAB-TOF) m/z: [M+H]+ calcd for C20H29O3,
317.2117; found, 317.2106.
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(4bS,8R)-8-(Hydroxymethyl)-2-isopropyl-4b,8-dimethyl-4b,5,6,7,8,8a-hexahydrophenanthrene-
3,4-diol
(19)
and
(4bS,8R)-8-(Hydroxymethyl)-2-isopropyl-4b,8-dimethyl-4b,5,6,7,8,8a-
hexahydrophenanthrene-3,4-dione (20). 18 (27.9 mg, 0.088 mmol) was heated for 3 h at 115 C
under Ar to afford 19, which was used for the next reaction without purification due to its
instability. After cooling of the reaction mixture to rt, anhyd CH2Cl2 (2.0 ml) and Ag2O (36.9 mg,
0.16 mmol) were added to the residue. The mixture was stirring at rt for 1 h under Ar. The mixture
was filtered through celite with CH2Cl2 and the filtrate was concentrated. The residue was purified
by silica gel column chromatography with EtOAc–hexane (1 : 7) to afford 20 (17.1 mg, 0.054
mmol, 62%, 2 steps from 18). 19: 1H NMR (400 MHz, CDCl3) δ: 1.00 (s, 3H), 1.19 (s, 3H), 1.22
(d, J = 6.8 Hz, 3H), 1.26 (d, J = 6.8 Hz, 3H), 1.29–1.52 (m, 2H), 1.74–1.95 (m, 4H), 2.48 (m, 1H),
2.84 (br d, J = 12.4 Hz, 1H), 3.00–3.07 (m, 1H), 3.26 (dd, J = 6.8, 10.8 Hz, 1H), 3.51 (dd, J = 5.6,
11.2 Hz, 1H), 5.09 (s, 1H), 5.60 (s, 1H), 5.80 (dd, J = 2.8, 9.6 Hz, 1H), 6.44 (dd, J = 3.2, 9.6 Hz,
1H), 6.49 (s, 1H); HRMS (FAB-TOF) m/z: [M]+ calcd for C20H28O3, 316.2038; found, 316.2031;
20: 1H NMR (400 MHz, CDCl3) δ: 1.18 (d, J = 6.4 Hz, 3H), 1.19 (d, J = 6.4 Hz, 3H), 1.26 (s, 3H),
1.49–1.54 (m, 2H), 1.58 (s, 3H), 1.67–1.76 (m, 2H), 1.92–2.04 (m, 1H), 3.16 (sept, J = 6.8 Hz,
1H), 3.28–3.34 (m, 1H), 3.44 (d, J = 11.6 Hz, 1H), 3.76 (d, J = 11.6 Hz, 1H), 6.40 (d, J = 6.8 Hz,
1H), 6.74 (d, J = 6.8 Hz, 1H), 6.93 (s, 1H), 7.74 (br s, 1H); 13C{1H} NMR (150 MHz, CDCl3) δ:
15.7, 17.9, 18.7, 21.3, 21.5, 27.0, 34.0, 34.5, 37.3, 38.0, 46.4, 71.1, 127.1, 136.4, 139.2, 140.7,
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141.3, 147.8, 181.7, 182.0; HRMS (FAB-TOF) m/z: [M]+ calcd for C20H26O3, 314.1882; found,
314.1875.
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(4bS,8R)-4-Hydroxy-8-(hydroxymethyl)-2-isopropyl-4b,8-dimethyl-5,6,7,8-
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tetrahydrophenanthren-3(4bH)-one (6). 20 (23.9 mg, 0.076 mmol) was dissolved in anhyd toluene
(1.0 ml). After refluxing for 4 h under Ar, the solution was concentrated. The residue was purified
by silica gel column chromatography with EtOAc–hexane (1: 7) to afford 6 (14.2 mg, 0.045 mmol,
59%). 1H NMR (400 MHz, CDCl3) δ: 1.18 (d, J = 6.4 Hz, 3H), 1.19 (d, J = 6.4 Hz, 3H), 1.26 (s,
3H), 1.49–1.54 (m, 2H), 1.58 (s, 3H), 1.67–1.76 (m, 2H), 1.92–2.04 (m, 1H), 3.16 (sept, J = 6.8
Hz, 1H), 3.28–3.34 (m, 1H), 3.44 (d, J = 11.6 Hz, 1H), 3.76 (d, J = 11.6 Hz, 1H), 6.40 (d, J = 6.8
Hz, 1H), 6.74 (d, J = 6.8 Hz, 1H), 6.93 (s, 1H), 7.74 (br s, 1H); 13C{1H} NMR (150 MHz, CDCl3)
δ: 17.7, 21.6, 21.8, 25.3, 25.7, 26.9, 33.0, 34.2, 42.6, 43.2, 71.5, 118.5, 127.5, 127.6, 133.2, 137.9,
141.6, 146.4, 163.5, 178.2; HRMS (FAB-TOF) m/z: [M]+ calcd for C20H26O3, 314.1882; found,
314.1894.
[(1R,4aS)-5-Hydroxy-7-isopropyl-1,4a-dimethyl-6-oxo-1,2,3,4,4a,6-hexahydrophenanthren-1-
yl]methyl 2-methoxybenzo[d][1,3]dioxole-5-carboxylate (26b). Triethylamine (0.017 ml, 0.12
mmol), DMAP (0.5 mg, 0.0041 mmol), MNBA (15.9 mg, 0.046 mmol) and 24b (8.6 mg, 0.044
mmol) were dissolved in anhyd CH2Cl2 (0.5 ml) and stirred at rt for 20 min. A solution of 6 (11.7
mg, 0.037 mmol) in anhyd CH2Cl2 (0.3 ml) was added to the mixture. After stirring at rt for 19.5
h, the reaction was quenched with aqueous sat. NH4Cl (5.0 ml). The mixture was extracted three
times with CH2Cl2. The combined organic layers were washed with brine, dried over Na2SO4, and
concentrated. The residue was purified by silica gel column chromatography with EtOAc–hexane
(1 : 7) to afford 26b (7.0 mg, 0.014 mmol, 38%) and recovered 6 (1.5 mg, 0.0048 mmol, 13%). 1H
NMR (400 MHz, CDCl3) δ: 1.18 (d, J = 6.8 Hz, 3H), 1.19 (d, J = 6.8 Hz, 3H), 1.40 (s, 3H), 1.53–
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1.58 (m, 1H), 1.61 (s, 3H), 1.67–1.77 (m, 3H), 1.96–2.06 (m, 1H), 3.17 (sept, J = 6.8 Hz, 1H),
3.35 (br d, J = 14.4 Hz, 1H), 3.42 (s, 3H), 4.21 (d, J = 11.2 Hz, 1H), 4.39 (d, J = 11.2 Hz, 1H),
6.34 (d, J = 7.2 Hz, 1H), 6.71 (d, J = 7.2 Hz, 1H), 6.91–6.93 (m, 3H), 7.51 (d, J = 1.2 Hz, 1H),
7.68 (dd, J = 2.0, 8.0 Hz, 1H), 7.75 (s, 1H) ; 13C{1H} NMR (100 MHz, CDCl3) δ:17.7, 21.7, 21.9,
25.0, 25.6, 26.9, 33.3, 35.0, 41.2, 43.1, 50.2, 72.5, 107.9, 109.2, 118.5, 119.9, 124.2, 125.3, 127.61,
127.63, 133.2, 137.9, 141.7, 146.2, 146.3, 150.1, 162.2, 165.8, 178.37; HRMS (FAB-TOF) m/z:
[M+H]+ calcd for C29H33O7, 493.2226; found, 493.2227.
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4-({[(1R,4aS)-5-Hydroxy-7-isopropyl-1,4a-dimethyl-6-oxo-1,2,3,4,4a,6-hexahydrophenanthren-
1-yl]methoxy}carbonyl)-1,2-phenylene dibenzoate (26d) and [(1R,4aS)-5-Hydroxy-7-isopropyl-
1,4a-dimethyl-6-oxo-1,2,3,4,4a,6-hexahydrophenanthren-1-yl]methyl
benzoate
(27).
Triethylamine (0.012 ml, 0.086 mmol), DMAP (3.8 mg, 0.031 mmol), MNBA (10.4 mg, 0.030
mmol) and 24d (11.5 mg, 0.032 mmol) were dissolved in anhyd CH2Cl2 (0.1 ml) and stirred at rt
for 40 min. A solution of 6 (8.1 mg, 0.026 mmol) in anhyd CH2Cl2 (0.6 ml) was added to the
mixture. After stirring at rt for 11 h, the reaction was quenched with aqueous sat. NH4Cl (0.5 ml).
The mixture was extracted three times with CH2Cl2. The combined organic layers were washed
with brine, dried over Na2SO4, and concentrated. The residue was purified by MPLC [RediSep®Rf
Teledyne Isco 4g, EtOAc–hexane (1 : 19)] to afford 26d (2.0 mg, 0.0030 mmol, 12%) and 27 (1.9
mg, 0.0045 mmol, 17%) along with recovery of 6 (4.5 mg, 56%). 26d: 1H NMR (400 MHz, CDCl3)
δ: 1.17 (d, J = 7.2 Hz, 3H), 1.18 (d, J = 7.2 Hz, 3H), 1.42 (s, 3H), 1.57–1.60 (m, 1H), 1.61 (s, 3H),
1.70–1.77 (m, 3H), 1.95–2.08 (m, 1H), 3.15 (sept, J = 7.2 Hz, 1H), 3.35 (br d, J = 14.8 Hz, 1H),
4.27 (d, J = 11.2 Hz, 1H), 4.45 (d, J = 11.2 Hz, 1H), 6.36 (d, J = 6.8 Hz, 1H), 6.73 (d, J = 6.8 Hz,
1H), 6.93 (s, 1H), 7.39 (q, J = 8.0 Hz, 4H), 7.49–7.59 (m, 3H), 7.74 (s, 1H), 8.02–8.07 (m, 6H);
13C{1H} NMR (150 MHz, CDCl3) δ: 17.7, 21.7, 21.8, 25.1, 25.6, 26.9, 33.2, 35.0, 41.2, 43.1, 72.9,
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118.6, 123.8, 125.1, 127.6, 127.7, 128.2, 128.6, 130.2, 133.2, 133.93, 133.97, 137.9, 141.7, 146.3,
146.7, 162.0, 163.8, 164.1, 165.1, 178.4; HRMS (FAB-TOF) m/z: [M+H]+ calcd for C41H39O8,
659.2645; found, 659.2664; 27: 1H NMR (400 MHz, CDCl3) δ: 1.18 (d, J = 6.8 Hz, 3H), 1.19 (d,
J = 6.8 Hz, 3H), 1.41 (s, 3H), 1.57–1.59 (m, 1H), 1.61 (s, 3H), 1.69–1.78 (m, 3H), 1.95–2.07 (m,
1H), 3.16 (sept, J = 6.8 Hz, 1H), 3.33–3.38 (m, 1H), 4.24 (d, J = 10.8 Hz, 1H), 4.42 (d, J = 10.8
Hz, 1H), 6.36 (d, J = 6.4 Hz, 1H), 6.71 (d, J = 6.4 Hz, 1H), 6.92 (s, 1H), 7.45 (t, J = 7.2 Hz, 2H),
7.58 (dt, J = 1.2, 7.2 Hz, 1H), 7.75 (s, 1H), 8.01–8.04 (m, 2H); 13C{1H} NMR (150 MHz, CDCl3)
δ: 17.8, 21.7, 21.9, 25.0, 25.6, 26.9, 33.3, 35.0, 41.2, 43.1, 72.5, 118.5, 127.6, 128.5, 129.6, 130.1,
133.1, 133.2, 138.0, 141.7, 146.3, 162.3, 166.5, 178.4; HRMS (FAB-TOF) m/z: [M]+ calcd for
C27H30O4, 418.2144; found, 418.2127.
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4-epi-Parvifloron A (4-epi-1)1 and [(1R,4aS)-5-Hydroxy-7-isopropyl-1,4a-dimethyl-6-oxo-
1,2,3,4,4a,6-hexahydrophenanthren-1-yl]methyl 3-methylbut-3-enoate (22). Triethylamine (0.012
ml, 0.086 mmol), DMAP (2.2 mg, 0.018 mmol), MNBA (17.2 mg, 0.050 mmol) and 3-
methylcrotonic acid (21, 6.1 mg, 0.061 mmol) were dissolved in anhyd CH2Cl2 (0.2 ml) and stirred
at rt for 30 min. The mixture was added to a solution of 6 (6.9 mg, 0.022 mmol) in anhyd CH2Cl2
(0.3 ml). After stirring at rt for 5 h, the reaction was quenched with aqueous sat. NH4Cl (4.0 ml).
The mixture was extracted three times with CH2Cl2. The combined organic layers were washed
with brine, dried over Na2SO4, and concentrated. The residue was purified by silica gel column
chromatography with EtOAc–hexane (1 : 20) to afford the mixture of 4-epi-1 and 22 [15.0 mg,
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0.0033 mmol, 15%, 4-epi-1 : 22 = 11 : 4 (determined from H NMR)]. 4-epi-1 : H NMR (400
MHz, CDCl3) δ: 1.18 (d, J = 6.8 Hz, 3H), 1.19 (d, J = 6.8 Hz, 3H), 1.31 (s, 3H),1.50–1.51 (m, 1H),
1.57 (s, 3H), 1.59–1.63 (m, 2H), 1.67–1.73 (m, 1H), 1.90 (d, J = 1.2 Hz, 3H), 1.91–2.03 (m, 1H),
2.16–2.17 (m, 3H), 3.16 (sept, J = 6.8 Hz, 1H), 3.31 (dd, J = 14.0, 4,0 Hz, 1H),3.99 (d, J = 11.2
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Hz, 1H), 4.21 (d, J = 11.2 Hz, 1H), 5.69 (t, J =1.6 Hz, 1H), 6.29 (d, J = 6.8 Hz, 1H), 6.71 (d, J =
6.8 Hz, 1H), 6.93 (s, 1H), 7.73 (s, 1H); 13C{1H} NMR (150 MHz, CDCl3) δ: 17.7, 20.4, 21.7, 21.9,
25.1, 25.6, 26.9, 27.5, 33.2, 34.8, 41.0, 43.1, 71.3, 115.9, 118.6, 127.5, 127.7, 133.2, 138.2, 141.6,
146.3, 157.3, 162.7, 166.7, 178.3; HRMS (FAB-TOF) m/z: [M]+ calcd for C25H32O4, 396.2301;
found, 396.2288. 22 : 1H NMR (400 MHz, CDCl3) δ: 1.18 (d, J = 6.8 Hz, 3H), 1.19 (d, J = 6.8 Hz,
3H), 1.31 (s, 3H), 1.40–1.51 (m, 1H), 1.57 (s, 3H), 1.60–1.63 (m, 1H), 1.63–1.73 (m, 2H), 1.80 (s,
3H), 1.89–2.00 (m, 1H), 3.06 (s, 2H), 3.16 (sept, J = 7.2 Hz, 1H), 3.30 (m, 1H), 3.98 (d, J = 11.2
Hz, 1H), 4.22 (d, J = 11.2 Hz, 1H), 4.85 (d, J = 0.8 Hz, 1H), 4.91(t, J = 1.6 Hz, 1H), 6.24 (d, J =
6.4 Hz, 1H), 6.70 (d, J = 6.4 Hz, 1H), 6.92 (s, 1H), 7.73 (s, 1H); 13C{1H} NMR (150 MHz, CDCl3)
δ: 17.7, 21.7, 21.9, 22.6, 25.2, 25.5, 26.9, 33.1, 34.7, 41.0, 43.0, 43.5, 72.3, 114.9, 118.6, 127.6,
133.2, 137.9, 141.7, 146.3, 162.2, 171.4, 178.4; HRMS (FAB-TOF) m/z: [M+H]+ calcd for
C25H33O4, 397.2379; found, 397.2380.
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[(1R,4aS)-5-Hydroxy-7-isopropyl-1,4a-dimethyl-6-oxo-1,2,3,4,4a,6-hexahydrophenanthren-1-
yl]methyl 4-(benzoyloxy)benzoate (25). Triethylamine (0.010 ml, 0.076 mmol), DMAP (0.6 mg,
0.050 mmol), MNBA (14.6 mg, 0.042 mmol) and 23 (9.3 mg, 0.038 mmol) were dissolved in
anhyd CH2Cl2 (0.6 ml) and stirred at rt for 40 min. The mixture was added a solution of 6 (7.2 mg,
0.023 mmol) in anhyd CH2Cl2 (0.4 ml). After stirring at rt for 2 h, the reaction was quenched with
aqueous sat. NH4Cl (2.0 ml). The mixture was extracted three times with CH2Cl2. The combined
organic layers were washed with brine, dried over Na2SO4, and concentrated. The residue was
purified by silica gel column chromatography with EtOAc–hexane (1 :15) to afford to 25 (5.6 mg,
0.010 mmol, 45%). 1H NMR (400 MHz, CDCl3) δ: 1.18 (d, J = 6.8 Hz, 3H), 1.19 (d, J = 6.8 Hz,
3H), 1.42 (s, 3H), 1.55–1.60 (m, 1H), 1.62 (s, 3H), 1.70–1.79 (m, 3H), 1.98–2.08 (m, 1H), 3.16
(sept, J = 6.8 Hz, 1H), 3.34–3.39 (m, 1H), 4.25 (d, J = 11.2 Hz, 1H), 4.44 (d, J = 11.6 Hz, 1H),
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2H), 7.64–7.69 (m, 1H), 7.75 (br s, 1H), 8.09–8.12 (m, 2H), 8.19–8.22 (m, 2H); C{1H} NMR
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(150 MHz, CDCl3) δ: 17.8, 21.7, 21.9, 25.1, 25.7, 26.9, 33.3, 35.0, 41.2, 43.1, 72.6, 118, 6, 122.0,
127.6, 127.7, 128.7, 130.3, 131.2, 133.2, 134.0, 137.9, 141.7, 146.4, 154.8, 162.1, 164.7, 165.8,
178.4; HRMS (FAB-TOF) m/z: [M]+ calcd for C34H34O6, 538.2355; found, 538.2363.
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4-epi-Parvifloron C (4-epi-2).1 n-Butylamine (2.4 µl, 0.024 mmol) was added to a solution of 25
(2.6 mg, 0.0048 mmol) in benzene (0.2 ml). After stirring at rt for 42 h, the mixture was directly
purified by silica gel column chromatography with EtOAc–hexane (1: 10) and RP-preparative
TLC with acetonitrile–water (5 : 1) to afford 4-epi-2 (0.6 mg, 0.0014 mmol, 29%). 1H NMR (400
MHz, CDCl3) δ: 1.18 (d, J = 7.2 Hz, 3H), 1.19 (d, J = 7.2 Hz, 3H), 1.40 (s, 3H), 1.52–1,55 (m,
1H), 1.61 (s, 3H), 1.68–1.77 (m, 1H), 1.96–2.06 (m, 1H), 3.16 (sept, J = 7.2 Hz, 1H), 3.32–3.38
(m, 1H), 4.20 (d, J = 11.2 Hz, 1H), 4.38 (d, J = 11.2 Hz, 1H), 5.34 (br s, 1H), 6.35 (d, J = 6.8 Hz,
1H), 6.72 (d, J = 6.8 Hz, 1H), 6.86 (br d, J = 8.4 Hz, 2H), 6.93 (s, 1H), 7.74 (br s, 1H), 7.93 (d, J
= 8.0 Hz, 2H); 13C{1H} NMR (150 MHz, CDCl3) δ: 17.8, 21.7, 21.9, 25.0, 25.7, 26.9, 33.3, 35.0,
41.3, 43.2, 72.3, 115.3, 118.6, 122.6, 127.6, 127.9, 131.9, 133.3, 138.4, 141.6, 146.4, 160.1, 162.7,
166.2, 178.3; HRMS (FAB-TOF) m/z: [M+H]+ calcd for C27H31O5, 435.2171; found, 435.2174.
4-epi-Parvifloron E (4-epi-3).1 n-Butylamine (2.6 µl, 0.026 mmol) was added to a solution of 26d
(1.7 mg, 0.0026 mmol) in benzene (0.1 ml). After stirring at rt, for 1.5 h the mixture was directly
purified by silica gel column chromatography with EtOAc–hexane (1: 3) to afford 4-epi-3 (0.9 mg,
0.0020 mmol, 77%). 1H NMR (400 MHz, CDCl3) δ: 1.17 (d, J = 6.8 Hz, 3H), 1.19 (d, J = 6.8 Hz,
3H), 1.39 (s, 3H), 1.41–1.46 (m, 1H), 1.61 (s, 3H), 1.67–1.76 (m, 3H), 1.96–2.95 (m, 1H), 3.16
(sept, J = 7.2 Hz, 1H), 3.35 (br d, J = 13.2 Hz, 1H), 3.55 (br s, 1H), 4.18 (d, J = 11.2 Hz, 1H), 4.37
(d, J = 11.2 Hz, 1H), 5.65 (br s, 1H), 6.34 (d, J = 6.4 Hz, 1H), 6.72 (d, J = 6.4 Hz, 1H), 6.90–6.92
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(m, 2H), 7.51–7.58 (m, 2H), 7.69–7.73 (m, 1H); C{1H} NMR (100 MHz, CD3CN, δ CD3=1.3
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ppm) δ: 18.3, 21.8, 22.0, 25.5, 25.9, 27.8, 34.0, 35.4, 42.1, 43.9, 72.7, 116.0, 117.1, 119.9, 123.2,
123.7, 128.3, 128.7, 134.3, 139.6, 142.2, 145.2, 147.2, 150.4, 163.2, 166.7, 179.0; HRMS (FAB-
TOF) m/z: [M+H]+ calcd for C27H31O6, 451.2121; found, 451.2113.
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Methyl (1R,4aS)-7-isopropyl-1,4a-dimethyl-5,6-dioxo-1,2,3,4,4a,5,6,9,10,10a-
decahydrophenanthrene-1-carboxylate (28). Ag2O (30.8 mg, 0.13 mmol) was added to a solution
of 15 (24.7 mg, 0.071 mmol) in anhyd CH2Cl2 (1.0 ml). After stirring at rt for 40 min under Ar,
the mixture was filtered through celite with CH2Cl2 and the filtrate was concentrated. The
residue was purified by silica gel column chromatography with EtOAc–hexane (1 : 20) to afford
28 (24.2 mg, 0.070 mmol, 99%). 1H NMR (400 MHz, CDCl3) δ: 1.09 (d, J = 6.8 Hz, 3H), 1.09
(d, J = 6.8 Hz, 3H), 1.24 (s, 3H), 1.25 (s, 3H), 1.30–1.41 (m, 1H), 1.60–1.71 (m, 5H), 2.01 (d, J
= 10.8 Hz, 1H), 2.46–2.49 (m, 2H), 2.75–2.78 (m, 1H), 2.90 (sept, J = 6.4 Hz, 1H), 3.68 (s, 3H),
6.38 (s, 3H); 13C{1H} NMR (150 MHz, CDCl3) δ: 16.5, 18.0, 20.2, 20.8, 21.4, 26.9, 33.3, 35.2,
36.7, 37.4, 45.5, 47.6, 52.0, 137.6, 144.1, 147.0, 148.0, 178.8, 179.9, 180.9; HRMS (FAB-TOF)
m/z: [M+Na]+ calcd for C21H28O4Na, 367.1885; found, 367.1902.
Methyl (1R,4aS)-5-hydroxy-7-isopropyl-1,4a-dimethyl-6-oxo-1,2,3,4,4a,6,10,10a-
octahydrophenanthrene-1-carboxylate (29). 28 (88.4 mg, 0.26 mmol) was dissolved in anhyd
toluene (2.0 ml). After refluxing for 8 h under Ar, the solution was concentrated. The residue
was purified by silica gel column chromatography with EtOAc–hexane (1 : 20) to afford 29 (79.6
mg, 0.23 mmol, 89%). 1H NMR (400 MHz, CDCl3) δ 1.13 (d, J = 6.8 Hz, 3H), 1.15 (d, J = 6.8
Hz, 3H), 1.22 (s, 3H), 1.32 (s, 3H), 1.63–1.81 (m, 5H), 2.13 (ddd, J = 2.4, 6.8, 19.2 Hz, 1H),
2.39–2.53 (m, 2H), 3.01–3.10 (m, 2H), 3.67 (s, 3H), 6.74 (dd, J = 3.2, 7.2 Hz, 1H), 6.78 (s, 1H),
7.47 (s, 1H); 13C{1H} NMR (150 MHz, CDCl3) δ: 17.1, 18.2, 18.9, 21.5, 21.8, 26.6, 27.7, 36.0,
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36.8, 38.1, 45.0, 47.3, 52.1, 126.5, 131.6, 136.1, 140.7, 143.8, 147.7, 178.5, 181.3; HRMS (FAB-
TOF) m/z: [M]+ calcd for C21H28O4, 344.1988; found, 344.1976.
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Methyl 12-(3-fluorobenzoyloxy)-11-hydroxyabieta-8,11,13-trien-18-oate (30). 3-Fluorobenzoic
acid (11.8 mg, 0.084 mmol), EDCI (0.014 ml, 0.079 mmol) and DMAP (1.1 mg, 0.009 mmol)
were dissolved in anhyd CH2Cl2 (0.3 mL) and stirred at rt for 25 min. Then the mixture was added
to a solution of 15 (22.9 mg, 0.066 mmol) in anhyd CH2Cl2 (0.7 mL). After stirring at rt for 210
min, the reaction was quenched with aqueous 10% NH4Cl (4.0 ml). The mixture was extracted
three times with CH2Cl2. The combined organic layers were washed with brine, dried over Na2SO4,
and concentrated. The residue was purified by silica gel column chromatography with EtOAc–
hexane (1 : 20) to afford 30 (10.5 mg, 0.022 mmol, 34%) and recovered 15 (10.1 mg, 0.029 mmol,
44%). 1H NMR (600 MHz, CDCl3) δ: 1.16 (d, J = 7.2 Hz, 3H), 1.19 (d, J = 7.2 Hz, 3H), 1.29 (s,
3H), 1.31–1.33 (m, 1H), 1.37 (s, 3H), 1.41–1.46 (m, 1H), 1.59–1.63 (m, 2H), 1.70–1.82 (m, 3H),
2.25 (d, J = 11.4 Hz, 1H), 2.79–2.85 (m, 2H), 2.89–2.96 (m, 1H), 3.13–3.17 (m, 1H), 3.68 (s, 3H),
5.12 (s, 1H), 6.61 (s, 1H), 7.39 (m, 1H), 7.52–7.55 (m, 1H), 7.90–7.92 (m, 1H), 8.03–8.05 (m,
1H); 13C{1H} NMR (150 MHz, CDCl3) δ: 16.9, 18.6, 20.3, 22.1, 22.9, 23.0, 27.6, 32.2, 35.7, 36.5,
38.9, 46.8, 48.4, 51.9, 117.2 (d, J = 23.1 Hz), 118.8, 121.3 (d, J = 21.6 Hz), 126.1, 130.6 (d, J =
7.2 Hz), 134.3, 134.7, 135.7, 137.7, 145.5, 162.7 (J = 247.1 Hz), 163.9, 179.3; HRMS (FAB-TOF)
m/z: [M]+ calcd for C28H33FO5, 468.2312; found, 468.2294.
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Methyl 12-(3-bromobenzoyloxy)-11-hydroxyabieta-8,11,13-trien-18-oate (31). The same
procedure as described for 30 was performed using 3-bromobenzoic acid (14.4 mg, 0.072 mmol)
and 16 (21.0 mg, 0.061 mmol) with reaction time of 150 min to afford 31 (7.0 mg, 0.013 mmol,
22%) and recovered 16 (7.4 mg, 0.021 mmol, 35%).1H NMR (600 MHz, CDCl3) δ: 1.16 (d, J =
7.2 Hz, 3H), 1.19 (d, J = 7.2 Hz, 3H), 1.29 (s, 3H), 1.30–1.33 (m, 1H), 1.37 (s, 3H), 1.40–1.45 (m,
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1H), 1.59–1.63 (m, 1H), 1.70–1.82 (m, 3H), 2.25 (d, J = 11.4 Hz, 1H), 2.79–2.84 (m, 2H), 2.90–
2.96 (m, 1H), 3.12–3.16 (m, 1H), 3.68 (s, 3H), 5.09 (s, 1H), 6.61 (s, 1H), 7.43 (t, J = 7.8 Hz, 1H),
7.81 (ddd, J = 1.2, 1.8, 7.8 Hz, 1H), 8.17 (ddd, J = 1.8, 1.8, 7.8 Hz, 1H), 8.37 (t, J = 1.8 Hz, 1H);
13C{1H} NMR (150 MHz, CDCl3) δ: 16.9, 18.6, 20.3, 22.1, 22.9, 23.1, 27.6, 32.2, 35.7, 36.5, 38.9,
46.8, 48.4, 52.0, 118.8, 122.9, 128.9, 130.4, 130.5, 133.3, 134.2, 134.6, 135.7, 137.1, 137.7, 145.5,
163.7, 179.3; HRMS (FAB-TOF) m/z: [M]+ calcd for C28H33BrO5, 528.1511; found, 528.1485.
Methyl 11-hydroxyabieta-12-(3-iodebenzoyloxy)-8,11,13-trien-18-oate (32). The same procedure
as described for 30 was performed using 3-iodebenzoic acid (22.1 mg, 0.089 mmol) and 16 (26.0
mg, 0.075 mmol) with reaction time of 40 min to afford 32 (9.6 mg, 0.017 mmol, 22%) and
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recovered 16 (16.2 mg, 0.047 mmol, 62%). H NMR (400 MHz, CDCl3) δ: 1.16 (d, J = 6.8 Hz,
3H), 1.18 (d, J = 6.8 Hz, 3H), 1.29 (s, 3H), 1.30–1.34 (m, 1H), 1.37 (s, 3H), 1.57–1.80 (m 5H),
2.25 (d, J = 10.8 Hz, 1H), 2.77–2.98 (m, 3H), 3.10–3.15 (m, 1H), 3.68 (s, 3H), 5.07 (s, 1H), 6.60
(s, 1H), 7.29–7.33 (m, 1H), 8.01 (d, J = 8.0 Hz, 1H), 8.20 (d, J = 7.6 Hz, 1H), 8.56–8.57 (m, 1H);
13C{1H} NMR (150 MHz, CDCl3) δ: 16.9, 18.6, 20.3, 22.1, 22.9, 23.1, 27.6, 31.0, 32.2, 35.7, 36.5,
38.9, 46.8, 48.4, 52.0, 94.2, 118.8, 129.5, 130.5, 134.2, 134.6, 135.7, 137.7, 139.1, 142.9, 145.5,
163.6, 179.3; HRMS (FAB-TOF) m/z: [M]+ calcd for C28H33IO5,576.1373; found,576.1358.
Methyl 11-hydroxyabieta-12-(3-nitrobenzoyloxy)-8,11,13-trien-18-oate (33). The same procedure
as described for 30 was performed using 3-nitrobenzoic acid (12.2 mg, 0.073 mmol) and 16 (20.4
mg, 0.059 mmol) with reaction time of 30 min to afford 33 (5.3 mg, 0.011 mmol, 18%) and
recovered 15 (6.0 mg, 0.017 mmol, 29%). 1H NMR (600 MHz, CDCl3) δ: 1.17 (d, J = 7.2 Hz, 3H),
1.20 (d, J = 7.2 Hz, 3H), 1.29 (s, 3H), 1.30–1.34 (m, 1H), 1.38 (s, 3H), 1.42–1.47 (m, 1H), 1.59–
1.64 (m, 1H), 1.70–1.82 (m, 3H), 2.26 (d, J = 12.0 Hz, 1H), 2.79–2.85 (m, 2H), 2.91–2.97 (m,
1H), 3.12 (br d, J = 13.8 Hz, 1H), 3,69 (s, 3H), 5.03 (s, 1H), 6.63 (s, 1H), 7.78 (t, J = 7.8 Hz, 1H),
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8.53–8.57 (m, 2H), 9.07–9.08 (m, 1H); 13C{1H} NMR (600 MHz, CDCl3) δ: 16.9, 18.6, 20.3, 22.0,
22.9, 23.1, 27.7, 32.2, 35.8, 36.4, 38.9, 46.7, 48.3, 52.0, 119.0, 125.2, 128.5, 130.2, 130.4, 134.5,
134.6, 135.9, 137.6, 145.3, 148.5, 163.0, 179.2; HRMS (FAB-TOF) m/z: [M]+ calcd for
C28H33NO7, 495.2257; found, 495.2249.
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Methyl 12-(3,5-dichlorobenzoyloxy)-11-hydroxyabieta-8,11,13-trien-18-oate (34). The same
procedure as described for 33 was performed using 3,5-dichlorobenzoic acid (15.0 mg, 0.079
1
mmol) and 16 (22.7 mg, 0.066 mmol) to afford 34 (5.6 mg, 0.011 mmol, 19%). H NMR (600
MHz, CDCl3) δ: 1.16 (d, J = 6.6 Hz, 3H), 1.18 (d, J = 6.6 Hz, 3H), 1.29 (s, 3H), 1.31–1.33 (m,
1H), 1.36 (s, 3H), 1.40–1.46 (m, 1H), 1.59–1.63 (m, 2H), 1.69–1.82 (m, 3H), 2.23 (d, J = 12.0 Hz,
1H), 2.75–2.82 (m, 2H), 2.90–2.96 (m, 1H), 3.12 (br d, J = 13.8 Hz, 1H), 3.68 (s, 3H), 4.99 (s,
13
1H), 6.61 (s, 1H), 7.66–7.67 (m, 1H), 8.09–8.11 (m, 2H); C{1H} NMR (150 MHz, CDCl3) δ:
16.9, 18.6, 20.3, 22.1, 22.9, 23.1, 27.6, 32.2, 35.8, 36.4, 38.9, 46.7, 48.3, 51.9, 118.9, 128.66,
128.74, 131.5, 133.9, 134.4, 134.5, 135.8, 135.9, 137.6, 145.3, 162.8, 179.2; HRMS (FAB-TOF)
m/z: [M]+ calcd for C28H32Cl2O5, 518.1627; found, 518.1638.
Methyl 12-(4-chlorobenzoyloxy)-11-hydroxyabieta-8,11,13-trien-18-oate (35). The same
procedure as described for 33 was performed using 4-chlorobenzoic acid (8.2 mg, 0.052 mmol)
and 16 (14.9 mg, 0.043 mmol) to afford 35 (6.4 mg, 0.013 mmol, 31%) and recovered 16 (8.1 mg,
0.023 mmol, 54%). 1H NMR (600 MHz, CDCl3) δ: 1.15 (d, J = 7.2 Hz, 3H), 1.18 (d. J = 7.2 Hz,
3H), 1.29 (s, 3H), 1.30–1.32 (m, 1H), 1.37 (s, 3H), 1.40–1.45 (m, 1H), 1.59–1.63 (m, 2H), 1.70–
1.82 (m, 3H), 2.25 (d, J = 11.4 Hz, 1H), 2.78–2.84 (m, 2H), 2.99–2.96 (m, 1H), 3.13–3.17 (m,
1H), 3.68 (s, 3H), 5.14 (s, 1H), 6.60 (s, 1H), 7.52 (d, J = 9.0 Hz, 2H), 8.17 (d, J = 7.8 Hz, 2H);
13C{1H} NMR (150 MHz, CDCl3) δ: 16.9, 18.6, 20.3, 22.1, 22.9, 23.0, 27.6, 32.2, 35.7, 36.5, 38.9,
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46.8, 48.4, 51.9, 118.8, 127.0, 129.3, 131.7, 134.3, 134.7, 135.6, 137.7, 140.8, 145.6, 164.2, 179.3;
HRMS (FAB-TOF) m/z: [M]+ calcd for C28H33ClO5, 484.2017; found, 484.2019.
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Methyl 12-benzoyloxy-11-hydroxyabieta-8,11,13-trien-18-oate (36). The same procedure as
described for 30 was performed using benzoic acid (6.9 mg, 0.056 mmol) and 16 (15.7 mg, 0.045
mmol) with reaction time of 20 h to afford 36 (3.8 mg, 0.0084 mmol, 19%). 1H NMR spectroscopic
data was identical to those in the literature.12
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Methyl 11-hydroxyabieta-12-(3-methoxybenzoyloxy)-8,11,13-trien-18-oate (37). The same
procedure as described for 30 was performed using 3-methoxybenzoic acid (13.3 mg, 0.087 mmol)
and 16 (25.3 mg, 0.073 mmol) with reaction time of 240 min to afford 37 (10.8 mg, 0.022 mmol,
22%) and recovered 16 (6.2 mg, 0.018 mmol, 25%).1H NMR (600 MHz, CDCl3) δ: 1.16 (d, J =
7.2 Hz, 3H), 1.19 (d, J = 7.2 Hz, 3H), 1.29 (s, 3H), 1.30–1.34 (m, 1H), 1.37 (s, 3H), 1.41–1.45 (s,
1H), 1.59–1.63 (m, 2H), 1.70–1.82 (m, 3H), 2.26 (d, J = 11.4 Hz, 1H), 2.79–2.96 (m, 3H), 3.15–
3.18 (m, 1H), 3.68 (s, 3H), 3.89 (s, 3H), 5.20 (s, 1H), 6.60 (s, 1H), 7.21–7.23 (m, 1H), 7.45 (t, J =
13
8.4 Hz, 1H), 7.73–7.74 (m, 1H), 7.84–7.85 (m, 1H); C{1H} NMR (150 MHz, CDCl3) δ: 16.9,
18.6, 20.2, 22.1, 22.9, 23.0, 27.6, 32.2, 35.7, 36.5, 38.9, 46.8, 48.4, 51.9, 55.6, 114.7, 118.7, 120.7,
122.7, 129.8, 129.9, 134.1, 134.8, 135.5, 137.8, 145.6, 159.8, 164.9, 179.3; HRMS (FAB-TOF)
m/z: [M+H]+ calcd for C29H37O6, 481.2590; found, 481.2578.
Methyl 11-hydroxyabieta-12-(4-methoxybenzoyloxy)-8,11,13-trien-18-oate (38)
The same procedure as described for 33 was performed using 4-methoxybenzoic acid (18.6 mg,
0.12 mmol) and 16 (35.7 mg, 0.043 mmol) to afford 38 (9.0 mg, 0.019 mmol, 19%). 1H NMR (600
MHz, CDCl3) δ: 1.16 (d, J = 6.6 Hz, 3H), 1.18 (d, J = 6.6 Hz, 3H), 1.29 (s, 3H), 1.30–1.32 (m,
1H), 1.37 (s, 3H), 1.40–1.45 (m, 1H), 1.59–1.62 (m, 2H), 1.70–1.82 (m, 3H), 2.25 (d, J = 11.4 Hz,
1H), 2.78–2.96 (m, 3H), 3.15–3.20 (m, 1H), 3.68 (s, 3H), 3.91 (s, 3H), 5.29 (s, 1H), 6.59 (s, 1H),
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7.00–7.03 (m,2H), 8.18–8.20 (m, 2H); 13C{1H} NMR (150 MHz, CDCl3) δ: 16.9, 18.6, 20.2, 22.1,
22.9, 23.0, 27.6, 32.2, 35.7, 36.5, 38.9, 46.8, 48.4, 51.9, 55.6, 114.1, 118.6, 120.8, 132.6, 134.1,
134.9, 135.3, 137.9, 145.8, 164.3, 164.8, 179.3; HRMS (FAB-TOF) m/z: [M+H]+ calcd for
C29H37O6, 481.2590; found, 481.2602.
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Methyl 11-hydroxyabieta-12-naphthoyloxy-8,11,13-trien-18-oate (39). The same procedure as
described for 33 was performed using 2-naphthoic acid (14.4 mg, 0.084 mmol) and 16 (24.3 mg,
0.070 mmol) to afford 39 (9.7 mg, 0.019 mmol, 28%) and recovered 16 (15.0 mg, 0.043 mmol,
62%). 1H NMR (600 MHz, CDCl3) δ: 1.18 (d, J = 6.6 Hz, 3H), 1.21 (d, J = 6.6 Hz, 3H), 1.30 (s,
3H), 1.31–1.34 (m, 1H), 1.39 (s, 3H), 1.42–1.48 (m, 1H), 1.59–1.63 (m, 2H), 1.72–1.81 (m, 3H),
2.28 (d, J = 10.8 Hz, 1H), 2.80–2.84 (m, 1H), 2.89–2.98 (m, 2H) 3.18 (br d, J = 14.4 Hz, 1H), 3.69
(s, 3H), 5.27 (s, 1H), 6.63 (s, 1H), 7.61 (br t, J = 6.6 Hz, 1H), 7.67 (br t, J = 7.2 Hz, 1H), 7.94 (d,
J = 8.4 Hz, 1H), 7.98 (d, J = 8.4 Hz, 1H), 8.02 (d, J = 7.8 Hz, 1H), 8.22 (dd, J = 1.8, 8.4 Hz, 1H),
8.84 (s, 1H); 13C{1H} NMR (150 MHz, CDCl3) δ: 16.9, 18.6, 20.2, 22.1, 22.9, 23.1, 27.6, 32.2,
35.7, 36.5, 38.9, 46.8, 48.4, 51.9, 118.7, 125.4, 125.7, 127.0, 127.9, 128.7, 129.0, 129.6, 132.3,
132.5, 134.1, 134.9, 135.5, 136.0, 137.9, 145.7, 165.2, 179.3; HRMS (FAB-TOF) m/z: [M+H]+
calcd for C32H37O5, 501.2641; found, 501.2632.
Methyl 12-(3-biphenyloxy)-11-hydroxyabieta-8,11,13-trien-18-oate (40). The same procedure as
described for 33 was performed using 3-biphenylcarboxylic acid (16.6 mg, 0.083 mmol) and 16
(24.0 mg, 0.069 mmol) to afford 40 (12.4 mg, 0.024 mmol, 34%) and recovered 16 (10.2 mg, 0.029
mmol, 43%).1H NMR (600 MHz, CDCl3) δ: 1.18 (d, J = 7.2 Hz, 3H), 1.20 (d, J = 7.2 Hz, 3H),
1.29 (s, 3H), 1.31–1.33 (m, 1H), 1.38 (s, 3H), 1.42–1.46 (m, 1H), 1.59–1.63 (m, 2H), 1.71–1.83
(m, 3H), 2.26 (d, J = 11.4 Hz, 1H), 2.79–2.97 (m, 3H), 3.17 (d, J = 13.8 Hz, 1H), 3.68 (s, 3H),
5.23 (s, 1H), 6.61 (s, 1H), 7.41 (t, J = 7.2 Hz, 1H), 7.49 (t, J = 7.8 Hz, 2H), 7.62 (t, J = 7.8 Hz,
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