Synthesis and biological evaluation of neopeltolide and analogs

Article abstract of DOI:10.1021/jo2023685

The synthesis of neopeltolide analogues that contain variations in the oxazole-containing side chain and in the macrolide core are reported along with the GI₅₀ values for these compounds against MCF-7, HCT-116, and p53 knockout HCT-116 cell lin

Full text of DOI:10.1021/jo2023685

Article
pubs.acs.org/joc
Synthesis and Biological Evaluation of Neopeltolide and Analogs
Yubo Cui,† Raghavan Balachandran,‡ Billy W. Day,*,†,‡ and Paul E. Floreancig*,†
‡
†Department of Chemistry and Department of Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260,
United States
S
* Supporting Information
ABSTRACT: The synthesis of neopeltolide analogues that
contain variations in the oxazole-containing side chain and in
the macrolide core are reported along with the GI50 values for
these compounds against MCF-7, HCT-116, and p53 knockout
HCT-116 cell lines. Although biological activity is sensitive
to changes in the macrocycle and the side chain, several
analogues displayed GI50 values of <25 nM. Neopeltolide and
several of the more potent analogues were significantly less
potent against p53 knockout cells, suggesting that p53 plays an
auxiliary role in the activity of these compounds.
available carboxylates such as benzoate or octanoate abrogates
activity.6b Maier and co-workers reported6a that changes to
some of the alkenes in the side chain were tolerated and that
incorporating an E-alkene between C4′ and C5′ provided an
approximately 40% increase in potency against one cell line and
equivalent potency against two other cell lines. The cytotoxicity
of several analogues correlated to their ability to inhibit NADH
oxidation in submitochondrial bovine heart particles,6a in
accord with the hypothesis of biological activity arising from
electron transport disruption. Neither the macrocycle or the
oxazole subunit showed biological activity, indicating that both
components are necessary to effect cytotoxicity. Scheidt, Crews,
and co-workers observed cell line-specific cytotoxicity,6b
signifying that neopeltolide does not act as a general poison.
Prior efforts at modifying the macrocyclic subunit proceeded
through pathways in which the point of diversification was
introduced at an early stage in the sequence and focused on the
synthesis of stereoisomers or structurally simplified analogues.
Structural variations of the side chain have been directed
toward dramatic simplifications or toward complex acids that
require a preparative effort that matches the natural subunit.
The objective of our neopeltolide analogue program is to
employ a late stage diversification strategy to introduce func-
tional groups to the macrolactone core that enhance hydro-
philicity and potentially provide a handle to append to a drug
delivery agent and to design side chain analogues that are more
accessible than the natural side chain while retaining key
elements to effect a potent biological response.
INTRODUCTION
■
The isolation of neopeltolide (1) from the Daedalopelta
sponge of the Neopeltidae family off the Jamaican coast1
quickly sparked a significant research effort2 that was based on
the observation of extremely potent cytotoxic and antifungal
activity for a compound of moderate structural complexity
(Figure 1). Wright and co-workers reported1 IC50 values of
0.56, 1.2, and 5.1 nM against P388 murine leukemia, A-549
human lung adenosarcoma, and NCI-ADR-RES human ovarian
sarcoma cell lines, respectively. Cytostatic activity was
postulated for two cell lines that contain p53 mutations. Flow
cytometry experiments showed that neopeltolide arrests the cell
cycle at the G1 stage. Neopeltolide also showed an MIC
(minimum inhibitory concentration) of approximately 1 μM
against the pathogenic fungus Candida albicans. The correct
atomic connectivity for 1 was established by NMR analysis1 and
the absolute and relative stereochemical assignments were
determined unambiguously through total synthesis.3 Several
total, formal, and partial syntheses followed the complete
structural determination.4
Kozmin and co-workers showed4d that neopeltolide
suppresses ATP synthesis through cytochrome bc1 inhibition.
This activity is also exhibited by the structurally similar but
more complex macrolide leucascandrolide A (2).5 Synthetic
studies have led to the preparation and biological analysis of
several analogues.6 These studies showed that altering the
stereochemical orientations around the macrocycle causes a
moderate to large drop in biological activity.6a−c Fuwa and co-
workers demonstrated6c that the C9 methyl and the C11
methoxy groups can be deleted with minimal consequence to
biological activity. These observations are significant because
shorter synthetic sequences are employed to access the
simplified structures compared to the natural product.
Replacing the oxazole-containing side chain with commercially
Our synthesis of neopeltolide4g proceeded through the
DDQ-mediated cyclization7 of 3 to 4 (Scheme 1). The Δ8,9
alkene group that is required for oxidative carbocation
Received: November 30, 2011
Published: February 13, 2012
© 2012 American Chemical Society
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Figure 1. Natural product cytochrome bc1 inhibitors.
Scheme 1. Late-Stage Diversification for Neopeltolide Analogue Synthesis
formation can be reduced by stereoselective hydrogenation en
route to the natural product and can serve as a site for late-stage
diverted total synthesis8 to produce analogues. Given that the
potency of the natural product is already sufficiently high, our
objectives were directed toward preparing analogues that are
easier to prepare, that offer improved physical properties, or
that contain a reactive site on the hydrophobic macrocycle for
prodrug development. Alkene functionalization allowed the
facile synthesis of several analogues from 4, including 8,9-
dehydroneopeltolide (5), 9-epi-neopeltolide (6), 8,9-epoxyneo-
peltolide (7), and 8,9-dihydroxyneopeltolide (8).6d The brevity
of our approach has also allowed us to accrue sufficient quanti-
ties of 4 to prepare analogues with alternate side chains that can
be prepared more efficiently than the oxazole-containing chain
in the natural product. In this paper, we report the synthesis of
8-hydroxyneopeltolide and several side-chain analogues of
neopeltolide. The cytotoxic activity of these compounds against
MCF7, HCT-116, and a p53 knockout variation of HCT-116
cells is also disclosed.
of 4, to BH3·THF followed by NaOOH led to diastereomeric
alcohols 10 and 11 in an approximately 1:1 ratio. The stereo-
chemical assignments for these compounds were confirmed by
NOESY experiments.9 This was the first alkene functionaliza-
tion reaction on 9, which has been shown by crystallography to
exist in a cup-shaped conformation that presents the Re-face of
the alkene for reaction,4g whereby no stereocontrol was
observed. Previous reactions have employed sterically more de-
manding alkene functionalization reagents, leading us to attri-
bute this result to the sterically undemanding nature of borane
rather than on any conformational mobility in the lactone.10
Commonly employed bulkier reagents such as thexylborane
and dicyclohexylborane were unreactive toward the alkene,
but diethylborane11 reacted with 9 efficiently to form 10 as a
single stereoisomer. Coupling 10 and 11 with acid 1212 pro-
ceeded under Mitsunobu conditions13 with high regiocontrol
at the less hindered C5 center to provide analogues 13
and 14.
Amide Analogue Synthesis. Converting the ester linkage
between the macrolactone and the side chain to an amide
linkage provides an additional opportunity for enhancing the
polarity of the structure while increasing the expected in vivo
stability. To prepare the amide-linked analogue (Scheme 3) we
converted 15, available in two steps from 3,6d to a mesylate
under standard conditions and effected a displacement with
RESULTS AND DISCUSSION
■
Hydroboration Studies. The successful formation of diol
86d led us to consider the preparation of a monohydroxy
derivative through hydroboration (Scheme 2). Exposing 9,
prepared through a stereoselective NaBH4-mediated reduction
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Scheme 2. Synthesis of 8-Hydroxyneopeltolide
Scheme 3. Synthesis of Amide-Linked Neopeltolide
NaN3 to yield 16. Reduction of 16 by catalytic hydrogenation
provided the amine, which coupled smoothly to 12 to yield
amide 17.
ring. The route (Scheme 4) began by the esterification of
m-bromohydrocinnamic acid (18) followed by a Sonogashira
coupling14 with the methyl carbamate of propargyl amine (19)
to yield 20. Selective cis-reduction of the alkyne was accom-
plished most effectively with H2 and P2-nickel,15 partial reduc-
tion of the ester group was achieved with DIBAL-H, and chain
extension through the Still−Gennari protocol provided
ester 21.16 Ester hydrolysis and Mitsunobu coupling to 15
yielded phenyl analogue 22.
A pyridine-containing side chain was prepared (Scheme 5)
from 6-bromo-2-pyridinecarboxaldehyde (23) through a
variation of the scheme that was developed for the benzene-
containing analogue. Exposing 23 to standard Horner−
Wadsworth−Emmons conditions17 provided the expected α,β-
unsaturated ester. The alkene group was reduced with NaBH4
and CuCl18 to yield 24. These conditions were required to
Preparation of Side-Chain Analogues. Many approaches
to the neopeltolide/leucascandrolide side chain have been
reported,12 but all require several steps due to the difficulties in
preparing the oxazole subunit and the appended Z-allylic
carbamate. A certain degree of structural complexity in this
subunit is required for biological activity, as evidenced by the
studies in which the side chain was replaced by benzoate and
octanoate groups. This led us to consider whether side chains
that contain other aromatic groups or that lacked the carbamate
group could show comparable biological activity while being
more synthetically accessible.
This study commenced with the synthesis of an analogue in
which the oxazole is replaced by a meta-substituted benzene
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Scheme 4. Synthesis of a Benzene-Containing Side Chain Analogue
Scheme 5. Synthesis of a Pyridine-Containing Analogue
Scheme 6. Synthesis of a Furan-Containing Analogue
circumvent the loss of the bromide group that was observed in
catalytic hydrogenation reactions. Coupling 24 with 19 under
Sonogashira conditions followed by partial alkyne reduction pro-
vided ester 25. Partial ester reduction, Still−Gennari coupling,
ester hydrolysis, and Mitsunobu esterification with 15 yielded an-
alogue 26.
We selected furan to be a suitable five-membered ring re-
placement for the oxazole group. The synthesis of this analogue
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Scheme 7. Synthesis of a Des-carbamate Analogue
Table 1. GI50 Values of Neopeltolide and Analogues
entry
compound
description
neopeltolide
MCF-7 GI50 (nM)
HCT116 GI50 (nM)
HCT116-p53KO GI50 (nM)
1
2
1
6960 260
30,000 150
1180 100
>50000
0.77 0.02
5.41 0.79
6.62 0.34
23.8 0.2
4310 40
9.9 0.4
49.4 0.9
49.8 0.8
47.9 0.2
4290 210
13 0.1
5
8,9-dehydroneopeltolide
9-epi-neopeltolide
3
6
4
7
8,9-epoxyneopeltolide
5
8
8,9-dihydroxyneopeltolide
8(R)-hydroxyneopeltolide
8(S)-hydroxy-9-epi-neopeltolide
amide-linked side chain
phenyl-containing side chain
pyridine-containing side chain
furan-containing side chain
des-carbamoyl side chain
paclitaxel
2770 30
43610 690
>50000
6
13
14
17
22
26
30
34
17
1
7
48 0.2
66 0.9
49 0.2
8
>50000
68 0.1
9
>50000
100
8
2940 40
24.2 0.1
730 10
72 0.3
10
11
12
13
4480 140
34750 500
>50000
2260
52.4 0.3
550
6.8 0.01
4
3
2.8 0.1
4
0.5
(Scheme 6) commenced with a Horner−Wadsworth−Emmons
extension of 5-bromofurfural (27) followed by Sonogashira
coupling with 19. All attempts at selective alkene reduction
failed, with alkyne reduction being a significant problem.
Reductive debromination was observed when alkene reduction
was attempted prior to the Sonogashira reaction. We decided to
continue the synthesis with the alkene intact based on Maier’s
observation6a that unsaturation at the 4′-5′ site does not have a
negative impact on potency. Alcohol 28 was accessed through a
sequence of alkyne partial reduction and ester reduction. Partial
ester reduction was not possible on the unsaturated ester. The
completion of the synthesis of analogue 30 followed the
sequence that was deveoped for the benzene- and pyridine-
containing analogues.
The role of the carbamate group was studied by preparing
(Scheme 7) an analogue that lacks this group. Commercially
available oxazole 31 was converted to ester 32 through a two
step sequence. This aldehyde was efficiently converted to
analogue 34 by following the previously developed routes.
Biological Results. The potency of these compounds was
measured in cell viability studies using MCF-7 breast cancer
cells, HCT-116 colon cancer cells, and a p53 knockout variant
of the HCT-116 cell line. These cell lines were selected based
on our desire to test the specificity of these compounds and to
probe the role of p53 in the biological response. Results were
obtained through the MTS (3-(4,5-dimethylthiazol-2-yl)-5-
(3-carboxymethoxyphenyl)-2-(4-sulfophenyl-2H-tetrazolium)
dye reduction assay with PMS (phenozine methosulfate) as
an electron acceptor.19 The assays were conducted over a 3-day
incubation period at 37 °C and were run in triplicate or
quintuplicate. Growth inhibition (GI) was calculated as defined
by the National Cancer Institute (GI = 100(T − T0)/(C − T0),
where T0 = cell density at time zero, T = cell density after 72 h
with analogue, and C = cell density at 72 h with vehicle).
Paclitaxel was used as a positive control to validate the quality
of the experimental results. The results are shown in Table 1.
These results showed some very interesting trends. The lack
of potency toward MCF-7 cells confirmed that neopeltolide
and analogues are not general cell poisons and show some cell
line selectivity. While MCF-7 cells have previously been shown
to be susceptible to the actions of neopeltolide,6b this cell line is
known to be heterogeneous, and therefore, variations in
biological responses are not uncommon.20 While no com-
pounds showed enhanced potency compared to neopeltolide,
several highly potent agents were identified. Modest changes to
the 8- and 9-positions are reasonably well tolerated, although
diol analogue 8 showed poor potency. Retaining the alkene at
this site led to the greatest potency and removed a step from
the synthetic sequence. Introducing a hydroxyl group at C8
provided a reasonably potent analogue that is more polar and
contains a handle for the formation of prodrugs.21 Changes in
the structure of the side chain are tolerated far less than changes
to the lactone core. The only reasonably potent analogue is 30,
in which a furan serves as a replacement for the oxazole. The lack
of potency for pyridyl-containing analogue 26 was surprising in
consideration of the basic nitrogen mapping onto the nitrogen
atom of the oxazole and suggests that biological responses are
quite sensitive to either protonation or to the precise spatial
orientation of the alkenyl groups on the oxazole. The carbamate
group proved to be essential for potency.
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0.2 mL of THF at −20 °C. The reaction was allowed to room tem-
perature while stirring overnight. A 10% NaOH solution (0.86 mL)
and a 30% aqueous H2O2 solution (0.34 mL) were successively added
dropwise at 0 °C. After 3 h at rt, the resulting mixture was extracted
with Et2O, and the combined extracts were washed with brine, dried
over MgSO4, filtered, and concentrated under reduced pressure. The
residue was purified by flash chromatography (EtOAc/CH2Cl2/
MeOH 1:1:0.1) to yield 10 (6.4 mg, 71% yield): 1H NMR (300
MHz, CDCl3) δ 4.80−4.88 (m, 1H), 3.69−3.88 (m, 2H), 3.33−3.39
(m, 1H), 3.32 (s, 3H), 3.12 (app t, J = 9.3 Hz, 1H), 2.59 (dd, J = 4.6,
13.6 Hz, 1H), 2.39 (dd, J = 9.8, 13.6 Hz, 1H), 2.22−2.27 (m, 1H),
1.97−2.06 (m, 2H), 1.73−1.83 (m, 2H), 1.48−1.62 (m, 4H), 1.19−
1.37 (m, 6H), 0.97 (d, J = 7.0 Hz, 3H), 0.92 (t, J = 7.4 Hz, 3H); 13C
NMR (75 MHz, CDCl3) δ 170.8, 79.2, 75.6, 72.1, 68.1, 62.8, 56.3,
42.2, 40.9, 38.6, 38.2, 37.8, 37.0, 34.7, 29.8, 19.0, 16.2, 13.9; IR (film)
3358, 2957, 2925, 2872, 1727, 1454, 1374, 1262, 1186, 1148, 1084,
1027, 799 cm−1; HRMS (ESI) m/z calcd for C18H32O6Na [M + Na]+
The results against the p53 knockout cell line provided useful
information regarding the growth inhibition mechanism.
Neopeltolide and the most potent analogues were less potent
against the p53 knockout cells, indicating that p53 plays a
supporting role in the biological responses of these compounds.
Increasing the polarity in the lactone subunit diminishes the
differences in cellular responses, suggesting that p53 plays no
role in cellular responses to these compounds. The most potent
compound among this group is alcohol 13. The potency of this
compound for the p53 knockout cells is nearly equivalent to the
potency of neopeltolide.
CONCLUSIONS
■
We have prepared neopeltolide and several analogues through
late-stage alkene functionalization and side-chain variation.
These compounds were tested for growth inhibition against
MCF-7, HCT-116, and p53 knockout HCT-116 cell lines. The
assays showed that (1) neopeltolide and analogues are not
general cytotoxins as demonstrated by notable cell line selectiv-
ity, (2) changes to the 8- and 9-centers on neopeltolide are
usually not highly detrimental to biological potency though no
alteration resulted in increased potency, (3) retaining the
alkene group that is required for the oxidative cyclization leads
to a potent analogue that can be prepared in one fewer step
than the natural product, while alkene hydroboration yields an
active analogue with increased polarity, (4) variations to the
side chain generally lead to significantly diminished potency,
with the only active analogue resulting from the replacement of
the oxazole group by a furan group, and (5) neopeltolide and
the potent analogues are more active toward cells that contain
p53, indicating that p53 plays an auxiliary role in biological
responses to these compounds. This study illustrates several
manners in which the structure of neopeltolide can and cannot
be altered in efforts to retain potency while altering physical
properties or accessibility and demonstrates the powerful role
that synthesis can play in understanding the structure−activity
relationships of medicinally interesting natural products.
367.2097, found 367.2084; [α]25 = +0.7 (CHCl3, c = 0.58).
D
Synthesis of Diol 11. To a solution of 9 (11.5 mg, 0.035 mmol) in
THF (0.4 mL) at −78 °C was added dropwise 1 M BH3·THF solution
(135 μL, 0.135 mmol), and then the reaction was allowed to room
temperature overnight. A 10% NaOH solution (60 μL) and a 30%
aqueous H2O2 solution (150 μL) were successively added dropwise at
0 °C. After 3 h at room temperature, the resulting mixture was
extracted with Et2O and the combined extracts were washed with
brine, dried over MgSO4, filtered, and concentrated under reduced
pressure. The residue was purified by flash chromatography (5%
MeOH in CH2Cl2) to afford 4.2 mg (35%) of 10 and 3.9 mg (32%) of
1
11: H NMR (300 MHz, CDCl3) δ 5.19−5.27 (m, 1H), 3.85−3.94
(m, 2H), 3.35−3.44 (m, 1H), 3.33 (s, 3H), 3.27−3.33 (m, 2H), 2.66
(dd, J = 3.8, 15.2 Hz, 1H), 2.50 (dd, J = 11.2, 15.4 Hz, 1H), 2.18 (s,
1H), 2.14 (dd, J = 3.5, 4.6 Hz, 1H), 2.00 (ddd, J = 2.4, 2.4, 12.4 Hz,
1H), 1.81−1.93 (m, 2H), 1.77 (dd, J = 3.4, 10.7 Hz, 1H), 1.45−1.68
(m, 5H), 1.15−1.45 (m, 4H), 1.08 (d, J = 7.0 Hz, 3H), 0.91 (t, J = 7.3
Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 170.4, 80.0, 78.5, 72.9, 72.8,
67.9, 56.6, 41.9, 40.3, 39.3, 38.8, 37.2, 35.8, 33.8, 24.0, 18.8, 13.9; IR
(film) 3400, 2956, 2922, 1727, 1457, 1366, 1263, 1153, 1089 cm−1;
HRMS (ESI) m/z calcd for C18H32O6Na [M + Na]+ 367.2097, found
367.2089; [α]25 = +2.7 (CHCl3, c = 0.26).
D
Synthesis of Amide Analogue 17. To a mixture of the
macrocyclic alcohol 15 (11 mg, 0.031 mmol), triethylamine (48 μL,
0.34 mmol), and dichloromethane (0.5 mL) at 0 °C was added
methanesulfonyl chloride (8.0 μL, 0.10 mmol). The reaction was
stirred at 0 °C for 30 min, allowed to warm room temperature, and
stirred for 4 h. The reaction mixture was cooled to 0 °C, treated with
1 N HCl, and extracted with dichloromethane (3×). The organic
extracts were dried with MgSO4, filtered, and concentrated under
vacuum to afford the mesylate: 1H NMR (300 MHz, CDCl3) δ 5.12−
5.20 (m, 1H), 4.82 (ddd, J = 5.0, 11.3, 16.3 Hz, 1H), 3.80 (dddd, J =
2.2, 4.3, 11.2, 11.2 Hz, 1H), 3.52 (app t, J = 8.9 Hz, 1H), 3.31 (s, 3H),
3.23 (app t, J = 10.0 Hz, 1H), 3.03 (s, 3H), 2.65 (dd, J = 4.4, 14.5 Hz,
1H), 2.44 (dd, J = 10.7, 14.5 Hz, 1H), 2.12−2.19 (m, 1H), 2.03−2.08
(m, 1H), 1.84 (dd, J = 10.5, 13.4 Hz, 1H), 1.61−1.73 (m, 2H), 1.45−
1.59 (m, 5H), 1.10−1.41 (m, 7H), 0.99 (d, J = 6.7 Hz, 3H), 0.91 (t, J =
7.2 Hz, 3H). This crude product was redissolved in DMF (1 mL),
treated with sodium azide (16.9 mg, 0.26 mmol), and then stirred at
80 °C overnight. The reaction mixture was dispersed between water
and diethyl ether, and the organic layer was concentrated under
vacuum. Flash chromatography (30% ethyl acetate in pentane)
afforded azide 16 (5 mg, 42% over two steps): 1H NMR (300
MHz, CDCl3) δ 5.19 (ddd, J = 4.5, 10.0, 10.0 Hz, 1H), 4.02−4.09 (m,
2H), 3.54 (app t, J = 9.5 Hz, 2H), 3.30 (s, 3H), 2.61 (dd, J = 4.3, 14.5
Hz, 1H), 2.35 (dd, J = 10.8, 14.6 Hz, 1H), 1.84 (dd, J = 10.9, 14.7 Hz,
1H), 1.63−1.76 (m, 2H), 1.46−1.61 (m, 6H), 1.31−1.43 (m, 5H),
1.11−1.25 (m, 3H), 0.99 (d, J = 6.4 Hz, 3H), 0.92 (t, J = 7.3 Hz, 3H);
13C NMR (75 MHz, CDCl3) δ 170.6, 75.6, 75.3, 73.0, 69.4, 56.2, 44.0,
42.2, 40.1, 37.0, 35.9, 34.8, 31.3, 25.6, 19.0, 13.9; IR (film) 2956, 2922,
2871, 2100, 1731, 1460, 1438, 1382, 1272, 1244, 1197, 1165, 1086, 1032,
992, 797 cm−1; HRMS (ESI) m/z calcd for C18H31N3O4Na [M + Na]+
EXPERIMENTAL SECTION
■
General Procedures. Proton (1H NMR) and carbon (13C NMR)
nuclear magnetic resonance spectra were recorded at 300, 400, or 500
MHz and 75, 100, or 125 MHz, respectively. The chemical shifts are
given in parts per million (ppm) on the delta (δ) scale.
Tetramethylsilane (TMS) or the solvent peak was used as a reference
value, for 1H NMR: TMS (in CDCl3) = 0.00 ppm, CD3OD =3.31, for
13C NMR: TMS (in CDCl3) = 0.00, CD3OD = 49.00. Data are
reported as follows: (s = singlet; d = doublet; t = triplet; q = quartet;
dd = doublet of doublets; dt = doublet of triplets; br = broad).
Samples for IR were prepared as a thin film on a NaCl plate by
dissolving the compound in CH2Cl2 and then evaporating the CH2Cl2.
Analytical TLC was performed on precoated (25 mm) silica gel 60F-
254 plates. Visualization was done under UV (254 nm). Flash
chromatography was done using 32−63 60 Å silica gel. Methylene
chloride was distilled under N2 from CaH2. Reagent grade ethyl
acetate, diethyl ether, pentane and hexanes (commercial mixture) were
used as purchased for chromatography. Benzene was dried with 4 Å
molecular sieves. THF was distilled from sodium. Other reagents were
obtained from commercial sources without further purification. All
reactions were performed in oven or flame-dried glassware with
magnetic stirring unless otherwise noted.
Synthesis of Diol 10. A solution of BH3·Me2S (2 M in THF, 0.5
mL, 1.0 mmol) was added dropwise at rt to a solution of
triethylborane (1 M in THF, 2 mL, 2.0 mmol). After 20 min, 0.78
mL (0.62 mmol) of this freshly prepared diethylborane solution was
added dropwise into a solution of alkene 9 (8.3 mg, 0.026 mmol) in
376.2212, found 376.2239; [α]25 = +39.1 (CHCl3, c = 0.45).
D
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A mixture of 16 (5 mg, 0.013 mmol) and 10% Pd/C (5 mg) in
ethanol (0.5 mL) was stirred under a hydrogen atmosphere for 5 h.
The mixture was filtered through Celite and purified by flash
chromatography (10% MeOH in dichloromethane with 1%
After 1.5 h, the reaction mixture was partitioned between diethyl ether
and water. The organic phase was dried with sodium sulfate, filtered,
and concentrated under vacuum. Flash chromatography with 50%
ethyl acetate in hexanes gave 44 mg (80%) of the desired product: 1H
NMR (300 MHz, CDCl3) δ 7.27 (t, J = 7.0 Hz, 1H), 7.04−7.11 (m,
3H), 6.54 (d, J = 11.6 Hz, 1H), 5.67 (dt, J = 6.6, 11.5 Hz, 1H), 4.86
(brs, 1H), 4.06 (t, J = 5.4 Hz, 2H), 3.68 (s, 3H), 3.67 (s, 3H), 2.95 (t,
J = 7.8 Hz, 2H), 2.64 (t, J = 7.5 Hz, 2H).
A 25 mL round-bottom flask was charged the alkynyl ester (44 mg,
0.16 mmol) and dichloromethane (3 mL). The mixture was cooled to
−78 °C, and a 1 M DIBAL-H (0.21 mL, 0.21 mmol) solution in
hexanes was added dropwise under nitrogen. After 1 h of stirring at
−78 °C, the reaction was quenched with saturated ammonium
chloride aqueous solution. Flash chromatography with 40% ethyl
acetate in hexanes gave 25 mg (64%) of the desired product: 1H NMR
(300 MHz, CDCl3) δ 9.82 (s, 1H), 7.26 (t, J = 4.0 Hz, 1H), 7.02−7.11
(m, 3H), 6.54 (d, J = 11.6 Hz, 1H), 5.67 (dt, J = 6.6, 11.6 Hz, 1H),
4.81 (brs, 1H), 4.07 (t, J = 5.3 Hz, 2H), 3.68 (s, 3H), 2.96 (t, J = 7.4
Hz, 2H), 2.79 (t, J = 7.6 Hz, 2H).
A 25 mL round-bottom flask was charged methyl bis-
(trifluoroethyl)phosphonoacetate (27 μL, 0.13 mmol), 18-crown-6
(102 mg, 0.39 mmol), and THF (1 mL). The mixture was cooled
to −78 °C, and KHMDS (19 mg, 0.095 mmol) in 2 mL of THF was
added dropwise under nitrogen. After 30 min of stirring, the aldehyde
(17 mg, 0.068 mmol) in 2 mL of THF was added dropwise, followed
by 4 h of stirring at −78 °C. The reaction was quenched with saturated
NH4Cl aqueous solution and extracted with ethyl acetate. Flash
chromatography with 30% ethyl acetate in hexanes gave 17 mg (82%)
of the desired product: 1H NMR (300 MHz, CDCl3) δ 7.27 (t, J = 7.6
Hz, 1H), 7.12 (d, J = 7.7 Hz, 1H), 7.07 (s, 1H), 7.06 (d, J = 8.1 Hz,
1H), 6.54 (d, J = 11.6 Hz, 1H), 6.26 (dt, J = 7.5, 11.5 Hz, 1H), 5.80
(dt, J = 1.6, 11.5 Hz, 1H), 5.67 (dt, J = 6.7, 11.8 Hz, 1H), 4.84 (brs,
1H), 4.08 (t, J = 5.2 Hz, 2H), 3.70 (s, 3H), 3.68 (s, 3H), 2.99 (td, J =
1.3, 7.6 Hz, 2H); 13C NMR (75 MHz, CDCl3) δ 166.7, 149.2, 141.2,
136.4, 131.5, 128.9, 128.4, 127.4, 126.5, 120.0, 52.2, 51.1, 39.3, 35.0,
30.4; IR (film) 3399, 1719, 1643, 1570, 1453, 1251, 1147, 1071, 1023,
819 cm−1; HRMS (ESI) m/z calcd for C17H21NO4Na [M + Na]+
326.1368, found 326.1360.
1
ammonium hydroxide) to give 4 mg (83%) of the amine: H NMR
(300 MHz, CDCl3) δ 5.14−5.23 (m, 1H), 4.09−4.21 (m, 1H), 3.63
(m, 2H), 3.44 (app s, 1H), 3.31 (s, 3H), 2.57 (dd, J = 3.8, 14.7 Hz,
1H), 2.35 (dd, J = 10.8, 14.0 Hz, 1H), 2.17 (s, 1H), 1.86 (dd, J = 10.6,
14.6 Hz, 1H), 1.30−1.40 (m, 5H), 1.42−1.75 (m, 8H), 1.14 (t, J =
11.6 Hz, 2H), 0.98 (d, J = 6.1 Hz, 3H), 0.91 (t, J = 7.4 Hz, 3H); 13C
NMR (75 MHz, CDCl3) δ 171.2, 75.6, 74.7, 72.8, 69.0, 56.2, 44.3,
42.6, 42.3, 40.2, 39.5, 38.3, 37.0, 31.4, 25.7, 19.9, 13.9; IR (film) 3372,
2956, 2923, 2869, 1728, 1460, 1439, 1382, 1341, 1275, 1196, 1157,
1088, 1029, 795 cm−1; HRMS (ESI) m/z calcd for C18H33NO4Na
[M + Na]+ 350.2307, found 350.2320; [α]25D = +21.8 (CHCl3, c = 0.38).
The macrolactone amine (4 mg, 0.012 mmol), the oxazole acid 12
(8 mg, 0.027 mmol), diisopropylethylamine (9 μL, 0.05 mmol), and
CH2Cl2 (0.8 mL) were mixed and cooled to 0 °C. PyBOP (19 mg,
0.036 mmol) was added, and the mixture was allowed to warm room
temperature overnight. The reaction mixture was then concentrated
and purified by flash chromatography (40% pentane in ethyl acetate)
1
to afford 17 (5 mg, 77%): H NMR (300 MHz, CD3OD) δ 7.67 (s,
1H), 6.30 (dt, J = 2.1, 11.9 Hz, 1H), 6.10 (dt, J = 7.1, 11.5 Hz, 1H),
6.06 (d, J = 11.9 Hz, 1H), 5.99 (dt, J = 1.4, 11.5 Hz, 1H), 5.16−5.25
(m, 1H), 4.33 (dd, J = 1.7, 5.8 Hz, 2H), 4.16−4.22 (m, 1H), 4.08
(dddd, J = 1.3, 1.3, 10.9, 10.9 Hz, 1H), 3.71 (app t, J = 8.8 Hz, 1H),
3.68 (s, 3H), 3.56 (app t, J = 9.7 Hz, 1H), 3.31 (s, 3H), 3.01 (dt, J =
7.4, 7.4 Hz, 2H), 2.71 (t, J = 7.4 Hz, 2H), 2.67−2.74 (m, 1H), 2.32
(dd, J = 10.9, 14.8 Hz, 1H), 1.91 (dd, J = 10.9, 14.8 Hz, 1H), 1.69−
1.79 (m, 2H), 1.45−1.61 (m, 7H), 1.10−1.43 (m, 6H), 1.02 (d, J = 6.5
Hz, 3H), 0.96 (t, J = 7.3 Hz, 3H); 13C NMR (75 MHz, CD3OD) δ
173.2, 168.9, 161.9, 145.0, 142.6, 139.2, 136.1, 124.3, 116.0, 77.2, 77.1,
73.9, 56.5, 52.7, 45.5, 44.9, 43.6, 43.5, 41.2, 41.1, 38.1, 173.2, 168.9,
161.9, 145.0, 142.6, 139.2, 136.1, 124.3, 116.0, 77.2, 77.1, 73.9, 56.5,
52.7, 45.5, 44.9, 43.6, 43.5, 41.2, 41.1, 38.1, 37.4, 36.2, 32.7, 28.7, 26.7,
26.1, 20.1, 14.2; IR (film) 3413, 2922, 2851, 1725, 1711, 1660, 1631,
1550, 1533, 1462, 1377, 1260, 1086, 1018, 798 cm−1; HRMS (ESI)
m/z calcd for C31H47N3O8Na [M + Na]+ 612.3261, found 612.3264;
[α]25 = +10.7 (MeOH, c = 0.53).
Synthesis of Bromopyridine 24. To a suspension of 60% sodium
hydride (135 mg, 3.38 mmol) in THF (10 mL) under nitrogen was
added (EtO)2P(O)CH2CO2Et (0.62 mL, 3.1 mmol) dropwise at 0 °C.
After 30 min, 6-bromopicolinaldehyde (465 mg, 2.5 mmol) in 2 mL of
THF was added, and the reaction mixture was allowed to room
temperature. After 1 h the reaction mixture was partitioned between
diethyl ether and water. The organic phase was dried, filtered, and
concentrated under vacuum. Flash chromatography with 20% diethyl
ether in hexanes gave 615 mg (96%) of the desired product: 1H NMR
(300 MHz, CDCl3) δ 7.57 (t, J = 7.3 Hz, 1H), 7.53 (d, J = 15.5 Hz,
1H), 7.44 (d, J = 7.7 Hz, 1H), 7.46 (d, J = 7.5 Hz, 1H), 6.95 (d, J =
15.6 Hz, 1H), 4.22(q, J = 7.1 Hz, 2H), 1.33 (t, J = 7.1 Hz, 3H).
In a 25 mL round-bottom flask the unsaturated ester (595 mg, 2.32
mmol) and CuCl (241 mg, 2.43 mmol) were dissolved in 80%
methanol (13.5 mL) at 0 °C under nitrogen. NaBH4 (92 mg, 2.3
mmol) was added followed 1 h later by another portion of NaBH4 (92
mg, 2.3 mmol). One hour later, a third portion of NaBH4 (46 mg, 1.2
mmol) was added. After 30 min, the reaction mixture was partitioned
between diethyl ether and water, and the organic phase was dried,
filtered, and concentrated under vacuum. Flash chromatography with
20% diethyl ether in dichloromethane gave 448 mg (75%) of the
SyDnthesis of Ester 20. To a solution of 3-(3-bromophenyl)-
propanoic acid (1.603 g, 7.0 mmol) in methanol (20 mL) was added
dropwise SOCl2 (1.03 mL, 14.2 mmol) at 0 °C. The reaction was
allowed to room temperature and stirred overnight. Concentration at
reduced temperature and flash chromatography (20% ethyl acetate in
1
hexanes) afforded 1.727 g (quantitative yield) of the desired ester: H
NMR (300 MHz, CDCl3) δ 7.35 (s, 1H), 7.34 (d, J = 7.4 Hz, 1H),
7.12−7.19 (m, 2H), 3.68 (s, 3H), 2.92 (t, J = 7.6 Hz, 2H), 2.62 (t, J =
7.9 Hz, 2H).
A flame-dried 50 mL round-bottom flask was charged with the
methyl ester (122 mg, 0.50 mmol), PdCl2(PPh3)2 (35 mg, 0.050
mmol), PPh3 (26 mg, 0.10 mmol), CuI (9.5 mg, 0.050 mmol), distilled
diisopropylamine (0.64 mL, 4.5 mmol), and distilled THF (2 mL).
The reaction was degassed with argon for 15 min, and then methyl
prop-2-ynylcarbamate 19 (124 mg, 1.1 mmol) was added dropwise
with a syringe. The reaction mixture was heated to 55 °C overnight
under argon. Flash chromatography with 40% ethyl acetate in hexanes
1
gave 121 mg (88%) of the desired product: H NMR (300 MHz,
CDCl3) δ 7.14−7.26 (m, 4H), 5.12 (brs, 1H), 4.16 (d, J = 4.9 Hz,
2H), 3.71 (s, 3H), 3.67 (s, 3H), 2.91 (t, J = 7.8 Hz, 2H), 2.61 (t, J =
7.7 Hz, 2H); 13C NMR (75 MHz, CDCl3) δ 173.3, 140.6, 131.4, 129.2,
128.7, 128.5, 128.1, 127.2, 126.7, 51.6, 35.6, 29.7; IR (film) 3428,
2064, 1597, 1531, 1447, 1397, 1310, 1182, 874 cm−1; HRMS (ESI)
m/z calcd for C15H17NO4Na [M + Na]+ 298.1055, found 298.1047.
Synthesis of Benzene-Containing Side-Chain Ester 21. A 25
mL round-bottom flask was charged with Ni(OAc)2·4H2O (22 mg,
0.087 mmol) and 95% ethanol (1 mL), and a hydrogen atmosphere
was applied. A solution of NaBH4 in 95% ethanol (0.11 mL, 1 N with
0.1 N NaOH, 0.11 mmol) was added to the flask within 10 s. After
3 min, ethylenediamine (12 μL, 0.18 mmol) was added, followed by
another 3 min of stirring. Alkyne 20 (55 mg, 0.20 mmol) was added.
1
desired product: H NMR (300 MHz, CDCl3) δ 7.45 (t, J = 7.6 Hz,
1H), 7.31 (d, J = 7.8 Hz, 1H), 7.16 (d, J = 7.4 Hz, 1H), 4.13 (q, J = 7.2
Hz, 2H), 3.08 (t, J = 7.4 Hz, 2H), 2.78 (t, J = 7.4 Hz, 2H), 1.24 (t, J =
7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 172.4, 161.5, 141.3, 138.5,
125.5, 121.7, 60.2, 33.0, 32.3, 14.0; IR (film) 3213, 2051, 1536, 1435,
1410, 1347, 978, 863 cm−1; HRMS (ESI) m/z calcd for
C10H12BrNO2Na [M + Na]+ 279.9949, found 279.9957.
Synthesis of Ester 25. A flame-dried 50 mL round-bottom flask
was charged with 24 (194 mg, 0.75 mmol), PdCl2(PPh3)2 (52 mg,
0.074 mmol), PPh3 (39 mg, 0.15 mmol), CuI (14 mg, 0.076 mmol),
distilled diisopropylamine (0.96 mL, 6.8 mmol), and distilled THF (3 mL).
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The reaction was degassed with argon for 15 min, and then 19
(186 mg, 1.65 mmol) was added dropwise. The reaction mixture was
heated at 50 °C for 1.5 h under argon. Flash chromatography with
40% ethyl acetate in hexanes gave 206 mg (91%) of the desired
product: 1H NMR (300 MHz, CDCl3) δ 7.56 (t, J = 7.8 Hz, 1H), 7.26
(d, J = 7.8 Hz, 1H), 7.16 (d, J = 7.8 Hz, 1H), 5.28 (brs, 1H), 4.24 (d,
J = 5.7 Hz, 2H), 4.11 (q, J = 7.2 Hz, 2H), 3.71(s, 3H), 3.09 (t, J = 7.5
Hz, 2H), 2.78 (t, J = 7.5 Hz, 2H), 1.23 (t, J = 7.2 Hz, 3H).
solution, extracted with ethyl acetate (3×), and concentrated under
vacuum. Flash chromatography with 30% hexanes in ethyl acetate gave
51 mg (95%) of alcohol 28: 1H NMR (300 MHz, CDCl3) δ 6.44−6.12
(m, 5H), 5.51 (dd, J = 6.0, 11.7 Hz, 1H), 5.09 (br, 1H), 4.30 (br, 4H),
3.68 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 156.9, 154.9, 152.0,
129.1, 126.2, 123.6, 118.4, 116.0, 113.1, 59.8, 52.1, 42.0; IR (film)
3429, 3283, 1636, 1527, 1438, 1417, 1182, 966, 869 cm−1; HRMS
(ESI) m/z calcd for C12H15NO4Na [M + Na]+ 260.0899, found
260.0908.
A 25 mL round-bottom flask was charged with Ni(OAc)2·4H2O (31
mg, 0.12 mmol) and 95% ethanol (1 mL), and a hydrogen atmosphere
was applied. A solution of NaBH4 (0.15 mL, 1 N, 0.015 mmol) in 95%
ethanol with 0.1 N NaOH was added to the flask within 10 s. After
3 min, ethylenediamine (17 μL, 0.25 mmol) was added, followed by
another 3 min of stirring. The alkyne (90 mg, 0.31 mmol) was added.
After 1 h, the reaction mixture was partitioned between diethyl ether
and water. The organic phase was dried with sodium sulfate, filtered
and concentrated. Flash chromatography with 40% ethyl acetate in
Synthesis of Furan-Containing Side-Chain Ester 29. Alcohol
28 (51 mg) was dissolved in CH2Cl2 (3.3 mL) and acetonitrile
(1.2 mL) and cooled to 0 °C. Pyridine (28 μL, 0.35 mmol) was added,
followed by the Dess−Martin periodinane (144 mg, 0.34 mmol). After
2 h of stirring at 0 °C, the reaction mixture was concentrated and
purified with 40% ethyl acetate in hexanes to afford 35 mg (71%) of
1
the desired aldehyde: H NMR (300 MHz, CDCl3) δ 9.63 (d, J = 7.9
Hz, 1H), 7.20 (d, J = 15.6 Hz, 1H), 6.79 (d, J = 3.5 Hz, 1H), 6.55 (dd,
J = 7.9, 15.6 Hz, 1H), 6.43 (d, J = 3.5 Hz, 1H), 6.26 (d, J = 11.8 Hz,
1H), 5.75 (dt, J = 6.3, 11.8 Hz, 1H), 5.07 (brs, 1H), 4.30 (t, J = 5.8 Hz,
2H), 3.71 (s, 3H).
1
hexanes gave 59 mg (65%) of the desired product: H NMR (300
MHz, CDCl3) δ 7.57 (t, J = 7.7 Hz, 1H), 7.05 (d, J = 6.9 Hz, 1H), 7.02
(d, J = 6.6 Hz, 1H), 6.46 (d, J = 11.7 Hz, 1H), 5.97 (dt, J = 6.9, 11.5
Hz, 1H), 5.97 (brs, 1H), 4.30 (t, J = 6.1 Hz, 2H), 4.15 (q, J = 7.1 Hz,
2H), 3.68 (s, 3H), 3.13 (t, J = 7.4 Hz, 2H), 2.82 (t, J = 7.3 Hz, 2H),
1.22 (t, J = 7.1 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 173.0, 159.3,
157.1, 154.9, 136.6, 133.0, 129.9, 122.1, 120.9, 60.3, 51.8, 39.2, 32.9,
32.7, 14.0; IR (film) 3422, 3201, 3144, 2047, 1600, 1553, 1370, 1324,
853 cm−1; HRMS (ESI) m/z calcd for C15H20N2O4Na [M + Na]+
315.1321, found 315.1311.
Synthesis of Allylic Alcohol 28. To a suspension of 60% sodium
hydride (63 mg, 1.6 mmol) in THF (5 mL) was added (EtO)2P(O)-
CH2CO2Me (0.41 mL, 2.53 mmol) dropwise at 0 °C under nitrogen.
One hour later, 5-bromofuran-2-carbaldehyde 27 (204 mg, 1.17
mmol) in 5 mL of THF was added dropwise, and the reaction mixture
was allowed to warm rt over 0.5 h. The reaction mixture was
partitioned between diethyl ether and water. The organic phase was
dried, filtered, and concentrated under vacuum. Flash chromatography
with 20% diethyl ether in hexanes gave 261 mg (97%) of the desired
ester: 1H NMR (300 MHz, CDCl3) δ 7.32 (d, J = 15.7 Hz, 1H), 6.54
(d, J = 2.9 Hz, 1H), 6.40 (d, J = 3.0 Hz, 1H), 6.29 (d, J = 15.7 Hz,
1H), 3.78 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 166.9, 152.5, 129.7,
125.3, 116.6, 115.7, 114.0, 51.5.
A 25 mL round-bottom flask was charged with methyl bis-
(trifluoroethyl)phosphonoacetate (86 μL, 0.41 mmol), 18-crown-6
(330 mg, 1.23 mmol), and THF (4 mL). The mixture was cooled to
−78 °C, and KHMDS (61 mg, 0.29 mmol) in 2 mL of THF was
added dropwise under nitrogen. After 30 min of stirring, the freshly
prepared aldehyde (35 mg, 0.15 mmol) in 4 mL of THF was added
dropwise, followed by 3 h of stirring at −78 °C. The reaction was
quenched with saturated aqueous NH4Cl solution, extracted with ethyl
acetate, and concentrated under vacuum. Flash chromatography first
with 30% ethyl acetate in pentane, and then 20% ethyl acetate in
1
toluene gave 30 mg (70%) of the desired product 29: H NMR (300
MHz, CDCl3) δ 7.93 (dd, J = 11.9, 15.5 Hz, 1H), 6.66 (dd, J = 11.6,
11.6 Hz, 1H), 6.56 (d, J = 15.5 Hz, 1H), 6.49 (d, J = 3.5 Hz, 1H), 6.32
(d, J = 3.5 Hz, 1H), 6.22 (d, J = 11.6 Hz, 1H), 5.69 (d, J = 11.2 Hz,
1H), 5.60−5.70 (m, 1H), 5.12 (brs, 1H), 4.29 (td, J = 1.5, 6.2 Hz, 2H),
3.75 (s, 3H), 3.69 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.9,
157.1, 153.3, 152.3, 143.8, 128.5, 127.1, 123.8, 118.1, 117.2, 113.6,
113.0, 52.1, 51.2, 40.0; IR (film) 3340, 2950, 1708, 1608, 1528, 1438,
1253, 1197, 1169, 1020, 785 cm−1; HRMS (ESI) m/z calcd for
C15H17NO5Na [M + Na]+ 314.1004, found 314.1028.
To a flame-dried 25 mL round-bottom flask was charged the ester
(310 mg, 1.34 mmol), PdCl2(PPh3)2 (93 mg, 0.13 mmol), PPh3 (69.8
mg, 0.266 mmol), CuI (25.8 mg, 0.136 mmol), distilled triethylamine
(1.70 mL, 12.2 mmol), and distilled THF (5 mL). The reaction was
degassed with argon for 15 min, and then methyl prop-2-
ynylcarbamate 19 (310 mg, 2.75 mmol) was added dropwise. The
reaction mixture was heated at 50 °C for 1.5 h under argon. Flash
chromatography with 40% ethyl acetate in hexanes gave 289 mg (82%)
Synthesis of Oxazole 32. To a suspension of 60% sodium
hydride (63 mg, 1.3 mmol) in THF (5 mL) was added (EtO)2P(O)-
CH2CO2Me (0.41 mL, 2.5 mmol) dropwise at 0 °C under nitrogen.
Thirty minutes later, 2-methyloxazole-4-carbaldehyde 31 (107 mg,
0.96 mmol) in 2 mL of THF was added dropwise, and the reaction
mixture was kept at 0 °C for 1.5 h. The reaction mixture was
partitioned between diethyl ether and water. The organic phase was
dried, filtered, and concentrated under vacuum. Flash chromatography
with 5% diethyl ether in hexanes gave 151 mg (93%) of the desired
1
of the coupled product: H NMR (300 MHz, CDCl3) δ 7.34 (d, J =
1
15.7 Hz, 1H), 6.59 (d, J = 3.5 Hz, 1H), 6.57 (d, J = 3.5 Hz, 1H), 6.33
(d, J = 15.7 Hz, 1H), 5.79 (brs, 1H), 4.25 (d, J = 5.6 Hz, 2H), 3.78 (s,
3H), 3.71 (s, 3H).
ester: H NMR (300 MHz, CDCl3) δ 7.69 (s, 1H), 7.47 (d, J = 15.6,
1H), 6.58 (dt, J = 2.6, 15.8 Hz, 1H), 3.78 (s, 3H), 2.49 (s, 1H).
The ester (71 mg, 0.42 mmol) was stirred under a hydrogen
atmosphere in methanol (10 mL) with 10% Pd/C (71 mg) for 2 h.
The resulting mixture was then filtered through Celite and purified by
flash chromatography with 40% ethyl acetate in hexanes to give 59 mg
(82%) of the desired product 32: 1H NMR (300 MHz, CDCl3) δ 7.30
(t, J = 1.1 Hz, 1H), 3.68 (s, 3H), 2.81 (t, J = 7.5 Hz, 2H), 2.65 (td, J =
1.1, 7.1 Hz, 2H), 2.42 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 175.1,
160.3, 136.2, 128.5, 51.7, 32.4, 20.4, 14.4; IR (film) 3158, 1710, 1549,
1442, 1426, 1359, 1226, 1145, 841 cm−1; HRMS (ESI) m/z calcd for
C8H11NO3Na [M + Na]+ 192.0637, found 192.0635.
A 25 mL round-bottom flask was charged with Ni(OAc)2·4H2O (47
mg, 0.19 mmol) and 95% ethanol (1 mL), and a hydrogen atmosphere
was applied. A solution of NaBH4 (0.25 mL, 1 N, 0.015 mmol) in 95%
ethanol with 0.1 N NaOH was added to the flask within 10 s. After
3 min, ethylenediamine (26 μL, 0.37 mmol) was added, followed by
another 3 min of stirring. The coupled product (123 mg, 0.467 mmol)
was added to the resulting black suspension followed by washing wth
95% EtOH. After 1.5 h, the reaction mixture was filtered through a pad
of silica gel and concentrated under vacuum. Flash chromatography
with 30% THF in hexanes gave 80 mg (65%) of the reduced product:
1H NMR (300 MHz, CDCl3) δ 7.40 (d, J = 15.7 Hz, 1H), 6.62 (d, J =
3.5 Hz, 1H), 6.35 (d, J = 3.5 Hz, 1H), 6.27 (d, J = 15.6, 1H), 6.22 (d,
J = 10.4 Hz, 1H), 5.68 (dt, J = 6.4, 11.8 Hz, 1H), 5.11 (brs, 1H), 4.29
(t, J = 5.4 Hz, 2H), 3.79 (s, 3H), 3.70 (s, 3H).
Synthesis of Des-carbamyl Side-Chain Ester 33. A 25 mL
round-bottom flask was charged with 32 (48 mg, 0.28 mmol) and
dichloromethane (3 mL). The reaction was cooled to −78 °C, and a
1 M DIBAL-H solution in hexanes (0.42 mL, 0.42 mmol) was added
dropwise under nitrogen. After 1.5 h of stirring at −78 °C, the reaction
was quenched with saturated aqueous ammonium chloride solution.
Flash chromatography with 40% ethyl acetate in hexanes gave 27 mg
The (Z)-alkene (60 mg, 0.23 mmol) in dichloromethane (3 mL)
was cooled to −78 °C under nitrogen. DIBAL-H (1.34 mL, 1 M in
hexanes) was added dropwise, followed by 1 h of stirring at −78 °C.
The reaction was quenched with saturated ammonium chloride
1
(69%) of the desired aldehyde: H NMR (300 MHz, CDCl3) δ 9.82
(s, 1H), 7.29 (t, J = 5.2 Hz, 1H), 2.81 (app s, 4H), 2.42 (s, 1H).
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A 25 mL round-bottom flask was charged with methyl bis-
(trifluoroethyl)phosphonoacetate (114 μL, 0.54 mmol), 18-crown-6
(430 mg, 1.63 mmol), and THF (5 mL). The mixture was cooled
to −78 °C, and KHMDS (80 mg, 0.40 mmol) in 5 mL of THF was
added dropwise under nitrogen. After 30 min of stirring, the aldehyde
(26 mg, 0.19 mmol) in 5 mL of THF was added dropwise, followed by
5 h of stirring at −78 °C. The reaction was quenched with saturated
aqueous NH4Cl solution and extracted with ethyl acetate. Flash
chromatography with 30% ethyl acetate in pentane gave 23 mg (71%)
(t, J = 7.4 Hz, 2H), 2.66 (dd, J = 4.2, 13.7 Hz, 1H), 2.30 (dd, J = 10.1,
13.6 Hz, 1H), 2.05 (apq, J = 12.7 Hz, 2H), 1.76−1.90 (m, 3H), 1.51−
1.67 (m, 4H), 1.22−1.38 (m, 4H), 0.97 (d, J = 7.2 Hz, 3H), 0.94 (t, J =
7.3 Hz, 3H); 13C NMR (100 MHz, CD3OD) δ 173.1, 167.0, 162.0,
150.1, 142.4, 139.3, 136.1, 121.8, 116.1, 78.7, 77.9, 77.6, 71.1, 69.0,
68.9, 56.6, 52.7, 43.3, 41.2, 40.0, 39.7, 38.3, 36.7, 36.0, 33.8, 29.1, 26.5,
20.2, 17.0, 14.3; IR (film) 3366, 2958, 2924, 2873, 1714, 1520, 1461,
1417, 1264, 1182, 1154, 1091, 820 cm−1; HRMS (ESI) m/z calcd for
C31H46N2O10Na [M + Na]+ 629.3050, found 629.3055; [α]25D = +13.3
(CHCl3, c = 0.36).
1
of the desired product 33: H NMR (300 MHz, CDCl3) δ 7.29 (s,
1H), 6.26 (dt, J = 7.3, 11.5 Hz, 1H), 5.82 (dt, J = 1.7, 11.5 Hz, 1H),
3.71 (s, 3H), 2.98 (dtd, J = 1.6, 7.2, 7.2 Hz, 2H), 2.64 (dd, J = 6.9, 7.6
Hz, 2H), 2.42 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 166.7, 161.3,
149.1, 139.7, 133.9, 120.1, 51.1, 27.5, 25.6, 13.9; IR (film) 2921, 1722,
1646, 1581, 1439, 1201, 1177, 1096, 820 cm−1; HRMS (ESI) m/z
calcd for C10H13NO3Na [M + Na]+ 218.0793, found 218.0786.
Representative Protocol for Side-Chain Ester Cleavage. The
side- chain ester was dissolved in THF (∼0.2 M) at rt. Aqueous LiOH
(10 equiv) was added, and the reaction mixture was stirred at rt for
4 h. The reaction mixture was acidified with 2 N HCl at 0 °C to pH 3
and extracted with ethyl acetate (3×). The organic phase was dried
with Na2SO4, filtered, and concentrated under vacuum. Flash chroma-
tography with 5% methanol in dichloromethane gave the side chain
acids.
Hydroxy Analogue 14. The general esterification procedure was
followed with 11 (2.6 mg, 0.0075 mmol), 12 (3.6 mg, 0.013 mmol),
PPh3 (4.4 mg, 0.017 mmol), and DIAD (3.4 μL, 0.017 mmol) in
benzene (0.3 mL) After 2 h, the reaction was quenched with 1 drop of
water, concentrated under vacuum, and purified with flash
chromatography (30% THF in pentane) to afford the desired product
(2.1 mg, 45%): 1H NMR (400 MHz, CDCl3) δ 7.39 (s, 1H), 6.34 (dt,
J = 7.3, 11.5 Hz, 1H), 6.29 (dt, J = 1.5, 11.6 Hz, 1H), 6.10 (dt, J = 6.3,
11.9 Hz, 1H), 4.89 (dt, J = 1.6, 11.4 Hz, 1H), 5.52 (brs, 1H), 5.20−
5.28 (m, 2H), 4.32 (t, J = 5.8 Hz, 2H), 4.22 (apt, J = 14.9 Hz, 1H),
3.69 (s, 3H), 3.65 (dd, J = 1.7, 12.1 Hz, 1H), 3.79−3.42 (m, 1H), 3.32
(s, 3H), 3.21 (d, J = 9.7 Hz, 1H), 3.04 (dtd, J = 1.6, 7.5, 7.5 Hz, 2H),
2.72 (t, J = 7.1 Hz, 2H), 2.61 (dd, J = 3.8, 15.4 Hz, 1H), 2.42 (dd, J =
11.4, 15.4 Hz, 1H), 2.10−2.17 (m, 1H), 2.00 (ddd, J = 3.0, 12.1, 15.7
Hz, 1H), 1.80−1.88 (m, 2H), 1.60−1.69 (m, 2H), 1.41−1.56 (m, 4H),
1.25−1.38 (m, 4H), 1.07 (d, J = 7.1 Hz, 3H), 0.92 (t, J = 7.3 Hz, 3H);
13C NMR (100 MHz, CDCl3) δ 170.4, 165.3, 149.6, 136.4, 133.9,
133.1, 120.5, 116.7, 78.3, 72.9, 70.4, 67.5, 56.6, 53.4, 42.0, 39.3, 37.3,
35.7, 34.9, 33.7, 33.2, 31.9, 27.7, 25.6, 23.9, 22.7, 18.8, 13.9; IR (film)
3406, 2956, 2923, 2853, 1713, 1643, 1533, 1377, 1261, 1151, 1117,
798 cm−1; HRMS (ESI) m/z calcd for C31H46N2O10Na [M + Na]+
Benzene-containing side-chain acid: 1H NMR (300 MHz,
CDCl3) δ 7.26 (t, J = 7.8 Hz, 1H), 7.03−7.10 (m, 3H), 6.55 (d, J =
11.6 Hz, 1H), 6.34 (dt, J = 7.5, 11.3 Hz, 1H), 5.81 (d, J = 11.5 Hz,
1H), 5.64 (dt, J = 6.5, 11.8 Hz, 1H), 4.84 (brs, 1H), 4.09 (app s, 2H),
3.69 (s, 3H), 3.00 (dt, J = 7.5, 7.5 Hz, 2H), 2.77 (t, J = 7.6 Hz, 2H);
13C NMR (75 MHz, CDCl3) δ 169.9, 157.2, 150.5, 141.0, 136.4, 131.6,
128.8, 128.3, 128.1, 127.6, 126.6, 120.2, 52.4, 39.6, 34.9, 30.6; IR (film)
3336, 2924, 1700, 1641, 1531, 1435, 1260, 1194, 1152, 803 cm−1;
HRMS (ESI) m/z calcd for C16H19NO4Na [M + Na]+ 312.1212,
found 312.1215.
629.3050, found 629.3079; [α]25 = +6.7 (CHCl3, c = 0.21).
D
Benzene-Containing Side-Chain Analogue 22. The general
esterification procedure was followed by 15 (2.2 mg, 0.0067 mmol),
the phenyl-containing side chain acid 74 (7.1 mg, 0.024 mmol), PPh3
(7.0 mg, 0.027 mmol), and DIAD (5.4 μL, 0.027 mmol) in benzene
(0.5 mL). The mixture was stirred for 10 min and then was purified by
flash column chromatography (30% THF in hexanes) to yield 3.5 mg
Furan-containing side chain acid: 1H NMR (400 MHz, CDCl3)
δ 8.01 (dd, J = 12.0, 15.4 Hz, 1H), 6.78 (t, J = 11.5 Hz, 1H), 6.60 (d,
J = 15.5 Hz, 1H), 6.50 (d, J = 3.5 Hz, 1H), 6.33 (d, J = 3.3 Hz, 1H), 6.23
(d, J = 11.9 Hz, 1H), 5.73 (d, J = 11.2 Hz, 1H), 5.66 (dt, J = 6.4, 11.9
Hz, 1H), 5.12 (brs, 1H), 4.32 (app s, 1H), 3.70 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 170.7, 157.3, 153.5, 152.3, 145.1, 128.6, 127.1,
124.2, 117.9, 117.1, 113.8, 112.9, 52.2, 40.3; IR (film) 3452, 2941,
1701, 1524, 1253, 1189, 1173, 788 cm−1; HRMS (ESI) m/z calcd for
C14H15NO5Na [M + Na]+ 300.0848, found 300.0859.
1
(87%) of the desired product: H NMR (400 MHz, CD3OD) δ 7.27
(t, J = 7.8 Hz, 1H), 7.13 (d, J = 5.8 Hz, 1H), 7.13 (s, 1H), 7.09 (d, J =
7.8 Hz, 1H), 6.52 (d, J = 11.6 Hz, 1H), 6.36 (dt, J = 7.6, 11.6 Hz, 1H),
5.85 (dt, J = 1.5, 11.6 Hz, 1H), 5.65 (dt, J = 6.5, 11.6 Hz, 1H), 5.14−
5.20 (m, 2H), 4.02−4.07 (m, 1H), 3.99 (apd, J = 5.3, 2H), 3.66 (apt,
J = 9.7 Hz, 1H), 3.64 (s, 3H), 3.54 (apt, J = 9.5 Hz, 1H), 3.27 (s, 3H),
3.00 (dt, J = 7.8, 7.8 Hz, 2H), 2.79 (t, J = 7.4 Hz, 2H), 2.67 (dd, J =
4.3, 14.8 Hz, 1H), 2.28 (dd, J = 11, 14.8 Hz, 1H), 1.75−1.89 (m, 3H),
1.61−1.73 (m, 2H), 1.44−1.60 (m, 4H), 1.25−1.42 (m, 5H), 1.11
(ddd, J = 2.0, 11.0, 13.0 Hz, 1H), 0.96 (d, J = 6.7 Hz, 3H), 0.93 (t, J =
7.3 Hz, 3H); 13C NMR (100 MHz, CD3OD) δ 173.1, 166.9, 150.6,
142.6, 138.0, 131.8, 130.0, 129.4, 128.4, 127.6, 121.4, 77.1, 77.0, 73.9,
71.3, 69.1, 56.4, 52.4, 45.3, 43.5, 43.2, 41.1, 40.4, 38.0, 37.4, 36.2, 36.0,
32.6, 31.9, 26.0, 22.3, 20.0, 14.1; IR (film) 3338, 2956, 2923, 2854,
1717, 1643, 1527, 1460, 1375, 1250, 1180, 1156, 1111, 1084, 1033,
800 cm−1; HRMS (ESI) m/z calcd for C34H49NO8Na [M + Na]+
1
Des-carbamyl side-chain acid: H NMR (300 MHz, CDCl3) δ
7.31 (s, 1H), 6.25 (dt, J = 7.3, 11.1 Hz, 1H), 5.85 (d, J = 11.0 Hz, 1H),
2.97 (dt, J = 7.1, 7.1 Hz, 2H), 2.68 (t, J = 7.0 Hz, 2H), 2.45 (s, 3H);
13C NMR (75 MHz, CDCl3) δ 170.0, 161.8, 148.6, 139.1, 134.1, 121.2,
27.5, 24.9, 13.7; IR (film) 3139, 2922, 2537, 1700, 1643, 1577, 1437,
1203, 1096, 1017, 935, 822 cm−1; HRMS (EI) m/z calcd for
C9H11NO3 [M+] 181.0739, found 181.0737.
General Procedure for the Mitsunobu Coupling. A one-dram
vial was charged with the macrocyclic alcohol (1 equiv), oxazolic acid
(4 equiv), and PPh3 (4 equiv), and benzene (∼0.05 M alcohol
concentration) was added . DIAD (4 equiv) was added to the reaction
mixture. After an indicated period (see individual reactions for details),
the mixture was concentrated under vacuum. The resulting residue
was purified by flash column chromatography to afford the desired
product.
622.3356, found 622.3322; [α]25 = +14.2 (MeOH, c = 0.33).
D
Pyridyl-Containing Side-Chain Analogue 26. A 25 mL round-
bottom flask was charged with 25 (80 mg, 0.27 mmol) and
dichloromethane (3.5 mL). The mixture was cooled to −78 °C, and
a 1 M DIBAL-H solution in hexanes (0.33 mL, 0.33 mmol) was added
dropwise under nitrogen. After 2 h of stirring at −78 °C, the reaction
was quenched with saturated aqueous ammonium chloride solution.
Flash chromatography with 40% ethyl acetate in hexanes gave 28 mg
(42%) of the desired product, 14 mg (18%) of recovered starting
Hydroxy Analogue 13. The general esterification procedure was
followed with 10 (5.8 mg, 0.017 mmol), 12 (7.0 mg, 0.025 mmol),
PPh3 (8.8 mg, 0.034 mmol), and DIAD (6.7 μL, 0.034 mmol) in
benzene. Two hours later, the reaction was quenched with 1 drop of
water, concentrated under vacuum, and purified with flash
chromatography (30% THF in pentane) to afford the desired product
1
1
material, and 25 mg (37%) of overreduced alcohol: H NMR (300
(4.5 mg, 42%): H NMR (400 MHz, CD3OD) δ 7.70 (s, 1H), 6.39
MHz, CDCl3) δ 9.88 (t, J = 1.2 Hz, 1H), 7.57 (t, J = 7.7 Hz, 1H),
7.05(d, J = 7.5 Hz, 1H), 7.03 (d, J = 7.7 Hz, 1H), 6.45 (d, J = 11.7 Hz,
1H), 5.95 (dt, J = 6.6, 11.7 Hz, 1H), 5.76 (brs, 1H), 4.31 (td, J = 1.6,
6.5 Hz, 2H), 3.68 (s, 3H), 3.15 (t, J = 6.8 Hz, 2H), 2.98 (t, J = 7.2 Hz,
2H).
(dt, J = 7.7, 12.0 Hz, 1H), 6.31 (d, J = 11.9 Hz, 1H), 6.06 (dt, J = 6.1,
12.2 Hz, 1H), 5.90 (d, J = 10.6 Hz, 1H), 5.31 (aps, 1H), 4.33 (d, J =
5.6 Hz, 2H), 4.07 (dd, J = 6.8, 9.4 Hz, 1H), 3.75 (apt, J = 6.1 Hz, 1H),
3.67 (s, 3H), 3.49 (apt, J = 10.1 Hz, 1H), 3.39−3.43 (m, 1H), 3.33 (s,
3H), 3.19 (dd, J = 2.0, 8.5 Hz, 1H), 3.04 (dt, J = 7.4, 7.4 Hz, 2H), 2.74
2233
dx.doi.org/10.1021/jo2023685 | J. Org. Chem. 2012, 77, 2225−2235

The Journal of Organic Chemistry
Article
A 25 mL round-bottom flask was charged methyl bis(trifluoroethyl)-
phosphonoacetate (44 μL, 0.21 mmol), 18-crown-6 (165 mg,
0.624 mmol), and THF (2 mL). The mixture was cooled to
−78 °C, and KHMDS (30 mg, 0.15 mmol) in 3 mL of THF was
added dropwise under nitrogen. After 30 min of stirring, the aldehyde
(27 mg, 0.11 mmol) in 3 mL of THF was added dropwise, followed by
4 h of stirring at −78 °C. The reaction was quenched with saturated
aqueous NH4Cl solution and extracted with ethyl acetate. Flash
chromatography with 10% THF in dichloromethane gave 24 mg
(71%) of the desired ester: 1H NMR (300 MHz, CDCl3) δ 7.57 (t, J =
7.7 Hz, 1H), 7.04 (d, J = 7.1 Hz, 1H), 7.02 (d, J = 6.7 Hz, 1H), 6.48
(d, J = 11.7 Hz, 1H), 6.30 (dt, J = 7.5, 11.5 Hz, 1H), 6.06 (brs, 1H),
6.01 (dt, J = 6.1, 11.4 Hz, 1H), 5.81 (dt, J = 1.6, 11.5 Hz, 1H), 4.29
(t, J = 6.3 Hz, 2H), 3.70 (s, 3H), 3.67 (s, 3H), 3.12 (dtd, J = 1.0, 7.4,
7.4 Hz, 2H), 2.95 (t, J = 7.8 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ
166.7, 160.2, 157.3, 155.0, 149.2, 136.8, 132.9, 130.4, 122.1, 120.9,
120.0, 52.0, 51.1, 39.1, 37.4, 28.7; IR (film) 3399, 1719, 1643, 1570,
1530, 1453, 1521, 1147, 1023, 819 cm−1; HRMS (ESI) m/z calcd for
C16H20N2O4Na [M + Na]+ 327.1321, found 327.1302.
The methyl ester (18 mg, 0.060 mmol) was dissolved in THF (0.35
mL) at rt. After 1 N LiOH aqueous solution (0.90 mL, 0.90 mmol)
was added, the reaction mixture was stirred at room temperature for
5 h. The reaction mixture was adjusted to pH 8 at 0 °C, and was
extracted with 2 mL of ethyl acetate. The aqueous layer was acidified
to pH 2, with ethyl acetate extraction at every 2 pH intervals. The
combined organic phase was dried with MgSO4, concentrated,
redissolved in 10% methanol in dichlromethane, filtered through a
thin plug of silica gel and concentrated under vacuum. The salt was
obtained (15 mg, 85%) and used directly in the next Mitsunobu
reaction without further purification.
1249, 1190, 1064, 994 cm−1; HRMS (ESI) m/z calcd for
C32H45NO9Na [M + Na]+ 610.2992, found 610.3017; [α]25 = +5.1
D
(MeOH, c = 0.20).
Des-carbamyl Analogue 34. The general esterification procedure
was followed with 15 (2.2 mg, 0.0067 mmol), the des-carbamyl side-
chain acid (4.9 mg, 0.027 mmol), PPh3 (9.4 mg, 0.036 mmol), and
DIAD (7.1 μL, 0.036 mmol) in benzene (0.5 mL). The mixture was
stirred for 10 min and then was purified by flash column
chromatography (20% EtOAc in DCM, then 40% EtOAc in hexanes)
1
to yield 2.5 mg (76%) of the desired analogue: H NMR (400 MHz,
CD3OD) δ 7.54 (t, J = 1 Hz, 1H), 6.34 (dt, J = 7.4, 11.5 Hz, 1H), 5.88
(dt, J = 1.7, 11.5 Hz, 1H), 5.14−5.20 (m, 2H), 4.07 (dddd, J = 2.2, 2.2,
11.5, 11.5 Hz, 1H), 3.67 (app t, J = 9.7, 1H), 3.57 (app t, J = 10.8 Hz,
1H), 3.28 (s, 3H), 2.97 (dtd, J = 1.6, 7.1, 7.1 Hz, 2H), 2.70 (dd, J =
4.3, 14.8 Hz, 1H), 2.64 (t, J = 7.3, 2H), 2.30 (dd, J = 11.0, 14.8 Hz,
1H), 1.87 (dd, J = 10.9, 14.0 Hz, 1H), 1.80−1.86 (m, 1H), 1.66−1.76
(m, 2H), 1.46−1.62 (m, 4H), 1.26−1.44 (m, 6H), 1.29 (s, 3H), 1.12
(ddd, J = 1.8, 11.0, 12.8 Hz, 1H), 0.97 (t, J = 5.8 Hz, 3H), 0.94 (t, J =
7.3 Hz, 3H); 13C NMR (100 MHz, CD3OD) δ 173.0, 167.7, 164.4,
150.8, 141.6, 136.9, 122.5, 78.0, 77.9, 74.8, 72.2, 70.0, 57.3, 46.1, 44.3,
44.1, 41.9, 38.8, 38.3, 37.1, 33.4, 29.8, 27.1, 26.8, 20.9, 15.0, 14.4; IR
(film) 2956, 2922, 2836, 1718, 1642, 1580, 1458, 1382, 1334, 1261,
1175, 1087, 1030, 797 cm−1; HRMS (ESI) m/z calcd for C27-
H41NO7Na [M + Na]+ 514.2781, found 514.2766; [α]25 = +27.8
D
(MeOH, c = 0.21).
Growth Inhibition Assays. Cell proliferation was evaluated uing
the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-
2-(4-sulfophenyl)-2H-tetrazolium) dye reduction assay with PMS
(phenazine methosulfate) as electron acceptor performed in triplicate
or quintuplicate. Briefly, cells were seeded in 96-well plates at 1000 or
2000 cells per well and incubated for 24 h at 37 °C. Cells were then
exposed to various concentrations (serial 3-fold dilutions) of the
indicated compounds for 72 h at 37 °C. An MTS solution was added,
and the cells were incubated at 37 °C for 2 h. The absorption signals
were measured at 490 and 650 nm. Growth inhibition was calculated
as defined by the National Cancer Institute [GI50 = 100 × (T - T0)/
(C − T0); T0 = cell density at time zero; T = cell density of the tested
well after period of exposure to tested compound; C = cell density of
the vehicle treated].
The general esterification procedure was followed with 15 (2.6 mg,
0.008 mmol), the pyridine-containg side chain acid (9.8 mg, 0.034
mmol), PPh3 (16.8 mg, 0.064 mmol), and DIAD (12.5 μL, 0.064
mmol) in benzene (0.5 mL). The mixture was stirred for 10 min and
then was purified by flash column chromatography (30% THF in
pentane, then 50% EtOAc in pentane) to yield 3.2 mg (67%) of the
1
desired analogue: H NMR (300 MHz, CDCl3) δ 7.59 (t, J = 7.7 Hz,
1H), 7.00−7.09 (m, 3H), 6.49 (d, J = 11.7 Hz, 1H), 5.94−6.04 (m,
1H), 5.94 (dt, J = 1.4, 15.6 Hz, 1H), 5.10−5.21 (m, 2H), 5.04 (brs,
1H), 4.31 (t, J = 6.5 Hz, 2H), 4.06 (tdd, J = 2.2, 4.2, 11.3 Hz, 1H),
3.69 (s, 3H), 3.51−3.60 (m, 2H), 3.32 (s, 3H), 2.99 (t, J = 8.0 Hz,
2H), 2.72 (dd, J = 6.8, 14.9 Hz, 2H), 2.58 (dd, J = 4.4, 9.3 Hz, 1H),
2.36 (dd, J = 7.0, 10.8 Hz, 1H), 1.85−1.96 (m, 1H), 1.62−1.79 (m,
3H), 1.45−1.58 (m, 4H), 1.11−1.43 (m, 10H), 0.98 (d, J = 6.4 Hz,
3H), 0.92 (t, J = 7.3 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 170.9,
165.8, 159.7, 157.2, 155.2, 148.5, 136.9, 133.1, 130.3, 122.3, 121.9,
120.9, 75.6, 75.4, 73.4, 69.8, 67.8, 56.2, 52.0, 44.0, 42.4, 42.3, 40.0,
36.9, 36.5, 36.2, 35.3, 31.7, 31.0, 25.6, 19.0, 13.9; IR (film) 2955, 2923,
1722, 1651, 1570, 1455, 1375, 1264, 1182, 1085, 1031, 966, 820 cm−1;
HRMS (ESI) m/z calcd for C33H48N2O8Na [M + Na]+ 623.3308,
found 623.3356; [α]25 = +22.4 (CHCl3, c = 0.32).
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra for all compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: (B.W.D.) bday@pitt.edu, (P.E.F.) florean@pitt.edu.
■
Notes
Furan-ContainingD Side-Chain Analogue 30. The general
esterification procedure was followed with 15 (2.2 mg, 0.0067
mmol), the furan-containing side-chain acid (5.6 mg, 0.013 mmol),
PPh3 (3.9 mg, 0.015 mmol), and DIAD (3.0 μL, 0.015 mmol) in
benzene (0.5 mL). The mixture was stirred for 10 min and then was
purified with flash column chromatography (50% EtOAc in pentane)
to afford 2.0 mg (50%) of the desired analogue: 1H NMR (400 MHz,
CDCl3) δ 8.01 (dd, J = 12.0, 16.0 Hz, 1H), 6.74 (t, J = 11.7 Hz, 1H),
6.60 (d, J = 15.6 Hz, 1H), 6.51 (d, J = 3.4 Hz, 1H), 6.33 (d, J = 3.5 Hz,
1H), 6.24−6.28 (m, 1H), 5.76 (d, J = 11.1 Hz, 1H), 5.60−5.69 (m,
1H), 5.23−5.26 (m, 1H), 5.12−5.19 (m, 1H), 5.07 (brs, 1H), 4.28 (t,
J = 6.6 Hz, 2H), 4.10 (apt, J = 11.4 Hz, 1H), 3.70 (s, 3H), 3.57−3.62
(m, 2H), 3.32 (s, 3H), 2.60 (dd, J = 4.4, 14.5 Hz, 1H), 2.36 (dd, J =
10.8, 14.1 Hz, 1H), 1.82−1.94 (m, 2H), 1.70−1.75 (m, 2H), 1.45−
1.62 (m, 4H), 1.23−1.39 (m, 6H), 1.12−1.19 (m, 1H), 0.98 (d, J = 6.5
Hz, 3H), 0.92 (t, J = 7.3 Hz, 3H); 13C NMR (100 MHz, CD3OD) δ
173.1, 167.1, 154.8, 145.2, 130.1, 128.7, 125.1, 118.7, 114.9, 114.3,
77.1, 77.0, 73.9, 71.3, 69.1, 56.4, 52.5, 45.2, 43.5, 41.1, 40.4, 37.9, 37.4,
36.0, 32.6, 26.0, 20.0, 14.1; IR (film) 2947, 2854, 1713, 1528, 1376,
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the National Institutes of Health, Institute of General
Medicine (GM062924), for generous support of this work.
■
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dx.doi.org/10.1021/jo2023685 | J. Org. Chem. 2012, 77, 2225−2235

The Journal of Organic Chemistry
Article
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