Application of Negishi cross-coupling to the synthesis of the cyclic tripeptides OF4949-III and K-13

Article abstract of DOI:10.1021/jo9018792

(Chemical Equation Presented) Syntheses of the cyclic tripeptides OF4949-III 1 and K-13 2 are reported, in which the key steps are intermolecular and intramolecular Negishi cross-coupling reactions, respectively. In addition, the synthesis of a protected

Full text of DOI:10.1021/jo9018792

pubs.acs.org/joc
Application of Negishi Cross-Coupling to the Synthesis of the Cyclic
Tripeptides OF4949-III and K-13
Luca Nolasco, Manuel Perez Gonzalez, Lorenzo Caggiano, and Richard F. W. Jackson*
Department of Chemistry, The University of Sheffield, Dainton Building, Sheffield S3 7HF, United Kingdom
r.f.w.jackson@shef.ac.uk
Received September 1, 2009
Syntheses of the cyclic tripeptides OF4949-III 1 and K-13 2 are reported, in which the key steps are
intermolecular and intramolecular Negishi cross-coupling reactions, respectively. In addition, the
synthesis of a protected isomer of K-13 25 is reported. The synthesis of K-13 features a tripeptidic
organozinc reagent 11, one of the most highly functionalized such reagents to be described. An
O-aryltyrosine derivative 15, prepared by SNAr reaction between Boc-tyrosine and 2-fluorobenzal-
dehyde, followed by Dakin reaction, iodination, and methylation, is used as a common intermediate
for all of the syntheses described. The routes to this class of cyclic tripeptide are among the shortest
reported to date and demonstrate the high functional group tolerance of the carbon-zinc bond
toward peptide derivatives.
Introduction
development of new cyclization methods.4 In this paper,
we describe how the Negishi cross-coupling between amino
acid and peptide-derived organozinc halides, on one hand,
and aryl iodides, on the other, can be employed in short
syntheses of both OF4949-III and K-13. A preliminary
account of a part of this work has appeared.5
Previous syntheses of OF4949-III, and protected deriva-
tives, have featured the use of suitably protected isodityr-
osine derivatives (prepared by asymmetric hydrogenation,6
asymmetric electrophilic amination,7 asymmetric glycine
anion chemistry,8 or metal-mediated nucleophilic aromatic
substitution9), which have been elaborated and then subjected
to macrolactamization. An alternative approach constructs
Cyclic peptides, in which the conformation of the peptide
backbone is constrained,1 are biologically significant. There
are many examples of naturally occurring cyclic peptides,
but among the simplest are cyclic tripeptides including the
aminopeptidase inhibitor OF4949-III 12 and the ACE in-
hibitor K-13 2.3 These compounds are formally derived by
oxidative cyclization of simple linear tripeptides, containing
a tyrosine residue at each terminus. In the biosynthesis of
OF4949-III, it is the tyrosine residue at the N-terminus that is
subject to oxidation, while for K-13, it is the tyrosine residue
at the C-terminus. The synthesis of cyclic tripeptides 1 and 2
has presented an opportunity to showcase methods for the
stereocontrolled synthesis of the R-amino acid components,
which then rely on macrolactamization procedures to com-
plete the synthesis, and also provide motivation for the
(4) Zhu, J. Synlett 1997, 133–144.
(5) Perez-Gonzalez, M.; Jackson, R. F. W. Chem. Commun. 2000, 2423–
2424.
(6) Schmidt, U.; Weller, D.; Holder, A.; Lieberknecht, A. Tetrahedron
Lett. 1988, 29, 3227–3230.
(1) Feliu, L.; Planas, M. Int. J. Pept. Res. Ther. 2005, 11, 53–97.
(2) Sano, S.; Ikai, K.; Katayama, K.; Takesako, K.; Nakamura, T.;
Obayashi, A.; Ezure, Y.; Enomoto, H. J. Antibiot. 1986, 39, 1685–1696.
(3) Yasuzawa, T.; Shirahata, K.; Sano, H. J. Antibiot. 1987, 40, 455–458.
(7) Evans, D. A.; Ellman, J. A. J. Am. Chem. Soc. 1989, 111, 1063–1072.
(8) Boger, D. L.; Yohannes, D. J. Org. Chem. 1990, 55, 6000–6017.
(9) Pearson, A. J.; Zhang, P. L.; Lee, K. J. Org. Chem. 1996, 61, 6581–
6586.
8280 J. Org. Chem. 2009, 74, 8280–8289
Published on Web 10/08/2009
DOI: 10.1021/jo9018792
r
2009 American Chemical Society

Nolasco et al.
JOCArticle
the macrocycle through formation of the biaryl ether using
oxidative coupling of two (halogenated) tyrosine residues
in an acyclic tripeptide precursor10 or by intramolecular
nucleophilic aromatic substitution by one tyrosine residue
on the other, the latter activated by a metal carbonyl frag-
ment.11 Previous approaches to the synthesis of K-13 have
employed similar strategies, using elaboration of suitably
protected isodityrosine derivatives,7,8,12-15 biomimetic oxidative
tyrosine coupling,16 or macrocyclic biaryl ether formation by
nucleophilic aromatic substitution using halotyrosine resi-
dues activated either by metal carbonyl fragments11 or by
ortho-electron-withdrawing substituents.17
SCHEME 1. Proposed Routes to OF4949-III
The palladium-catalyzed Negishi cross-coupling reaction
between aromatic iodides and the organozinc reagent
derived from protected iodoalanine to generate phenylala-
nine derivatives has been known for some time.18,19 The
synthesis of OF4949-III and K-13 offered an opportunity to
test the effectiveness of this reaction using highly functiona-
lized aryl iodides and also to explore whether it might be
applied to peptide-derived organozinc reagents in an intra-
molecular manner. It is worth observing that DMF is an
excellent solvent for the preparation and stabilization of
organozinc reagents (possibly through promotion of partial
ionization of the zinc-iodine bond, thereby reducing the
tendency of the carbon-zinc bond to protonate)20 and, of
course, in peptide chemistry.
compound 4 could be prepared from the Ser-Asn derivative 5
and the tyrosine derivative 6. However, the zinc reagent
produced by this disconnection, 4, contains a carbon-zinc
bond at the N-terminus, and previous work had already
established that the stability toward elimination of a
carbon-zinc bond at the N-terminus of a dipeptide was
substantially less than a corresponding bond at the C-terminus.21
For this reason, the viability of reagent 4 was sufficiently
uncertain that a simple reordering of steps was preferred,
whereby the Negishi cross-coupling was to be carried out in
an intermolecular manner between 8 and 9, with subsequent
macrolactamization of intermediate 7 (step b, Scheme 1).
Compound 8 was envisaged to be easily prepared from
tyrosine derivative 6. A further issue to be determined
experimentally was whether the primary amide function in
8 would be compatible with Negishi cross-coupling or indeed
whether the extra polarity of this group might result in
solubility problems.
Results and Discussion
The initial strategy considered for the synthesis of
OF4949-III 1 (Scheme 1) relied on formation of the protected
macrocycle 3, which had been previously synthesized by both
Boger8 and Pearson,9 using an intramolecular Negishi reac-
tion (step a). Initial disconnection at the more oxygenated
aromatic residue has the advantage that it leads, ultimately,
to the same intermediate for the synthesis of both OF4949-
III and K-13 (see below). In principle, a suitable precursor to
(10) Nishiyama, S.; Suzuki, Y.; Yamamura, S. Tetrahedron Lett. 1988, 29,
559–562.
In the context of the planned synthesis of K-13, the initial
target was the protected derivative 10 first made by Evans7
and then subsequently by Rich11 and Zhu.17 Disconnection
of 10 leads to a C-terminal organozinc reagent 11, which
previous precedent had suggested might be a credible inter-
mediate,21 and therefore allow the viability of an intramole-
cular Negishi reaction to be assessed. A suitable precursor to
organozinc reagent 11 could be prepared from the Ser-Tyr
derivative 14 and the O-aryl tyrosine derivative 13
(Scheme 2).
(11) Janetka, J. W.; Rich, D. H. J. Am. Chem. Soc. 1997, 119, 6488–6495.
(12) Boger, D. L.; Yohannes, D. J. Org. Chem. 1989, 54, 2498–2502.
(13) Rao, A. V. R.; Gurjar, M. K.; Reddy, A. B.; Khare, V. B. Tetrahedron
Lett. 1993, 34, 1657–1660.
(14) Beugelmans, R.; Bigot, A.; Zhu, J. P. Tetrahedron Lett. 1994, 35,
7391–7394.
(15) Pearson, A. J.; Lee, K. S. J. Org. Chem. 1994, 59, 2304–2313.
(16) Nishiyama, S.; Suzuki, Y.; Yamamura, S. Tetrahedron Lett. 1989, 30,
379–382.
(17) Bigot, A.; Bois-Choussy, M.; Zhu, J. Tetrahedron Lett. 2000, 41,
4573–4577.
(18) Jackson, R. F. W.; Moore, R. J.; Dexter, C. S.; Elliot, J.; Mowbray,
C. E. J. Org. Chem. 1998, 63, 7875–7884.
(19) Rilatt, I.; Caggiano, L.; Jackson, R. F. W. Synlett 2005, 2701–2719.
(20) Caggiano, L.; Jackson, R. F. W.; Meijer, A.; Pickup, B. T.; Wilkinson,
K. A. Chem.;Eur. J. 2008, 14, 8798–8802.
(21) Dunn, M. J.; Jackson, R. F. W. Tetrahedron 1997, 53, 13905–13914.
J. Org. Chem. Vol. 74, No. 21, 2009 8281

Nolasco et al.
JOCArticle
SCHEME 2. Proposed Route to K-13
SCHEME 3. Preparation of O-Aryl Tyrosine 15
Synthesis of O-Aryl Tyrosine 15. The only components in
the synthetic plans not commercially available were the
O-arylated tyrosine derivatives 6 and 13, both derived from
a common precursor 15. The synthesis of iodide 15
(Scheme 3) proceeded by SNAr reaction between N-Boc-
L-tyrosine and 2-fluorobenzaldehyde to give the biaryl ether
16 (85%), which was then converted into the methyl ester 17
(95%). Use of the free carboxylic acid of tyrosine proved
essential because direct use of the corresponding methyl ester
gave rac-17 under the same conditions. Treatment of alde-
hyde 17 with m-CPBA gave the formate ester, which was
immediately converted into the corresponding phenol 18
(76%), which had previously been made by an alternative
three-step route in 30% overall yield.22 Interestingly, use of a
different batch of m-CPBA, which contained more water,
gave the corresponding phenol directly, shortening the pre-
sent route to three steps from protected tyrosine. Iodination
of the phenol 18, following Jung’s conditions,22 gave the
5-iodo derivative 19 that was directly methylated to give 15
(89% from 18 over two steps); small amounts of the corre-
sponding 3,5-diiodo derivative 20 were also isolated in some
runs. This procedure allowed the synthesis of compound 15
in five steps on a multigram scale in 55% overall yield from
commercially available N-Boc-tyrosine and 2-fluorobenzaldehyde,
with only one chromatographic purification necessary at the
end of the synthesis.
SCHEME 4. Synthesis of OF4949-III 1
Interestingly, when the methylation of 16 was scaled-up, a
byproduct identified as the dimethyl acetal 21 was identified,
whose formation appears to require the presence of metha-
nol. It seems possible that methanol can be formed by
decomposition of methyl bicarbonate, itself formed by reac-
tion of sodium bicarbonate with iodomethane. The acetal 21
was found to be unstable on storage at room temperature,
and after a few months, it was converted almost entirely into
the aldehyde 17.
reaction between the organozinc reagent 923 and the aryl
iodide 22 proceeded to give the cross-coupled product 23 in
high yield (Scheme 4). The efficiency of this reaction further
demonstrates the high functional group tolerance (especially
Synthesis of OF4949-III. Boc deprotection of 15 was
achieved with HCl in methanol, obtained from methanol
and acetyl chloride, and was followed by coupling with the
active ester Boc-Asn-ONp to give the modified dipeptide 22.
Although the presence of the primary amide function in 22
might have compromised the planned Negishi cross-coupling,
(23) Dumez, E.; Snaith, J. S.; Jackson, R. F. W.; McElroy, A. B.;
Overington, J.; Wythes, M. J.; Withka, J. M.; McLellan, T. J. J. Org. Chem.
2002, 67, 4882–4892.
(22) Jung, M. E.; Starkey, L. S. Tetrahedron 1997, 53, 8815–8824.
8282 J. Org. Chem. Vol. 74, No. 21, 2009

Nolasco et al.
JOCArticle
SCHEME 5. Suggested Transesterification of Protected
OF4949-III 3 with CD3OD
TABLE 1. Z-OF4949-III-OMe 3 Physical Data
present work
(sample after
present
work
(sample
chromato-
graphy)
Boger8
178-182
-74, c = 0.1 -73, c = 0.35
Pearson9
recrystallized)
mp °C
D
181-183
245-246
þ55, c = 0.1 þ73, c = 0.1
259-260
[R]20
(MeOH)
TABLE 2. Variation of Specific Rotation of Z-OF4949-III-OMe 3 with
Concentration
[R]20D in CHCl3
[R]20D in CH2Cl2
toward acidic protons) of organozinc iodides. Recently,
more examples of the tolerance of amide protons by organo-
zinc reagents have been reported.24 The tripeptide 23 was
deprotected under acidic conditions and subjected to macro-
cyclization to give protected OF4949-III 3. Using Boger’s
procedure,8 the methyl ester of the macrocycle 23 was
hydrolyzed to give the corresponding acid 24, which was
then subjected to hydrogenolysis8 to give OF4949-III 1
(Scheme 4), in 12 steps and with 20% overall yield from
Boc-tyrosine. The 1H NMR spectrum of OF4949-III 1
matched that reported by Evans7 (see Supporting Infor-
mation), and in addition, the specific rotation [R]D -30 (c =
0.5, 0.1 N HCl) was comparable, both in sign and magnitude,
with all previous reports.7,8,10
c = 1.02
c = 0.41
c = 0.20
c = 0.04
þ42
þ55
þ59
þ99
þ54
þ68
þ70
reaction may have occurred with the solvent (CD3OD)
leading to the trideuteromethyl ester 3a (Scheme 5). In order
to explore this possibility, treatment of our sample with
sodium bicarbonate and CD3OD was carried out, which
did indeed result in the apparent disappearance of the signal
at δ 52.5 and a 13C NMR spectrum which now matched
Pearson’s spectrum perfectly (apart from the two additional
signals referred to above). Mass spectrometry of our sample,
including high-resolution mass measurement, confirmed the
incorporation of a CD3 group. Of course, exchange of a CH3
As well as comparison of the data for OF4949-III 1 itself,
comparison of the data for protected OF4949-III 3 with that
already reported was made.8,9 Although both previous
groups had used CD3OD as solvent for the NMR experi-
ments, we found that the solubility of our sample of pro-
tected OF4949-III 3 in this solvent was poor, especially after
recrystallization, although it was sufficient to allow NMR
group with a CD3 group cannot remove the signal in the 13
C
spectrum, but the carbon atom of a CD3 group will exhibit a
7-line splitting pattern; in addition, there would now be no
enhancement of the 13C signal through NOE, reducing the
signal intensity further. Taken together, these effects might
be expected to result in a substantial reduction in signal
strength, so that the signal is rendered indistinguishable from
baseline noise.
1
spectra to be obtained. Comparison of the H spectrum of
our sample of protected OF4949-III 3 in CD3OD (4 mg of 3
in 1 mL of CD3OD, to mimic Pearson’s spectrum as closely
as possible) showed an excellent match with that reported by
Pearson9 and a reasonable match with that reported by
Boger, although Boger’s description8 of the methylene pro-
tons of the Z-protecting group as a singlet is at variance with
what both Pearson and we have observed. It is possible that
this apparent discrepancy may arise due to differences in the
concentration at which the respective spectra were recorded.
In order to be completely confident of our assignment of the
structure of our sample of compound 3, a comprehensive
NMR investigation was carried out in both CD3OD and
CDCl3, the details of which are included in the Supporting
Information.
Despite this excellent match of our NMR data with
Pearson’s data for OF4949-III-OMe 3,9 some discrepancies
between our physical data and those already reported by
Boger8 and Pearson9 were identified (see Table 1). A much
higher melting point was recorded as was a different sign
(although identical magnitude) for the optical rotation
(Table 1). While the higher melting point and low solubility
of our sample of Z-OF4949-III-OMe 3 in methanol could be
due to the formation of a different polymorph, perhaps due
to the fact that we were able to purify our material by
recrystallization, it is very hard to rationalize the discrepancy
in the sign of specific rotation, especially since we converted
Z-OF4949-III-OMe 3 using Boger’s route into OF4949-III 1,
and our physical and spectroscopic data for OF4949-III
match the literature values, including Boger’s,8 in all re-
spects. A study of the influence of concentration on specific
rotation of Z-OF4949-III-OMe 3 in chloroform and dichlor-
omethane (in which solvent Z-OF4949-III-OMe 3 was more
soluble than in methanol) revealed significant variations
(Table 2), perhaps pointing to aggregation. All specific
rotations recorded were positive. The specific rotation
of each of the amino acid building blocks used for our
synthesis of Z-OF4949-III-OMe 3 was checked and in each
case was found to be consistent with the natural S-isomer,
ruling out the possibility that we had inadvertently made
ent-3. Furthermore, no evidence for epimerization of any of
Comparison of Pearson’s 13C NMR spectrum of protected
OF4949-III 3 in CD3OD with ours showed two additional
signals in the aliphatic carbon range of Pearson’s spectrum
(in addition to the three expected for compound 3 due to the
methylene group in each amino acid side chain); these signals
most likely arise due to minor impurities. There was one
additional signal at δ 52.5 in our 13C NMR spectrum which
was not evident in Pearson’s spectrum. A complete assignment
of the 13C NMR spectrum demonstrated that this signal was
the methyl ester carbon, and it therefore appeared possible
that, prior to Pearson’s data accumulation, a transesterification
(24) Manolikakes, G.; Dong, Z. B.; Mayr, H.; Li, J. S.; Knochel, P.
Chem.;Eur. J. 2009, 15, 1324–1328.
J. Org. Chem. Vol. 74, No. 21, 2009 8283

Nolasco et al.
JOCArticle
SCHEME 6. Synthesis of Protected iso-K-13 25
SCHEME 7. Synthesis of K-13 2 by Intramolecular Negishi
Reaction
the intermediates in our route was found, so we (and
Pearson) had not inadvertently prepared a diastereoisomer of
Z-OF4949-III-OMe 3.
There are some similar inconsistencies in the data we
observed for the free carboxylic acid 24. For example, the
specific rotation of our sample of 24 was [R]D þ57 (c=0.28,
1
MeOH), with Boger reporting8 [R]D -87. In the H NMR
spectrum, the methylene protons of the Z-protecting group
appear as an AB system in our spectrum but are reported as a
singlet in Boger’s spectrum. Such differences may again be
accounted for by the influence of concentration.
Synthesis of Protected iso-K-13. The success of this short
route to OF4949-III 1 encouraged us to explore further
application of the Negishi reaction in the synthesis of an
isomer of K-13, protected iso-K-13 25 (Scheme 6). This
compound closely resembles OF4949-III but has a tyrosine
residue in place of the asparagine residue. Deprotection of 15
and coupling with a protected tyrosine gave the dipeptide 26,
which was subjected to Negishi reaction with 9 to give the
macrocyclization precursor 27. In a similar way, the macro-
cyclization was achieved via peptide coupling to give the
protected iso-K-13 25.
Synthesis of K-13. The retrosynthetic plan for K-13 made
use of the intramolecular Negishi reaction that we had
considered for use in the approach to OF4949-III but was
rejected in this latter case due to the (relative) instability of
reagents contains a carbon-zinc bond at the N-terminus of a
peptide. In the event, conversion of the tyrosine derivative 15
into the required carboxylic acid 13, followed by coupling
with the dipeptide 14, gave the modified tripeptide 12.21
Conversion of 12 into the iodide 28, followed by treatment
with zinc (activated by treatment with iodine), and then
addition of this solution of the presumed organozinc reagent
11 to a dilute solution of a catalyst derived from Pd2(dba)3
and P(o-tol)3 gave the desired macrocyclic peptide 10, albeit
in modest yield (35% from iodide 28). Although it is possible
that zinc could insert into the aromatic carbon-iodine bond,
this process is normally slower than insertion of zinc into an
aliphatic carbon-iodine bond.25 In the event, no evidence
for the formation of byproduct arising from insertion of zinc
into the aromatic carbon-iodine bond was found. Conver-
sion of macrocyclic peptide into K-13 2 was achieved follow-
ing Evans’ procedure,7 via the intermediate 29 (Scheme 7).
Our sample of synthetic K-13 exhibited physical and spectro-
scopic data that were in close agreement with those previously
reported.3,7,8
In conclusion, it has been demonstrated that organozinc
iodides derived from amino acids and peptides are useful
intermediates in the preparation of naturally occurring cyclic
tripeptides and their analogues. Further applications of
this general approach to peptide modification can be en-
visaged.
Experimental Section
General Procedure 1: Boc Deprotection and Peptide Coupling.
AcCl (5 equiv) was added slowly to a rapidly stirred solution of
the Boc-protected amine (1 equiv) in MeOH/THF (3:1) at rt.
The mixture was stirred overnight, and the solvent was removed
under reduced pressure. Trituration with Et2O/PE (1:1) gave
i
a white solid, which was dissolved in dry DMF and Pr2NEt
(1 equiv), HOBt (1 equiv), and the required N-protected amino
acid added. EDCl (1 equiv) was added to the stirred solution in
small portions over a period of 10 min at 0 °C, and the solution
was then stirred at rt for 8 to 48 h. The solution was partitioned
between EtOAc and water, and the aqueous layer was re-extracted
with EtOAc. The combined organic phases were washed with
saturated citric acid, sodium bicarbonate, water, and brine. The
organic fraction was dried over MgSO4 and the solvent removed
under reduced pressure.
General Procedure 2: Zinc Activation and Insertion into the
C-I Bond. A flame-dried flask was charged with zinc powder
(25) Majid, T. N.; Knochel, P. Tetrahedron Lett. 1990, 31, 4413–4416.
8284 J. Org. Chem. Vol. 74, No. 21, 2009

Nolasco et al.
JOCArticle
(from 3 to 6 equiv) and placed under a N2 atmosphere. Dry
DMF and TMSCl were added, and the solution was stirred for
15 min at rt. Stirring was stopped, and the suspension was
allowed to settle and the solution removed by syringe. The
remaining solid was dried using a heating gun at reduced
pressure. The activated zinc was cool to rt, and dry DMF
(enough volume to obtain a 1 to 0.5 M solution of the iodo-
amino acid used) and the iodoalanine derivative (1.5 to 2 equiv)
were added and the suspension was rapidly stirred until just
a trace of starting material was detectable via TLC (80%
Et2O/PE). Zn insertion into the C-I bond is an exothermic
reaction, and the excess heat was removed by an ice bath. Aryl
iodide (1 equiv), Pd2(dba)3 (3 mol %), and P(o-Tol)3 (12 mol %)
were added to the suspension at rt, and the mixture was stirred
overnight at 50 °C under N2. The suspension was filtered
through silica gel and the solvent removed under reduced
pressure. The mixture was purified via flash chromatography.
2-(S)-tert-Butoxycarbonylamino-3-[4-(2-formylphenoxy)phe-
nyl]propionic acid 16. 2-Fluorobenzaldehyde (18 g, 145.0 mmol)
was added to a rapidly stirred solution of N-tert-butoxycarbo-
nyl-L-tyrosine (13.57 g, 48.2 mmol) and K2CO3 (20 g, 145.0 mmol)
in dry DMF (35 mL) at room temperature under nitrogen. The
solution was stirred for 8 days at 70 °C and then cooled. The
solvent was removed under reduced pressure, and aqueous
NaOH (300 mL, 0.5 M) was added and the mixture extracted
with Et2O (2ꢀ100 mL). HCl (2 N) was added to the aqueous
layer until pH = 2 and was then extracted with Et2O (3ꢀ75 mL).
The organic layer was washed with water (2ꢀ100 mL) and brine
(1ꢀ100 mL), dried over MgSO4, and the solvent removed under
reduced pressure to afford a brown foam (15.75 g, 85%), which
was used directly for the next step. A sample was recrystallized
to afford the acid 16 as a white solid: mp 76-77 °C (CHCl3/PE);
[R]20D þ43.1 (c=1, CHCl3); νmax (KBr disk) 3511 (br m, OH),
1724 (s sh, CdO), 1706 (s sh, CdO), 1672 (s sh, CdO) cm-1; δH
(500 MHz, CDCl3) 1.42 (9H, s, C(CH3)3), 3.07 (1H, dd, J=13.5,
6.5 Hz, β), 3.21 (1H, br d, J=13.5 Hz, β), 4.62 (1H, br d, J=
6.0 Hz, R), 5.03 (1H, d, J=7.5 Hz, NH), 6.88 (1H, d, J=8.0 Hz,
Ar), 7.00 (2H, d, J=8.0 Hz, Ar), 7.18 (1H, t, J=7.5 Hz, Ar), 7.21
(2H, d, J=8.5 Hz, Ar), 7.50 (1H, td, J=7.5, 2.0 Hz, Ar), 7.92
(1H, dd, J=7.5, 2.0 Hz, Ar), 10.47 (1H, s, CHO); carboxylic acid
proton not observed; δC (100 MHz, CDCl3) 28.3, 37.3, 54.3,
80.4, 118.4, 119.3, 119.5, 123.4, 126.8, 128.5, 131.1, 135.8, 155.3,
155.4, 160.0, 175.7, 189.5; m/z (EI) 385 (Mþ, 18%), found Mþ
385.1529; C21H23NO6 requires 385.1525.
155.0, 155.4, 160.0, 172.2, 189.3; m/z (EI) 399 (Mþ, 0.2%), found
Mþ 399.1673; C22H25NO6 requires 399.1682.
2-(S)-tert-Butoxycarbonylamino-3-[4-(2-dimethoxymethylph-
enoxy)phenyl]propionic acid methyl ester 21. When the methyla-
tion to prepare the methyl ester 17 was scaled-up, the formation
of an unexpected byproduct was observed (25% yield, by NMR)
that was identified as the dimethyl acetal 21. The product is not
stable, and after long storage on the bench, it decomposes to the
aldehyde 17. The acetal 21 was purified by chromatography
(isocratic 16% EtOAc/PE) and obtained as a pale yellow viscous
oil, as a mixture with the aldehyde 17 (20%): [R]20D þ37.0 (c=
1.3, CHCl3); νmax (reflex) 2975 (br w, Ar-H), 1713 (s br, CdO),
1693 (s br, CdO) cm-1; δH (400 MHz, CDCl3) 1.30 (9H, s,
C(CH3)3), 2.88 (1H, dd, J=14.0, 6.5 Hz, β), 2.97 (1H, dd, J=
14.0, 5.5 Hz, β), 3.23 (6H, br s, OMe), 3.60 (3H, s, OMe),
4.41-4.48 (1H, m, R), 4.90 (1H, d, J=8.0 Hz, NH), 5.50 (1H, s,
CH-acetal), 6.74-6.79 (3H, m, Ar), 6.95 (2H, d, J=8.5 Hz Ar),
7.01-7.06 (1H, m, Ar), 7.13-7.19 (1H, m, Ar), 7.51 (1H, dd, J=
7.5, 2.0 Hz, Ar); δC (100 MHz; CDCl3) 27.9, 37.2, 51.8, 53.5,
79.5, 98.9, 117.9 (x 2), 118.8, 123.2, 127.3, 129.1, 129.4, 130.1 (x 2),
153.9, 154.7, 156.4, 171.9 (this is a partial peak listing); m/z (ES)
468 (MNaþ, 95%), found MNaþ 468.2005; C24H31NO7Na
requires 468.1998.
2-(S)-tert-Butoxycarbonylamino-3-[4-(2-hydroxyphenoxy)ph-
enyl]propionic acid methyl ester 18. mCPBA (70%, 6.16 g,
25 mmol) was added in small portions to a rapidly stirred
suspension of the aldehyde 17 (5.34 g, 13.4 mmol) and NaHCO3
(3.15 g, 37.5 mmol) in CHCl3 (60 mL). The solution was stirred
at 60 °C for 24 h. Solid Na2SO3 (3.15 g, 25 mmol) was added, and
the mixture was stirred for 1 h. The solvent was removed under
reduced pressure to afford a brown foam, and water (150 mL)
was added and the mixture extracted with EtOAc (3ꢀ75 mL).
The organic layer was washed with saturated solution of NaH-
CO3 (2ꢀ100 mL) and brine (1ꢀ100 mL), dried over MgSO4, and
solvent removed under reduced pressure. Purification was car-
ried out by flash chromatography (gradient: 20% EtOAc/
PE-50% EtOAc/PE) to afford the phenol 18 as a white solid
(3.95 g, 76%) was obtained. A small sample was crystallized
from CHCl3 giving the phenol 18 as a white solid: mp 63-64 °C
(CHCl3); [R]20D þ47.0 (c=1, CHCl3), lit.22 [R]20D þ39.9 (c=1,
CHCl3); δC (100 MHz, CDCl3) 28.3, 37.6, 52.3, 54.4, 80.0, 116.3,
117.9, 119.1, 120.6, 124.8, 130.7, 131.2, 143.3, 147.6, 155.0,
155.9, 172.3. Other spectroscopic data were consistent with that
reported by Jung.22
2-(S)-tert-Butoxycarbonylamino-3-[4-(2-formylphenoxy)phe-
nyl]propionic acid methyl ester 17. MeI (12.14 mL, 195 mmol)
was added dropwise to a rapidly stirred solution of the car-
boxylic acid 16 (15 g, 39 mmol) and NaHCO3 (5.8 g, 69 mmol) in
dry DMF (130 mL), and the solution was stirred at rt for 2 days.
The solution was removed under reduced pressure, diluted with
aqueous KOH (250 mL, 0.5 N), and extracted with EtOAc (3ꢀ
150 mL). The organic layer was washed with water (2ꢀ200 mL)
and brine (1 ꢀ 150 mL), dried over MgSO4, and the solvent
removed under reduced pressure to afford the methyl ester 17
(15.23 g, 95%) that was used directly for the Perkin reaction. A
small amount of the mixture was purified by chromatography
(isocratic CH2Cl2) to afford methyl ester 17 as a colorless oil:
2-(S)-tert-Butoxycarbonylamino-3-[4-(5-iodo-2-methoxyphe-
noxy)phenyl]propionic acid methyl ester 15.22 Chloramine T
hydrate (1.70 g, 7.47 mmol) was slowly added over 10 min to a
rapidly stirred solution of NaI (1.12 g, 7.47 mmol) and phenol 18
(3 g, 7.74 mmol) in DMF (30 mL) at rt and left to stir for 2 h.
Water (40 mL) was added to the solution and then 2 N HCl until
pH = 3. Water (225 mL) was added, and the solution was
extracted with EtOAc (3ꢀ90 mL). The organic layer was washed
with aqueous Na2S2O3 (100 mL, 10%), water (100 mL), and
brine (100 mL), dried over MgSO4, and the solvent removed
under reduced pressure to give the crude iodophenol 19 (4.42 g),
contaminated with 4-methylbenzenesulfonamide as Jung
noted,22 and which was used directly in the next step. MeI (5.3 g,
37.35 mmol) was added to a rapidly stirred solution of the crude
iodophenol 19 (3.94 g), used without purification from the
previous step, 18-crown-6 (98 mg, 0.38 mmol), and K2CO3
(2.06 g, 14.9 mmol) in DMF (9.4 mL) at rt and was left to stir
for 48 h at rt. Aqueous NH4OH (1.5 mL, 28%) was added and
the solution stirred for a further 20 min. Water (140 mL) was
added and the solution extracted with EtOAc (3ꢀ70 mL). The
organic layer was dried (MgSO4) and the solvent removed under
reduced pressure. The crude material was purified by column
chromatography (gradient 15-17% EtOAc/PE) and gave the
product 15 (3.24 g, 89% from phenol 18, based on the proportion
[R]20 þ43.1 (c = 1, CHCl3); found C 66.33%, H 6.33%,
D
N 3.38%; C22H25NO6 requires C 66.15%, H 6.31%, N 3.51%;
ν
max (KBr disk) 3358 (s sh, NH), 2990 (m sh, Ar-H), 2872 (m sh,
Ar-H), 1739 (s sh, CdO), 1691 (s br, CdO) cm-1; δH (500 MHz,
CDCl3) 1.43 (9H, s, C(CH3)3), 3.03 (1H, dd, J=13.5, 6.5 Hz, β),
3.15 (1H, dd, J=13.5, 5.5 Hz, β), 3.74 (3H, s, OMe), 4.56-4.64
(1H, m, R), 5.12 (1H, br d, J=8.5 Hz, NH), 6.88 (1H, d, J=
8.5 Hz, Ar), 7.00 (2H, d, J=8.5 Hz, Ar), 7.14-7.21 (3H, m, Ar),
7.51 (1H, dt, J=1.5, 8.0 Hz, Ar), 7.93 (1H, dd, J=7.5, 2.0 Hz,
Ar), 10.50 (1H, s, CHO); δC (125 MHz, CDCl3) 28.3, 37.8, 52.3,
54.5, 79.9, 118.4, 119.4, 123.3, 126.8, 128.4, 131.0, 132.3, 135.8,
J. Org. Chem. Vol. 74, No. 21, 2009 8285

Nolasco et al.
JOCArticle
of crude iodophenol used) as a white solid: mp 91-92 °C (EtOAc/
PE); [R]20D þ35.8 (c=1, CHCl3); found C 50.16%, H 4.81%, N
2.58%; C22H26INO6 requires C 50.11%, H 4.97%, N 2.66%; νmax
(KBr disk) 3355 (m sh, NH), 2931 (w sh, Ar-H), 1737 (s sh, CdO),
1689 (s sh, CdO) cm-1; δH (500 MHz, CDCl3) 1.42 (9H, s,
C(CH3)3), 3.02 (1H, dd, J=13.5, 6.0 Hz, β), 3.08 (1H, dd, J=
13.5, 6.0 Hz, β), 3.71 (3H, s, OMe), 3.81 (3H, s, OMe), 4.53-4.60
(1H, m, R), 4.99 (1H, d, J=8.0 Hz, NH), 6.75 (1H, d, J=8.5 Hz,
Ar), 6.87 (2H, d, J = 8.5 Hz, Ar), 7.07 (2H, d,
J=8.5 Hz, Ar), 7.21 (1H, d, J=2.0 Hz, Ar), 7.41 (1H, dd, J=
8.5, 2.0 Hz, Ar); δC (125 MHz, CDCl3) 28.3, 37.7, 52.2, 54.4, 56.1,
80.0, 81.9, 114.7, 117.5, 129.3, 130.5, 130.7, 133.5, 146.1, 151.5,
155.0, 156.3, 172.3; m/z (EI) 527 (Mþ, 4%), found Mþ 527.0795;
C22H26INO6 requires 527.0805.
CdO), 1665 (br s, CdO), 1638 (br s, CdO) cm-1; δH (400 MHz,
CDCl3) 1.36 (9H, s, C(CH3)3), 1.42 (9H, s, C(CH3)3), 2.49 (1H, dd,
J=15.5, 6.0 Hz, β), 2.85-3.03 (4H, m, β), 3.07 (1H, dd, J=14.0, 5.0
Hz, β), 3.67 (3H, s, OMe), 3.79 (3H, s, OMe), 4.38-4.49 (2H, m, R),
4.70-4.78 (1H, m, R), 5.06 (2H, s, CH2-(Z)), 5.39 (1H, br d, J=8.0
Hz, NH), 5.64 (1H, br s, NH2), 5.87 (1H, br s, NH2), 6.05 (1H, br d,
J=6.5 Hz, NH), 6.76 (1H, br s, Ar), 6.81 (2H, d, J=8.5 Hz, Ar),
6.87-6.89 (2H, m, Ar), 7.03 (2H, d, J= 8.5 Hz, Ar), 7.26-7.36
(6H, m, Ar þ NH); δC (100 MHz, CDCl3) 27.9, 28.3, 36.7, 37.2, 37.5,
50.9, 52.3, 53.6, 55.3, 56.0, 66.8, 80.4, 82.4, 112.7, 117.2, 122.1, 125.6,
128.0, 128.1, 128.5, 129.1, 129.9, 130.4, 136.4, 144.6, 150.3, 155.6, 156.8,
170.7, 170.9, 171.5; two carbon signals are obscured; m/z (ES) 793
(MHþ, 30%), found MHþ 793.3674; C41H53N4O12 requires 793.3660.
9-(S)-Benzyloxycarbonylamino-12-(S)-carbamoylmethyl-4-meth-
oxy-10,13-dioxo-2-oxa-11,14-diazatricyclo[15.2.2.13,7]docosa-1-
(20),3,5,7(22),17(21),18-hexaene-15-(S)-carboxylic acid methyl
ester 3. Peptide 23 (845 mg, 1.07 mmol) was dissolved in TFA/
CH2Cl2 (1:1, 30 mL) and stirred for 30 min at rt. The solvent was
removed under reduced pressure, the solid triturated with Et2O
(2ꢀ5 mL), and the solvent decanted, leaving a tan solid. The
sample was dried under vacuum then dissolved in dry DMF
(130 mL). iPr2NEt (1.38 g, 10.7 mmol) was added to the solution
and stirred for 10 min. The solution was poured into a dropping
funnel and slowly added to a stirred solution of HATU (1.63 g,
4.28 mmol) in dry DMF (200 mL) at 0 °C, over a period of 2 h.
The solution was stirred overnight at rt then poured into water
(500 mL) and extracted with EtOAc (3ꢀ200 mL). The organic
layer was washed with water (2ꢀ150 mL) and brine (2ꢀ150 mL),
dried over MgSO4, and the solvent removed under reduced
pressure to afford the crude compound. Flash chromatography
(CH2Cl2-4% MeOH/CH2Cl2) gave Z-OF4949-III-OMe 3
(393 mg, 60%) as a tan solid. Crystallization of a sample from
MeOH yielded the product 3 as a white solid: mp 257-260 °C
(MeOH); [R]20D þ42.1 (c=1.02, CHCl3); νmax (reflex) 3436 (w
sh, NH), 3327 (w sh, NH), 3287 (w sh, NH), 1763 (m sh, CdO),
1650 (s sh, CdO) cm-1; δH (400 MHz, CDCl3) 2.35-2.60 (3H,
m, βb, βb, βaR), 2.78 (1H, br d, J=13.5 Hz, βcR), 2.96 (1H, dd, J=
13.5, 4.0 Hz, βcS), 3.27 (1H, dd, J=13.0, 3.0 Hz, βaS), 3.76 (3H, s,
OMe), 3.88 (3H, s, OMe), 4.50-4.60 (2H, m, Rb, Rc), 4.79-4.90
(1H, m, Ra), 5.02 (1H, d, J=12.5 Hz, CH2-(Z)), 5.12 (1H, d, J=
12.5 Hz, CH2-(Z)), 5.68 (1H, d, J=7.0 Hz, NH), 5.82 (1H, d, J=
2.0 Hz, Hsh), 5.95 (1H, br s, NH), 6.42 (1H, br s, NH), 6.50 (1H,
d, J=8.0 Hz, Hd), 6.72 (1H, d, J=8.0 Hz, He), 6.82 (1H, d, J=
8.0 Hz, Hf), 7.00 (1H, dd, J=8.0, 2.0 Hz, Hg), 7.08 (1H, d, J=
8.0 Hz, Hh), 7.24 (1H, d, J=8.0 Hz, Hi), 7.26-7.36 (6H, m, Z þ
NH), 8.21 (1H, br d, J=8.5 Hz, NH); δC (100 MHz, CDCl3) 37.3
(βc), 38.6 (βa), 39.2 (βb), 48.3 (Rb), 52.5 (q), 53.5 (Ra), 53.6 (Rc),
55.8 (p), 66.7 (u), 111.4 (e), 115.6 (sh), 121.8 (f), 122.7 (g), 123.5
(d), 127.1 (m), 127.8 (ꢀ2, v), 128.0 (w), 128.4 (ꢀ2, z), 130.3 (i),
132.1 (h), 133.2 (o), 136.3 (y), 147.6 (j), 149.1 (k), 153.7 (n), 155.8
(s), 169.4 (CdO), 169.7 (CdO), 171.7 (r), 173.1 (x); m/z (ES) 619
(MHþ, 100%), found MHþ 619.2400; C32H35N4O9 requires
619.2404. Details of the assignment are included in the Support-
ing Information, together with the NMR data in CD3OD, and
the NMR spectra in CD3OD resulting from treatment with
NaHCO3. The ESI-MS of the NMR sample showed a single
mass ion at 644, corresponding to the Naþ adduct of the
trideuteromethyl ester 3a; found MNaþ 644.2391; C32H31D3N4-
O9Na requires 644.2409.
2-(S)-tert-Butoxycarbonylamino-3-[4-(3,5-diiodo-2-methoxy-
phenoxy)phenyl]propionic acid methyl ester 20. In some runs,
purification of compound 15 also allowed the isolation of the
diiodo product 20 as a white solid: mp 64-65 °C (Et2O/PE);
[R]20 þ25.0 (c=1, CHCl3); νmax (KBr disk) 3554 (s sh, NH),
D
2970 (w sh, ArH), 1734 (s sh, CdO), 1688 (s sh, CdO) cm-1; δH
(250 MHz, CDCl3) 1.42 (9H, s, C(CH3)3), 3.02 (1H, dd, J=14.0,
6.0 Hz, β), 3.12 (1H, dd, J=14.0, 6.0 Hz, β), 3.72 (3H, s, OMe),
3.84 (3H, s, OMe), 4.54-4.65 (1H, m, R), 5.01 (1H, d, J=8.0 Hz,
NH), 6.89 (2H, d, J=8.5 Hz, Ar), 7.11 (2H, d, J=8.5 Hz, Ar),
7.18 (1H, d, J=2.0 Hz, Ar), 7.85 (1H, d, J=2.0 Hz, Ar); δC
(125 MHz, CDCl3) 28.3, 37.7, 52.3, 54.5, 60.9, 80.0, 87.3, 94.0,
118.0, 130.0, 130.8, 131.6, 141.6, 149.6, 151.5, 155.1, 155.6,
172.3; m/z (FABþ) 654 (MHþ 7%), found MHþ 653.9834;
C22H26I2NO6 requires 653.9850.
2-(S)-(2-(S)-tert-Butoxycarbonylamino-3-carbamoylpropion-
ylamino)-3-[4-(5-iodo-2-methoxyphenoxy)phenyl]propionic acid
methyl ester 22. Compound 22 was synthesized following Gen-
eral Procedure 1. Deprotection of compound 15 (2.8 g,
5.31 mmol) was achieved with AcCl (2.08 g, 26.5 mmol) in
MeOH/THF (20 mL) and triturated with Et2O/PE (3ꢀ12 mL).
Peptide coupling was achieved with Boc-Asn-ONp (1.87 g, 5.31 mmol
and iPr2NEt (0.69 g, 5.31 mmol) in dry DMF (8 mL). The solution
was stirred for 60 h at rt, and then the solvent was removed under
reduced pressure. The crude material was triturated with Et2O (3ꢀ10
mL) and dried under vacuum to afford the product 22 (3.05 g, 90%)
as a white solid: mp 208-210 °C (EtOAc/PE); [R]20D þ9.0 (c=1.2,
CHCl3); νmax (film) 3433 (m sh, NH), 3329 (br m, NH), 2978 (w sh,
ArH), 1741 (s sh, CdO), 1687 (s sh, CdO), 1662 (s sh, CdO), 1645
(ssh, CdO) cm-1;δH (500MHz, CDCl3) 1.44(9H, s, C(CH3)3), 2.54
(1H, dd, J=16.0, 6.0 Hz, β1),2.92(1H,brd,J=16.0 Hz, β1), 3.01 (1H,
dd, J=14.0, 6.5 Hz, β2), 3.10 (1H, dd, J=13.5, 5.5 Hz, β2), 3.69 (3H, s,
OMe), 3.81 (3H, s, OMe), 4.43-4.50 (1H, m, R1), 4.77 (1H, q, J=
7.0 Hz, R2), 5.45(1H, brs, NH2), 5.81 (1H, br s, NH2), 6.04(1H, brd,
J=7.0 Hz, NH-R1), 6.75 (1H, d, J=8.5 Hz, Ar), 6.86 (2H, d, J=
8.5 Hz, Ar), 7.10 (2H, d, J=8.0 Hz, Ar), 7.22 (1H, d, J=2.0 Hz, Ar),
7.34 (1H, br d, J=5.5 Hz, NH-R2), 7.41 (1H, dd, J=9.0, 2.0 Hz, Ar);
δC (125 MHz, CDCl3) 28.3, 36.7, 37.3, 51.0, 52.3, 53.7, 56.1, 80.4, 82.0,
114.7, 117.4, 129.5, 130.5, 130.6, 133.6, 146.0, 151.5, 155.7, 156.4,
170.8, 171.4, 173.3; m/z (EI) 567(Mþ - tBuOH, 0.8%), found Mþ -
tBuOH 567.0498; C22H22IN3O7 requires 567.0503.
3-{4-[5-(2-(S)-Benzyloxycarbonylamino-2-tert-butoxycarbon-
ylethyl)-2-methoxyphenoxy]phenyl}-2-(S)-(2-(S)-tert-butoxycarbo-
nylamino-3-carbamoylpropionylamino)propionic acid methyl ester 23.
Compound 23 was synthesized following General Procedure 2. Zinc
activation and insertion were achieved using Zn (620 mg, 9.48 mmol)
and TMSCl (200 μL) in dry DMF (1 þ 3 mL) and Z-I-Ala-OtBu
(1.54 g, 3.8 mmol) to give zinc reagent 9. Coupling was performed
with the aryl iodide 22 (2.03 g, 3.16 mmol) with Pd2(dba)3 (87 mg, 95
μmol) and P(o-Tol)3 (115 mg, 380 μmol) in DMF (3 mL). The crude
product was purified by flash chromatography (100% CH2Cl2-5%
MeOH/CH2Cl2) and gave the product 23 (1.88 g, 75%) as a yellow
amorphous solid: mp 105-108 °C (THF/PE); [R]20D þ79.0 (c=0.5,
CHCl3); νmax (reflex) 3307 (m sh, NH), 1729 (br s, CdO), 1683 (s sh,
9-(S)-Benzyloxycarbonylamino-12-(S)-carbamoylmethyl-4-meth-
oxy-10,13-dioxo-2-oxa-11,14-diazatricyclo[15.2.2.13,7]docosa-1-
(20),3,5,7(22),17(21),18-hexaene-15-(S)-carboxylic acid 24.
Following the procedure of Boger,8 Z-OF4949-III-OMe 3 (40
mg, 0.065 mmol) and LiOH monohydrate (8 mg, 0.195 mmol)
were dissolved in THF/MeOH/H2O 3:1:1 (2 mL) and stirred at
rt for 4 h. HCl (1 M, 2 mL) was added and then water (3 mL),
and the aqueous solution was extracted with CHCl3/iPrOH 5:1
(5 ꢀ 2 mL). The organic fractions were collected, dried over
8286 J. Org. Chem. Vol. 74, No. 21, 2009

Nolasco et al.
JOCArticle
MgSO4, evaporated under reduced pressure, and triturated with
Et2O (2ꢀ2 mL) to afford the acid 24 (37 mg, 95%) as a white
(341 mg, 0.65 mmol) was achieved with AcCl (254 mg, 3.24 mmol)
in MeOH/THF (2.5 mL) and triturated with Et2O/PE (2ꢀ2 mL).
Peptide coupling with Boc-Tyr(OMe)-OH (191 mg, 0.65 mmol)
was achieved with iPr2NEt (84 mg, 0.65 mmol), HOBt (87 mg,
0.65 mmol), and EDCI (124 mg, 0.65 mmol) in dry DMF (1.7 mL).
The solution was stirred overnight at rt and partitioned between
EtOAc (10 mLꢀ3) and water. The combined organic phases
were washed with saturated citric acid, bicarbonate, water, and
brine. The solution was dried over MgSO4 and the solvent
removed under reduced pressure. The crude material was pur-
ified via flash chromatography (gradient: 70% Et2O/PE-100%
Et2O-100% EtOAc) to afford the dipeptide 26 (323 mg, 71%)
as a white solid: mp 135-136 °C (CH2Cl2/PE); [R]20D þ25.0 (c=
1.1, CHCl3); νmax (reflex) 3327 (br w, NH), 2949 (br w, Ar-H),
flaky solid: mp 142-145 °C (MeOH); [R]20 þ57.1 (c=0.28,
D
CH3OH) and [R]20D þ31.2 (c=0.56, CH3OH), lit.8 [R]22D -87
(c=0.27, CH3OH); νmax (reflex) 3292 (br w, OH and NH), 2931
(br w, Ar-H), 1651 (br s, CdO) cm-1; δH (400 MHz, CD3OD)
2.53 (1H, dd, J=15.5, 8.5 Hz, β), 2.59-2.70 (2H, m, β), 2.82 (1H,
dd, J=14.0, 1.0 Hz, β), 2.99 (1H, dd, J=14.0, 6.0 Hz, β), 3.38
(1H, dd, J=13.0, 3.5 Hz, β), 3.84 (3H, s, OMe), 4.43 (1H, dd, J=
6.0, 1.5 Hz, R), 4.70 (1H, dd, J=12.5, 3.5 Hz, R), 4.79 (1H, dd, J=
8.5, 5.0 Hz, R), 5.02 (1H, d, J=12.5 Hz, CH2-(Z)), 5.14 (1H, d,
J=12.5 Hz, CH2-(Z)), 5.87 (1H, d, J=2.0 Hz, Hsh), 6.46 (1H,
dd, J=8.0, 2.0 Hz, Ar), 6.78 (1H, d, J=8.0 Hz, Ar), 6.84 (1H, dd,
J=8.0, 2.5 Hz, Ar), 6.97 (1H, dd, J=8.0, 2.5 Hz, Ar), 7.18 (1H,
dd, J=8.0, 2.0 Hz, Ar), 7.28-7.40 (6H, m, Ar); 6 exchangeable
protons; δC (125 MHz, CD3OD) 38.3, 39.6, 40.2, 50.0, 54.9,
55.1, 56.6, 67.6, 113.0, 117.2, 122.9, 123.4, 124.9, 129.1, 129.5,
131.0, 131.6, 133.2, 133.8, 135.5, 138.2, 149.2, 150.5, 155.2,
157.3, 171.2, 171.9, 174.2, 174.5; m/z (ES) 627 (MNaþ 100%),
found MNaþ 627.2039; C31H32N4O9Na requires 627.2067.
OF4949-III, 1. Following the procedure described by Boger,8
Z-OF4949-III-OH 24 (37 mg, 61.2 mmol) was dissolved in
MeOH (10 mL) and Pd/C 10% (10 mg) was added to the stirred
solution. The flask was evacuated and filled with H2 three times
and then stirred overnight under hydrogen (1 atm.). The reac-
tion was not complete by TLC analysis, so the suspension was
filtered through Celite/glass wool and the solvent removed
under reduced pressure. The crude material was redissolved in
MeOH (10 mL), and Pd/C 10% (10 mg) was added. The flask
was evacuated and filled with hydrogen (ꢀ3) and stirred under
hydrogen overnight. The suspension was filtered through Celite/
glass wool and the solvent removed under reduced pressure to
give OF4949-III 1 (27 mg, 95%) as a white solid: mp 218-224 °C
(dec.) (lit. mp 219-225 °C dec., natural: 217-225 °C dec.);7 δH
(500 MHz, D2O) 2.48 (1H, dd, J=15.5, 10.0 Hz, βb), 2.55 (1H, t,
J=13.0 Hz, βa), 2.76 (1H, dd, J=15.5, 4.0 Hz, βb), 2.97 (1H, dd,
J=15.5, 6.0 Hz, βc), 3.05 (1H, dd, J=15.0, 2.0 Hz, βc), 3.29 (1H,
dd, J=13.0, 3.5 Hz, βa), 3.82 (3H, s, OMe), 4.14 (1H, dd, J=6.0,
2.0 Hz, Rc), 4.36 (1H, dd, J=12.5, 3.5 Hz, Ra), 4.73 (1H, dd,
J=10.0, 4.0 Hz, Rb), 5.77 (1H, d, J=2.0 Hz, Hsh), 6.75 (1H,
dd, J=8.0, 2.0 Hz, Hd), 6.82 (1H, dd, J=8.0, 2.5 Hz, Hf), 6.96
(1H, d, J=8.5 Hz, He), 6.97 (1H, dd, J=8.0, 2.5 Hz, Hg), 7.14
(1H, dd, J=8.5, 2.0 Hz, Hh), 7.37 (1H, dd, J=8.5, 2.0 Hz, Hi); δC
(125 MHz, D2O) 35.2 (βc), 38.7 (βb), 38.8 (βa), 49.1 (Rb), 52.4
(Rc), 55.8 (OCH3), 56.8 (Ra), 112.3 (e), 115.1 (sh), 115.8, 121.4 (f),
122.2 (g), 124.3 (d), 124.6, 130.7 (i), 131.9 (h), 135.8, 147.8, 148.8,
152.2, 167.4, 170.0, 174.2.
1735 (m sh, CdO), 1685 (m sh, CdO), 1654 (m sh, CdO) cm-1
H (500 MHz, CDCl3) 1.39 (9H, s, C(CH3)3), 2.91-3.06 (4H, m,
;
δ
β), 3.64 (3H, s, OMe), 3.75 (3H, s, OMe), 3.79 (3H, s, OMe),
4.22-4.33 (1H, br m, R), 4.73 (1H, dd, J = 13.0, 6.0 Hz, R),
4.89-4.99 (1H, br m, NH), 6.31 (1H, d, J=7.5 Hz, NH), 6.73
(1H, d, J=8.5 Hz, Ar), 6.78-6.82 (4H, m, Ar), 6.92 (2H, d, J=
8.5 Hz, Ar), 7.09 (2H, d, J=8.5 Hz, Ar), 7.18 (1H, d, J=2.0 Hz,
Ar), 7.40 (1H, dd, J=8.5, 2.0 Hz, Ar); δC (125 MHz, CDCl3)
28.2, 37.3 (2 carbons), 52.2, 53.3, 55.2, 55.8, 56.0, 80.2, 81.9,
114.0, 114.6, 117.4, 128.3, 129.2, 130.3, 130.5, 133.5, 140.0,
146.0, 151.4, 155.3, 156.3, 158.6, 170.8, 171.3; m/z (ES) 705
(MHþ, 50%), found MHþ 705.1688; C32H38N2O8I requires
705.1673.
3-{4-[5-(2-(S)-Benzyloxycarbonylamino-2-tert-butoxycarbon-
ylethyl)-2-methoxyphenoxy]phenyl}-2-(S)-[2-(S)-tert-butoxycar-
bonylamino-3-(4-methoxyphenyl)propionylamino]propionic acid
methyl ester 27. Compound 27 was synthesized following Gen-
eral Procedure 2. Zinc activation and insertion were achieved
using Zn (42 mg, 0.64 mmol) and TMSCl (10 μL) in dry DMF
(100 þ 200 μL) and Z-I-Ala-OtBu (104 mg, 0.25 mmol) to give
zinc reagent 9. Coupling was performed with the aryl iodide 26 (150
mg, 0.21 mmol) with Pd2(dba)3 (6 mg, 6.4 μmol) and P(o-Tol)3 (8
mg, 26 μmol). The crude material was purified via flash chromatog-
raphy (gradient: 40-70% EtOAc/ihexane) to afford the product 27
(146 mg, 80%) as a white solid: mp 70-74 °C (Et2O); [R]20D þ32.2 (c
=1.0, CHCl3);νmax (solution 0.8 g/mL CHCl3) 3022 (s sh, NH), 1716
(br s, CdO), 1678 (br m, CdO) cm-1; δH (400 MHz, CDCl3) 1.36
(9H, s, C(CH3)3), 1.38 (9H, s, C(CH3)3), 2.91-3.02 (6H, m, β), 3.63
(3H, s, OMe), 3.74 (3H, s, OMe), 3.77 (3H, s, OMe), 4.23-4.33 (1H,
br m, R),4.41-4.46 (1H, m, R), 4.67-4.78 (1H, br m, R), 5.01 (1H, br
d, NH), 5.05 (2H, s, CH2-(Z)), 5.25 (1H, br d, NH), 6.33 (1H, d,
J=7.5 Hz, NH), 6.75-6.82 (5H, m, Ar), 6.84-6.90 (4H, m, Ar),
7.04-7.10 (2H, m, Ar), 7.25-7.35 (5H, m, Ar); δC (100 MHz,
CDCl3) 27.9, 28.2, 37.2, 37.3, 37.4, 52.2, 53.4, 55.12, 55.15, 55.8,
55.9, 66.8, 80.1, 82.3, 112.6, 114.0, 117.0, 122.3, 125.4, 128.0, 128.1,
128.3, 128.5, 128.9, 129.5, 130.2, 130.3, 131.0, 136.3, 144.5, 150.4,
155.5, 157.0, 158.6, 170.5, 170.8, 171.4; m/z (ES) 856 (MHþ, 100%),
found MHþ 856.4041; C47H58N3O12 requires 856.4021.
9-(S)-Benzyloxycarbonylamino-4-methoxy-12-(S)-(4-methox-
ybenzyl)-10,13-dioxo-2-oxa-11,14-diazatricyclo[15.2.2.13,7]doc-
osa-1(20),3,5,7(22),17(21),18-hexaene-15-(S)-carboxylic acid methyl
ester 25. Compound 27 (135 mg, 0.16 mmol) was dissolved in
TFA (2.5 mL) and stirred for 1 h at rt. The solvent was removed
under reduced pressure, and the residual solid was triturated
with Et2O (2ꢀ2 mL) and dried under vacuum. The solid was
dissolved in dry DMF (12 mL), and iPr2NEt (205 mg, 1.59 mmol)
was added under nitrogen. The solution was stirred for 10 min
then poured into a dropping funnel and slowly added to a stirred
solution of HATU (240 mg, 0.63 mmol) in dry DMF (19 mL) at
0 °C. The mixture was stirred overnight at rt under nitrogen. The
solution was poured into water (50 mL) and extracted with Et2O
(2ꢀ20 mL) and EtOAc (20 mL). The combined organic layers
were washed with water (50 mL) and brine (50 mL), dried over
MgSO4, and the solvent was removed under reduced pressure.
The sample was dissolved in 0.1 N aqueous HCl, and optical
rotation, NMR, and accurate mass of the hydrochloride salt
were recorded: [R]20 -26.5 (c = 1.1, 0.1 N HCl) and [R]20
D
D
-30.0 (c=0.5, 0.1 N HCl), lit. [R]30D -35 (c=1.4, 1 N HCl),7
[R]30D -34 (c=1.0, 0.1 N HCl),8 [R]27D -38.2 (c=1.06, 0.1 N
HCl).10 OF4949-III HCl: δH (500 MHz, D2O) 2.45-2.56 (1H,
3
m, β), 2.57-2.75 (2H, m, β), 2.94-3.11 (2H, m, β), 3.35 (1H, br
d, J=11.0 Hz, β), 3.81 (3H, s, OMe), 4.14 (1H, br d, J=3.5 Hz, R),
5.74 (1H, br s, Hsh), 6.75 (1H, br d, J=7.5 Hz, Ar), 6.83 (1H, br
d, J=8.0 Hz, Ar), 6.96 (2H, br d, J=8.0 Hz, Ar), 7.13 (1H, br d,
J=7.0 Hz, Ar), 7.36 (1H, br d, J=7.0 Hz, Ar), two R protons
not observed, presumably located under the HOD peak
4.66-4.76, together with 7 exchangeable protons; δC (125 MHz,
D2O) 35.1, 37.6, 38.5, 49.0, 52.4, 54.2, 55.8, 112.3, 115.0, 121.5,
122.3, 124.3, 124.5, 130.7, 132.0, 134.7, 147.8, 148.7, 152.4,
167.4, 170.4, 173.9, 174.4; m/z (ES) 471 (MHþ, 75%), found
MHþ 471.1882; C23H27N4O7 requires 471.1880.
2-(S)-[2-(S)-tert-Butoxycarbonylamino-3-(4-methoxyphenyl)-
propionylamino]-3-[4-(5-iodo-2-methoxyphenoxy)phenyl]propio-
nic acid methyl ester 26. Compound 26 was synthesized follow-
ing General Procedure 1. Deprotection of compound 15
J. Org. Chem. Vol. 74, No. 21, 2009 8287

Nolasco et al.
JOCArticle
The crude solid was purified via flash chromatography
(gradient: 5-10% acetone/CH2Cl2) to afford protected iso-K-
13 25 (52 mg, 48%) as a white solid: mp 132-133 °C (MeOH);
[R]20D þ35.4 (c=0.8, CHCl3); νmax (solution 0.8 g/mL CHCl3)
3422 (m sh, NH), 3018 (s sh, NH), 2957 (w sh, Ar-H), 1740,
1715, and 1673 (br m, CdO) cm-1; δH (400 MHz, CDCl3) 2.41
(1H, t, J=13.0 Hz, βa), 2.70 (1H, dd, J=14.0, 2.0 Hz, βc), 2.77
(1H, dd, J=14.0, 7.5 Hz, βb), 2.91 (1H, dd, J=14.0, 4.5 Hz, βb),
3.11 (1H, dd, J=14.5, 6.0 Hz, βc), 3.31 (1H, dd, J=13.5, 4.0 Hz,
βa), 3.75 (3H, s, OMe), 3.82 (3H, s, OMe), 3.88 (3H, s, OMe),
4.42-4.48 (2H, m, Rb, Rc), 4.85-4.91 (1H, m, Ra), 5.09 (1H, d,
J=12.5 Hz, CH2-(Z)), 5.18 (1H, d, J=12.5 Hz, CH2-(Z)), 5.52
(1H, d, J=7.5 Hz, NH), 5.84 (1H, d, J=2.0 Hz, Hsh), 5.86 (1H, d,
J=10.0 Hz, NH), 6.44 (1H, d, J=8.0 Hz, NH), 6.51 (1H, dd, J=
8.0, 2.0 Hz, Hd), 6.73 (1H, d, J=8.5 Hz, He), 6.79 (2H, br d, J=
8.5 Hz, Ar), 6.87 (2H, br s, Ar), 7.05 (1H, d, J=8.5 Hz, Ar), 7.08
(2H, d, J=9.0 Hz, Ar), 7.27 (1H, d, J=8.5 Hz, Ar), 7.35-7.39
(5H, m, Ar); δC (100 MHz, CDCl3) 37.2, 38.4, 39.1, 52.7, 53.1
(2 carbons), 54.1, 55.2, 55.9, 66.7, 111.5, 114.2, 115.6, 121.7,
123.1, 123.8, 127.2, 127.4, 128.0, 128.1, 128.5, 130.4, 130.5,
131.8, 132.5, 136.5, 147.8, 149.1, 154.2, 155.6, 158.8, 168.6,
169.2, 171.5; m/z (ES) 704 (MNaþ, 100%), found MNaþ
704.2584; C38H39N3O9Na requires 704.2584.
2-(S)-tert-Butoxycarbonylamino-3-[4-(5-iodo-2-methoxyphe-
noxy)phenyl]propionic acid 13. Lithium hydroxide monohydrate
(312 mg, 7.43 mmol) was added in one portion to a rapidly
stirred solution of the methyl ester 15 (1.8 g, 3.41 mmol) in a
mixture of THF (20 mL) and water (5 mL) at rt. The reaction
was stirred overnight, and the solvents were removed under
reduced pressure. The resulting white solid was dissolved in
water (40 mL) and acidified with citric acid (10% aqueous
solution) until a white precipitate appeared. Et2O (20 mL) was
added, and the phases were separated. The aqueous layer was
extracted with Et2O (2 ꢀ 20 mL), and the combined organic
fractions were washed with saturated brine (20 mL), dried over
Na2SO4, and filtered. The solvent was removed under reduced
pressure to give the acid 13 (1.75 g, 99%) as a white solid: mp
61-64 °C; [R]20D þ30.8 (c=1.0, CHCl3); νmax (KBr disk) 3322
(CO2H), 1717 (CdO), 1576, 1506, 1491 (Ar), 1223 (C-N), 1166
(C-O) cm-1; δH (500 MHz, CDCl3) 1.33 (1 H, br s, CO2H), 1.43
(9 H, s, C(CH3)3), 3.04 (1 H, dd, J=14.0, 6.5 Hz, β), 3.17 (1 H,
dd, J=14.0, 5.0 Hz, β), 3.80 (3 H, s, OMe), 4.53-4.63 (1 H, br m,
R), 4.96 (1 H, br d, J=8.0 Hz, NH), 6.74 (1 H, d, J=9.0 Hz, Ar),
6.87 (2 H, br d, J=8.5 Hz, Ar), 7.12 (2 H, br d, J=8.0 Hz, Ar),
7.23 (1 H, br s, Ar), 7.41 (1 H, dd, J = 8.5, 2.0 Hz, Ar); δC
(125 MHz, CDCl3) 28.3, 37.0, 54.3, 56.1, 80.4, 81.9, 114.7, 117.5,
129.5, 130.4, 130.6, 133.6, 146.0, 151.5, 155.5, 156.5, 176.2; m/z
(EIþ) 513 (3%, Mþ), 457 (3, Mþ - C4H8), 396 (9, Mþ - C4H8 -
CO2 - NH3), 339 (100, ArCH2þ), found Mþ 513.0666; C21H24-
N1O6I requires 513.0648.
OMe), 3.75 (3 H, s, OMe), 3.78 (3 H, s, OMe), 3.80-3.86 (1 H,
m, β-OH), 3.87-3.91 (1 H, m, β-OH), 4.23-4.30 (1 H, m, R),
4.56 (1 H, dt, J=7.5, 3.5 Hz, R), 4.68 (1 H, q, J=7.0 Hz, R), 4.96
(1 H, br d, J=6.5 Hz, NH), 6.54 (1 H, br d, J=7.5 Hz, NH), 6.75
(1 H, d, J=9.0 Hz, Ar), 6.79 (2 H, br d, J=8.5 Hz, Ar), 6.87 (2 H,
br d, J=8.5 Hz, Ar), 7.02 (2 H, br d, J=8.5 Hz, Ar), 7.11 (3 H, br
d, J=8.5 Hz, Ar and NH), 7.22 (1 H, d, J=2.0 Hz, Ar), 7.42 (1 H,
dd, J=8.5, 2.0 Hz, Ar); δC (125 MHz, CDCl3) 28.2, 36.8, 37.0,
52.6, 54.1, 55.0, 55.2, 56.0, 62.7, 80.9, 81.9, 114.1, 114.7, 117.6,
127.9, 129.5, 130.4, 130.5, 130.7, 133.7, 145.8, 151.5, 155.6,
156.5, 158.7, 170.4, 170.7, 171.4, one carbon signal obscured;
m/z (EIþ) 775 (2%, Mþ - CH3 - H), 339 (100, ArCH2þ), found
M
þ - CH3 - H, 775.1572; C34H38N3O10I requires 775.1602.
2-(S)-[2-(S)-{2-(S)-tert-Butoxycarbonylamino-3-[4-(5-iodo-2-
methoxyphenoxy)phenyl]propionylamino}-3-(4-methoxyphenyl)-
propionylamino]-3-iodopropionic acid methyl ester 28. (PhO)3-
PMeI (11.14 g, 24.6 mmol) was added to a stirred solution of the
alcohol 12 (9.75 g, 12.3 mmol) in DMF (40 mL) at rt under
nitrogen. After 1 h, the reaction was quenched by the slow
addition of MeOH (2 mL) and was stirred for a further 30 min.
The reaction was diluted with water (200 mL) resulting in a
precipitate. CH2Cl2 (200 mL) was added, and the aqueous layer
was separated and extracted with CH2Cl2 (2 ꢀ 100 mL). The
combined organic fractions were washed with aqueous sodium
sulfite (10% in H2O, 100 mL), water (100 mL), and brine
(100 mL), dried over Na2SO4, and filtered. The solvent was
removed under reduced pressure to give a crude solid which was
purified by recrystallization from cold Et2O (100 mL, 0 °C). The
precipitate was filtered, washed with cold Et2O, and dried to give
the diiodide 28 (8.1 g, 73%) as a white solid: mp 162 °C (dec.)
(EtOAc); [R]20 þ10.0 (c=0.6, CHCl3); found C 46.57%; H
D
4.40%; N 4.53%; C35H41N3O9I2 requires C 46.63%; H 4.58%;
N 4.66%; νmax (KBr disk) 1730, 1690, 1648, (CdO), 1530, 1512,
1492 (Ar), 1248, 1223 cm-1; δH (500 MHz, CDCl3) 1.38 (9 H, s,
C(CH3)3, 2.93 (1 H, dd, J=14.0, 7.0 Hz, β), 2.99-3.07 (3 H, m,
β), 3.49 (1 H, dd, J=10.5, 4.5 Hz, β), 3.53 (1 H, dd, J=10.5,
4.5 Hz, β), 3.77 (6 H, s, OMe), 3.79 (3 H, s, OMe), 4.31 (1 H, br d,
J=6.0 Hz, R), 4.60 (1 H, q, J=7.0 Hz, R), 4.67 (1 H, dt, J=7.5,
4.5 Hz, R), 4.91 (1 H, br s, NH), 6.40 (1 H, br d, J=6.0 Hz, NH),
6.64 (1 H, br s, NH), 6.74 (1 H, d, J=8.5 Hz, Ar), 6.81 (2 H, br d,
J=8.5 Hz, Ar), 6.88 (2 H, br d, J=8.0 Hz, Ar), 7.02 (2 H, br d, J=
8.0 Hz, Ar), 7.14 (2 H, br d, J=8.0 Hz, Ar), 7.24 (1 H, br d, J=
2.0 Hz, Ar), 7.42 (1 H, dd, J=8.5, 2.0 Hz, Ar); δC (125 MHz,
CDCl3) 7.0, 28.4, 37.8, 38.0, 53.0, 53.2, 54.5, 55.3, 56.1, 80.7,
82.0, 114.4, 114.8, 117.7, 127.9, 129.6, 130.4, 130.7, 131.0, 133.8,
147.4, 152.9, 155.0, 157.6, 159.6, 169.3, 170.5, 171.2, one carbon
signal obscured; m/z (EIþ) 773(2%, Mþ - HI), 339 (10, ArCH2þ),
128 (100, HI), found Mþ - HI, 773.1787; C35H40N3O9I requires
773.1809.
15-(S)-tert-Butoxycarbonylamino-4-methoxy-12-(S)-(4-meth-
oxybenzyl)-11,14-dioxo-2-oxa-10,13-diazatricyclo[15.2.2.13,7]-
docosa-1(20),3,5,7(22),17(21),18-hexaene-9-(S)-carboxylic acid
methyl ester 10. Iodine (4 mg, 0.016 mmol) was added to a
rapidly stirred suspension of zinc (24 mg, 0.38 mmol) in DMF
(0.5 mL) at rt under nitrogen. After 30 min, a solution of the
diiodide 28 (300 mg, 0.33 mmol) in DMF (0.5 mL) was added,
and the reaction was stirred for a further 30 min. The solution of
the organozinc iodide 11 was then added dropwise to a stirred
solution of Pd2dba3 (9.2 mg, 3 mol %, 0.01 mmol) and P(o-Tol)3
(12.2 mg, 12 mol %, 0.04 mmol) in THF (140 mL), and the
reaction was heated at 60 °C and stirred for 16 h. The solvent was
removed under reduced pressure to give a crude oil which was
dissolved in EtOAc (25 mL), washed with water (2ꢀ10 mL) and
saturated brine (10 mL), dried over Na2SO4, and filtered. The
solvent was removed under reduced pressure to give a crude
solid which was purified by column chromatography [silica,
CH2Cl2-acetone, 10:1] to give the macrocyclic peptide 10 (75 mg,
35%): mp 247-248 °C (lit. mp 245-246 °C);7 Rf[CH2Cl2-acetone,
2-(S)-[2-(S)-{2-(S)-tert-Butoxycarbonylamino-3-[4-(5-iodo-2-
methoxyphenoxy)phenyl]propionylamino}-3-(4-methoxyphenyl)-
propionylamino]-3-hydroxypropionic acid methyl ester 12. HOBt
(555 mg, 4.11 mmol), iPr2NEt (650 μL, 3.72 mmol), and EDCI
hydrochloride (695 mg, 3.63 mmol) were added to a rapidly
stirred solution of the acid 13 (1.70 g, 3.31 mmol) and
H-Tyr(OMe)-Ser-OMe HCl 14 (1.18 g, 3.55 mmol) in DMF
3
(16 mL) at rt under nitrogen. The reaction was stirred overnight
and then poured into water (200 mL). The resulting white
precipitate was filtered and washed with water (200 mL), dried
under vacuum, and gave, without the need for further purifica-
tion, the tripeptide 12 (2.46 g, 94%) as a white solid (a sample
was recrystallized): mp 192-193 °C (CHCl3); [R]20D -14.0 (c=
1.0, acetone); found
C 52.93%; H 5.31%; N 5.28%;
C35H42N3O10I requires C 53.10%; H 5.35%; N 5.31%; νmax
-
(KBr disk) 3314 (OH), 1743, 1730, 1675, 1645 (CdO), 1512,
1493 (Ar), 1250, 1224 cm-1; δH (500 MHz, CDCl3) 1.34 (9 H, s,
C(CH3)3), 2.85-3.10 (4 H, m, β), 3.42 (1 H, brs, OH), 3.74 (3 H, s,
8288 J. Org. Chem. Vol. 74, No. 21, 2009

Nolasco et al.
JOCArticle
10:1] 0.3; [R]20 þ41.3 (c = 0.9, CH2Cl2); found C 64.85%; H
4.40-4.48 (2 H, m, R), 6.38 (1 H, d, J=2.0 Hz, Ar), 6.57-6.62
(2 H, m, Ar), 6.66 (1 H, dd, J=8.0, 2.5 Hz, Ar), 6.73 (1 H, dd, J=
8.0, 2.0 Hz, Ar), 6.80 (1 H, d, J=8.0 Hz, Ar), 6.93-6.99 (3 H,
m, Ar), 7.04 (1 H, dd, J=8.5, 2.5 Hz, Ar), 7.29 (1 H, dd, J=8.0,
2.0 Hz, Ar); δC (125.7 MHz, CD3OD) 22.4, 36.6, 38.7, 39.1, 54.3,
55.9, 57.3, 115.8, 117.5, 118.8, 120.8, 122.1, 125.4, 128.2, 130.7,
131.2, 132.0 (2 carbons, assigned from 1H-13C correlation),
132.8, 147.5, 147.8, 157.0, 158.2, 171.5, 172.2, 172.9, 175.5. The
NMR data are closely comparable with that reported by Evans.
In the 1H spectrum, we observe close overlap of two R-proton
signals, where Evans reports resolved signals.7 In the 13C
spectrum, we note two clearly resolvable signals at 147.5 and
147.9 and a slightly different chemical shift for one of the
R-carbon signals at 54.3 (this rather broad signal is assigned
through 1H-13C correlation). In addition, the shift for the
carboxylic acid carbon, which we note at 175.5, was reported
by Evans at 177.8.7 These minor differences are most likely
accounted for by chemical shift concentration dependence.
D
6.19%; N 6.46%; C35H41N3O9 requires C 64.90%; H 6.38%; N
6.49%; δH (500 MHz, CDCl3) 1.42 (9 H, s, C(CH3)3), 2.64 (1 H,
dd, J=13.0, 10.0 Hz, β), 2.74 (1 H, t, J=12.0 Hz, β), 2.80 (1 H, dd,
J=14.5, 4.5 Hz, β), 3.07 (1 H, dd, J=12.0, 5.0 Hz, β), 3.17 (1 H, br
dd, J=13.5, 3.5 Hz, β), 3.21 (1 H, dd, J=15.0, 4.5 Hz, β), 3.62 (3 H,
s, OMe), 3.67 (3 H, s, OMe), 3.81 (3 H, s, OMe), 3.81-3.87 (1 H, br
m, R), 4.07-4.16 (1 H, br m, R), 4.26-4.31 (1 H, m, R), 5.24 (1 H,
br d, J=7.5 Hz, NH), 5.41 (1 H, d, J=4.5 Hz, NH), 6.00 (1 H, br s, Ar),
6.14 (1 H, br d, J=5.5 Hz, NH), 6.44 (1 H, dd, J=8.5, 2.0 Hz, Ar),
6.68 (2 H, br d, J=8.5 Hz, Ar), 6.71 (2 H, br dd, J=8.0, 2.5 Hz,
Ar), 6.96 (2 H, d, J=8.5 Hz, Ar), 7.04 (2 H, br dt, J=8.0, 2.5 Hz,
Ar), 7.22 (1 H, br s, Ar); δC (125 MHz, CDCl3) 28.4, 29.3, 35.2,
38.6, 39.5, 52.5, 53.7, 55.1, 56.0, 56.4, 57.4, 79.8, 112.1, 113.9, 118.0,
121.2, 122.5, 122.7, 127.9, 128.3, 129.8, 130.1, 131.4, 132.5, 148.5,
148.8, 155.0, 155.3, 158.6, 169.9, 170.6; m/z (EIþ) 647 (2%, Mþ),
575 (5, MHþ - BuO), 547 (30, Mþ - C4H8 - CO2), 298 (100,
t
ArCH2þ), found Mþ, 647.2831; C35H41N3O9 requires 647.2843.
K-13, 2. Following the literature procedure described by
Evans,7 the Boc-protected derivative 10 (155 mg, 0.24 mmol),
thioanisole (850 μL), and TFA (6 mL) in CH2Cl2 (17.5 mL),
followed by Ac2O (2.1 mL) in a solvent mixture of CH2Cl2/
pyridine (5:1, 21 mL), gave after purification by column chro-
matography [silica, CH2Cl2-MeOH, 98:2 to 95:5] the acetyl
derivative 29 (124 mg, 88%). Again following the literature
procedure described by Evans,7 the methyl-protected derivative
29 (60 mg, 0.1 mmol), AlBr3 (1.0 M solution in dibromoethane,
2.97 mL, 2.97 mmol), and EtSH (4 mL) in CH2Cl2 (11 mL) gave
after purification by column chromatography [silica,
EtOAc-CH3CO2H, 93:7] K-13 2 (46 mg, 83%) as a pale yellow
solid: mp 265-270 °C (dec.) (MeOH/Et2O), lit.2 260-270 °C
(dec.);[R]20D-6.6 (c=1.4, MeOH), lit.7[R]20D-6.5 (c=0.46, MeOH),
natural3 [R]20D -3.4 (c=0.6, MeOH); δH (500 MHz, CD3OD)
2.03 (3 H, s, OAc), 2.77 (1 H, t, J=12.0 Hz, βa), 2.85 (1 H, dd, J=
13.5, 5.0 Hz, βb), 2.91 (1 H, dd, J=15.5, 9.0 Hz, βc), 2.95 (1 H,
dd, J=13.0, 6.0 Hz, βb), 3.01 (1 H, dd, J=12.5, 5.5 Hz, βa), 3.17
(1 H, dd, J=15.5, 2.0 Hz, βc), 4.17 (1 H, t, J=5.5 Hz, Rb),
Acknowledgment. We thank Dr. R.J. Butlin and Dr. P.D.
Kemmitt (Astra Zeneca, Alderley Park, UK) for helpful
discussions, Professors J. Zhu and D.H. Rich for copies of
NMR spectra, and Professors D.L. Boger and A.J. Pearson
for helpful discussion relating to compound 3. We also thank
Astra Zeneca for partial funding of a studentship (L.N.), and
the Spanish Ministerio de Educacion y Cultura and the
EU for a Marie Curie fellowship, HPMF-CT-1999-00050
(both to M.P.G.).
ꢀ
Supporting Information Available: Data comparison for
Z-OF4949-III-OMe 3 and NMR structure assignment of
Z-OF4949-III-OMe 3; data comparison and NMR structure
assignment for OF4949-III 1; supporting NMR spectra for
structural assignments; H and 13C NMR spectra for all com-
1
pounds. This material is available free of charge via the Internet
at http://pubs.acs.org.
J. Org. Chem. Vol. 74, No. 21, 2009 8289