Synthesis of pelorol and its analogs and their inhibitory effects on phosphatidylinositol 3-kinase

Article abstract of DOI:10.3390/md14060118

There are numerous biologically active substances with novel structures and unique physiological functions in marine organisms. These substances are important sources of new lead compounds. Pelorol is a natural product isolated from marine organisms that possesses a novel structure with high bioactivity. In this paper, the synthesis of pelorol has been completed, and the synthesis of some intermediates has been optimized and scaled up. Five pelorol analogs have also been prepared. Preliminary biological activity testing demonstrated that compounds 5 and 6 might be potential lead compounds for cancer therapy.

Full text of DOI:10.3390/md14060118

marine drugs
Article
Synthesis of Pelorol and Its Analogs and Their
Inhibitory Effects on Phosphatidylinositol 3-Kinase
Yongjie Luo 1, Huixuan Chen 1, Jiang Weng 1 and Gui Lu 1,2,
*
1
Institute of Medicinal Chemistry, School of Pharmaceutical Sciences, Sun Yat-sen University,
Guangzhou 510006, China; 18666353586@163.com (Y.L.); chenhx33@mail2.sysu.edu.cn (H.C.);
wengj2@mail.sysu.edu.cn (J.W.)
Institute of Human Virology, Sun Yat-sen University, Guangzhou 510080, China
Correspondence: lugui@mail.sysu.edu.cn; Tel./Fax: +86-20-3994-3048
2
*
Academic Editor: Patrizia Diana
Received: 16 April 2016; Accepted: 18 May 2016; Published: 21 June 2016
Abstract: There are numerous biologically active substances with novel structures and unique
physiological functions in marine organisms. These substances are important sources of new lead
compounds. Pelorol is a natural product isolated from marine organisms that possesses a novel
structure with high bioactivity. In this paper, the synthesis of pelorol has been completed, and the
synthesis of some intermediates has been optimized and scaled up. Five pelorol analogs have also
been prepared. Preliminary biological activity testing demonstrated that compounds
be potential lead compounds for cancer therapy.
5 and 6 might
Keywords: marine organisms; pelorol; total synthesis; PI3K inhibitor; anti-tumor activity
1. Introduction
Natural products play significant roles in drug discovery and development [1]. Marine organisms
have been extensively investigated because they produce natural substances; for instance,
245 furanosesterterpenoids from marine organisms were described in at least 133 articles from 1996 to
2006 [2]. The number of publications may be higher if halogenated monoterpenes, sesquiterpenes, and
polyterpenes extracted from the sponges are considered [
3
]. Labdane-type diterpenes are excellent
examples of natural products with important pharmaceutical activities (Figure 1). Most of these
derivatives possess significant biological properties such as anti-tumor, anti-HIV, anti-inflammatory,
antifungal, and antibacterial activities [4–8].
Pelorol is a labdane-type diterpene isolated from the sponge [9,10]. It exhibits promising activity
against trypanosome and Plasmodium. In vitro tests and mouse models reveals that pelorol is a src
homology 2-containing inositol 5-phosphatase (SHIP) activators.
Phosphatidylinositol 3-kinases (PI3Ks) are a family of lipid kinases involved in cellular functions
such as cell growth, proliferation, differentiation, motility, survival, and intracellular trafficking.
The targeting of the PI3K pathway is one of the most promising approaches for the treatment of
cancers. Moreover, SHIP can negatively regulate the PI3K pathway. The increased activity of SHIP can
reduce the anti-apoptotic effect of the PI3K-Akt signaling pathway [11,12]. Thus, pelorol might also be
a potential PI3K inhibitor.
However, natural pelorol is difficult to extract, and the synthetic of pelorol is rarely described.
As far as we know, Andersen and co-workers [13] described a new strategy to synthesize pelorol with
5% overall yield in 2005. Their route is difficult to scale up because of numerous reaction steps and
strict reaction conditions. In 2012, Baran and co-workers [14] developed another efficient method
for the synthesis of pelorol, and they realized the gram-scale preparation of the key intermediate
“borono-sclareolide”. Hence, new methods and technologies are still highly desirable for the synthesis,
Mar. Drugs 2016, 14, 118; doi:10.3390/md14060118
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semi-synthesis, chemical modification and bioactivity assay of pelorol and related marine natural
products, in order to provide technical support for the development of marine drug.
Figure 1. Representative bioactive compounds of labdane-type diterpenes.
2. Results and Discussion
2.1. Chemistry
In this paper, the synthesis of pelorol has been completed, optimized and scaled up based on
Baran’s method (Scheme 1). Five pelorol analogs 2–6 have also been prepared (Figure 2).
Commercially available terpenoid (+)-sclareolide (
configurations at C-5, C-9, and C-10 with pelorol ( ), was used as starting material.
to a mixture of and = 4.59) with an excellent yield (99%); this mixture was used for the
7), which exhibits the same absolute
1
7
was reduced
8
9 (8/9
subsequent transformation without additional separation. Benzene is commonly used for iodination.
Considering its toxicity, we replaced benzene with toluene and obtained product 10 with 78% yield.
A sequential dehydroiodination/hydrolysis reaction (AgF in pyridine followed by K2CO3 in methanol)
produced intermediate 11 with 89% overall yield. AgF is a precious metal salt and 1.5 equiv. of fresh
AgF was essential in this reaction. To reduce the production costs, recycled AgF catalyst can be used,
and in this case, 2.0 equiv. of catalyst was needed to ensure complete conversion. Hydroboration of
11 resulted in a mixture of diastereomers in 95% combined yield, and borono-sclareolide (12) can be
separated by column chromatography in 50% yield.
Figure 2. Pelerol analogs 2–6 in our work.

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Scheme 1. Synthesis of
I2, toluene, hv, 80 ˝C,1 h; (
2 h; ( ) BH3
THF, THF, 0 ˝C–RT, 12 h; (
CH2Cl2, –78 ˝C, 1 h; ( 6H2O, TBHP, NaOH, CTAB, H2O, 80 ˝C, 48 h; (
) FeCl3
12 h; (j) BI3, CH2Cl2, –78 ˝C, 1 h.
1
and
) AgF, pyridine, room temperature (RT), 12 h; (
) S-Phos, CsF, Pd(OAc)2, 1,4-dioxane, 50 ˝C, 18 h; (
) MeI, K2CO3, DMF, RT,
2
. Reagents and conditions: (
a
) DIBAL, CH2Cl2,
) K2CO3, MeOH, 0 ˝C–RT,
) SnCl4,
´
78 ˝C, 1 h; (
b) PIDA,
c
d
e
¨
f
g
h
¨
i
At first, we followed Baran’s method and used aryl bromide with ethyl substituent (18) to couple
with 12, but the subsequent oxidation of intermediate 20 suffered from low yield. We have tried several
different oxidants, such as DCC, PDC, ethylene oxide and potassium permanganate, but failed to
improve the yield. Furthermore, subsequent reaction systems were quite complicated. Considering
these problems, we changed the aryl bromide substrate to vinyl-substituted 13, and found that the
coupling reaction proceeded smoothly with up to 81% yield. What is more, this modification could
remove two steps for the total synthesis of pelorol. The subsequent cyclization of 14 was performed
at
´
78 ˝C to avoid the secondary reaction of the vinyl functional group. This cyclization provided
the tetracyclic intermediate 15 in high yield (78%). Compounds 14 and 15 can also be prepared in
gram-scale with comparable yields.
The oxidation of 15 via TBHP can generate 16 [15]. The synthesis of pelorol (1) was completed
by the esterification of 16 with MeI and the selective cleavage of aryl methyl ether with BI3. The total
yield of this route was 4.4%, which was similar to that of Andersen et al. [13]. The direct demethylation
of 16 afforded compound 2 in 62% yield.
As we mentioned before, borono-sclareolide (12) could couple with ethyl-substituted 18 under
Suzuki Coupling conditions developed by Buchwald [16]. A favorable yield of the coupling product
19 (73%) was obtained. The subsequent cyclization afforded 20 in excellent yield (92%). 20 was then
oxidized by PCC to produce 21 in 27% yield; here the low yield might be due to the existence of
two electron-donating methoxy groups on the phenyl ring of 20. The demethylation of 20 and 21

Mar. Drugs 2016, 14, 118
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provided
4
(95% yield) and
3
(75% yield), respectively (Scheme 2). The low yield in the latter reaction
might be due to side reactions between ketone and BI3.
Scheme 2. Synthesis of
3 and 4. Reagents and conditions: (a) S-Phos, CsF, Pd(OAc)2, 1,4-dioxane,
50 ˝C, 12 h; (b) SnCl4, CH2Cl2, ´20 ˝C, 1 h; (c) PCC, 40 ˝C, 20 h; (d) BI3, CH2Cl2, ´78 ˝C, 1 h.
Intermediate 15 can be further oxidized to aryl aldehyde 22 under mild conditions [17
,
18].
Subsequent transformation of 22 via the formation of oxime and dehydration could yield 23
(80%) [19 20]. The demethylation of 22 and 23 afforded (75% yield) and (75% yield), respectively
(Scheme 3). In this way, we have obtained five pelorol analogs 2–6.
,
5
6
Scheme 3. Synthesis of
RT, 8 h; (
5
and
6
. Reagents and conditions: (
a
) NMO, H4K2O6Os, THF:acetone:H2O=2:1:1,
b
) NaIO4, CH2Cl2, 0 ˝C–RT, 3 h; (
c
) NH2OH HCl, Et3N, RT, 4 h; (d
¨
) Cl3COCOOCCl3, CH2Cl2,
RT, 8 h; (e) BI3, CH2Cl2, ´78 ˝C, 1 h.
2.2. PI3K Enzymatic Activity Assay
All the newly prepared pelorol and analogs have been assessed in vitro in terms of biological
activity against PI3K kinase, and the results are summarized in Table 1. Under the assay condition,
IC50 value of pelorol was 38.17 M. The carboxylic acid-substituted compound showed slightly
increased activity (20.70 M). Among all these analogs, (with acetyl substituent) and (with
aldehyde substituent) were the best PI3K inhibitors with IC50 of 8.76 M and 5.06 M, respectively [13].
Cyano-substituted compound showed a significant decrease in activity (IC50 = 49.51 M), while
compound with ethyl substituent on the phenyl ring exhibited poor performance (IC50 = 83.69 M).
We assumed that electronic effects might influence the inhibitory activity of compounds against PI3K
We have also found that dimethoxy-substituted compound 20 displayed weaker inhibitory activity
α
µ
2
µ
3
5
µ
µ
6
µ
4
µ
α
.

Mar. Drugs 2016, 14, 118
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when comparing with corresponding phenolic hydroxy-substituted compound
4
. The most efficient
compound
5 was also subjected to PI3Kβ, PI3Kγ, PI3Kδ tests, and it exhibited significant inhibitory
activity against PI3Kβ (IC50 = 8.90 µM).
Table 1. Inhibition of pelorol and analogs against PI3Kα (µM) a.
5 b
Compound
1
2
3
4
6
20
49.51 >100
M, for PI3Kγ is >100 µM, for
IC50
38.17
20.70
8.76
83.69
5.06
Average of three replicates; b For compound
5
, IC50 value for PI3K
β
is 8.90
µ
a
PI3Kδ is >100 µM.
2.3. Antiproliferative Assays in Vitro
Eight human cancer cell lines were used in the antiproliferative bioassay of pelorol and its analogs,
the results were summarized in Table 2. The inhibitory activities of pelorol were poor. Compounds
and also exhibited poor antiproliferative activities in these cancer cells, albeit showed reasonable
activity against PI3K . In contrast, compound displayed the highest inhibitory activities and
2
4
2
α
5
suppressed most of the cancer cells, especially MOLT-4 (leukemia cell), U937 (leukemia cell), and
DU145 (prostate cancer cell), with IC50 at micromolar concentration levels. Although cyano-substituted
compound 6 demonstrated moderate activity in kinase test, 6 could efficiently suppress a few tumor
cells, especially MOLT-4 and DU145. Based on the above analysis, pelorol analogs
potential lead compounds for cancer therapy.
5 and 6 might be
Table 2. Relative IC50 values (µM) of pelorol and analogs against tumor cell lines a.
Compound
1
2
3
4
5
6
MCF-7
K562
Hela
DU145
MOLT-4
SK-BR-3
U937
PC3
>30
>30
>30
72.69
>30
>30
>30
>30
>30
>30
>30
>30
>30
>30
22.3
>30
>30
>30
>30
>30
>30
>30
>30
>30
>30
>30
38.9
16.11
13.15
9.01
4.27
19.14
5.99
16.5
>30
12.05
8.13
2.89
>30
N.D. b
>30
N.D.
N.D.
N.D.
>30
12.85
>30
18.36
a
Average of three replicates; b N.D.: not determined.
3. Materials and Methods
All commercial reagents and anhydrous solvents were obtained from commercial sources and
1
were distilled from standard drying agents unless otherwise specified. H NMR spectra were recorded
on a Bruker AVANCE III 400 spectrometer (Bruker Corp., Billerica, MA, USA) and referenced to
tetramethylsilane in appropriate organic solutions. Chemical shifts were expressed as δ units using
tetramethylsilane as internal standard (in NMR description: s, singlet; d, doublet; t, triplet; q, quartet;
m, multiplet; bs, broad signal; J, joules; Hz, hertz). Mass spectra were measured with an Agilent 6120
spectrometer (Agilent Tech., Santa Clara, CA, USA) using an ESI+APCI source coupled to an Agilent
1200 HPLC system (Agilent Tech.) operating in reverse mode. High-resolution mass spectra were
recorded on an ESI-ion trap mass spectrometer (Shimadzu LCMS-IT-TOF, Shimadzu, Kyoto, Japan),
and the results agreed with the theoretical values to within 5 ppm. Purity of all biologically evaluated
compounds was greater than 95%.
3.1. Chemistry
(1R,2R,4aS,8aS)-1-(Iodoethyl)-2,5,5,8a-tetramethyldecahydronaphthalen-2-yl formate (10) [14]:
To a solution of (+)-sclareolide (10.00 g, 40.0 mmol, 1.0 equiv.) in 200 mL CH2Cl2 was added 1.0 M

Mar. Drugs 2016, 14, 118
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˝
78 C. The reaction
solution of DIBAL in heptane (48.0 mL, 48.0 mmol, 1.2 equiv.) dropwise at
´
mixture was then stirred for another 60 min. Water was slowly added, the reaction mixture was
warmed to room temperature and stirred overnight, extracted with CH2Cl2 (4 50 mL), washed with
saturated brine (50 mL), dried over Na2SO4. Evaporation of the solvent afforded a white solid, which
was used immediately in the next step.
ˆ
The white solid in 90 mL anhydrous toluene was treated with PIDA (18.04 g, 56 mmol, 1.4 equiv.)
and I2 (12.18 g, 48 mmol, 1.2 equiv.). The purple reaction mixture was vigorously stirred at 74 ˝C for
60 min under the irradiation of flood lamp (150 W). The reaction mixture was cooled, concentrated
under reduced pressure, diluted with saturated brine, and extracted with EtOAc. The organic layers
were combined, washed with saturated Na2S2O3, dried over Na2SO4. The solution was filtered and
concentrated under reduced pressure. The residue was quickly diluted with anhydrous MeOH, stirred
1
and cooled at
NMR (400 MHz, CDCl3)
´
78 ˝C. The resulting white solid 10 (7.87 g, 78% yield) was collected via filtration. H
δ
: 8.02 (s, 1H), 3.36 (dd, J = 10.7, 2.9 Hz, 1H), 3.13 (dd, J = 10.7, 4.6 Hz, 1H),
2.55 (d, J = 12.7 Hz, 1H), 2.46 (d, J = 2.0 Hz, 1H), 1.93–1.85 (m, 2H), 1.69 (d, J = 3.5 Hz, 1H), 1.57 (s, 3H),
1.47 (d, J = 1.0 Hz, 3H), 1.38 (s, 1H), 1.25 (s, 2H), 1.07 (d, J = 2.3 Hz, 1H), 0.88 (s, 3H), 0.85 (d, J = 0.8 Hz,
3H), 0.79 (s, 3H). 13C NMR (101 MHz, CDCl3)
δ: 160.3, 88.3, 62.1, 55.3, 41.6, 40.8, 39.6, 38.9, 33.2, 33.1,
21.4, 20.4, 19.7, 18.4, 14.8, ´3.2. (Figure S1).
(+)-Drim-9(11)-en-8-ol (11) [14]: A solution of compound 10 (2.32 g, 6.13 mmol, 1.0 equiv.) in
anhydrous pyridine (20 mL) was treated with silver (I) fluoride (1.16 g, 9.2 mmol, 1.5 equiv.) at room
temperature. The reaction flask was covered with aluminum foil to prevent light. The solution was
stirred at room temperature for 12 h, then concentrated in vacuo, diluted with Et2O (20 mL), and
filtered through celite pad. The dark grey solid (AgF) can be recycled. The filter cake was washed with
Et2O (20 mL). The filtrate was combined, washed with saturated NaHCO3 and saturated Na2S2O3
(
VNaHCO {VNa S O
“
5 : 1, 45 mL), then washed with brine (50 mL), dried over Na2SO4. The solution
3
2
2
3
was filtered and concentrated under reduced pressure to afford unstable pale yellow syrup which was
used immediately in the next step.
A solution of yellow syrup i˝n 90 mL MeOH was treated with powdered, oven-dried K2CO3
(
1.01 g, 7.35 mmol, 1.2 equiv.) at 0 C. The reaction was warmed to room temperature and vigorously
stirred for 2 h. The mixture was concentrated under reduced pressure, diluted with Et2O (20 mL),
washed with H2O (60 mL), and extracted with Et2O (2 20 mL). The combined Et2O extracts were
ˆ
dried over Na2SO4, filtered and concentrated under reduced pressure to afford compound 11 as
1
oyster white solid (1.18 g, 89% yield). H NMR (400 MHz, CDCl3)
δ: 5.21 (s, 1H), 4.83 (s, 1H), 2.01 (d,
J = 9.5 Hz, 1H), 1.79 (d, J = 12.6 Hz, 1H), 1.69 (t, J = 13.5 Hz, 2H), 1.53 (d, J = 14.8 Hz, 1H), 1.47 (s, 1H),
1.40 (s, 3H), 1.38–1.30 (m, 2H), 1.25 (s, 1H), 1.15 (d, J = 14.2 Hz, 1H), 1.08 (s, 3H), 0.98 (d, J = 11.0 Hz,
1H), 0.87 (s, 3H), 0.84 (s, 3H). 13C NMR (101 MHz, CDCl3)
δ
: 166.6, 103.7, 73.3, 53.5, 44.2, 41.8, 40.0,
39.0, 33.8, 33.2, 30.6, 29.68, 22.4, 21.6, 20.2, 19.1. (Figure S2).
1
Borono-sclareolide (12) [14]: Yield 50%, white solid. H NMR (400 MHz, CDCl3)
δ
: 6.62 (s, 1H),
1.95 (d, J = 11.6 Hz, 1H), 1.79–1.74 (m, 1H), 1.63 (d, J = 8.0 Hz, 2H), 1.56–1.50 (m, 1H), 1.42 (s, 3H),
1.38–1.34 (m, 1H), 1.33-1.23 (m, 1H), 1.17 (s, 4H), 0.98–0.90 (m, 2H), 0.85 (s, 3H), 0.82 (s, 3H), 0.80 (s,
3H), 0.75 (d, J = 7.6 Hz, 1H). 13C NMR (101 MHz, CDCl3)
δ: 83.9, 61.6, 56.9, 42.5, 40.4, 39.5, 37.0, 33.3,
33.2, 23.1, 21.0, 20.9, 18.3, 14.6. (Figure S3).
(1R,2R,4aS,8aS)-1-(2,3-diMethoxy-5-vinylbenzyl)-2,5,5,8a-tetramethyldecahydronaphthalen-2-ol
14): To the borono-sclareolide 12 (1.00 g, 4.0 mmol, 1.0 equiv.) was added bromide 13 (1.94 g, 8 mmol
(
,
2.0 equiv.), S-Phos (0.25 g, 0.6 mmol, 0.15 equiv.), CsF (1.82 g, 12 mmol, 3.0 equiv.) and 50 mL
anhydrous dioxane. The solution was degassed for 20 min by bubbling N2 under sonication. Pd(OAc)2
(0.09 g, 0.4 mmol, 0.1 equiv.) was immediately added under N2, then the reaction mixture was heated
˝
at 50 C for 18 h. The solution was cooled to room temperature and filtered through a celite pad,
concentrated under reduced pressure. The crude product was purified by column chromatography on
1
silica gel (petroleum ether/EtOAc = 30:1) to afford 14 (1.22 g, 80.5% yield) as colorless oil. H NMR
(400 MHz, CDCl3) δ: 6.87 (d, J = 1.6 Hz, 1H), 6.81 (d, J = 1.7 Hz, 1H), 6.63 (dd, J = 17.5, 10.8 Hz, 1H),

Mar. Drugs 2016, 14, 118
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5.63 (d, J = 17.5 Hz, 1H), 5.18 (d, J = 10.9 Hz, 1H), 3.86 (s, 3H), 3.85 (s, 3H), 2.84 (dd, J = 14.5, 5.1 Hz,
1H), 2.66 (s, 1H), 2.60 (d, J = 4.9 Hz, 1H), 1.86 (d, J = 12.5 Hz, 1H), 1.75 (d, J = 12.8 Hz, 1H), 1.62 (s, 3H),
1.41 (d, J = 14.0 Hz, 2H), 1.33 (d, J = 16.6 Hz, 2H), 1.28 (s, 3H), 1.10 (dd, J = 13.2, 3.6 Hz, 1H), 0.91 (s,3H),
0.85 (s, 3H), 0.83-0.81 (m, 1H), 0.80 (s, 3H). 13C NMR (101 MHz, CDCl3)
δ: 152.6, 146.3, 138.1, 136.8,
133.5, 121.5, 112.9, 107.0, 73.7, 62.9, 60.7, 56.1, 55.7, 43.8, 41.8, 40.3, 39.5, 33.5, 33.3, 25.1, 24.2, 21.6, 20.3,
18.6, 15.5. (Figure S4).
(4aS,6aR,11aR,11bS)-9,10-diMethoxy-4,4,6a,11b-tetramethyl-7-vinyl-2,3,4,4a,5,6,6a,11,11a,11b-
decahydro-1H-benzo[a]fluorene (15): To a stirred solution of 14 (232 mg, 0.6 mmol, 1.0 equiv.) in
˝
CH2Cl2 (60 mL), SnCl4 (0.6 mL) was added dropwise at
´
78 C under N2. The resulting mixture was
stirred for an additional 1 h. Upon the completion of the reaction (monitored by TLC), the solution
was diluted with CH2Cl2 (90 mL) and poured into ice. The aqueous phase was extracted with CH2Cl2
(2
ˆ
20 mL), the combined CH2Cl2 extracts were dried over Na2SO4, filtered and concentrated under
reduced pressure. The residue was purified by column chromatography on silica gel (petroleum
ether/EtOAc = 15:1) to give 15 as yellow-green crystal (173 mg, 78.3% yield). H NMR (400 MHz,
1
CDCl3) δ: 7.06 (dd, J = 17.4, 10.9 Hz, 1H), 6.81 (s, 1H), 5.49 (dd, J = 17.3, 1.3 Hz, 1H), 5.17 (dd, J = 10.9,
1.3 Hz, 1H), 3.86 (s, 3H), 3.84 (s, 3H), 2.72 (dd, J = 14.7, 6.2 Hz, 1H), 2.56–2.47 (m, 1H), 2.42–2.35 (m,
1H), 1.73 (s, 3H), 1.61 (s, 2H), 1.43 (s, 2H), 1.26 (s, 1H), 1.18 (d, J = 4.3 Hz, 1H), 1.11 (s, 3H), 1.04 (s, 3H),
1.01–0.95 (m, 2H), 0.87 (s, 6H). 13C NMR (101 MHz, CDCl3)
δ: 150.6, 145.5, 145.3, 135.8, 134.3, 128.3,
113.6, 107.7, 64.2, 60.4, 57.0, 56.0, 47.9, 42.5, 40.1, 39.5, 37.1, 33.4, 33.1, 25.3, 21.6, 21.1, 19.7, 18.4, 16.1.
(Figure S5).
(4aS,6aR,11aR,11bS)-Methyl-9,10-dimethoxy-4,4,6a,11b-tetramethyl-2,3,4,4a,5,6,6a,11,11a,11b-
decahydro-1H-benzo[a]fluorene-7-carboxylate (17): To a mixture of 15 (100 mg, 0.27 mmol, 1.0 equiv.)
and ferric chloride hexahydrate (40 mg) was added TBHP (1.2 mL, 70% aqueous solution), CTAB
(
2 g) and 8 mL water. NaOH (40 mg, 1.0 mmol) was added after 3 h, and the mixture was heated at
90 ˝C for 48 h. After the completion of the reaction, dilute HCl and crushed ice were added. The
mixture was extracted with EtOAc (2 50 mL), washed with saturated brine, dried over Na2SO4,
ˆ
then concentrated to dryness. The residue was dissolved in 2 mL DMF, then potassium carbonate
(350 mg) and MeI (0.4 mL) were added. The solution was stirred overnight, quenched with 10 mL
brine. The mixture was extracted with Et2O (2
evaporated to dryness. The residue was purified by column chromatography on silica gel (petroleum
ether/EtOAc = 8:1) to give 17 as colorless oil (34 mg, 33.3% yield). H NMR (400 MHz, CDCl3)
ˆ
20 mL), washed with brine, dried over MgSO4, and
1
δ: 7.03
(s, 1H), 3.88 (s, 3H), 3.86 (s, 3H), 3.84 (s, 3H), 2.71 (dd, J = 14.7, 6.2 Hz, 1H), 2.60–2.52 (m, 1H), 2.46 (dd,
J = 9.1, 3.2 Hz, 1H), 1.66 (s, 2H), 1.40 (d, J = 6.2 Hz, 2H), 1.32 (s, 3H), 1.24 (s, 3H), 1.06 (s, 3H), 0.99 (d,
J = 6.7 Hz, 1H), 0.94 (s, 1H), 0.90 (d, J = 2.8 Hz, 2H), 0.86 (s, 3H), 0.85 (s, 3H). 13C NMR (101 MHz,
CDCl3)
δ: 168.3, 149.8, 148.8, 148.3, 137.1, 121.2, 111.5, 64.8, 60.4, 57.1, 56.0, 51.8, 48.1, 42.5, 40.2, 37.1,
36.4, 33.4, 33.1, 25.3, 21.1, 20.0, 19.5, 18.35, 16.3. (Figure S6).
Pelorol (
1
): To a solution of methyl ester 17 (11 mg, 0.028 mmol, 1.0 equiv.) in 4 mL CH2Cl2
˝
was added BI3 (129 mg, 0.336 mmol, 12 equiv.) in 2 mL CH2Cl2 dropwise at
The mixture was stirred for an additional 0.5 h, then poured into H2O and extracted with CH2Cl2
´78 C under N2.
(
2 ˆ 50 mL). The combined CH2Cl2 extracts were dried over Na2SO4, filtered and concentrated under
reduced pressure. The residue was purified by column chromatography on silica gel (petroleum
ether/EtOAc = 3:1) to provide
1
1
as colorless oil (6.5 mg, 61.6% yield). H NMR (400 MHz, CDCl3)
δ:
7.09 (s, 1H), 5.59 (s, 2H), 3.83 (s, 3H), 2.61 (d, J = 6.2 Hz, 1H), 2.54–2.47 (m, 2H), 1.66 (d, J = 6.2 Hz,
2H), 1.58–1.53 (m, 2H), 1.41 (dd, J = 8.8, 3.4 Hz, 2H), 1.25 (s, 3H), 1.23 (s, 3H), 1.05 (s, 3H), 0.98 (d,
J = 4.5 Hz, 1H), 0.96–0.93 (m, 1H), 0.85 (d, J = 5.6 Hz, 6H). 13C NMR (101 MHz, CDCl3)
δ: 168.3, 149.4,
143.7, 140.6, 130.0, 118.0, 114.8, 65.2, 57.1, 51.7, 48.5, 42.5, 40.2, 37.2, 36.5, 33.3, 33.1, 24.3, 21.1, 19.9, 19.5,
18.4, 16.3. (Figure S12). HRMS (ESI): m/z [M-H]´ calcd. for [C23H32O4]´: 371.2228, found: 371.2220.
ras3D0 = ´64.5 (c = 0.41, MeOH).
(4aS,6aR,11aR,11bS)-9,10-diHydroxy-4,4,6a,11b-tetramethyl-2,3,4,4a,5,6,6a,11,11a,11b-decahydro-
1H-benzo[a]fluorene-7-carboxylic acid (2): To a solution of 16 (13 mg, 0.033 mmol, 1.0 equiv.) in 8 mL

Mar. Drugs 2016, 14, 118
8 of 12
CH2Cl2 was slowly added BI3 (158 mg, 0.396 mmol, 12 equiv.) in 2 mL CH2Cl2 at
The mixture was stirred for an additional 0.5 h, then poured into H2O and extracted with CH2Cl2
´
78 ˝C under N2.
(
2 ˆ 50 mL). The combined CH2Cl2 extracts were dried over Na2SO4, filtered and concentrated under
reduced pressure. The residue was purified by column chromatography on silica gel (petroleum
ether/EtOAc = 1:1) to provide
1
2
as colorless oil (7.7 mg, 64.1% yield). H NMR (400 MHz, DMSO-d6)
δ
: 12.15 (s, 1H), 8.98 (d, J = 113.4 Hz, 2H), 6.91 (s, 1H), 2.63 (d, J = 12.4 Hz, 1H), 2.34 (d, J = 13.2 Hz,
1H), 1.97 (s, 1H), 1.54 (s, 1H), 1.49–1.45 (m, 2H), 1.39–1.33 (m, 2H), 1.21 (s, 3H), 1.16 (d, J = 7.1 Hz,
2H), 1.11 (s, 3H), 0.99 (s, 3H), 0.90 (s, 1H), 0.81 (s, 6H). 13C NMR (101 MHz, DMSO-d6)
: 169.1, 147.2,
δ
145.2, 142.9, 130.3, 117.8, 115.1, 65.1, 60.2, 57.1, 48.1, 42.5, 37.1, 36.7, 33.6, 33.2, 24.9, 21.5, 20.1, 19.5,
18.4, 16.5. (Figure S13). HRMS (ESI): m/z [M-H]´ calcd. for [C22H30O4]´: 357.2071, found: 357.2059.
ras3D0 = ´11.61 (c = 0.37, MeOH).
(1R,2R,4aS,8aS)-1-(5-Ethyl-2,3-diMethoxybenzyl)-2,5,5,8a-tetramethyldecahydronaphthalen-2-ol
1
(
19) [14]: Yield 73%, colorless oil. H NMR (400 MHz, CDCl3)
δ
: 6.66 (s, 1H), 6.56 (s, 1H), 3.83 (s, 6H),
2.80 (s, 2H), 2.61–2.53 (m, 3H), 1.82 (s, 2H), 1.67 (s, 1H), 1.61 (s, 3H), 1.41 (d, J = 6.6 Hz, 2H), 1.33 (d,
J = 15.8 Hz, 2H), 1.28 (s, 3H), 1.20 (t, J = 7.5 Hz, 3H), 1.09 (d, J = 3.4 Hz, 1H), 0.90 (s, 3H), 0.85 (s, 3H),
0.80 (s, 3H). 13C NMR (101 MHz, CDCl3)
δ: 152.3, 144.3, 140.0, 137.6, 122.0, 109.6, 73.7, 62.8, 60.56, 56.1,
55.6, 43.7, 41.8, 40.3, 39.4, 33.5, 33.3, 28.8, 25.3, 24.3, 21.6, 20.3, 18.6, 15.7, 15.4. (Figure S7).
(4aS,6aR,11aR,11bS)-7-Ethyl-9,10-diMethoxy-4,4,6a,11b-tetramethyl-2,3,4,4a,5,6,6a,11,11a,11b-
1
decahydro-1H-benzo[a]fluorene (20) [14]: Yield 92%, colorless oil. H NMR (400 MHz, CDCl3)
δ: 6.53
(s, 1H), 3.85 (s, 3H), 3.84 (s, 3H), 2.76–2.68 (m, 2H), 2.59 (dd, J = 30.3, 10.4 Hz, 2H), 2.41 (d, J = 11.8 Hz,
1H), 1.81 (s, 1H), 1.79–1.73 (m, 3H), 1.61 (d, J = 13.1 Hz, 3H), 1.44 (d, J = 10.6 Hz, 3H), 1.29–1.25 (m, 3H),
1.13 (s, 3H), 1.07 (s, 3H), 1.00 (s, 1H), 0.90 (s, 6H). 13C NMR (101 MHz, CDCl3)
δ: 150.4, 144.8, 143.6,
135.8, 133.7, 111.1, 64.3, 60.3, 57.1, 56.0, 47.9, 42.6, 40.2, 39.3, 37.1, 33.4, 33.1, 25.3, 24.7, 21.4, 21.2, 19.7,
18.4, 16.2, 16.1. (Figure S8).
1-((4aS,6aR,11aR,11bS)-9,10-diMethoxy-4,4,6a,11b-tetramet-hyl-2,3,4,4a,5,6,6a,11,11a,11b-decahydro-
1
1H-benzo[a]fluoren-7-yl)ethanone (21) [14]: Yield 27%, white solid. H NMR (400 MHz, CDCl3)
δ
: 6.81
(s, 1H), 3.88 (s, 3H), 3.86 (s, 3H), 3.64 (d, J = 4.3 Hz, 1H), 2.71 (dd, J = 14.7, 6.2 Hz, 1H), 2.58 (d, J = 13.0
Hz, 1H), 2.52 (s, 3H), 2.32 (d, J = 12.5 Hz, 1H), 1.62 (d, J = 5.9 Hz, 6H), 1.40 (d, J = 9.1 Hz, 2H), 1.25 (s,
3H), 1.14 (s, 1H), 1.05 (s, 3H), 0.92 (s, 1H), 0.85 (d, J = 5.6 Hz, 6H). 13C NMR (101 MHz, CDCl3)
δ: 201.9,
149.6, 147.9, 147.6, 137.4, 130.5, 110.0, 65.0, 60.5, 57.2, 56.2, 48.0, 42.5, 40.2, 37.1, 36.4, 33.4, 33.1, 30.3, 25.2,
21.1, 20.6, 19.4, 18.4, 16.3. (Figure S9).
1-((4aS,6aR,11aR,11bS)-9,10-diHydroxy-4,4,6a,11b-tetramethyl-2,3,4,4a,5,6,6a,11,11a,11b-decahydro-
1H-benzo[a]fluoren-7-yl)ethanone (
CH2Cl2 was slowly added BI3 (413 mg, 1.05 mmol, 12 equiv.) in 2 mL CH2Cl2 at
The mixture was stirred for an additional 0.5 h, then poured into H2O and extracted with CH2Cl2
3
): To a solution of 21 (34 mg, 0.088 mmol, 1.0 equiv.) in 5 mL
´
78 ˝C under N2.
(
2 ˆ 30 mL). The combined CH2Cl2 extracts were dried over Na2SO4, filtered and concentrated.
The residue was purified by column chromatography on silica gel (petroleum ether/EtOAc = 4:1) to
provide
1
3
as colorless oil (23.5 mg, 75% yield). H NMR (400 MHz, CDCl3)
δ: 6.94 (s, 1H), 5.80 (d,
J = 157.3 Hz, 2H), 2.61 (dd, J = 14.2, 6.3 Hz, 1H), 2.51 (d, J = 12.9 Hz, 1H), 2.46 (s, 3H), 2.41 (d, J = 12.6
Hz, 1H), 1.64 (d, J = 5.9 Hz, 2H), 1.53 (dd, J = 9.7, 3.0 Hz, 2H), 1.64 (d, J = 5.9 Hz, 2H), 1.53 (dd, J = 9.7,
3.0 Hz, 2H), 1.42 (d, J = 4.8 Hz, 2H), 1.26 (s, 6H), 1.23 (s, 2H), 1.04 (s, 3H), 0.84 (d, J = 6.3 Hz, 6H). 13
C
NMR (101 MHz, CDCl3) δ: 201.5, 148.3, 143.3, 140.8, 130.3, 127.3, 113.7, 65.3, 57.2, 48.5, 42.5, 40.3, 37.1,
36.3, 33.4, 33.1, 29.7, 24.3, 21.1, 20.3, 19.5, 18.4, 16.3. (Figure S14). HRMS (ESI): m/z [M-H]´ calcd. for
30
´
[C23H32O3] : 355.2279, found: 355.2270. rasD = ´18.0 (c = 0.36, MeOH).
(4aS,6aR,11aR,11bS)-7-Ethyl-4,4,6a,11b-tetramethyl-2,3,4,4a,5,6,6a,11,11a,11b-decahydro-1H-benzo
[a]fluorene-9,10-diol (
added BI3 (431 mg, 1.10 mmol, 12 equiv.) in 2 mL CH2Cl2 at
for an additional 0.5 h, then poured into H2O and extracted with CH2Cl2 (2
CH2Cl2 extracts were dried over Na2SO4, filtered and concentrated. The residue was purified by
column chromatography on silica gel (petroleum ether/EtOAc = 4:1) to provide as colorless oil
4
): To a solution of 20 (34 mg, 0.092 mmol, 1.0 equiv.) in 5 mL CH2Cl2 was slowly
˝
´
78 C under N2. The mixture was stirred
ˆ
30 mL). The combined
4

Mar. Drugs 2016, 14, 118
9 of 12
1
(29.9 mg, 95% yield). H NMR (400 MHz, CDCl3) δ: 6.49 (s, 1H), 2.61 (s, 2H), 2.48 (s, 2H), 2.35 (s, 1H),
1.77 (s, 2H), 1.69 (s, 1H), 1.60–1.53 (m, 3H), 1.43 (d, J = 4.1 Hz, 2H), 1.25 (s, 3H), 1.18 (s, 3H), 1.08 (s, 3H),
1.03 (s, 3H), 0.87 (s, 6H). 13C NMR (101 MHz, CDCl3)
δ
: 144.8, 141.4, 137.9, 130.9, 128.7, 113.7, 64.6, 57.1,
48.1, 42.5, 40.1, 39.3, 37.1, 33.4, 33.1, 24.5, 24.2, 21.4, 21.1, 19.7, 18.4, 16.2, 15.9. (Figure S15). HRMS (ESI):
m/z [M-H] calcd. for [C23H34O2] : 341.2486, found: 341.2481. ras3D0 = ´161.3 (c = 0.54, MeOH).
(4aS,6aR,11aR,11bS)-9,10-diMethoxy-4,4,6a,11b-tetramethyl-2,3,4,4a,5,6,6a,11,11a,11b-decahydro-
1H-benzo[a]fluorene-7-carbaldehyde (22): To compound 15 (60 mg, 0.16 mmol, 1.0 equiv.) in 4 mL
solvent (THF:acetone:H2O = 2:1:1) at room temperature was added NMO (0.7 mL) and H4K2O6Os
(1 mg). The reaction mixture was stirred at room temperature for 12 h. Then the mixture was
´
´
quenched with 5 mL saturated NaHS2O3, extracted with CH2Cl2 (2
ˆ
30 mL). The combined CH2Cl2
extracts were dried over Na2SO4, filtered and concentrated. The residue was dissolved in 10 mL
CH2Cl2, then NaIO4 (68.4 mg in 2 mL H2O) was added at room temperature for 3 h. The mixture was
extracted with EtOAc (2 ˆ 30 mL), washed with saturated brine (50 mL), dried over Na2SO4, filtered
and concentrated. The residue was purified by column chromatography on silica gel (petroleum
1
ether/EtOAc = 8:1) to provide 22 as colorless oil (36.8 mg, 61% yield). H NMR (400 MHz, CDCl3)
δ
: 10.32 (s, 1H), 7.21 (s, 1H), 3.88 (s, 3H), 3.82 (s, 3H), 2.70 (d, J = 6.2 Hz, 1H), 2.53 (s, 1H), 2.42 (d,
J = 12.1 Hz, 1H), 1.87 (s, 1H), 1.73 (d, J = 12.8 Hz, 2H), 1.63 (d, J = 3.3 Hz, 1H), 1.56 (s, 1H), 1.52 (s, 1H),
1.46–1.40 (m, 1H), 1.37 (d, J = 13.3 Hz, 2H), 1.19 (s, 2H), 1.14 (s, 1H), 1.02 (s, 3H), 0.96 (s, 2H), 0.83 (s,
6H). 13C NMR (101 MHz, CDCl3)
δ: 189.9, 153.2, 150.7, 136.1, 127.0, 108.1, 63.9, 60.4, 56.7, 55.9, 48.7,
42.4, 40.8, 40.1, 37.1, 33.3, 33.0, 25.5, 23.7, 21.1, 19.8, 18.3, 16.1. (Figure S10).
(4aS,6aR,11aR,11bS)-9,10-diMethoxy-4,4,6a,11b-tetramethyl-2,3,4,4a,5,6,6a,11,11a,11b-decahydro-
1H-benzo[a]fluorene-7-carbonitrile (23): To a solution of 22 (49 mg, 0.13 mmol, 1.0 equiv.) and
Et3N (25.6 mg, 0.14 mmol, 1.1 equiv.) in 2 mL CH2Cl2 was slowly added NH2OH HCl (10 mg,
¨
˝
1.4 mmol, 10 equiv.) at 0 C. The mixture was stirred for an additional 4 h at room temperature. Then
Cl3COCOOCCl3 (43 mg, 0.15 mmol, 1.2 equiv.) was added, releasing a large number of bubbles. The
reaction mixture was stirred at room temperature for 12 h, then extracted with CH2Cl2 (2
The combined CH2Cl2 extracts were dried over Na2SO4, filtered and concentrated. The residue was
ˆ
50 mL).
purified by column chromatography on silica gel (petroleum ether/EtOAc = 8:1) to provide 23 as
1
colorless oil (38.7 mg, 79.6% yield). H NMR (400 MHz, CDCl3)
δ
: 6.86 (s, 1H), 3.91 (s, 3H), 3.83 (s, 3H),
2.71 (d, J = 6.2 Hz, 1H), 2.62 (s, 1H), 2.53 (s, 1H), 1.82–1.76 (m, 1H), 1.72 (d, J = 6.5 Hz, 2H), 1.61 (s, 2H),
1.47 (s, 2H), 1.25 (d, J = 5.4 Hz, 2H), 1.14 (s, 3H), 1.04 (s, 3H), 0.99 (s, 1H), 0.95 (d, J = 10.3 Hz, 1H), 0.88
(s, 6H). 13C NMR (101 MHz, CDCl3)
δ: 151.8, 149.5, 148.8, 135.5, 117.0, 112.9, 98.2, 63.1, 59.5, 56.2, 55.2,
46.3, 41.5, 39.1, 36.1, 35.8, 32.4, 32.1, 24.4, 20.8, 20.1, 18.3, 17.2, 15.1. (Figure S11).
(4aS,6aR,11aR,11bS)-9,10-diHydroxy-4,4,6a,11b-tetramethyl-2,3,4,4a,5,6,6a,11,11a,11b-decahydro-
1H-benzo[a]fluorene-7-carbaldehyde (
CH2Cl2 was slowly added BI3 ( 431 mg, 1.10 mmol, 12 equiv.) in 2 mL CH2Cl2 at
The mixture was stirred for an additional 0.5 h, then poured into H2O and extracted with CH2Cl2
5
): To a solution of 22 (34 mg, 0.092 mmol, 1.0 equiv.) in 5 mL
´
78 ˝C under N2.
(
2 ˆ 30 mL). The combined CH2Cl2 extracts were dried over Na2SO4, filtered and concentrated.
The residue was purified by column chromatography on silica gel (petroleum ether/EtOAc = 4:1) to
provide
1
5
as colorless oil (23.5 mg, 75% yield). H NMR (400 MHz, CDCl3)
δ
: 10.26 (s, 1H), 7.37 (s, 1H),
6.80 (s, 1H), 6.14 (s, 1H), 2.72 (dd, J = 14.7, 5.9 Hz, 1H), 2.54 (d, J = 13.4 Hz, 2H), 1.92 (s, 1H), 1.76 (s,
3H), 1.58 (d, J = 12.1 Hz, 1H), 1.43 (d, J = 11.4 Hz, 2H), 1.26 (s, 2H), 1.22 (s, 3H), 1.07 (s, 3H), 1.00 (d,
J = 13.8 Hz, 2H), 0.88 (s, 6H). 13C NMR (101 MHz, CDCl3)
δ: 190.5, 154.5, 147.3, 142.0, 129.2, 124.3,
111.2, 64.2, 56.8, 49.0, 42.4, 40.7, 40.1, 37.1, 33.3, 33.1, 24.6, 23.8, 21.1, 19.8, 18.3, 16.1. (Figure S16). HRMS
30
´
´
(ESI): m/z [M-H] calcd. for [C22H30O3] : 341.2122, found: 341.2107. rasD = 48.6 (c = 0.23, MeOH).
(4aS,6aR,11aR,11bS)-9,10-diHydroxy-4,4,6a,11b-tetramethyl-2,3,4,4a,5,6,6a,11,11a,11b-decahydro-
1H-benzo[a]fluorene-7-carbonitrile (
CH2Cl2 was slowly added BI3 (140 mg, 0.36 mmol, 12 equiv.) in 1 mL CH2Cl2 at
6
): To a solution of 23 (11 mg, 0.03 mmol, 1.0 equiv.) in 5 mL
˝
´78 C under
N2. The mixture was stirred for an additional 0.5 h, then poured into H2O. The solution was
extracted with CH2Cl2 (2 30 mL). The combined CH2Cl2 extracts were dried over Na2SO4, filtered
ˆ

Mar. Drugs 2016, 14, 118
10 of 12
and concentrated. The residue was purified by column chromatography on silica gel (petroleum
1
ether/EtOAc = 3:1) to provide
6
as colorless oil (7.6 mg, 75% yield). H NMR (400 MHz, CDCl3)
δ
: 6.89
(s, 1H), 4.13 (d, J = 7.2 Hz, 2H), 2.60 (dd, J = 20.5, 8.7 Hz, 2H), 2.45 (s, 1H), 2.06 (s, 1H), 1.73 (d, J = 12.9
Hz, 3H), 1.40 (s, 1H), 1.25 (s, 3H), 1.10 (s, 2H), 1.02 (s, 2H), 0.86 (s, 9H). 13C NMR (101 MHz, CDCl3)
δ:
152.9, 145.6, 141.8, 129.8, 118.3, 116.7, 95.3, 64.4, 57.2, 47.´6, 42.5, 40.1, 37.0, 36.8, 33.4, 33.1, 24.5, 21.9,
´
21.1, 19.4, 18.3, 16.2. (Figure S17). HRMS (ESI): m/z [M-H] calcd. for [C22H29NO2] : 338.2126, found:
338.2119. ras3D0 = 10.2 (c = 0.53, MeOH).
3.2. Kinase Assays of PI3K
PI3K reactions were performed in 50 mM HEPES at pH 7.5 with 1 mM EGTA, 100 mM NaCl,
3 mM MgCl2, 2 mM DTT, and 0.03% CHAPS. All tested compounds were dissolved in 100% DMSO.
PIP2 and ATP were used as substrates, and the final reaction volume was 10
PI3K inhibitors, 1.65 nM enzyme, 50 M PIP2, and 25 M ATP were used for every 10
volume with inhibitor concentrations ranging from 0.5 nM to 10 M. After incubating for 1 h at room
L of Kinase-Glo reagent. Raw data were
µL. To evaluate the
α
µ
µ
µL reaction
µ
temperature, the reactions were quenched by adding 10
collected from Flexstation program.
µ
3.3. Antiproliferative Assays in Vitro
The following cell lines, MCF-7, SK-BR-3, K562, Hela, MOLT-4, DU145, U937, and PC3 were
purchased from Shanghai Cell Bank, Chinese Academy of Sciences. The cells were maintained at
˝
37 C in a 5% CO2 incubator in DMEM (Gibco, Invitrogen, Carlsbad, CA, USA) or RPMI1640 (Gibco,
Invitrogen) containing 10% FBS. Cell proliferation was determined by CCK8 assay (DOjinDo, Kyoto,
Japan). Cells were seeded at a density of 800–1000 cells/well in 384 well plates and treated with
solvent control or various concentration of compounds. After 72 h incubation, CCK8 reagent was
added and absorbance was measured at 450 nm by using Envision 2104 multi-label Reader (Perkin
Elmer, Waltham, MA, USA). Dose-response curves were plotted to determine the IC50 values using
Prism 5.0 (Graph Pad software Inc., San Diego, CA, USA).
4. Conclusions
Pelorol is natural product isolated from marine organisms, which possesses novel structure with
high bioactivity. To solve the source problem of pelorol, we have developed an efficient and practical
synthetic route for the preparation of pelorol in large scale. Moreover, the synthesis of some key
intermediates has been optimized and scaled up. Five pelorol analogs have been prepared, their
PI3K and tumor cell inhibitory activities have also been evaluated. This work is useful for further
route optimization, structural modifications, activity assays and large-scale preparation of pelorol and
related analogs.
1
Supplementary Materials: The following are available online at www.mdpi.com/link, Figures S1–S17: H and
13C NMR spectra of compounds.
Acknowledgments: This work was financially supported by the National High-tech R&D Program of China
(863 Program, No. 2013AA092903) and the Guangdong Province Natural Science Foundation (No. 2015A030313184).
Author Contributions: Y.L and H.C. performed experiments for the synthesis, structure confirmation, PI3K
enzymatic activity assay and antiproliferative assays of the compounds; G.L. supervised the research work; and
all authors contributed to writing the paper.
Conflicts of Interest: The authors declare no conflict of interest.

Mar. Drugs 2016, 14, 118
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Abbreviations
The following abbreviations are used in this manuscript:
CHAPS
CTAB
DCC
DIBAL
DMEM
DTT
3-[(3-Cholamidopropyl)dimethylammonio]-1-propane sulfonate
Hexadecyl trimethyl ammonium bromide
Dicyclimide
Diisobutylaluminium hydride
Dulbecco minimum essential medium
Dithiothreitol in Ethyl acetate
Ethylenebis(oxyethylenenitrilo)tetraacetic acid
Fetal calf serum
EGTA
FBS
HEPES
NMO
PCC
2-[4-(2-Hydroxyethyl)-1-piperazinyl]ethanesulfonic acid
4-Methylmorpholine N-oxide
Pyridinum chlorochromate
PDC
Pyridinium dichromate
PIDA
TBHP
TLC
Iodobenzene diacetate
tert-Butylhydroperoxide
Thin layer chromatography
S-Phos
2-Dicyclohexylphosphino-21,61-diMethoxy-1,11-biphenyl
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