Total synthesis of exochelin MN and analogues.

Article abstract of DOI:10.1021/jo0256078

The first total synthesis of exochelin MN is described along with rationally designed analogues. The required L-threo-beta-hydroxyamino acid components were constructed using either Sharpless asymmetric aminohydroxylation reactions or an aldol reaction of imidazolidinone 19. A new concise procedure for the preparation of the constituent six-membered cyclic hydroxamate was developed. In addition, a plausible mechanism for exochelin MN-mediated iron(III) transport was proposed. Biological studies of these compounds will be used to evaluate this hypothesis.

Full text of DOI:10.1021/jo0256078

Tota l Syn th esis of Exoch elin MN a n d An a logu es
Li Dong and Marvin J . Miller*
Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall,
Notre Dame, Indiana 46556-5670
Marvin.J .Miller.2@nd.edu
Received February 11, 2002
The first total synthesis of exochelin MN is described along with rationally designed analogues.
The required L-threo-â-hydroxyamino acid components were constructed using either Sharpless
asymmetric aminohydroxylation reactions or an aldol reaction of imidazolidinone 19. A new concise
procedure for the preparation of the constituent six-membered cyclic hydroxamate was developed.
In addition, a plausible mechanism for exochelin MN-mediated iron(III) transport was proposed.
Biological studies of these compounds will be used to evaluate this hypothesis.
In tr od u ction
Exochelins are a class of extracellular siderophores
(low-molecular mass iron chelators) isolated from a
variety of microorganisms belonging to the genus Myco-
bacteria.1-3 They play a crucial role in the iron(III)
assimilation and transport process of mycobacteria.4-6
Exochelins are responsible for the acquisition of iron(III)
from the environment to form an iron(III)-exochelin
complex, which can be recognized by receptors in the cell
wall. The sequestered iron is then further transferred and
utilized by the mycobacteria.7-9 In 1996, a new compound
in this family, exochelin MN (1a , Figure 1), was isolated
by Ratledge and co-workers from culture broth of M.
neoaurum.10 The molecule possesses impressive biological
properties. It can transport iron not only into M. neoau-
rum but also into M. leprae cells, which are causative
agents of leprosy.10 The fact that other exochelins do not
mediate iron uptake in M. leprae suggests a specific
uptake mechanism involving exochelin MN. Since the
exochelin produced by M. leprae cannot be directly
identified, studies concerning the mode of action of
exochelin MN could advance our understanding of the
iron acquisition mechanisms of this species and also
facilitate the development of novel antileprosy and an-
timycobacterial agents in the future.
F IGURE 1.
tide backbone characterized by two hydroxamic acid units
and an unusual amino acid moiety, threo-â-hydroxy-L-
histidine, which has only been reported as a key compo-
nent of pseudobactin PF244.11 Such challenging struc-
tural novelty combined with exciting biological activity
makes exochelin MN an attractive target for total
synthesis.
Exochelin MN coordinates iron(III) octahedrally with
its two cis-hydroxamate groups in addition to the hydroxy
and imidazole nitrogen of the â-hydroxyhistidine.10 As it
is rare that nitrogen is involved in the chelation of iron-
(III) by siderophores, studies of the â-hydroxyhistidine
moiety will provide insights into the function of this
structural motif. Based on the unique properties of the
imidazole functionality, we propose a novel mechanism
for the reversible coordination of iron(III) by exochelin
MN. We suggest that the iron binding ability of exochelin
MN is strongly influenced by environmental pH. At
neutral pH (∼7.0), exochelin MN, a hexadentate ligand,
should be able to acquire iron effectively from the growth
media, while under slightly acidic conditions (pH < 6.5)
protonation of the imidazole nitrogen of â-hydroxyhisti-
dine would drastically reduce its affinity for iron (tet-
radentate ligand) and subsequently trigger the release
of iron. In this way, the coordination of iron(III) by
exochelin MN could be regulated by subtle changes of
pH within the physiological range. A pH-dependent iron-
The structure of exochelin MN has been fully eluci-
dated by spectroscopic techniques as well as derivatiza-
tion and GC analysis.10 Key features include a hexapep-
(1) Macham, L. P.; Ratledge, C. J . Gen. Microbiol. 1975, 89, 379-
382.
(2) Barclay, R.; Ratledge, C. J . Bacteriol. 1983, 153, 1138-1146.
(3) Sharman, G. J .; Williams, D. H.; Ewing, D. F.; Ratledge, C.
Biochem. J . 1995, 305, 187-796.
(4) Raymond, K. N.; Muller, G. I.; Matzanke, B. F. Top. Curr. Chem.
1984, 123, 49-102.
(5) Winkelmann, G. Biotechnology 1986, 4, 215-243.
(6) Winkelmann, G. Handbook Microb. Iron Chelates (Siderophores)
1991, 65-105.
(7) Ratledge, C. Nature 1964, 203, 428-429.
(8) Snow, G. A. Bacteriol. Rev. 1970, 34, 99-125.
(9) Gobin, J .; Horwitz, M. A. J . Exp. Med. 1996, 183, 1527-1532.
(10) Sharman, G. J .; Williams, D. H.; Ewing, D. F.; Ratledge, C.
Chem. Biol. 1995, 8, 553-561.
(11) Hancock, D. K.; Coxon, B.; Wang, S. Y.; White, E. V.; Reeder,
D. J . J . Chem. Soc., Chem. Commun. 1993, 468-469.
10.1021/jo0256078 CCC: $22.00 © 2002 American Chemical Society
Published on Web 05/29/2002
J . Org. Chem. 2002, 67, 4759-4770
4759

Dong and Miller
SCHEME 1. Resu lts of AA Rea ction on Differ en t
Su bstr a tesa
a
Reagents and conditions: (a) EtOH, H2SO4, reflux; BnBr,
K2CO3, DMF, rt, 82-87% for two steps; (b) BnOCONH2, NaOH,
K2[OsO2(OH)4], (DHQD)2AQN, t-BuOCl, n-propanol/H2O, rt.
F IGURE 2. Retrosynthetic analysis.
generate two tripeptide fragments 2 and 3 as plausible
precursors (Figure 2). Compound 2 could be further
simplified to â-alanine and threo-â-hydroxy-L-amino acid
4. L-Ornithine derivatives 5 and 6 were envisioned to be
the building blocks for the construction of the other
sector, 3.
In developing our approach to the synthesis of 1a -d ,
we viewed a practical preparation of highly functionalized
threo-â-hydroxy-L-amino acid 4 as a pivotal step. We were
intrigued by the possibility of exploiting the Sharpless
asymmetric aminohydroxylation reaction (AA reaction)
for enantioselectively introducing the amino and hydroxy
groups in one step. Since it has been demonstrated that
this protocol could be successfully applied to the prepara-
tion of the threo-â-hydroxy-L-tyrosine,12 we decided to
first prepare the â-hydroxyamino acid units of analogues
1b-d utilizing this methodology.
binding study of exochelin MN is underway to evaluate
this hypothesis.
As part of our studies in this area, several exochelin
MN analogues were designed (1b-d , Figure 2). In these
compounds, the imidazole of â-hydroxyhistidine was
replaced by phenol and catechol, which are common iron-
binding ligands found in siderophores. Evaluation of
molecular models showed that these analogues could
coordinate iron(III) in a fashion similar to that of exoch-
elin MN. However, it is of special interest to note that
these ligands, unlike imidazole, are not readily intercon-
vertible between their protonated and depronated forms
under physiological conditions. We expect that the results
from iron-binding and growth promotion studies of these
analogues could provide further evidence for our hypoth-
esis regarding the reversible iron-binding mechanisms
of exochelin MN.
The substrates for the aminohydroxylation, 7-10, were
assembled by esterification and subsequent benzylation
of the corresponding cinnamic acid derivatives (Scheme
1).13,14 Under the optimal conditions established by
Sharpless and co-workers, the AA reaction was performed
on these compounds as summarized in Scheme 1. To our
delight, most of the reactions gave satisfactory results
as compounds 11-13 were able to be prepared in enan-
tiomerically enriched form and in reasonable yields.15,16
Herein, we report the first total synthesis of exochelin
MN and analogues thereof. Our journey toward this end
witnessed the development of three generations of ap-
proach. Through the evolution of the synthetic strategy,
a highly convergent and flexible approach has been
devised, which culminated in the successful synthesis of
the target molecules. Furthermore, this work provides a
platform from which entry to other analogues of biological
interest could also easily be realized.
(12) Tao, B.; Schlingloff, G.; Sharpless, K. B. Tetrahedron Lett. 1998,
39, 2507-2510.
Resu lts a n d Discu ssion
(13) Hamamichi, N.; Natrajan, A.; Hecht, S. M. J . Am. Chem. Soc.
1992, 114, 6278-6291.
F ir st-Gen er a tion Ap p r oa ch . Our first synthetic plan
envisaged the cleavage at the middle peptide bond to
(14) Doherty, D. G. J . Am. Chem. Soc. 1955, 77, 4887-4892.
4760 J . Org. Chem., Vol. 67, No. 14, 2002

Total Synthesis of Exochelin MN and Analogues
SCHEME 2. Syn th esis of
(2S,3S)-â-Hyd r oxyh istid in e by Asym m etr ic Ald ol
Rea ction a
The only exception was the reaction of compound 10,
which produced an inseparable mixture of regioisomers.
Encouraged by these results, we set out to examine the
possibility of a straightforward approach to (2S,3S)-â-
hydroxyhistidine from urocanic acid methyl ester 15
(Scheme 1). Unfortunately, this strategy could not be
implemented despite the structural similarity between
cinnamic acid ester and 15. The possible chelation of the
imidazole with osmium(VIII) was assumed to be the
reason for these failed attempts.17 To test this hypothesis,
compounds 16-18 (Scheme 1) were prepared and sub-
jected to the aminohydroxylation conditions.18,19 The goal
of introducing these N1 protecting groups was to block
the possible coordination of the imidazole with osmium-
(VIII) through inductive or steric effects. However, at-
tempts on these substrates were unsuccessful. These, as
well as results from further studies,20 indicated that the
notion of extending the scope of the AA reaction to
nitrogen-containing heterocycles was, in fact, problem-
atic, and a new plan had to be devised.
After considering several possibilities, the approach
that emerged as the most attractive commenced with the
aldol reaction of imidazolidinone 1921 and known alde-
hyde 2022 followed by the exhaustive deprotection of the
resulting adducts to afford amino acid 23.21 Employing
the procedure developed by Oshima and co-workers,23
aldol products 21 and 22 were obtained in good yield.
Without separation, the mixture was hydrolyzed to
generate (2S,3S)-â-hydroxyhistidine hydrochloride 23
with high optical purity,24 which was then protected in
two steps to provide bis-Cbz compound 25 (Scheme 2).25
a
Reagents and conditions: (a) Ti(O-n-Bu)4, t-BuOK, 20, THF,
0 °C, 56%; (b) 6 M HCl, reflux, 93%; (c) Cbz-S, TEA, dioxane/H2O,
0 °C to rt, 54%; (d) CbzCl, NaHCO3, H2O, rt.
The rapid decomposition of compound 25 made it neces-
sary to use the crude material immediately after prepa-
ration, and no full characterization was attempted.
With these important â-hydroxyamino acids in hand,
we turned our attention to their coupling reactions with
â-alanine dipeptide 29,26 as outlined in Scheme 3. By
carefully monitoring the reactions, esters 11-13 were
able to be saponified in excellent yields. The resulting
acids 26-28 were then coupled with â-alanyl-â-alanine
methyl ester hydrochloride 29 to afford the corresponding
tripeptide methyl esters 30-32.27 In the next transfor-
mation, however, we found that the poor solubility of
these esters and basic lability of the benzyl carbamate,
especially with the participation of the neighboring
hydroxy group, made the hydrolysis reactions quite
problematic. Finally, after some experimentation, the
combination of CH3CN/MeOH/H2O provided the best
results. However, attempts to hydrolyze the methyl ester
of compound 30 always led to the concomitant loss of the
Cbz group and oxazolidinone 33 was obtained as the
exclusive product.
(15) The methyl ester derivatives of compounds 7 and 8 were not
soluble in the solvent system. Reaction of the methyl ester version of
compound 9 gave lower enantioselectivity (65% ee) despite the facile
purification (the separation of compound 13 from excess benzyl
carbamate was problematic).
(16) The enantiomeric excess of the aminohydroxylation products
was determined by Mosher’s reagent derivatization and 19F NMR
studies. In the case of compound 12, it was found that the solvent
(CDCl3 or DMSO-d6) employed for the experiment drastically affected
the results. Currently, the enantiomeric excess of this compound has
not been unequivocally determined and further studies are ongoing.
The absolute configuration of representative product 11 was unam-
biguously determined by saponification and hydrogenolytic removal
of the Cbz and benzyl groups, followed by comparison of the optical
rotation of resulting â-hydroxytyrosine with the literature value.
Herbert, R. B.; Wilkinson, B.; Ellames, G. J . Can. J . Chem. 1994, 72,
114-117.
(17) Rudolph, J .; Sennhenm, P. C.; Vlaar, C. P.; Sharpless, K. B.
Angew. Chem., Int. Ed. Engl. 1996, 35, 2810-2812.
(18) Ilizuka, K.; Akahane, K.; Mosose, D.; Nakazawa, M.; Tanouchi,
T. J . Med. Chem. 1981, 24, 1139-1148.
Having addressed the synthesis of tripeptide 2, the
next task was the construction of fragment 3 from
compounds 5 and 6. The synthesis of compound 5 was
accomplished by N-methylation of known nitrone 36 in
good yield.28,29 Hydroxamate 6 was prepared from the
same precursor in a three-step sequence, involving
deprotection of the nitrone, cyclization and hydrogenoly-
(19) Kosaka, K.; Maruyama, K.; Nakamura, H.; Ikeda, M. J .
Heterocycl. Chem. 1991, 28, 1941-1944.
(20) Competition studies were performed to further explore this
assumption. When a mixture of equal equivalents of 7 and 15 or 16
was subjected to aminohydroxylation conditions, compound 11 was not
detected. In a separate experiment, when the reaction of 16 was
conducted in the presence of a stoichiometric amount of osmium
reagent, no consumption of the substrates was observed.
(21) (a) Fitzi, R.; Seebach, D. Tetrahedron 1988, 44, 5277-5292. (b)
Fitzi, R.; Seebach, D. Angew. Chem., Int. Ed. Engl. 1986, 25, 345-
346.
(25) Kitaka, A.; Sngano, Y.; Otasuka, M. Tetrahedron 1988, 44,
2811-2820. Coupling reactions of compound 24 generally gave very
poor results (∼10% yield).
(22) Kelly, J . L.; Miller, C. A.; McLean, E. W. J . Med. Chem. 1977,
20, 721-723.
(23) Han, Z.; Yorimitsu, H.; Shinokubo, H.; Oshima, K. Tetrahedron
Lett. 2000, 41, 4415-4418.
(24) Taraz, K.; Wever, M.; Budzikiewicz, H. Z. Naturforsch. Sect.
B-A 1998, 53, 1520-1524. The optical rotations of compound 23 and
its enantiomer we synthesized matched the literature values at 589
nm (unpublished results obtained through personal correspondence
with the author. We thank Dr. H. Budzikiewicz at Institut fu¨r
Organische Chemie der Universita¨t zu Ko¨ln for his help and discus-
sion).
(26) The general procedure for peptide synthesis was employed to
prepare these â-alanine dipeptides. For example, 25: Cbz protection
of â-alanine (CbzCl, NaOH, 95%), coupling of this compound with
â-alanine methyl ester hydrochloride (EDC, HOBt, DMAP, 91%) ,and
removal of the Cbz protecting group from the resulting dipeptide by
hydrogenolysis (H2, Pd/C, 100%).
(27) Carpino, L. A. J . Am. Chem. Soc. 1993, 115, 4397-4398.
(28) Lin, Y.-M.; Miller, M. J . J . Org. Chem. 1999, 64, 7451-7458.
(29) McDermott, J . R.; Benoiton, N. L. Can. J . Chem. 1973, 51,
1915-1919.
J . Org. Chem, Vol. 67, No. 14, 2002 4761

Dong and Miller
SCHEME 3. Syn th esis of th e Tr ip ep tid e
F r a gm en tsa
SCHEME 4. Syn th esis of th e P r otected An a logu e
42a
a
Reagents and conditions: (a) LiOH, THF/H2O, 0 °C; (b) EDC,
HOAt, DMAP, 29, CH2Cl2, 0 °C to rt; (c) LiOH, CH3CN/MeOH/
H2O, 0 °C to rt, 88%; (d) 31: CH3CN/MeOH/H2O, 0 °C; 32: LiOH,
THF/H2O, 0 °C.
sis (Scheme 4). However, these deceptively simple trans-
formations were found to be among the principal hurdles
in the synthesis due to the highly variable yields,
especially in the hydrogenolysis step. Although enough
material was accumulated for the investigation of the
following steps, possible remedies to this problem were
sought later.
a
Reagents and conditions: (a) TFA, H2O, 60 °C; 1 M HCl,
CH2Cl2, rt, 82%; EDC, HOBt, NaHCO3, CH3CN, rt, 65%; (b) H2,
10% Pd/C, rt, 100%; (c) 38, EDC, HOAt, DMAP, DMF, 0 °C to rt;
TEA, rt, 58%; (d) TFA, CH2Cl2, 0 °C to rt; 5, EDC, HOAt, DMAP,
DMF, 0 °C to rt; TEA, rt, 35% for two steps; (e) NH2OH‚HCl,
CH3OH, 60 °C, 75%; (f) 35, BOP, (i-Pr)2EtN, DMF, 0 °C to rt, 41%.
We encountered some unanticipated difficulties in the
next several coupling reactions. Although ample litera-
ture precedent indicated that amino groups could be
selectively acylated in the presence of hydroxamates,30
we found that the carbodiimide-mediated coupling reac-
tion of 6 and 38 always led to a mixture of the desired
product 39 and bis-coupled product 40. This competitive
acylation of the hydroxamate seriously compromised the
yields of this and subsequent coupling reactions. After
TFA-mediated Boc deprotection of 39, the reaction of the
resulting amine salt and compound 5 generated tripep-
tide 41. A number of other coupling reagents (HATU,
BOP) were investigated in an attempt to improve the
efficiency of these coupling reactions. Unfortunately, no
satisfactory conditions surfaced during these studies.
Finally, treatment of compound 41 with hydroxylamine
hydrochloride removed the nitrone and furnished com-
pound 3.31
With the preparation of the above fragments, an
important stage in the synthesis had been reached. The
remaining task was the union of fragments 3 and 2. The
preparation of the phenol analogue 42 was pursued first
(Scheme 4). Several conditions were examined to effect
the last coupling reaction. Eventually, the successful
solution to the union of 3 and 35 was accomplished by
utilizing BOP and (iPr)2EtN to yield the protected
analogue 42.32
Secon d -Gen er a tion Ap p r oa ch . Despite the success
described above, it was clear that considerable difficul-
ties, notably arising from the assembly of fragment 2,
would be encountered if the above route were followed
(30) (a) Bergeron, R. J .; Phanstiel, O. IV J . Org. Chem. 1992, 57,
7140-7143. (b) Akiyama, M.; Shimizu, K.; Aiba, S.; Katoh, H. Bull.
Chem. Soc. J pn. 1985, 58, 1421-1425.
(31) Hu, J .; Miller, M. J . J . Org. Chem. 1994, 59, 4848-4861.
(32) Bergeron, R. J .; Liu, C. Z.; Mcmanis, J . S.; Xia, M. X.; Algee, S.
E.; Wiegand, J . J . Med. Chem. 1994, 37, 1411-1417.
4762 J . Org. Chem., Vol. 67, No. 14, 2002

Total Synthesis of Exochelin MN and Analogues
SCHEME 5. Syn th esis of P r otected An a logu e 42a
SCHEME 6. Syn th esis of Exoch elin MNa
a
Reagents and conditions: (a) BOP, (i-Pr)2EtN, 43, DMF/
CH3CN, 0 °C to rt, 31%; (b) TFA, CH2Cl2, 0 °C to rt; 28, EDC,
HOAt, DMAP, DMF, 0 °C to rt, 37% for two steps.
to access the target compounds. Recognizing the impor-
tance of developing a convergent synthesis of 1a -d , an
alternative synthetic plan was devised as shown in
Scheme 5. According to this strategy, exochelin MN and
its analogues could be derived from the common ad-
vanced intermediate, pentapeptide 44 (Scheme 5). Sub-
sequent studies showed that the convergence provided
by this approach was vital to the success of these
syntheses.
In this alternative approach, an orthogonal protecting
group had to be employed for the amino group of the
â-alanine dipeptide to allow its selective removal at the
later stage of the synthesis in the presence of both Cbz
and benzyl protecting groups. After an extensive survey
of a variety of candidates (Boc, Fmoc, and Alloc), Boc was
found to best serve this purpose.33 Therefore, the coupling
reaction of N-Boc â-alanine dipeptide 4326 and compound
3 furnished pentapeptide 44, which was exposed to TFA
to remove the Boc group. The amine salt then reacted
with carboxylic acid 28 to produce protected analogue 42
in moderate yield (Scheme 5). In this way, compounds
1a -d should be readily accessed by adjusting the last
â-hydroxyamino acids.
Th ir d -Gen er a tion Ap p r oa ch . While the results of
the second-generation approach were certainly gratifying,
a more efficient route was desirable to render the
synthesis practical. In appraisal of the setbacks involved
in previous approaches, it was noted that the free cyclic
hydroxamate was the primary source of frustration
because of its apparent interference in acylation reac-
tions. It should also be mentioned that all the intermedi-
ates containing a hydroxamate moiety had to be purified
by careful reversed-phase chromatography, and the
strong iron-binding ability of these compounds made
their isolation and purification quite difficult. To circum-
vent these problems, we recognized the necessity of
incorporating a hydroxamate protecting group strategy,
and a benzyl group was selected for this purpose.
a
Reagents and conditions: (a) NH2OH‚HCl, 3 Å molecular
sieves, TEA, CH3OH, reflux; BnBr, K2CO3, DMF, rt, 65% for two
steps; (b) HBr/HOAc, CH2Cl2, rt, 92%; (c) 38, EDC, HOAt, DMAP,
CH2Cl2, 0 °C to rt, 94%; (d) TFA, CH2Cl2, rt; NaHCO3 (aq), 92%;
(e) 5, EDC, HOAt, CH2Cl2, 0 °C to rt, 92%; (f) NH2OH‚HCl,
CH3OH, 60 °C, 85%; 43, BOP, (iPr)2EtN, DMF, 0 °C to rt; BnBr,
K2CO3, DMF, rt, 74% for two steps; (g) TFA, CH2Cl2, 0 °C to rt;
NaHCO3 (aq); 25, EDC, HOAt, 0 °C to rt, DMF, 44% for two steps;
(j) H2, Pd(OH)2, rt, 36%.
The synthesis of exochelin MN by this revised route is
outlined in Scheme 6. Compound 37 had previously been
prepared from nitrone 36 in modest yield, and initially
we believed the application of this method in conjunction
with benzyl protection would provide the most expedi-
tious means of obtaining compound 45. However, after
some experimentation, we developed a more concise and
efficient protocol through a one-pot deprotection-cycliza-
tion reaction followed by benzylation. In this fashion,
compound 45 was able to be obtained in good yield and
in a short time! An added benefit of this approach was
that this reaction proved very amenable to scale-up since
it could be conducted in concentrated solution without
polymerization.
(33) The Fmoc group proved to be too labile under basic conditions
and also caused solubility problems. On the other hand, the Alloc group
could be easily introduced but was not able to be cleanly removed.
J . Org. Chem, Vol. 67, No. 14, 2002 4763

Dong and Miller
60 (30-70 µm irregular particles). Reversed-phase chroma-
tography was performed on C-18 silica gel (37-53 µm par-
ticles). During all hydrogenolysis reactions, the solvent was
purged with argon prior to the addition of the catalyst.
The next challenge in our synthesis was to find a
protocol to selectively remove the Cbz group in the
presence of the hydroxamate-benzyl group. This could
be readily achieved by treatment with 33% HBr in acetic
acid.34 Finally, we were pleased to find that, as expected,
the introduction of hydroxamate-benzyl protecting group
made the subsequent coupling and deprotection reactions
proceed smoothly and exochelin MN was obtained in
excellent overall yields (4.7% from the longest linear
sequence). It should be pointed out that the second
hydroxamate formed in this sequence was also protected
as a benzyl ether to facilitate the purification. Interest-
ingly, it seemed that this free hydroxamate was not
reactive under coupling reaction conditions, which was
consistent with the literature reports as mentioned
before. In the last global deprotection reaction, we found
that the employment of Pd/C led to serious iron(III)
contamination of the products while Pd(OH)2 proved to
be a superior catalyst. The spectroscopic data of our
synthetic sample (IR, MS, 1H and 13C NMR) matched
those of the natural product kindly provided by Professor
Colin Ratledge. Analogues 1b-d were prepared in a
similar fashion by varying the last â-hydroxyamino acid.
It is worth noting that all intermediates in the third-
generation approach were purified by regular-phase
chromatography. This greatly simplified the procedures
and contributed to the improved yields and overall
efficiency.
(E)-Eth yl 2-Ben zyloxycin n a m a te (9). To a solution of
2-hydroxycinnamic acid (1.0 g, 6.1 mmol) in absolute EtOH
(20 mL) was added concentrated H2SO4 (0.5 mL) dropwise with
vigorous stirring. After being refluxed for 5 h, the reaction
mixture was concentrated under reduced pressure. The result-
ing residue was dissolved in EtOAc (30 mL), washed with H2O
(3 × 10 mL), dried (MgSO4), filtered, and concentrated to give
an off-white solid. To a mixture of this solid and K2CO3 (1.580
g, 11.5 mmol) in DMF (6 mL) was added benzyl bromide (0.979
g, 0.681 mL, 5.7 mmol). The mixture was stirred overnight at
room temperature and partitioned between EtOAc (30 mL) and
H2O (15 mL). The organic layer was further washed with H2O
(3 × 10 mL), dried (Na2SO4), filtered, and concentrated under
reduced pressure. The crude product was purified by column
chromatography (1:10 EtOAc/hexanes) to afford 9 as a white
solid (1.490 g, 87%): mp 45-47 °C; IR (neat) 1705, 1630 cm-1
;
1H NMR (300 MHz, CDCl3) δ 8.09 (d, 1 H, J ) 8.1 Hz), 7.53-
6.90 (m, 9 H), 6.53 (d, 1 H, J ) 8.1 Hz), 5.12 (s, 2 H), 4.23 (q,
2 H, J ) 6.9 Hz), 1.33 (t, 3 H, J ) 6.9 Hz); 13C NMR (75 MHz,
CDCl3) δ 167.6, 157.4, 140.0, 136.8, 131.5, 128.9, 128.8, 128.1,
127.3, 124.0, 121.2, 119.0, 113.0, 70.4, 60.5, 14.5; HRFABMS
m/z calcd for C18H19O3 [MH]+ 283.1334, found 283.1351.
Gen er a l P r oced u r e for Am in oh yd r oxyla tion Rea c-
t ion s: E t h yl (2S,3R)-2-Ben zyloxyca r b on yla m in o-3-(4-
ben zyloxyp h en yl)-3-h yd r oxyp r op ion a te (11) a n d Eth yl
(2S,3R)-3-Ben zyloxyca r bon yla m in o-3-(4-ben zyloxyp h e-
n yl)-2-h yd r oxyp r op ion a te (11b). A 1 N NaOH solution (3.05
mL, 3.05 mmol) was diluted with H2O (4.5 mL). Part of this
solution (0.5 mL) was transferred into a vial to dissolve K2-
[OsO2(OH)4] (14.7 mg, 0.04 mmol). To the rest of the solution
were added n-propanol (4 mL) and benzyl carbamate (469 mg,
3.1 mmol) with rigorous stirring, followed by dropwise addition
of freshly prepared tert-butyl hypochlorite (331 mg, 0.346 mL,
3.05 mmol). After 5 min, an n-propanol solution (3.5 mL) of
(DHQD)2AQN (34.3 mg, 0.04 mmol), R,â-unsaturated ester (7-
10) (1.0 mmol), and the aqueous K2[OsO2(OH)4] solution were
added. For compounds 11 and 12: After being stirred for 2 h
at room temperature, the reaction mixture was cooled to 0 °C,
filtered, washed with cold H2O/n-propanol (1:1), and dried to
give the crude product. For compound 13 and 14: After being
stirred for 2 h at room temperature, the reaction mixture was
quenched with NaHSO3 (0.5 g) and diluted with EtOAc (8 mL).
After separation of the layers, the aqueous layer was further
extracted with EtOAc (3 × 10 mL). The combined extracts were
washed with brine (5 mL), dried (MgSO4), filtered and con-
centrated under reduced pressure to give the crude product.
The crude material was purified by column chromatography
(5:1 hexanes/EtOAc or 20:1 CH2Cl2/EtOAc) to afford the
desired compounds. 11: white crystals (45%); mp 104-106 °C;
IR (KBr) 3482, 1726, 1690 cm-1; 1H NMR (600 MHz, CDCl3) δ
7.45-7.25 (m, 10 H), 7.26 (d, 2 H, J ) 8.4 Hz), 6.94 (d, 2 H, J
) 8.4 Hz), 5.55 (d, 1 H, J ) 8.4 Hz), 5.19 (m, 1 H), 5.05 (s, 2
H), 5.03 (s, 2 H), 4.55 (d, 1 H, J ) 5.4 Hz), 4.25 (q, 2 H, J )
7.2 Hz), 2.52 (m, 1 H), 1.23 (t, 3 H, J ) 7.2 Hz); 13C NMR (150
MHz, CDCl3) δ 170.8, 159.8, 137.7, 132.2, 128.9, 128.7, 128.4,
128.2, 127.7, 127.5, 115.0, 73.8, 70.2, 67.3, 62.1, 60.1, 14.3;
HRFABMS m/z calcd for C26H26NO6 [MH]+ 448.1760, found
448.1785. 11b: a white solid; mp 118-120 °C; IR (KBr) 3364,
Con clu sion s
In conclusion, the first total synthesis of exochelin MN
and several analogues has been achieved. Biological
assays and pH-dependent iron(III)-binding studies of
these compounds are underway and will be published in
due course. Investigations in this area will significantly
augment the understanding of the iron transport pro-
cesses of mycobacteria, especially the controlled iron(III)
release by exochelin, and should also facilitate the search
for potent remedies for mycobacterial infections. In this
process, a new concise procedure for the preparation of
the six-membered cyclic hydroxamate was developed. We
have also shown that Sharpless asymmetric aminohy-
droxylation reaction and the asymmetric aldol reaction
of imidazolidinone 19 provided an entry to a number of
related â-hydroxyamino acids. We believe our efforts in
this area will lead to an array of synthetically and
biologically interesting moieties in the future.
Exp er im en ta l Section
Gen er a l P r oced u r es. Tetrahydrofuran (THF) was distilled
from sodium metal/benzophenone ketyl. Methylene chloride
(CH2Cl2), acetonitrile (CH3CN), dioxane, and triethylamine
(TEA) were distilled from CaH2. N,N-Dimethylformamide
(DMF) was distilled from CaH2 and stored over 3 Å molecular
sieves. All other reagents were used as received. Unless
otherwise noted, all nonaqueous reactions were carried out
under a dry argon atmosphere with oven-dried glassware (120
°C, at least 12 h). Melting points were measured on a capillary
melting point apparatus and are uncorrected. Unless otherwise
noted, all NMR spectra were recorded at 300 MHz. Silica gel
flash column chromatography was performed using silica gel
1
1719, 1692 cm-1; H NMR (300 MHz, DMSO-d6) δ 7.70 (d, 1
H, J ) 9.3 Hz), 7.45-7.30 (m, 15 H), 7.22 (d, 2 H, J ) 8.4 Hz),
6.94 (d, 2 H, J ) 8.4 Hz), 5.55 (d, 1 H, J ) 7.8 Hz), 5.07 (s, 2
H), 5.01 (d, 2 H, J ) 11.4 Hz), 4.97 (d, 2 H, J ) 11.4 Hz), 4.87
(dd, 1 H, J ) 5.1, 9.3 Hz), 4.22 (dd, 1 H, J ) 5.4, 9.3 Hz), 3.95
(q, 2 H, J ) 6.9 Hz), 1.01 (t, 3 H, J ) 7.2 Hz); 13C NMR (75
MHz, CDCl3) δ 173.0, 158.7, 155.9, 137.2, 136.5, 128.9, 128.8,
128.4, 128.3, 127.7, 115.2, 73.7, 70.3, 67.2, 62.8, 56.2, 14.3;
HRFABMS m/z calcd for C26H26NO6 [MH]+ 448.1760, found
448.1753.
(34) Okonya, J . F.; Kolasa, T.; Miller, M. J . J . Org. Chem. 1995, 60,
1932-1935.
4764 J . Org. Chem., Vol. 67, No. 14, 2002

Total Synthesis of Exochelin MN and Analogues
Eth yl (2S,3R)-2-Ben zyloxyca r bon yla m in o-3-(3,4-d iben -
zyloxyp h en yl)-3-h yd r oxyp r op ion a t e (12) a n d E t h yl
(2S,3R)-3-Ben zyloxyca r bon yla m in o-3-(3,4-d ib en zyloxy-
p h en yl)-2-h yd r oxyp r op ion a te (12b). 12: white crystals
H, J ) 3.0 Hz), 5.04 (d, 1 H, J ) 12.6 Hz), 4.99 (d, 1 H, J )
13.2 Hz), 4.37 (d, 1 H, J ) 3.0 Hz); 13C NMR (150 MHz, CD3-
OD) δ 171.5, 157.2, 137.0, 134.5, 128.3, 127.8, 127.6, 116.4,
67.8, 66.4, 60.0; HRFABMS m/z calcd for C14H15N3O5 [MH]+
305.0722, found 305.0727.
1
(34%); mp 109-110 °C; IR (KBr) 3359, 1733, 1697 cm-1; H
NMR (600 MHz, CDCl3) δ 7.44-7.25 (m, 15 H), 7.00 (s, 1 H),
6.88 (m, 2 H), 5.68 (d, 1 H, J ) 9.0 Hz), 5.10 (s, 2 H), 5.07 (s,
2 H), 5.00 (s, 2 H), 4.53 (dd, 1 H, J ) 9.6, 3.0 Hz), 4.13 (m, 2
H), 3.08 (s, br, 1 H), 1.19 (t, 3 H, J ) 7.2 Hz); 13C NMR (150
MHz, CDCl3) δ 170.8, 156.5, 149.0, 148.8, 137.3, 136.3, 133.2,
128.6 (2), 128.2, 128.0 (2), 127.5, 127.4, 119.3, 114.7, 112.9,
73.5, 71.3, 71.2, 67.1, 61.9, 60.1, 14.2; FABMS m/z calcd for
Gen er a l P r oced u r e for Hyd r olysis of Eth yl Ester s 11-
13. (2S,3R)-2-Ben zyloxyca r b on yla m in o-3-(4-b en zylox-
yp h en yl)-3-h yd r oxyp r op ioic Acid (26). To a solution of 11
(80.0 mg, 0.182 mmol) in THF/H2O (1.6:1, 3 mL) was added 1
N LiOH solution (0.214 mL, 0.214 mmol) at 0 °C. After being
stirred at 0 °C for 1 h, the reaction mixture was concentrated
under reduced pressure to remove the THF. The residue was
diluted with H2O (2 mL) and washed with Et2O (3 × 2 mL).
The aqueous layer was acidified to pH 3.0 with 10% citric acid
and extracted with EtOAc (3 × 7 mL). The combined organic
layers were washed with brine (3 mL), dried (MgSO4), filtered,
and concentrated under reduced pressure to afford 26 as white
crystals (75.2 mg, 98%): mp 110-112 °C; IR (KBr) 3495, 1742,
1242 cm-1; 1H NMR (300 MHz, DMSO-d6) δ 7.46-6.94 (m, 14
H), 5.13 (m, 1H), 5.08 (s, 2 H), 4.96 (s, 2 H), 4.26 (dd, 1 H, J )
9.0, 3.0 Hz); 13C NMR (75 MHz, DMSO-d6) δ 171.9, 171.3,
157.5, 156.2, 137.2, 137.1, 134.3, 128.5, 128.3, 127.8, 127.7,
127.4, 127.3, 114.1, 71.8, 69.2, 65.3, 60.5; HRFABMS m/z calcd
for C24H24NO6 [MH]+ 422.1604, found 422.1587.
C
33H33NO7 [M]+ 555, found 555. 12b: A white solid; mp 104-
1
105 °C; IR (KBr) 3450, 1722, 1691 cm-1; H NMR (300 MHz,
DMSO-d6) δ 7.45-7.26 (m, 15 H), 7.00 (s, 1 H), 6.90 (m, 2 H),
5.55 (d, 1 H, J ) 10.5 Hz), 5.18 (m, 1 H), 5.14 (m, 4 H), 5.06
(d, 2 H, J ) 4.8 Hz), 4.39 (m, 1 H), 4.23 (q, 2 H, J ) 6.9 Hz),
3.08 (d, 1 H, J ) 4.2 Hz), 1.26 (t, 3 H, J ) 7.2 Hz); 13C NMR
(75 MHz, CDCl3) δ 172.9, 155.8, 149.2, 148.9, 137.5, 137.3,
136.4, 132.5, 128.7, 128.6, 128.3, 128.0, 128.0, 127.7, 127.4,
120.0, 115.1, 114.2, 73.6, 71.6, 71.5, 67.2, 62.8, 56.2, 14.3;
FABMS m/z calcd for C33H33NO7 [M]+ 555, found 555.
Eth yl (2S,3R)-2-ben zyloxyca r bon yla m in o-3-(2-ben zy-
loxyp h en yl)-3-h yd r oxyp r op in oa te (13): a white solid (55%);
mp 74-75 °C; IR (KBr) 3442, 1746, 1706 cm-1; 1H NMR (600
MHz, CDCl3) δ 7.49-7.21 (m, 14 H), 6.94 (m, 2 H), 5.78 (d, 1
H, J ) 9.0 Hz), 5.62 (m, 1 H), 5.15 (d, 2 H, J ) 11.4 Hz), 5.06
(d, 2 H, J ) 11.4 Hz), 4.94 (s, 2 H), 4.86 (dd, 1 H, J ) 9.6, 2.4
Hz), 4.15 (m, 2 H), 3.31 (d, 1 H, J ) 5.4 Hz), 1.19 (t, 3 H, J )
7.2 Hz); 13C NMR (150 MHz, CDCl3) δ 171.2, 156.5, 155.2,
136.8, 136.5, 129.0, 128.5, 128.2, 128.0 (2), 127.9, 127.1, 120.8,
111.4, 70.0, 69.8, 66.8, 61.6, 58.1, 14.1; HRFABMS m/z calcd
for C26H26NO6 [MH]+ 450.1917, found 450.1931.
(2S,3R)-2-Ben zyloxycar bon ylam in o-3-(3,4-diben zyloxy-
p h en yl)-3-h yd r oxyp r op ioic a cid (27): white crystals (94%);
mp 103-104 °C; IR (KBr) 3419, 1734, 1269 cm-1 1H NMR
;
(300 MHz, DMSO-d6) δ 7.44-6.88 (m, 18 H), 5.14 (d, 1H, J )
4.5 Hz), 5.09 (s, 2 H), 5.06 (s, 2 H), 4.95 (s, 2 H), 4.25 (dd, 1 H,
J ) 9.0, 4.5 Hz); 13C NMR (75 MHz, DMSO-d6) δ 172.6, 158.6,
156.9, 148.6, 148.0, 138.1, 135.9, 132.0, 129.1, 129.0, 128.5,
128.3, 128.2, 127.9, 119.6, 114.5, 113.5, 72.6, 71.0, 70.8, 65.9,
61.1; FABMS m/z 527 (M+), 510 (M - 17).
(2S,3S)-â-Hyd r oxyh istid in e (23). To a solution of Ti(O-
n-Bu)4 (0.507 mL, 2.5 mmol) in THF (6.5 mL) was added KO-
t-Bu (260 mg, 2.5 mmol) at room temperature. After being
stirred for 10 min, the solution was cooled to 0 °C and a
solution of 19 (260 mg, 1.0 mmol) in THF (5 mL) was added
in small portions. After the mixture was stirred for 10 min, a
solution of 20 (507 mg, 1.5 mmol) in THF (7 mL) was added
dropwise, and the mixture was stirred for 4 h at 0 °C. The
reaction mixture was quenched with addition of 1 N HCl (3
mL) and diluted with Et2O (3 × 10 mL). The combined organic
layers were washed with brine (3 × 5 mL), dried (MgSO4),
filtered, and concentrated to generate a yellow gum. The crude
product was purified by column chromatography (1-5%
MeOH/CH2Cl2). The pale yellow partially crystalline mixture
(286.1 mg, 56%) contained 21 and 22.
The mixture (80.0 mg, 0.131 mmol) was refluxed with 6 N
HCl (2 mL) for 8 h. After being cooled to room temperature,
the mixture was washed with Et2O (4 × 2 mL), filtered, and
concentrated under reduced pressure. The crude product was
purified by Dowex cation ion-exchange resin (50 × 8-400) to
give 23 as a pale yellow solid (29 mg, 93%): [R]D ) -9 (c ) 1
M, H2O, pH ) 4.3); IR (KBr) 3401, 1702, 1607 cm-1; 1H NMR
(300 MHz, D2O, pH ) 4.3) δ 8.52 (d, 1 H, J ) 1.2 Hz), 7.27
(dd, 1 H, J ) 1.2, 0.9 Hz), 5.41 (dd, 1 H, J ) 3.6, 0.9 Hz), 4.25
(d, 1 H, J ) 3.6 Hz); 13C NMR (75 MHz, D2O, pH ) 4.3) δ
171.4, 135.5, 134.7, 116.5, 65.1, 59.3; HRFABMS m/z calcd for
C6H10N3O3 [MH]+ 172.0722, found 172.0727.
(2S,3S)-N2-(Ben zyloxycar bon yl)-â-h ydr oxyh istidin e (24).
To a solution of 23 (100.0 mg, 0.482 mmol) in H2O (2.4 mL)
was added a solution of Cbz-succinimide (158.6 mg, 0.578
mmol) in dioxane (2.4 mL) and TEA (0.221 mL, 1.592 mmol)
at 0 °C. The resulting solution was stirred at 0 °C for 1 h and
then at room temperature overnight. The reaction mixture was
treated with H2O (10 mL) and washed with EtOAc (4 × 8 mL).
The aqueous layer was concentrated under reduced pressure,
and the residue was purified by column chromatography (35-
50% MeOH/CHCl3) to give 24 as light yellow crystals (79.1
mg, 54%): IR (KBr) 3422, 1702, 1607 cm-1; 1H NMR (600 MHz,
CD3OD) δ 7.82 (s, 1 H,), 7.27 (m, 5 H), 7.02 (s, 1 H), 5.24 (d, 1
(2S,3R)-2-Ben zyloxycar bon ylam in o-3-(2-ben zyloxyph e-
n yl)-3-h yd r oxyp r op ioic a cid (28): colorless glass (93%); IR
1
(neat) 3410, 1721, 1498 cm-1; H NMR (300 MHz, DMSO-d6)
δ 7.55-6.87 (m, 14 H), 5.80 (d, 1 H, J ) 9.3 Hz), 5.73 (m, 1 H),
5.13 (d, J ) 11.7 Hz), 5.04 (d, J ) 12.0 Hz), 4.91 (m, 2 H), 4.41
(m, 1 H); 13C NMR (75 MHz, CDCl3) δ 175.3, 156.9, 155.3,
136.9, 129.2, 128.9, 128.6, 128.2, 128.1, 127.2, 127.0, 121.1,
111.8, 107.3, 70.3, 69.7, 67.2, 58.0; HRFABMS m/z calcd for
C
24H24NO6 [MH]+ 422.1604, found 422.1620.
Gen er a l P r oced u r e for Cou p lin g Rea ction s of 29 a n d
26-28. N-N-[(2S,3R)-2-Ben zyloxyca r bon yla m in o-3-(4-be-
n yloxyp h en yl)-3-h yd r oxyp r op ion yl]-â-a la n yl-â-a la n in e
Meth yl Ester (30). To a stirred solution of 29 (241.6 mg, 1.148
mmol), 26 (406.3 mg, 0.965 mmol), and HOAt (143.1 mg, 1.05
mmol) in CH2Cl2 (8 mL) at 0 °C were added EDC (220.4 mg,
1.148 mmol) and DMAP (294.3 mg, 2.412 mmol). After being
stirred at room temperature overnight, the reaction mixture
was partitioned between EtOAc (25 mL) and H2O (7 mL). The
organic layer was washed with 10% citric acid (3 × 5 mL), 5%
NaHCO3 (3 × 5 mL), and brine (5 mL), dried (MgSO4), filtered,
and concentrated to give the crude product. This was purified
by column chromatography (2-4% MeOH/CH2Cl2) to afford 30
as a white solid (356.3 mg, 64%): mp 188-190 °C; IR (KBr)
1
3294, 1737, 1696, 1649 cm-1; H NMR (300 Hz, DMSO-d6) δ
7.97 (t, 1 H, J ) 5.7 Hz), 7.92 (t, 1 H, J ) 5.4 Hz), 7.45-6.88
(m, 14 H), 5.47 (d, 1 H, J ) 6.0 Hz), 5.13 (m, 1 H), 5.07 (s, 2
H), 4.94 (m, 2 H), 4.14 (dd, 1 H, J ) 12.6, 3.3 Hz), 3.58 (s, 3
H), 3.27 (m, 4 H), 2.48 (t, 2 H, J ) 7.2 Hz), 2.17 (t, 2 H, J )
6.6 Hz); 13C NMR (75 MHz, DMSO-d6) δ 172.5, 171.2, 170.4,
158.1, 137.9, 135.2, 131.9, 129.1, 129.0, 128.5, 128.4, 128.0,
127.9, 115.5, 114.7, 100.2, 72.7, 69.8, 66.0, 61.9, 52.1, 36.1, 35.8,
35.4, 34.3; HRFABMS m/z calcd for C33H36N3O8 [MH]+ 578.2502,
found 578.2500.
N,N-[(2S,3R)-2-Ben zyloxyca r b on yla m in o-3-(3,4-d ib e-
n yloxyp h en yl)-3-h yd r oxyp r op ion yl]-â-a la n yl-â-a la n in e
m eth yl ester (31): a white solid (66%); mp 187-188 °C; IR
(KBr) 3294, 1738, 1696, 1649 cm-1; 1H NMR (300 Hz, DMSO-
d6) δ 7.96 (t, 1 H, J ) 5.4 Hz), 7.90 (t, 1 H, J ) 5.1 Hz), 7.43-
6.95 (m, 18 H), 5.49 (s, br, 1 H), 5.08 (s, 2 H), 5.05 (s, 2 H),
J . Org. Chem, Vol. 67, No. 14, 2002 4765

Dong and Miller
4.97 (d, 1 H, J ) 12.9 Hz), 4.89 (d, 1 H, J ) 12.9 Hz), 4.15 (dd,
1 H, J ) 9.0, 3.0 Hz), 3.57 (s, 3 H), 3.23 (m, 4 H), 2.44 (t, 2 H,
J ) 6.9 Hz), 2.18 (t, 2 H, J ) 6.6 Hz); 13C NMR (75 MHz,
DMSO-d6) δ 172.5, 171.2, 170.5, 156.6, 148.6, 148.0, 138.1,
138.0, 137.7, 136.1, 129.1, 129.0, 128.5, 128.4, 128.3, 128.1,
127.9, 119.7, 114.5, 113.5, 72.8, 71.0, 70.8, 66.0, 61.9, 52.1, 36.1,
35.8, 35.4, 34.3; HRFABMS m/z calcd for C38H41N3O9 [M +
Na]+ 706.2741, found 706.2722.
aqueous layer was acidified to pH 3 with 1 N HCl and
extracted with EtOAc (3 × 15 mL). The combined extracts were
washed with brine (5 mL), dried (MgSO4), filtered, and
concentrated under reduced pressure to give a pale yellow oil.
After trituration from hexanes and Et2O, 5 was obtained as a
light yellow powder (71.8 mg, 85%): mp 106-108 °C; IR (neat)
1698, 1454 cm-1; 1H NMR (300 MHz, DMSO-d6, 70 °C) δ 8.31
(m, 1 H), 7.93 (s, 1 H), 7.51-7.38 (m, 10 H), 5.16 (s, 2 H), 4.57
(s, br), 4.01 (m, 2 H), 2.87 (s, 3 H), 1.96-1.78 (m, 4 H); 13C
NMR (75 MHz, CDCl3, 20 °C) δ 173.8, 173.6, 157.5, 156.7,
137.4,137.2, 136.6, 131.5, 130.0, 129.7, 128.8, 128.8, 128.3,
128.2, 128.0, 67.9, 65.9, 58.0, 30.9, 25.6, 24.5; HRFABMS m/z
calcd for C21H25N2O5 [MH]+ 385.1763, found 385.1751.
(S)-3-Ben zyloxyca r bon yla m in o-1-h yd r oxyp ip er id in -2-
on e (37). A mixture of 36 (3.7 g, 10 mmol), hexanes (20 mL),
0.5 N HCl (40 mL), and TFA (10 mL) was heated at 60 °C for
15 min. The reaction mixture was concentrated under reduced
pressure to give a light yellow oil. To this residue were added
CH2Cl2 (40 mL) and 1 N HCl (60 mL). The mixture was heated
at 40 °C briefly to dissolve the residue and allowed to stir at
room temperature for 40 min. After separation of the layers,
the aqueous phase was washed with CH2Cl2 (3 × 10 mL) and
hexanes (5 mL), filtered, and concentrated to give N2-benzy-
loxycarbonyl-N5-hydroxy-L-ornithine hydrochloride (2.62 g,
82%) as a white foam: 1H NMR (300 MHz, D2O) δ 7.43 (m, 5
H), 5.13 (s, 2 H), 4.21 (m, 1 H), 3.29 (m, 2 H), 1.99-1.78 (m, 4
H).
N,N-[(2S,3R)-2-Ben zyloxycar bon ylam in o-3-(2-ben yloxy-
p h en yl)-3-h yd r oxyp r op ion yl]-â-a la n yl-â-a la n in e m eth yl
ester (32): a colorless glass (54%); IR (neat) 3339, 1728, 1654
cm-1; 1H NMR (300 Hz, CDCl3) δ 7.46-6.88 (m, 14 H), 6.89 (t,
1 H, J ) 5.4 Hz), 6.48 (t, 1 H, J ) 5.7 Hz), 5.85 (t, 1 H, J ) 8.4
Hz), 5.58 (s, br, 1 H), 5.13 (d, 1 H, J ) 11.4 Hz), 5.06 (d, 1 H,
J ) 11.7 Hz), 4.92 (s, 2 H), 4.57 (dd, 1 H, J ) 8.4, 1.8 Hz), 4.21
(d, 1 H, J ) 4.2 Hz), 3.61 (s, 3 H), 3.52-3.31 (m, 4 H), 2.48 (t,
2 H, J ) 6.3 Hz), 2.26 (m, 2 H); 13C NMR (75 MHz, CDCl3) δ
173.4, 171.8, 171.4, 156.8, 155.1, 136.9, 136.4, 128.9, 128.6,
128.5, 128.2, 128.0, 127.5, 127.1, 121.1, 111.6, 77.4, 70.3, 68.8,
67.1, 58.5, 52.1, 36.2, 35.2, 33.9; HRFABMS m/z calcd for
C
31H36N3O8 [MH]+ 578.2502, found 578.2503.
N,N-[(2S,3R)-2-Ben zyloxyca r b on yla m in o-3-(3,4-d ib e-
n yloxyp h en yl)-3-h yd r oxyp r op ion yl]-â-a la n yl-â-a la n in e
(34). To a solution of 30 (15.2 mg, 0.022 mmol) in CH3CN/
MeOH (1:1, 0.6 mL) was added a 1 N LiOH solution (0.033
mL, 0.033 mmol) at 0 °C. After being stirred at 0 °C for 3 h,
the reaction mixture was diluted with H2O (2 mL) and washed
with Et2O (3 × 2 mL). The aqueous layer was acidified to pH
3.0 with 10% citric acid and extracted with EtOAc (3 × 3 mL).
The combined organic layers were washed with brine (1 mL),
dried (MgSO4), filtered, and concentrated under reduced
pressure to afford 34 as a white solid (6.4 mg, 43%): IR (neat)
To a mixture of the above compound (524.0 mg, 1.645 mmol)
in CH3CN (100 mL) were added HOBt (266.5 mg, 1.809 mmol),
NaHCO3 (359.3 mg, 4.277 mmol), and EDC (377.0 mg, 1.974
mmol) at 0 °C, and the mixture was stirred at room temper-
ature for 24 h. The mixture was concentrated under reduced
pressure to give a light yellow residue. The residue was treated
with EtOAc (70 mL) and washed with 10% citric acid (2 × 15
mL) and 5% NaHCO3 (3 × 10 mL). The organic phase was
dried (Na2SO4), filtered, and concentrated under reduced
pressure to give crude 37 (282.2 mg, 65%) as an off-white solid.
An analytical sample was obtained as a white solid by
reversed-phase chromatography (H2O/MeOH, 2:1-1:2): IR
1
3321, 1726 cm-1; H NMR (300 Hz, DMSO-d6) δ 8.28 (t, 1 H,
J ) 5.1 Hz), 7.98 (t, 1 H, J ) 5.4 Hz), 7.51-6.88 (m, 18 H),
5.26 (d, 1 H, J ) 6.9 Hz), 5.14 (s, 2 H), 5.12 (s, 2 H), 5.06 (m,
2 H), 4.09(d, 2 H, J ) 5.4 Hz), 3.59 (d, 1 H, J ) 6.0 Hz), 3.22
(m, 4 H), 2.36 (t, 2 H, J ) 6.6 Hz), 2.25 (m, 2 H); 13C NMR (75
Hz, DMSO-d6) δ 171.8, 171.0, 170.1, 158.6, 149.0, 148.8, 137.4,
137.3, 131.9, 128.8, 128.5, 128.4, 128.3, 128.2, 128.0, 127.9,
126.9, 119.5, 114.6, 112.6, 80.0, 72.8, 70.7, 70.4, 61.7, 43.2, 36.0,
35.3, 35.2, 34.1; FABMS m/z calcd for C37H40N3O9 [MH]+ 670,
found 670.
1
(neat) 3307, 1706, 1649 cm-1; H NMR (300 MHz, CDCl3) δ
7.36 (m, 5 H), 5.68 (d, 2 H, J ) 6.0 Hz), 5.12 (s, 2 H), 4.25 (m,
1 H), 3.65 (m, 2 H), 2.39-1.70 (m, 4 H); 13C NMR (75 MHz,
CDCl3) δ 165.6, 156.6, 137.6, 128.7, 128.3, 128.2, 67.1, 51.8,
50.4, 28.1, 20.4; HRFABMS m/z calcd for C13H17N2O4 [MH]+
265.1188, found 265.1183.
N,N-[(2S,3R)-2-Ben zyloxycar bon ylam in o-3-(2-ben yloxy-
p h en yl)-3-h yd r oxyp r op ion yl]-â-a la n yl-â-a la n in e (35). To
a solution of 31 (32.6 mg, 0.056 mmol) in THF/H2O (1:1, 1 mL)
was added a 1 N LiOH solution (0.085 mL, 0.085 mmol) at 0
°C. After being stirred at 0 °C for 1 h, the reaction mixture
was concentrated to remove the THF. The residue was diluted
with H2O (2 mL) and washed with Et2O (2 × 2 mL). The
aqueous layer was acidified to pH 3.0 with 10% citric acid and
extracted with EtOAc (3 × 4 mL). The combined organic layers
were washed with brine (2 mL), dried (MgSO4), filtered, and
concentrated under reduced pressure to afford 35 as a colorless
(S)-3-Am in o-1-h yd r oxyp ip er id in -2-on e (6). Compound
37 (1.638 g, 6.204 mmol) was stirred in MeOH (40 mL) in the
presence of 10% Pd/C (163.8 mg) under H2 (1 atm) for 1 h.
After the compound was filtered through a reversed-phase
silica plug, the solvent was removed under reduced pressure
to produce 6 (0.81 g, 100%) as a white foam: IR (neat) 3352,
1
1634 cm-1; H NMR (300 MHz, D2O) δ 3.61 (t, 2 H, J ) 3.3
Hz), 3.50 (m, 1 H), 2.20-1.59 (m, 4 H); 13C NMR (75 MHz,
CDCl3) δ 167.5, 51.6, 50.8, 29.3, 20.7; HRFABMS m/z calcd
for C5H11N2O2 [MH]+ 131.0821, found 131.0827.
glass (26.7 mg, 84%): IR (neat) 3307, 1718, 1652 cm-1 1H
;
NMR (300 Hz, CDCl3) δ 7.43-6.82 (m, 14 H), 6.11 (d, 1 H, J
) 8.7 Hz), 5.71 (d, 1 H, J ) 3.6 Hz), 5.66 (s, br), 5.04 (m, 2 H),
4.91 (d, 1 H, J ) 12.6 Hz), 4.82 (d, 1 H, J ) 12.6 Hz), 4.65 (m,
1 H), 4.17 (d, 1 H, J ) 3.6 Hz), 3.36 (m, 4 H), 2.44 (m, 2 H),
2.30 (m, 2 H); 13C NMR (75 MHz, CDCl3) δ 175.3, 172.9, 172.5,
171.3, 160.2, 157.1, 155.7, 155.0, 137.1, 136.5, 136.4, 130.4,
129.1, 128.9, 128.7, 128.2, 128.0, 127.9, 127.4, 127.3, 127.0,
126.6, 121.4, 121.0, 112.3, 111.7, 77.6, 73.3, 70.7, 70.2, 68.6,
67.0, 61.7, 59.1; HRFABMS m/z calcd for C30H34N3O8 [MH]+
564.2346, found 564.2346.
N2-Ben zyloxycar bon yl-N2-m eth yl-N5-ph en ylm eth ylen e-
N5-oxid e-L-or n ith in e (5). To a suspension of 36 (100.0 mg,
0.271 mmol) and MeI (0.135 mL, 2.162 mmol) in THF (4 mL)
was added NaH (60%) (32.4 mg, 0.810 mmol) at 0 °C. The
reaction mixture was stirred at room temperature for 24 h and
quenched with addition of MeOH. The mixture was concen-
trated under reduced pressure and partitioned between Et2O
(20 mL) and H2O (8 mL). After separation of the layers, the
N5-Ben zyloxycar bon yl-N2-ter t-bu tyloxycar bon yl-N-[(S)-
1-h yd r oxy-2-oxo-3-p ip er id yl]-L-or n ith in a m id e (39). To a
stirred solution of 6 (1.892 g, 5.173 mmol) and HOAt (0.744 g,
5.691 mmol) in CH2Cl2 (6 mL) was added EDC (1.19 g, 6.201
mmol) at 0 °C. After being stirred at 0 °C for 15 min, compound
38 (0.800 g, 6.20 mmol) was added followed by the addition of
DMAP (0.946 g, 7.755 mmol). The mixture was stirred at room
temperature for 9 h, and TEA (0.719 mL, 5.174 mmol) was
added. After the mixture was stirred for another 24 h, the
solvent was removed under reduced pressure. The resulting
residue was partitioned between 10% citric acid (10 mL) and
EtOAc (30 mL). The aqueous layer was further extracted with
EtOAc (2 × 10 mL). The combined extracts were washed with
brine (5 mL), dried (Na2SO4), filtered, and concentrated under
reduced pressure. The crude material was purified by reversed-
phase chromatography (2:1 MeOH/H2O) to give 39 (1.285 g,
58%) as an off-white foam: IR (neat) 3309, 2480, 1690, 1655
4766 J . Org. Chem., Vol. 67, No. 14, 2002

Total Synthesis of Exochelin MN and Analogues
cm-1; 1H NMR (300 MHz, CD3OD) δ 7.33 (m, 5 H), 7.03 (s, br,
1 H), 6.73 (m, 1 H), 5.10 (s, br, 1 H), 5.06 (s, 2 H), 4.43 (dd, 1
H, J ) 5.1, 10.2 Hz), 4.06 (s, br, 1 H), 3.60 (m, 2 H), 3.15 (m,
2 H), 2.09-1.54 (m, 8 H), 1.44 (s, 9H); 13C NMR (75 MHz, CD3-
OD) δ 173.7, 166.1, 157.9, 156.6, 137.3, 128.3, 127.8, 127.7,
79.4, 66.2, 57.2, 54.5, 51.5, 50.3, 40.3, 29.7, 27.6, 26.3, 26.0,
20.6, 17.3; HRFABMS m/z calcd for C23H35N4O7 [MH]+ 479.2506,
found 479.2523.
dropwise to the above solution at 0 °C, and the mixture was
stirred at 0 °C for 15 min. After being stirred at room
temperature overnight, the reaction mixture was concentrated
under reduced pressure. The residue was treated with EtOAc,
washed with 5% NaHCO3 (2 × 3 mL), 10% citric acid (2 × 3
mL), brine (2 mL), dried (Na2SO4), filtered, and concentrated
under reduced pressure. The crude material was purified by
reversed-phase chromatography (3:1 MeOH/H2O) to generate
44 (62.4 mg, 31%) as a light yellow foam: IR (neat) 3306, 1653,
1540 cm-1; 1H NMR (300 MHz, DMSO-d6) δ 8.09 (d, 1 H, J )
6.0 Hz), 7.97 (m, 1 H), 7.88 (m, 1 H), 7.35-7.24 (m, 10 H),
6.72 (m, 1 H), 5.09 (s, br, 2 H), 4.99 (s, 2 H), 4.60 (m, 1 H),
4.30 (m, 1 H), 4.21 (m, 1 H), 3.45 (m, 2 H), 3.40 (m, 2 H), 3.23
(t, 2 H, J ) 7.2 Hz), 3.10 (m, 2 H), 2.95 (m, 2 H), 2.80 (s, 3 H),
2.51 (m, 2 H), 2.19 (t, 2 H, J ) 7.5 Hz), 1.89-1.42 (m, 12 H),
1.36 (s, 9 H); 13C NMR (75 MHz, DMSO-d6) δ 173.4, 171.2,
171.0, 170.4, 170.3, 164.7, 156.1, 155.4, 137.2, 136.9, 128.3,
127.8, 127.3, 79.2, 77.6, 66.4, 65.1, 57.8, 52.2, 51.2, 50.8, 49.5,
46.8, 35.7, 34.6, 32.4, 32.0, 29.8, 29.4, 28.2, 27.5, 25.8, 23.4,
20.3; HRFABMS m/z calcd for C43H63N8O13 [MH]+ 899.4515,
found 899.4510.
N5-Ben zyloxyca r bon yl-[N2-ben zyloxyca r bon yl-N5-N-N-
[(2S,3R)-2-ben zyloxycar bon ylam in o-3-(2-ben yloxyph en yl)-
3-h yd r oxyp r op ion yl]-â-a la n yl-â-a la n yl-N5-h yd r oxy-N2-
m eth yl-L-or n ith yl]-N-[(S)-1-h yd r oxy-2-oxo-3-p ip er id yl]-
L-or n ith in a m id e (42). To a stirred solution of compound 44
(32.4 mg, 0.036 mmol) in CH2Cl2 (1 mL) was added TFA (1
mL) at 0 °C. After being stirred at room temperature for 45
min, the mixture was concentrated under reduced pressure
and azeotroped with toluene twice. To a mixture of the above
residue, 28 (15.2 mg, 0.036 mmol), and BOP (15.9 mg, 0.036
mmol) in DMF (0.8 mL) was added DIPEA (0.006 mL, 0.02
mmol) dropwise at 0 °C. The mixture was stirred at 0 °C for
15 min and at room temperature overnight. The reaction
mixture was treated with EtOAc (6 mL), washed with 5%
NaHCO3 (2 × 2 mL), 10% citric acid (2 × 2 mL), and brine (2
mL), dried (Na2SO4), filtered, and concentrated under reduced
pressure. The crude product was purified by reverse-phase
chromatography (3:1 MeOH/H2O) to yield 42 (16.0 mg, 37%)
as a light yellow foam.
(S)-3-Ben zyloxyca r bon yla m in o-1-ben zyloxyp ip er id in -
2-on e (45). To a stirred solution of 36 (370.0 mg, 1.0 mmol)
in MeOH (10 mL) was added hydroxylamine hydrochloride
(73.2 mg, 1.05 mmol). The mixture was refluxed for 20 min.
To this solution were then added 3 Å molecular sieves and
TEA (202.0 mg, 2.0 mmol). The mixture was refluxed for an
additional 1 h and filtered through a pad of Celite. The filtrate
was concentrated under reduced pressure, and the resulting
residue was partitioned between EtOAc (25 mL) and H2O (8
mL). After separation of the layers, the organic layer was dried
(Na2SO4), filtered, and concentrated under reduced pressure
to give a red residue.
To a solution of the above compound in DMF (1.5 mL) were
added K2CO3 (1.38 g, 10.0 mmol) and BnBr (0.595 mL, 5.0
mmol). The reaction mixture was stirred at room temperature
overnight and diluted with EtOAc (50 mL). This mixture was
washed with H2O (3 × 15 mL) and brine (15 mL), dried
(MgSO4), filtered, and concentrated under reduced pressure.
The crude product was purified by column chromatography
(CH2Cl2/EtOAc, 8:1) to provide 45 as white needles (230.1 mg,
65%): [R]D ) -45° (c ) 1.0, CH2Cl2); mp 86-88 °C; IR (neat)
3326, 1718, 1670 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.37 (m,
10 H), 5.72 (s, br, 1 H), 5.12 (s, 2 H), 4.95 (d, 1 H, J ) 10.5
Hz), 4.90 (d, 1 H, J ) 10.2 Hz), 4.17 (m, 1 H), 3.41 (m, 1 H),
3.33 (m, 1 H), 2.41 (m, 1 H), 1.86 (m, 1 H), 1.79 (m, 1 H), 1.55
(dq, 1 H, J ) 12.3, 4.5 Hz); 13C NMR (75 MHz, CDCl3) δ 168.1,
162.2, 136.8, 135.8, 129.7, 128.9, 128.6, 128.2, 76.1, 67.0, 52.9,
51.4, 28.3, 20.9; HRFABMS m/z calcd for C20H23N2O4 [MH]+
355.1658, found 355.1641.
N5-Ben zyloxycar bon yl-(N2-ben zyloxycar bon yl-N2-m eth -
yl-N5-p h en ylm eth ylen e-N5-oxid e-L-or n ith yl)-N-[(S)-1-h y-
dr oxy-2-oxo-3-piper idyl]-L-or n ith in am ide (41). To a stirred
solution of 39 (1.968 g, 4.12 mmol) in CH2Cl2 (10 mL) was
added TFA (8 mL) at 0 °C. After the mixture was stirred at
room temperature for 40 min, the solvent was removed under
reduced pressure to give the amine TFA salt (2.030 g, 100%)
as a light yellow foam. Employing the procedure described for
the preparation of 39, reaction of 5 and the above salt afforded
compound 41 as an off-white foam (0.949 g, 31%) after
reversed-phase column chromatography (3:1 MeOH/H2O): IR
(neat) 3306, 1686 cm-1; 1H NMR (300 MHz, CDCl3) δ 8.18 (m,
1 H), 7.74-7.27 (m, 15 H), 5.65 (s, br, 1 H), 5.11 (s, 2 H), 5.02
(s, 2 H), 4.72 (m, 1 H), 4.51 (m, 1 H), 4.26 (m, 1 H), 3.89 (m, 2
H), 3.51 (m, 2 H), 3.16 (m, 2 H), 2.85 (s, 3 H), 2.03-1.45 (m,
12 H); 13C NMR (75 MHz, CDCl3) δ 174.5, 172.0, 170.7, 165.0,
157.3, 157.0, 136.8, 136.4, 135.7, 130.8, 130.7, 130.5, 128.9 (2),
128.7, 128.6, 128.3, 128.2, 127.9, 67.8, 66.7, 66.2, 58.5, 52.6,
50.4, 50.3, 40.2, 30.5, 29.7, 27.5, 25.9, 25.3, 24.3, 20.5; HR-
FABMS m/z calcd for C39H49N6O9 [MH]+ 745.3561, found
745.3549.
N5-Ben zyloxyca r bon yl-[N2-ben zyloxyca r bon yl-N5-N-N-
[(2S,3R)-2-ben zyloxycar bon ylam in o-3-(2-ben yloxyph en yl)-
3-h yd r oxyp r op ion yl]-â-a la n yl-â-a la n yl-N5-h yd r oxy-N2-
m eth yl-L-or n ith yl]-N-[(S)-1-h yd r oxy-2-oxo-3-p ip er id yl]-
L-or n ith in a m id e (42). To a stirred solution of 41 (74.7 mg,
0.10 mmol) in MeOH (2 mL) was added hydroxylamine
hydrochloride (7.7 mg, 0.11 mmol). The mixture was warmed
to 60-70 °C and stirred for 20 min. The solution was
concentrated under reduced pressure, and the resulting resi-
due was triturated using MeOH and Et2O to give 3 as a light
yellow foam (519.4 mg, 75%) that was used without purifica-
tion.
To a stirred solution of compound 3 (48.0 mg, 0.07 mmol),
compound 35 (39.4 mg, 0.07 mmol), and BOP (31.1 mg, 0.07
mmol) in DMF (0.8 mL) was added DIPEA (9.2 mg, 0.07 mmol)
dropwise at 0 °C. The mixture was stirred at 0 °C for 15 min
and at room temperature overnight. The reaction mixture was
treated with EtOAc (6 mL), washed with 5% NaHCO3 (2 × 3
mL), 10% citric acid (2 × 3 mL), and brine (3 mL), dried (Na2-
SO4), filtered, and concentrated under reduced pressure. The
crude product was purified by reversed-phase chromatography
(3:1 MeOH/H2O) to yield 42 (37.6 mg, 41%) as a light yellow
foam: IR (neat) 3307, 1654 cm-1; 1H NMR (300 MHz, DMSO-
d6) δ 8.11 (m, 1 H), 7.90 (m, 2 H), 7.56-6.92 (m, 24 H), 5.59
(m, 1 H), 5.16 (s, 2 H), 5.09 (s, br, 2 H), 4.99 (s, 2 H), 4.87 (d,
1 H, J ) 10.2 Hz), 4.83 (d, 1 H, J ) 10.2 Hz), 4.60 (s, br, 1 H),
4.44 (d, 1 H, J ) 8.4 Hz), 4.30 (m, 1 H), 4.22 (m, 1 H), 3.45 (m,
2 H), 3.34-3.25 (m, 6 H), 2.94 (m, 2 H), 2.80 (s, 3 H), 2.44 (m,
2 H), 2.17 (m, 2 H), 1.88-1.44 (m, 12 H); 13C NMR (75 MHz,
DMSO-d6) δ 173.4, 171.2, 170.9, 170.5, 169.9, 164.6, 158.2,
156.1, 155.9, 155.3, 154.3, 137.2, 137.0, 136.9, 136.7, 130.5,
129.9, 128.4, 128.3, 128.2, 127.9, 127.7, 127.4, 127.3, 126.9,
126.8, 126.6, 120.6, 120.0, 112.6, 111.5, 79.2, 75.8, 69.4, 69.0,
66.8, 66.4, 65.1, 60.4, 59.3, 57.8, 52.2, 51.2, 50.8, 49.5, 46.8,
34.6, 32.3, 32.0, 29.4, 27.5, 25.8, 23.3, 20.3; HRFABMS m/z
calcd for C62H76N9O16 [MH]+ 1201.5332, found 1201.5298.
N5-Ben zyloxyca r bon yl-(N2-ben zyloxyca r bon yl-N5-N,N-
ter t-bu tyloxyca r bon yl-â-a la n yl-â-a la n yl-N5-h yd r oxy-N2-
m eth yl-L-or n ith yl)-N-[(S)-1-h yd r oxy-2-oxo-3-p ip er id yl]-
L-or n ith in a m id e (44). To a stirred solution of compound 3
(131.6 mg, 0.192 mmol) and 43 (56.4 mg, 0.192 mmol) in DMF
(2 mL) was added BOP (84.9 mg, 0.192 mmol). A solution of
DIPEA (24.8 mg, 0.192 mmol) in DMF (0.3 mL) was added
(S)-3-Am in o-1-b en zyloxyp ip er id in -2-on e H yd r ob r o-
m id e (46). To a solution of 45 (350 mg, 1.0 mmol) in CH2Cl2
(8 mL) was added HBr (33% w/v in acetic acid) (8 mL). After
J . Org. Chem, Vol. 67, No. 14, 2002 4767

Dong and Miller
being stirred at room temperature for 1 h, the reaction mixture
was concentrated under reduced pressure. The residue was
dissolved in CHCl3 (20 mL) and concentrated again. The
residue was triturated using CHCl3 and hexanes to give 46
as a white solid (276 mg, 92%): mp 194-195 °C; IR (KBr)
58.7, 52.4, 51.3, 40.0, 30.5, 30.1, 28.0, 26.1, 25.2, 24.4, 21.2;
HRFABMS m/z calcd for C46H55N6O9 [MH]+ 835.4031, found
835.4027.
N5-Ben zyloxyca r b on yl-(N5-b en zyloxy-N2-b en zyloxy-
car bon yl-N5-N,N-ter t-bu tyloxycar bon yl-â-alan yl-â-alan yl-
N2-m et h yl-L-or n it h yl)-N-[(S)-1-b en zyloxy-2-oxo-3-p ip -
er id yl]-L-or n ith in a m id e (50). To a stirred solution of 49
(332.2 mg, 0.398 mmol) in MeOH (5 mL) was added hydroxy-
lamine hydrochloride (29.1 mg, 0.418 mmol). The mixture was
warmed to 60-70 °C and stirred for 20 min. The solution was
concentrated under reduced pressure, and the resulting resi-
due was triturated with MeOH and Et2O to give the hydroxy-
lamine hydrochloride derivative (263.7 mg, 85%) as a white
foam.
1
3436, 1676 cm-1; H NMR (300 MHz, D2O) δ 7.47 (m, 5 H),
4.98 (m, 2 H), 4.07 (m, 1 H), 3.61 (m, 2 H), 2.27 (m, 1 H), 2.07
(m, 1 H), 1.95-1.82 (m, 2 H), 13C NMR (75 MHz, D2O) δ 165.0,
134.2, 130.2, 129.6, 129.0, 76.1, 50.5, 49.9, 24.9, 19.9; HR-
FABMS m/z calcd for C12H17N2O2 [MH]+ 221.1290, found
221.1291.
N5-Ben zyloxyca r bon yl-N-[(S)-1-ben zyloxy-2-oxo-3-p i-
p er id yl]-N2-ter t-bu tyloxyca r bon yl-L-or n ith in a m id e (47).
To a stirred suspension of 46 (295.1 mg, 0.980 mmol), 38 (422.0
mg, 1.151 mmol), and HOAt (160.0 mg, 1.176 mmol) in CH2-
Cl2 (5 mL) were added EDC (262.1 mg, 1.372 mmol) and DMAP
(311.3 mg, 2.546 mmol) at 0 °C. After being stirred at 0 °C for
15 min and room temperature overnight, the reaction mixture
was treated with EtOAc (40 mL) and H2O (10 mL). After
separation of the layers, the organic layer was washed with
5% NaHCO3 (2 × 15 mL), 10% citric acid (2 × 15 mL), and
brine (10 mL), dried (MgSO4), filtered, and concentrated under
reduced pressure. The crude material was purified by column
chromatography (2% MeOH/CH2Cl2) to give 47 (523 mg, 94%)
To a stirred solution of the above compound (260.6 mg, 0.333
mmol) and 43 (86.6 mg, 0.333 mmol) in CH3CN/DMF (3:1, 2
mL) were added BOP (147.3 mg, 0.333 mmol) and DMAP
(488.2 mg, 0.333 mmol) at 0 °C. The mixture was stirred at 0
°C for 10 min and at room temperature overnight. The reaction
mixture was concentrated under reduced pressure and parti-
tioned between EtOAc (45 mL) and H2O (10 mL). The organic
phase was further washed with 5% NaHCO3 (2 × 8 mL), 10%
citric acid (2 × 4 mL), and brine (3 mL), dried (MgSO4), filtered,
and concentrated under reduced pressure. To a solution of the
above residue in DMF (1 mL) were added K2CO3 (229.8 mg,
1.665 mmol) and BnBr (0.158 mL, 1.332 mmol). After being
stirred at room temperature overnight, the suspension was
diluted with EtOAc (25 mL) and washed with H2O (3 × 15
mL) and brine (15 mL). After separation of the layers, the
organic layer was dried (MgSO4), filtered, and concentrated
under reduced pressure. The residue was purified by column
chromatography (1-4% MeOH/CH2Cl2) to provide 50 as a
white solid (266.1 mg, 74% for two steps): IR (neat) 3308, 1656,
1529 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.37-6.97 (m, 20 H),
5.32 (m, 1 H), 5.14 (s, 2 H), 5.07 (s, 2 H), 4.90 (d, 2 H, J ) 10.5
Hz), 4.87 (d, 2 H, J ) 10.5 Hz), 4.76 (m, 2 H), 4.55 (m, 1 H),
4.40 (m, 1 H), 3.96 (m, 1 H), 3.42-3.13 (m, 10 H), 2.89 (s, 3
H), 2.33 (m, 2 H), 2.07 (m, 2 H), 1.86-1.45 (m, 12 H), 1.39 (s,
9 H); 13C NMR (75 MHz, CDCl3) δ 172.1, 171.4, 167.5, 157.3,
156.3, 136.9, 136.7, 135.4, 134.3, 129.7, 129.6, 129.4, 129.0,
128.8, 128.7, 128.7, 128.4, 128.2, 128.0, 79.2, 77.6, 76.7, 76.2,
67.9, 66.9, 57.9, 52.2, 44.2, 51.3, 40.0, 37.0, 36.0, 35.0, 32.5,
30.3, 30.1, 28.7, 28.0, 26.1, 25.2, 23.7, 21.2; HRFABMS m/z
calcd for C57H75N8O13 [MH]+ 1078.5375, found 1078.5387.
N5-Ben zyloxyca r b on yl-(N5-b en zyloxy-N2-b en zyloxy-
ca r bon yl-N5,N-â-a la n yl-â-a la n yl-N2-m eth yl-L-or n ith yl)-N-
[(S)-1-ben zyloxy-2-oxo-3-p ip er id yl]-L-or n ith in a m id e (51).
To a solution of compound 50 (85.2 mg, 0.082 mmol) in CH2-
Cl2 (1.0 mL) was added TFA (1.0 mL) at 0 °C. The reaction
mixture was stirred at room temperature for 40 min and
concentrated under reduced pressure. The residue was dis-
solved in CH2Cl2 (10 mL) and washed with 5% NaHCO3 (2 ×
3 mL), dried (Na2SO4), filtered, and concentrated under
reduced pressure to give 51 as an oily solid (68.1 mg, 87%):
IR (neat) 3319, 1660 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.58
(m, 1 H), 7.36-7.16 (m, 20 H), 5.36 (m, 1 H), 5.14 (s, 2 H),
5.07 (s, 2 H), 4.90 (d, 2 H, J ) 10.5 Hz), 4.87 (d, 2 H, J ) 10.5
Hz), 4.76 (m, 2 H), 4.55 (m, 1 H), 4.36 (m, 1 H), 3.82 (m, 1 H),
3.47-3.32 (m, 6 H), 3.13 (m, 2 H), 2.97 (t, 2 H, J ) 6.0 Hz),
2.87 (s, 3 H), 2.33 (t, 2 H, J ) 6.0 Hz), 2.17 (m, 2 H), 1.85-
1.53 (m, 12 H); 13C NMR (75 MHz, CDCl3) δ 174.2, 172.1, 171.4,
167.6, 156.8, 156.6, 136.9, 136.6, 135.4, 134.3, 129.8, 129.5,
129.4, 129.3, 129.0, 128.8, 128.8, 128.7, 128.5, 128.4, 128.3,
128.1, 125.8, 77.5, 76.7, 76.2, 67.9, 66.9, 58.1, 53.7, 51.4, 51.3,
40.0, 38.0, 38.4, 35.0, 32.5, 30.5, 30.0, 27.9, 26.1, 25.2, 23.4,
21.3; HRFABMS m/z calcd for C52H67N8O11 [MH]+ 979.4929,
found 979.4962.
1
as a white solid: IR (neat) 3308, 1698, 1525 cm-1; H NMR
(300 MHz, CDCl3) δ 7.47 (m, 10 H), 5.37 (m, 2H), 5.08 (s, 2
H), 4.93 (d, 2 H, J ) 10.5 Hz), 4.88 (d, 2 H, J ) 10.5 Hz), 4.43
(m, 1 H), 4.29 (m, 1 H), 3.32 (m, 4 H), 2.19-1.62 (m, 8 H),
1.50 (s, 9 H), 13C NMR (75 MHz, CDCl3) δ 172.7, 167.7, 157.1,
137.0, 135.4, 129.7, 129.0, 128.7, 128.7, 128.3, 128.2, 79.9, 76.1,
66.8, 53.7, 51.3, 40.2, 30.6, 30.6, 28.6, 28.0, 26.1, 21.1; HR-
FABMS m/z calcd for C30H41N4O7 [MH]+ 569.2975, found
569.2981.
N5-Ben zyloxyca r bon yl-N-[(S)-1-ben zyloxy-2-oxo-3-p i-
p er id yl]-L-or n ith in a m id e (48). To a solution of compound
47 (204.5 mg, 0.423 mmol) in CH2Cl2 (2 mL) was added TFA
(2 mL) at 0 °C. After being stirred at room temperature for 40
min, the solution was concentrated under reduced pressure.
The residue was dissolved in CH2Cl2 (20 mL), washed with
5% NaHCO3 (2 × 6 mL), dried (Na2SO4), filtered, and concen-
trated under reduced pressure to give 48 as a colorless glass
1
(182.3 mg, 92%): IR (neat) 3316, 1660, 1254 cm-1; H NMR
(300 MHz, CDCl3) δ 7.91 (d, 1 H, J ) 6.9 Hz), 7.41-7.14 (m,
10 H), 5.57 (t, 2 H, J ) 5.7 Hz), 5.06 (s, 2 H), 4.92 (d, 2 H, J
) 10.5 Hz), 4.89 (d, 2 H, J ) 10.5 Hz), 4.39 (m, 1 H, J ) 6.3
Hz), 3.39 (m, 1 H), 3.29 (m, 2 H), 3.16 (m, 2 H), 2.24-1.50 (m,
8 H), 13C NMR (75 MHz, CDCl3) δ 175.7, 168.0, 156.9, 137.0,
135.4, 129.7, 129.2, 129.0, 128.7, 128.4, 128.3, 128.2, 76.1, 66.7,
54.9, 51.3, 51.1, 40.8, 32.5, 28.1, 26.2, 21.1; HRFABMS m/z
calcd for C25H33N4O5 [MH]+ 469.2451, found 469.2444.
N5-Ben zyloxycar bon yl-(N2-ben zyloxycar bon yl-N2-m eth -
yl-N5-ph en ylm eth ylen e-N5-oxide-L-or n ith yl)-N-[(S)-1-ben -
zyloxy-2-oxo-3-p ip er id yl]-L-or n ith in a m id e (49). To a mix-
ture of 48 (110.0 mg, 0.235 mmol), 5 (99.3 mg, 0.258 mmol),
and HOAt (38.4 mg, 0.282 mmol) in CH2Cl2 (4 mL) was added
EDC (58.4 mg, 0.305 mmol) at 0 °C. After being stirred at 0
°C for 15 min and room temperature overnight, the reaction
mixture was diluted with EtOAc (15 mL) and H2O (4 mL).
After separation of the layers, the organic layer was washed
with 5% NaHCO3 (2 × 4 mL), 10% citric acid (2 × 4 mL), and
brine (3 mL), dried (MgSO4), filtered, and concentrated under
reduced pressure. The crude material was purified by column
chromatography (4% MeOH/CH2Cl2) to give 49 (177.2 mg, 92%)
as a white solid: IR (neat) 3307, 1670 cm-1 1H NMR (300
;
MHz, CDCl3) δ 8.19 (m, 1 H), 7.36 (m, 20 H), 5.40 (m, 1H),
5.12 (s, 2 H), 5.05 (s, 2 H), 4.90 (d, 2 H, J ) 10.5 Hz), 4.86 (d,
2 H, J ) 10.5 Hz), 4.73 (m, 1 H), 4.59 (m, 1 H), 4.40 (m, 1 H),
3.92 (m, 2 H), 3.38-3.09 (m, 4 H), 2.87 (s, 3 H), 2.13-1.48 (m,
12 H); 13C NMR (75 MHz, CDCl3) δ 171.9, 170.7, 167.6, 157.5,
157.2, 136.9, 136.6, 135.4, 135.1, 130.7, 129.7, 129.0, 128.9,
128.8, 128.8, 128.7, 128.4, 128.2, 128.1, 76.1, 68.0, 66.9, 66.4,
Gen er a l P r oced u r e for th e F in a l Cou p lin g Rea ction :
N5-Ben zyloxyca r bon yl-[N5-ben zyloxy-N2-ben zyloxyca r -
bon yl-N5,N,N-[(2S,3S)-2-ben zyloxyca r bon yla m in o-3-h y-
d r oxy-3-(4-im id a zoylp r op ion yl)]-â-a la n yl-â-a la n yl-N2-
m eth yl-L-or n ith yl]-N-[(S)-1-ben zyloxy-2-oxo-3-p ip er id yl]-
4768 J . Org. Chem., Vol. 67, No. 14, 2002

Total Synthesis of Exochelin MN and Analogues
L-or n ith in a m id e (52). To a solution of 24 (115.7 mg, 0.379
mmol) and NaHCO3 (79.6 mg, 0.948 mmol) in H2O (2 mL) was
added CbzCl (0.057 mL, 0.398 mmol) dropwise with vigorous
stirring at room temperature. After the mixture was stirred
for 30 min, the same amounts of NaHCO3 and CbzCl were
added again. After an additional 30 min, the suspension was
washed with Et2O (2 × 3 mL). The aqueous layer was acidified
to pH 3 with 10% citric acid and extracted with EtOAc (4 × 3
mL). The combined extracts were dried (MgSO4), filtered, and
concentrated under reduced pressure to give crude 25 as a
clear glass (143.2 mg, 86%): 1H NMR (300 MHz, CDCl3) δ 8.13
(s, 1 H), 7.40 (m, 5 H), 7.32 (s, 1 H), 7.26 (m, 5 H), 6.01 (d, J
) 8.4 Hz, 1 H), 5.37 (m, 2 H), 5.32 (m, 1 H), 5.01 (m, 2 H),
4.70 (m, 1 H).
To a solution of crude 25 (36.1 mg, 0.082 mmol), 51 (80.2
mg, 0.082 mmol), and HOAt (19.5 mg, 0.102 mmol) in CH2Cl2
(2 mL) was added EDC (19.5 mg, 0.102 mmol) at 0 °C. The
mixture was stirred at 0 °C for 15 min and at room temper-
ature overnight. The reaction mixture was treated with EtOAc
(6 mL) and H2O (2 mL). After separation of the layers, the
organic phase was washed with 5% NaHCO3 (2 × 3 mL), 10%
citric acid solution (2 × 3 mL), and brine (3 mL), dried (Na2-
SO4), filtered, and concentrated under reduced pressure. The
crude product was purified by column chromatography (5%
MeOH/CH2Cl2) to produce 52 (45.6 mg, 44%) as a white solid:
IR (neat) 3307, 1654 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.39-
7.19 (m, 25 H), 7.19 (d, 2 H, J ) 7.2 Hz), 6.85 (d, 2 H, J ) 7.2
Hz), 5.22 (s, br, 1 H), 5.10-4.97 (m, 6 H), 4.88 (d, 2 H, J ) 9.9
Hz), 4.84 (d, 2 H, J ) 10.2 Hz), 4.76 (m, 2H), 4.57-3.96 (m, 3
H), 3.42-3.13 (m, 10 H), 2.89 (s, 3 H), 2.33 (m, 2 H), 2.26 (m,
2 H), 2.06-1.51 (m, 12 H); 13C NMR (75 MHz, CDCl3) δ 174.2,
172.0, 171.8, 170.8, 170.6, 167.5, 157.1, 156.8, 148.6, 137.1,
136.6, 135.4, 134.2, 131.5, 129.7, 129.5 (2), 129,4, 129.1, 129.0,
128.7, 128.3, 128.2 (2), 127.7, 127.3, 127.0, 114.8, 77.4, 76.5,
76.2, 70.1, 68.6, 67.9, 67.2, 67.0, 66.8, 58.0, 52.1, 51.3, 43.8,
40.1, 36.6, 36.3, 35.1, 34.0, 32.6, 30.5, 28.0, 26.1, 25.0, 23.4,
21.2; FABMS m/z calcd for C66H80N11O15 [MH]+ 1266, found
1266.
119.2, 114.9, 113.0, 77.4, 76.4, 76.1, 72.5, 71.3, 67.9, 67.1, 66.8,
60.9, 57.9, 52.3, 51.2, 43.7, 40.1, 36.5, 35.9, 35.2, 32.7, 30.5,
27.8, 26.2, 25.9, 24.7, 23.0, 21.1; FABMS m/z calcd for
C83H94N9O17 [MH]+ 1488, found 1488.
N5-Ben zyloxyca r b on yl-[N5-b en zyloxy-N2-b en zyloxy-
ca r bon yl-N5,N,N-[(2S,3R)-2-ben zyloxyca r bon yla m in o-3-
(2-ben zyloxyp h en yl)-3-h yd r oxyp r op ion yl]-â-a la n yl-â-a la -
n yl-N2-m e t h yl-L-or n it h yl]-N -[(S)-1-b e n zyloxy-2-oxo-3-
p ip er id yl]-L-or n ith in a m id e (55): a colorless glass (84%); IR
1
(neat) 3319, 1656, 1528 cm-1; H NMR (300 MHz, CDCl3) δ
7.49-7.14 (m, 32 H), 6.85 (m, 2 H), 6.62 (m, 1 H), 6.18 (m, 1
H); 5.60 (m, 1 H), 5.36 (m, 1 H), 5.12 (m, 2 H), 5.08 (s, 2 H),
5.04 (m, 2 H), 4.88-4.74 (m, 4 H), 4.64 (d, 1 H, J ) 7.5 Hz),
4.58 (m, 1 H), 4.40 (m, 1 H), 3.92 (s, br, 1 H), 3.48 (m, 2 H),
3.40 (m, 2 H), 3.28 (m, 2 H), 3.08 (m, 2 H), 2.83 (s, 3 H), 2.52
(m, 2 H), 2.28 (m, 2 H), 2.07 (m, 2 H), 1.84-1.48 (m, 12 H);
13C NMR (75 MHz, CDCl3) δ 174.1, 171.8, 171.6, 171.1, 167.6,
157.3, 157.0, 154.9, 137.0, 136.9, 136.5, 135.3, 134.3, 129.7,
129.5, 129.4, 129.3, 129.0, 128.8, 128.7, 128.6, 128.3, 128.1,
128.0, 127.9, 127.4, 127.2, 120.9, 111.4, 77.4, 76.3, 75.9, 70.1,
68.6, 67.9, 66.9, 66.7, 58.7, 57.9, 53.6, 52.4, 51.1, 43.8, 40.2,
36.6, 36.0, 35.0, 32.9, 30.6, 30.4, 27.7, 25.5, 21.1; FABMS m/z
calcd for C76H88N9O16 [MH]+ 1382, found 1382.
Gen er a l P r oced u r e for Dep r otection : N5-Hyd r oxy-
N5,N-(N-th r eo-â-h yd r oxy-L-h istid yl)-â-a la n yl-â-a la n yl-N2-
m eth yl-L-or n ith yl-N-(S)-(1-h yd r oxy-2-oxo-3-p ip er id yl)-L-
or n ith in a m id e (1a ). To a solution of 52 (51.7 mg, 0.037
mmol) in MeOH (2 mL) was added 10% Pd(OH)2/C (42.1 mg).
The reaction mixture was stirred under H2 (1 atm) for 1 h and
filtered through a reversed-phase silica plug. The filtrate was
acidified to pH 6-7 with 1 N HCl, filtered, and concentrated
under reduced pressure to give a light red glass. The product
was further purified by reversed-phase chromatography (1%
TFA in H2O/MeOH, 10:1) and HPLC (2% MeOH/H2O, 1% TFA
at 1 mL min-1, monitored at 221 nm) to give 1a as a pink solid
(9.1 mg, 36%): IR (neat) 3400, 1650 cm-1; 1H NMR (600 MHz,
D2O) δ 8.06 (s, 1 H Hz, Im), 7.56 (s, 1 H, Im), 4.96 (d, 1H, J )
3.3 Hz ImCHOH), 4.32 (m, 1 H, NHCHCO), 4.13 (m, 1 H,
COCHNH2), 3.81 (m, 2 H, 2 × NHCHCO), 3.50 (m, 4 H, 2 ×
CH2NOH), 3.23 (m, 2 H, CH2NH2), 3.17 (t, 2 H, J ) 6.0 Hz,
CH2NHCO), 2.89 (t, 2 H, J ) 6.0 Hz, CH2NHCO), 2.55 (s, 3
H, NCH3), 2.11 (m, 2 H, CH2CONH), 1.93 (m, 2 H, CH2CONH),
1.88-1.52 (m, 12 H, 3 × CHCH2CH2CH2); 13C NMR (150 MHz,
D2O) δ 169.5, 168.5, 167.3, 164.6, 162.6, 159.3, 131.5, 120.2,
116.6, 66.3, 56.9, 49.9, 47.8, 46.4, 43.9, 43.3, 35.0, 31.5, 31.2,
31.0, 27.7, 24.0, 23.1, 22.7, 19.3, 17.3, 16.2; HRFABMS m/z
calcd for C28H50N11O9 [M + Na]+ 706.3612, found 706.3629.
N5-Ben zyloxyca r b on yl-[N5-b en zyloxy-N2-b en zyloxy-
ca r bon yl-N5-N-N-[(2S,3R)-2-ben zyloxyca r bon yla m in o-3-
(4-ben zyloxyp h en yl)-3-h yd r oxyp r op ion yl]-â-a la n yl-â-a la -
n yl-N 2-m e t h yl-L-or n it h yl]-N -[(S)-1-b e n zyloxy-2-oxo-3-
p ip er id yl]-L-or n ith in a m id e (53): a white solid (64%); IR
1
(neat) 3314, 1652, 1513 cm-1; H NMR (300 MHz, CDCl3) δ
7.39-7.19 (m, 32 H), 6.85 (d, 2 H, J ) 8.1 Hz), 6.48 (m, 1 H),
6.16 (m, 1 H); 5.39 (m, 1 H), 5.25 (s, br, 1 H), 5.10 (m, 2 H),
5.02 (m, 2 H), 4.97 (s, 2 H), 4.88-4.75 (m, 4 H), 4.57 (m, 1 H),
4.41 (m, 1 H), 3.92 (s, br, 1 H), 3.58 (m, 2 H), 3.40 (m, 2 H),
3.31 (m, 2 H), 3.16 (m, 2 H), 2.84 (s, 3 H), 2.52 (m, 2 H), 2.39
(m, 2 H), 2.16 (m, 2 H), 2.00-1.50 (m, 12 H); 13C NMR (75
MHz, CDCl3) δ 174.1, 172.0, 170.9, 167.5, 158.4, 157.2, 157.1,
156.8, 137.2, 136.8, 136.6, 135.3(2), 134.2, 132.8, 129.7, 129.6,
129.4, 129.3, 129.0, 128.9, 128.8, 128.7(2), 128.6, 128.3, 128.1,
128.0, 127.9, 127.7, 127.6, 127.4, 127.2, 114.7, 77.4, 76.5, 76.0,
72.4, 70.1, 67.9, 67.1, 66.8, 60.9, 57.9, 52.1, 51.2, 40.0, 36.6,
36.0, 35.2, 32.6, 30.5, 38.0, 27.8, 25.8, 23.4, 23.0, 21.1; FABMS
m/z calcd for C76H88N9O16 [MH]+ 1382, found 1382.
N5,N,N-[(2S,3R)-2-Am in o-3-h yd r oxy-3-(4-h yd r oxyp h e-
n yl)p r op ion yl]-â-a la n yl-â-a la n yl-N5-h yd r oxy-N2-m eth yl-
L-or n ith yl-N-(S)-(1-h yd r oxy-2-oxo-3-p ip er id yl)-L-or n ith i-
n a m id e (1b): HPLC (2% MeOH/H2O, 1% TFA at 1 mL min-1
,
monitored at 283 nm); a pink solid (67%); UV (MeOH) λmax
283 nm; IR (neat) 3234, 1672, 1201 cm-1; 1H NMR (300 MHz,
CD3OD) δ 7.18 (dd, 2 H, J ) 1.8, 8.7 Hz, Ar), 6.77 (dd, 2 H, J
) 1.5, 8.7 Hz, Ar), 4.77 (m, 2H, NHCHCO, ArCHOH), 4.41
(m, 1 H, NHCHCO), 3.87 (m, 1 H, NHCHCO), 3.77 (d, 1 H, J
) 7.8 Hz, COCHNH2), 3.61 (m, 2 H, CH2NOH), 3.38 (m, 2 H,
CH2NOH), 3.23 (m, 4 H, 2 × CH2NHCO), 2.95 (m, 2 H, CH2-
NH2), 2.64 (s, 3 H, NCH3), 2.45 (t, 2 H, J ) 6.6 Hz, CH2CONH),
2.18 (m, 2 H, CH2CONH), 2.10-1.67 (m, 12 H, 3 × CHCH2CH2-
CH2); 13C NMR (75 MHz, CD3OD) δ 173.0, 171.8, 167.9, 160.4,
159.9, 157.9, 130.1, 118.0, 115.3, 114.2, 72.5, 61.0, 59.9, 53.2,
51.9, 50.4, 39.0, 35.7, 35.2, 35.0, 33.4, 32.2, 31.3, 28.7, 28.3,
27.5, 23.7, 21.7, 20.2; HRFABMS m/z calcd for C31H52N9O10
[MH]+ 710.3837, found 710.3818.
N5-Ben zyloxyca r b on yl-[N5-b en zyloxy-N2-b en zyloxy-
ca r bon yl-N5,N,N-[(2S,3R)-2-ben zyloxyca r bon yla m in o-3-
(3,4-d iben zyloxyp h en yl)-3-h yd r oxyp r op ion yl]-â-a la n yl-
â-a la n yl-N2-m eth yl-L-or n ith yl]-N-[(S)-1-ben zyloxy-2-oxo-
3-p ip er id yl]-L-or n ith in a m id e (54): a white solid (72%); IR
1
(neat) 3315, 1652, 1515 cm-1; H NMR (300 MHz, CDCl3) δ
7.39-7.05 (m, 36 H), 6.85 (dt, 2 H, J ) 8.7, 13.8 Hz), 6.52 (m,
1 H), 6.02 (m, 1 H); 5.37 (m, 1 H), 5.26 (m, 1 H), 5.11 (m, 2 H),
5.06 (m, 4 H), 4.95 (s, 2 H), 4.90-4.73 (m, 4 H), 4.40 (m, 2 H),
3.92 (s, br, 1 H), 3.55 (m, 2 H), 3.41 (m, 2 H), 3.38 (m, 2 H),
3.11 (m, 2 H), 2.84 (s, 3 H), 2.37 (m, 2 H), 2.08 (m, 2 H), 1.97-
1.49 (m, 12 H); 13C NMR (75 MHz, CDCl3) δ 174.1, 172.0, 171.9,
171.2, 170.4, 167.5, 157.1, 156.7, 149.0, 148.5, 137.6, 137.5,
136.8, 136.5, 135.3, 134.2, 133.9, 129.7, 129.6, 129.4, 129.3,
129.0, 128.7, 128.6, 128.3, 128.2, 128.0, 127.9, 127.6, 127.4,
N5,N,N-[(2S,3R)-2-Am in o-3-h yd r oxy-3-(3,4-d ih yd r oxy-
p h e n yl)p r op ion yl]-â-a la n yl-â-a la n yl-N 5-h yd r oxy-N 2-
m eth yl-L-or n ith yl-N-(S)-(1-h yd r oxy-2-oxo-3-p ip er id yl)-L-
or n ith in a m id e (1c): HPLC (2% MeOH/H2O, 1% TFA at 1
mL min-1, monitored at 283 nm); a pink glass (44%); IR (neat)
1
3235, 1670, 1200 cm-1; H NMR (300 MHz, CD3OD) δ 6.79-
6.67 (m, 3 H, Ar), 4.70 (m, 1 H, J ) 7.2 Hz, ArCHOH), 4.40
J . Org. Chem, Vol. 67, No. 14, 2002 4769

Dong and Miller
(m, 2 H, 2 × NHCHCO), 3.89 (m, 1 H, NHCHCO), 3.73 (d, 1
H, J ) 7.2 Hz, COCHNH2), 3.59 (m, 2 H, CH2NOH), 3.37 (m,
2 H, CH2NOH), 3.23 (m, 4 H, 2 × CH2NHCO), 2.92 (m, 2 H,
CH2NH2), 2.64 (s, 3 H, NCH3), 2.19 (m, CH2CONH), 2.09 (m,
2 H, CH2CONH), 1.98-1.69 (m, 12 H, 3 × CHCH2CH2CH2);
13C NMR (75 MHz, CD3OD) δ 173.3, 172.2, 167.9, 166.9, 160.2,
159.7, 145.7, 145.4, 131.0, 118.1, 117.9, 115.3, 114.1, 113.7,
72.5, 61.0, 60.0, 53.2, 52.0, 50.4, 39.1, 35.8, 35.2, 35.1, 32.3,
31.3, 28.7, 28.3, 27.5, 23.7, 21.7, 20.2; HRFABMS m/z calcd
for C31H52N9O11 [MH]+ 726.3786, found 726.3754.
13C NMR (75 MHz, CD3OD) δ 172.2, 171.8, 167.7, 166.9, 158.9,
157.9, 130.1, 129.8, 129.1, 127.9, 115.3, 72.4, 61.0, 59.9, 53.3,
51.6, 51.1, 50.2, 39.2, 35.7, 35.2, 35.0, 34.7, 33.4, 32.3, 31.3,
28.8, 27.5, 23.5, 20.6; HRFABMS m/z calcd for C31H52N9O10
[MH]+ 710.3837, found 710.3834.
Ack n ow led gm en t. This work was supported by
grants from the National Institutes of Health. The
authors are grateful to Donald R. Schifferl and Dr.
J aroslav Zajicek for assistance with NMR experiments
and Dr. William C. Boggess, J r., and Nonka Sevova for
performing MS analyses. Maureen Metcalf’s help in the
preparation of this manuscript is also highly appreci-
ated. We thank Dr. Colin Ratledge at University of Hull
for a generous gift of authentic exochelin MN.
N5,N,N-[(2S,3R)-2-Am in o-3-h yd r oxy-3-(2-h yd r oxyp h e-
n yl)p r op ion yl]-â-a la n yl-â-a la n yl-N5-h yd r oxy-N2-m eth yl-
L-or n ith yl-N-(S)-(1-h yd r oxy-2-oxo-3-p ip er id yl)-L-or n ith i-
n a m id e (1d ): HPLC (2% MeOH/H2O, 1% TFA at 1 mL min-1
,
monitored at 283 nm); a pink solid (65%); IR (neat) 1670, 1202
cm-1; 1H NMR (300 MHz, CD3OD) δ 7.37 (d, 1 H, J ) 7.8 Hz,
Ar), 7.16 (t, 1 H, J ) 7.2 Hz, Ar), 6.90-6.78 (m, 2 H, Ar), 5.24
(d, 1 H, J ) 6.0 Hz, ArCHOH), 4.43 (m, 2 H, 2 × NHCHCO),
4.09 (d, 1 H, J ) 6.3 Hz, COCHNH2), 3.92 (m, 1 H, NHCHCO),
3.64 (m, 2 H, CH2NOH), 3.37 (t, 2 H, J ) 7.2 Hz, CH2NOH),
3.26 (m, 4 H, 2 × CH2NHCO), 2.96 (m, 2 H, CH2NH2), 2.65
(m, 3 H, NCH3), 2.47 (t, 2 H, J ) 6.9 Hz, CH2CONH), 2.27 (m,
2 H, CH2CONH), 2.10-1.67 (m, 12 H, 3 × CHCH2CH2CH2);
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra for all compounds listed in the Experimental Section
except 11b and 12b. This material is available free of charge
via the Internet at http://pubs.acs.org.
J O0256078
4770 J . Org. Chem., Vol. 67, No. 14, 2002