Entropically favorable macrolactamization. Synthesis of isodityrosine peptide analogues by tandem Erlenmeyer condensation-macrolactamization

Article abstract of DOI:10.1021/jo9825198

Macrolactams containing a modified isodityrosine moiety were assembled by direct addition of a bis-4-aryliden-5(4H)-oxazolone, derived by double Erlenmeyer condensation of diaryl ether dicarboxaldehydes and an α,ω- diamine, derived from the same precursor. Tandem acylation of diamines with the bis-Erlenmeyer oxazolone gave macrolactams in yields of up to 30%. TECM demonstrates an entropically controlled 28-membered ring closure and allows rapid access to a variety of cyclic isodityrosine peptide analogues of the biologically active natural product bastadin-5.

Full text of DOI:10.1021/jo9825198

2500
J . Org. Chem. 1999, 64, 2500-2504
En tr op ica lly F a vor a ble Ma cr ola cta m iza tion . Syn th esis of
Isod ityr osin e P ep tid e An a logu es by Ta n d em Er len m eyer
Con d en sa tion -Ma cr ola cta m iza tion
Karl L. Bailey and Tadeusz F. Molinski*
Department of Chemistry, University of California, Davis, Davis, California 95616
Received December 29, 1998
Macrolactams containing a modified isodityrosine moiety were assembled by direct addition of a
bis-4-aryliden-5(4H)-oxazolone, derived by double Erlenmeyer condensation of diaryl ether dicar-
boxaldehydes and an R,ω-diamine, derived from the same precursor. Tandem acylation of diamines
with the bis-Erlenmeyer oxazolone gave macrolactams in yields of up to 30%. TECM demonstrates
an entropically controlled 28-membered ring closure and allows rapid access to a variety of cyclic
isodityrosine peptide analogues of the biologically active natural product bastadin-5.
In tr od u ction
Isodityrosine 1, an oxidatively coupled tyrosine dimer,
is a structural component of natural product cyclic
peptides with unique biological properties. For example,
K-13 (2) is a potent noncompetitive inhibitor of angio-
tensin converting enzyme (ACE)1 that is produced by
Micromonospora halophytica subsp. exilisia K-13.2 OF
4949 I (3) and other members of the family from cultures
of the fungus Penicillium rugulosum OF 4949 are inhibi-
tors of aminopeptidase B.3 The isodityrosine motif can
also be seen in piperazinomycin,4 the glycopeptide anti-
biotics vancomycin and ristocetin,5 and marine sponge
peptides eurypamide6 from Microciona eurypa, and bas-
tadin-5 (4) from Ianthella basta (Pallas).7 Bastadin-5, one
of a family of brominated isodityrosines peptides, mobi-
lizes Ca2+ from stores within the sarcoplasmic reticulum
(SR) through the Ry1R-FKBP Ca2+-receptor-channel com-
plex (EC50 2.3 µM).8
Isodityrosine plays an important role in mediating
biological activity. In a seminal study by Boger et al., the
essential structural elements that potentiate 1-based
inhibitors of both ACE and aminopeptidase were defined
by structure-activity studies using analogues of the K-13
and OF 4949 peptide families.9 The pharmacophore for
ACE inhibitory activity includes a rigid macrocycle
containing the oxidatively coupled catechol ether with a
free phenolic OH. The activity of aminopeptidase inhibi-
tors were tolerant to substitution at this position by a
phenolic OMe, but more significant perturbations at this
site abolished activity.9 We have found that the phenolic
diaryl ether moiety of 2 is essential for activation of the
Ry1R-FKBP Ca2+-receptor-channel complex.10 Thus, analy-
sis of biological activity in each of the isodityrosine
peptides recapitulates the primacy of the unique peptide
turn-element embodied in 1, a nonplanar phenolic diaryl
ether scaffold (C-O-C-C torsional angle ∼126°).
* Corresponding author. Tel: 530 752 6358, FAX: 530 752 8995,
e-mail: tfmolinski@ucdavis.edu.
(1) Kase, H.; Kaneko, M.; Yamada, K. J . Antibiot. 1987, 40, 450-
454.
(2) Yasuzawa, Y.; Shirata, K.; Sano, H. J . Antibiot. 1987, 40, 455-
458
(3) (a) Sano, S.; Ikai, K.; Kuroda, H.; Nakamura, T.; Obayashi, A.;
Ezure, Y.; Enomoto, H. J . Antibiot. 1986, 39, 1674-1684. (b) Sano, S.;
Ikai, K.; Katayama, K.; Takesako, K.; Nakamura, T.; Obayashi, A.;
Ezure, Y.; Enomoto, H. J . Antibiot. 1986, 39, 1685-1696.
(4) Tamai, S.; Kaneda, M.; Nakamura, S. J . Antibiot. 1982, 35,
1130-1136.
(5) Nagarajan, R. Glycopeptide Antibiotics. In Drugs and the
Pharmaceutical Sciences; Dekker: New York, 1994; Vol. 63.
(6) Reddy, M. V. R.; Harper, M. K.; Faulkner, D. J . Tetrahedron
1998, 54(36), 10649-10656.
(7) (a) Kazlauskus, R.; Lidgard, R. O.; Murphy, P. T.; Wells, R. J .;
Blount, J . F. Aust. J . Chem. 1981, 34, 765-786. (b) Franklin, M. A.;
Penn, S. G.; Lebrilla, C. B.; Lam, T. H.; Pessah, I. N.; Molinski, T. F.
J . Nat. Prod. 1996, 59, 1121-1127 and references cited within.
(8) (a) Franklin, M. A.; Penn, S. G.; Lebrilla, C. B.; Lam, T. H.;
Pessah, I. N.; Molinski, T. F. J . Nat. Prod. 1996, 59, 1121-1127. (b)
Pessah, I. N.; Molinski, T. F.; Meloy, T. D.; Wong, P.; Buck, E. D.; Allen,
P. D.; Mohr, F. C.; Mack, M. M. Am. J . Physiol. 1997, 41, C601-C614.
Our investigations of the receptor binding of 4 required
a method for synthesis of isodityrosine cyclic peptides
while allowing flexibility for incorporation of secondary
peptide elements. Strategies for ring closure of simple
isodityrosine peptides (e.g., 1-3) include conventional
amide bond coupling,11 closure of the diaryl ether by one-
(9) Boger, D. L.; Yohannes, D. Bioorg. Med. Chem. Lett. 1993, 3,
245-250.
(10) Pessah, I. N.; Molinski, T. F., unpublished results.
10.1021/jo9825198 CCC: $18.00 © 1999 American Chemical Society
Published on Web 03/09/1999

Tandem Erlenmeyer Condensation-Macrolactamization
J . Org. Chem., Vol. 64, No. 7, 1999 2501
electron oxidative coupling,12 modified Ullmann cou-
pling,13 and SNAr nucleophilic displacement of activated
aryl fluorides.14 The drawback in each method is the
requirement of multistep preparation of suitably func-
tionalized intermediates. With two exceptions,11a,12d-g
each method was deployed for synthesis of smaller ring
cyclic peptides (∼14-membered), and it was not obvious
they would be practicable for larger ring macrolactams.
We present here a convergent strategy that allows rapid
assembly of analogues of 4 in less than four steps from
simple aryl aldehydes by exploiting a tandem Erlenmeyer
condensation15-macrolactamization (TECM). Tight en-
tropic control of macrocyclization is afforded in TECM
by use of a relatively rigid Erlenmeyer bis-“azlactone”
(bis-4-aryliden-5(4H)-oxazolone) as an acylating agent in
stepwise tandem amide bond formation with similarly
constrained R,ω-diamines. The product is a cyclic peptide
analogue bearing two planar R,â-dehydroamino residues
that can be transformed with ease to relatively uncon-
strained isodityrosine peptidomimetics. Although Erlen-
meyer oxazolones have been used to make peptide bonds
previously,16 the present work appears to be their first
application to macrolactamization and the synthesis of
cyclic peptide analogues.17 Macrolactamization by TECM
complements oxidative coupling and SNAr coupling strat-
egies by allowing rapid access to analogues of 4 with
variable diamine components.
Sch em e 1a
a
(a) CuO, K2CO3, py, 140 °C, 15 h; (b) Ac2O, N-Bz-Gly,
Pb(OAc)2, 110 °C, 24 h; (c) CH3NO2, 16 equiv, AcOH, NH4OAc,
reflux, 3 h; (d) LiAlH4, THF, reflux, 12 h.
Resu lts a n d Discu ssion
(hippuric acid) under the conditions described by Finar
and Libman (Ac2O, Pb(OAc)2, reflux 24 h)19 followed by
workup and trituration of the crude product with EtOAc
to obtain 6 as a bright yellow solid (mp 279-281 °C, 69%;
average of 83% yield per CHdO group). Under these
conditions, the Z,Z-geometrical isomer 6 is obtained with
>19:1 selectivity.20 Diamine 7 was readily prepared from
5 by double Henry condensation-elimination (CH3NO2,
16 equiv, Ac2O, NH4OAc, HOAc, reflux, 3 h) followed by
reduction of the resultant bis-â-nitrostyrene (LiAlH4,
THF, reflux, 11 h; 87% for two steps, 93% per CHdO).
Heating 6 with (1R,2R)-1,2-diphenyl-1,2-diaminoeth-
ane in pyridine (50 °C, 5 mM in each component) gave a
chiral macrolactam 8 (CD, λ 252 nm, ∆ꢀ -8.9) in low yield
(∼6%) accompanied by polymeric material. Macrolactam-
ization under the same conditions with the conforma-
tionally flexible 3-oxapentane-1,5-diamine (interatomic
N-N distance in extended conformation, 7.2 Å) gave 9
in 6% yield while 1,7-heptanediamine (CHCl3, 50 °C,
N-N 7.5 Å) gave macrolactam 10 in 7% yield. In marked
contrast, condensation of 6 with the diamine 7 (N-N ∼
9 Å) resulted in a 4- to 5-fold increase in yield to a give
the regioisomeric 28-membered macrocycles 11a ,b as a
1:1 mixture in 30% combined yield after chromatogra-
phy.21 No Michael addition of amine to oxazolone was
observed under the conditions of macrolactamization.22
When reaction was carried out at higher temperatures
Dialdehyde 5 (Scheme 1),18 conveniently prepared by
Ullmann coupling of commercially available 3-hydroxy-
4-methoxybenzaldehyde with 4-bromobenzaldehyde (CuO,
K2CO3, pyridine, 83%), was treated with N-benzoylglycine
(11) (a) Guo, Z.; Machiya, K.; Salamonczyk, G. M.; Sih, C. J . J . Org.
Chem. 1998, 63, 4269-4276. (b) Evans, D. A.; Ellman, J . A. J . Am.
Chem. Soc. 1989, 111, 1063-1072.
(12) (a) Evans, D. A.; Dinsmore, C. J .; Ratz, A. M.; Evrad, D. A.;
Barrow, J . C. J . Am. Chem. Soc. 1997, 119, 3417-3418. (b) Evans, D.
A.; Dinsmore, C. J .; Watson, P. S.; Wood, M. R.; Richardson, T. I.;
Trotter, B. W.; Katz, J . L. Angew. Chem., Int. Ed. 1998, 37, 2704-
2708. (c) Evans, D. A.; Wood, M. R.; Watson, P. S.; Trotter, B. W.;
Richardson, T. I.; Barrow, J . C.; Katz, J . L. Angew. Chem., Int. Ed.
1998, 37, 2700-2704. (d) Nishiyama, S.; Suzuki, Y.; Yamamura, S.
Tetrahedron Lett. 1988, 29, 559-562. (e) Nishiyama, S.; Yamamura,
S. Tetrahedron Lett. 1982, 23, 1281-1284. (f) Nishiyama, S.; Suzuki,
T.; Yamamura, S. Tetrahedron Lett. 1982, 23, 3699-3702. (g) Nishi-
yama, S.; Suzuki, T.; Yamamura, S. Chem. Lett. 1982, 1851-1852.
(13) (a) Nicolaou, K. C.; Natarajan, S.; Li, H.; J ain, N. F.; Hughes,
R.; Solomon, M. E.; Ramanjulu, J . M.; Boddy, C. N. C.; Takayanagi,
M. Angew. Chem. Int. Ed. 1998, 37, 2708-2714. (b) Nicolaou, K. C.;
J ain, N. F.; Natarajan, S.; Hughes, R.; Solomon, M. E.; Li, H.;
Ramanjulu, J . M.; Takayanagi, M.; Koumbis, A. E.; Bando, T. Angew.
Chem., Int. Ed. 1998, 37, 2714-2716. (c) Nicolaou, K. C.; Takayanagi,
M.; J ain, N. F.; Natarajan, S.; Koumbis, A. E.; Bando, T.; Ramanjulu,
J . M. Angew. Chem., Int. Ed. 1998, 37, 2717-2719. (d) Nicolaou, K.
C.; Boddy, C. N. C.; Natarajan, S.; Yue, T.-Y.; Bra¨se, S.; Ramanjulu,
J . M. J . Am. Chem. Soc. 1997, 119, 3421-3422.
(14) (a) Beugelmans, R.; Bigot, A.; Bois-Choussy, M.; Zhu, J . J . Org.
Chem. 1996, 61, 771-774. (b) Beugelmans, R.; Bois-Choussy, M.;
Vergne, C.; Bouillon, J .-P.; Zhu, J . J . Chem. Soc., Chem. Commun.
1996, 9, 1029-1030. (c) Boger, D. L.; Zhou, J . C.; Borzilleri, R. M.;
Nukui, S.; Castle, S. L. J . Org. Chem. 1997, 62, 2054-2069.
(15) Erlenmeyer, E. Ann. 1893, 275, 1-20.
(16) (a) Schmidt, U.; Kumpf, S.; Neumann, K. J . C. S. Chem.
Commun. 1994, 1915-1916. (b) Breitholle, E. G.; Stammer, C. H.
Tetrahedron Lett. 1975, 28, 2381-2384.
(19) Finar, I. L.; Libman, D. D. J . Chem. Soc. 1949, 2726-2728.
(20) Assignment of Z,Z-6 configuration is based on NMR chemical
shift of vinyl protons, δ 7.19 (s, 1H), 7.27 (s, 1H), which are relatively
upfield shift of those for E-isomers. For example, vinyl signals for Z-i
and E-ii occur at δ 7.14 and δ 7.48 ppm, respectively (see review by
Rao, ref 24).
(17) There is one other reported example of the preparation a bis-
oxazolone, but no report of use in cyclic peptide formation; Omote, Y.;
Fujinuma, Y.; Sugiyama, N. J . C. S. Chem. Commun. 1968, 190. (b)
Omote, Y.; Fujinuma, Y.; Sugiyama, N. Bull. Chem. Soc. J pn. 1969,
42, 1752.
(18) All new compounds were characterized (>95% pure) by 1H NMR
(300 or 600 MHz), 13C NMR, IR, FAB, or MALDI MS and gave
satisfactory HRMS (∆mmu e 5 mmu).

2502 J . Org. Chem., Vol. 64, No. 7, 1999
Bailey and Molinski
is confirmed by the UV spectrum of the bis-oxazolone 6
(MeOH, λmax 408 nm, ꢀ 24000) which shows the typical
extended chromophore reported for closely related planar
benzylidene mono-oxazolones.24 Fortuitously, the tor-
sional angle (C10-C9-O-C10′, æ ) 126°) in i is very
close to that seen in 4 in both solid-state X-ray7a and
calculated solution conformations (MM2, æ ) 125.8°).10
While the geometry of the exo conformer ii precludes ring
formation and will likely lead to polymer, the endo
conformer i required for cyclization (intercarbonyl dis-
tance d ) 9.5 Å) is lower in energy and easily accessible
due to a relatively low barrier for interconversion of i and
ii by geared rotation about the diaryl ether “hinge”. A
similar analysis suggests that the diaryl ether moiety of
diamine 7 is also conformationally constrained, although
the aminoethyl side-chains are somewhat more flexible.
The interatomic distance between amine groups in the
extended conformation (N-N d ) ∼9.0 Å) closely matches
the intercarbonyl distance in 6 which allows for facile
macrolactamization. This suggests the optimal contact
N-N distance for macrolactamization is ∼ 9 Å. The other
two diamines (Scheme 2) lack the optimal N-N distance
(d ) 5.9-7.3 Å) to achieve an enthalpically favorable
transitional state due to torsional strain, or, as in the
case of 1,7-heptanediamine (N-N, d ) 9.8 Å), are too
conformationally mobile for efficient ring closure (entropic
barrier).
F igu r e 1. Ground state conformations of 6 (PM3) obtained
by molecular mechanics. Torsional angle æ is defined as C10-
C9-O-C10′ while angle ψ is defined as C9-O-C10′-C9′ and
d is the intercarbonyl distance.
(toluene, 110 °C) macrolactamization was faster but was
also accompanied by elimination of H2O and formation
of imidazolones (UV). Hydrogenation of the mixture
11a ,b (1 atm H2, Pd-C, MeOH) provided the isodi-
tyrosine cyclic peptide 12 (95%) as a mixture of isomers.
Con clu sion
The convergent TECM strategy is well-suited to prepa-
ration of isodityrosine-isodityramine cyclic analogues of
bastadin-5 (4). Twenty-eight-membered ring macrocycles
were obtained in four steps and in good overall yield
(∼20-26%) from a common precursor 5. TECM provides
for considerable variation of the isodityrosine theme that
is not readily duplicated with existing ring closures based
on oxidative coupling or SNAr nucleophilic substitution.
We will report the TECM synthesis of compounds related
to 4 and biological activity in due course.
The 5-fold increase in yield of macrolactams 11a ,b with
diamine 7 contrasts with the lower yielding cyclizations
of simple diamines and lends support to our proposal that
TECM coupling of 6 and 7 is channeled to form the
macrolactam 11a ,b. Diamines are acylated by stepwise
addition to an oxazolone group to give putative mono-
acylated amines which may undergo intermolecular
addition, leading to polymer, or macrolactamization by
intramolecular addition. Because the distance from the
primary NH2 group to oxazolone CdO in this intermedi-
ate will be similar to d, the CdO to CdO distance in 6
(Figure 1), the efficiency of macrolactamization is partly
governed by a close match of d to the corresponding N-N
distance in the diamine as shown from the following
analysis. Molecular mechanics calculations (PM3 level,
MacSpartan Plus) show that 6 exists in two significantly
populated ground-state configurations i and ii (see Figure
1).23 Both forms have planar conjugated arylidene ox-
azolones with limited degrees of rotational freedom. This
Exp er im en ta l Section
Gen er a l. Simple R,ω-diamines were purchased from Aldrich
and used as supplied except for 1,7-heptanediamine which was
distilled from KOH at reduced pressure. TLC was carried out
on plastic plates coated with silica (0.2 mm) containing a
fluorescent indicator and visualized under a UV lamp and then
exposed to I2 vapor or sprayed with a solution of vanillin in
ethanolic-H2SO4 or ninhydrin in ethanol followed by heating.
Purity of each compound was established as >95% by 1H NMR
and TLC or HPLC. Pyridine, dichloromethane, and THF were
distilled from glass over CaH2. MALDI MS was measured on
a custom-built FTMS instrument in the laboratory of Professor
Carlito Lebrilla in the Department of Chemistry, UC Davis
(Carroll, J . A.; Penn, S. G.; Fannin, S. T.; Wu, J . Y.; Cancilla,
M. T.; Green, M. K.; Lebrilla, C. B. Anal. Chem. 1996, 68,
1798-1804) using dihydroxybenzoic acid (DHB) as matrix.
FABMS and EIMS were provided by the UC Riverside MS
Facility.
Dia ld eh yd e (5). p-Bromobenzaldehyde (5.0 g, 27.0 mmol)
was added to a solution of 3-hydroxy-4-methoxybenzaldehyde
(Aldrich, 6.16 g, 40.05 mmol) in pyridine (60 mL). Oven-dried
potassium carbonate K2CO3 (7.5 g, 54.4 mmol) and CuO (4.3
g, 54.04 mmol) were added to the mixture which was subse-
quently heated to 115 °C under an atmosphere of N2 for 12 h.
The mixture was cooled, filtered over a bed of Celite, and
(21) Two isomers arise, in the present case, because the coupling
partners are nonsymmetrical and “head-to-head” or “head-to-tail”
condensations are equally probable. The isomers 11a ,b could be
separated by HPLC (reversed phase, C18, Dynamax, 1:1 MeOH/H2O),
but the head-tail orientations were not assigned.
(22) The balance of the recovered mass was insoluble polymer.
(23) A conformation almost identical in energy (∆E < 0.2 kcal mol-1
)
can be achieved by 180° rotation of the C6-C7 bond; however, this
does not change the distance dendo appreciably.
(24) Rao, Y. S.; Filler, R. Synthesis 1975, 749-764.

Tandem Erlenmeyer Condensation-Macrolactamization
J . Org. Chem., Vol. 64, No. 7, 1999 2503
solution containing the aldehyde, followed by an additional
wash with Ac2O (5 mL). The reaction refluxed (138 °C) under
atmospheric N2 for 24 h. The reaction mixture was cooled in
an ice bath, forming a heavy yellow precipitate which was
filtered and washed with cold Ac2O. The yellow amorphous
solid was dissolved in CHCl3 (750 mL), washed with water (3
× 200 mL), dried over Na2SO4, and concentrated to a yellow
paste which was triturated with EtOAc to yield 6 (746 mg,
Sch em e 2. Ma cr ola cta m iza tion Rea ction s of
Bis-oxa zolon e 6
69%). mp 279-281 °C; IR (NaCl, neat) ν 1792, 1766 (CO) cm-1
;
UV (CHCl3) λmax 408 nm (ꢀ 24000), 388 (26800); 1H NMR (300
MHz, CDCl3) δ 3.92 (s, 3H), 7.10 (d, 1H, J ) 8.3 Hz), 7.13 (d,
2H, J ) 8.7 Hz), 7.19 (s, 1H), 7.27 (s, 1H), 7.44-7.60 (m, 6H),
7.87 (dd, 1H, J ) 8.3, 1.8 Hz), 8.03 (bd, 2H, J ) 8.6 Hz), 8.16
(bd, 2H, J ) 7.6 Hz), 8.25 (d, 2H, J ) 8.7 Hz), 8.27 (d, 1H, J
) 1.8 Hz); 13C NMR (150.2 MHz, pyridine-d5) δ 56.6, 114.2,
117.9, 118.0, 126.1,126.5, 126.6, 128.3, 128.9, 129.3, 129.7,
129.9, 131.1, 131.3, 131.5, 131.7, 132.6, 133.0, 133.9, 134.1,
135.5, 144.6, 155.1, 161.4, 163.8; HREIMS found m/z 543.1548
(MH+), C33H23N2O6 requires 543.1556. Anal. Calcd for
C33H23N2O6: C, 73.06; H, 4.09; N, 5.16. Found: C, 73.03; H,
5.16.
Dia m in e (7). A solution of aldehyde 5 (1.5 g, 5.9 mmol) in
CH3NO2 (5.9 g, 96.0 mmol) and glacial acetic acid (3.4 mL)
was treated with NH4OAc (367 mg, 4.72 mmol). The mixture
was heated at reflux for 3 h and concentrated to give a yellow
solid. The solid was applied to a column of silica and eluted
with 2:3 EtOAc/hexane. Evaporation of the solvent gave the
bis-nitrostyrene as yellow foam (1.8 g, 89%) which was used
immediately in the next reaction. mp 130-132 °C; IR (NaCl,
neat) ν 1631, 1608, 1571, 1543, 1502 cm-1; UV (CHCl3) λmax
1
351 nm (ꢀ 19300); H NMR (300 MHz, CDCl3) δ 3.88 (s, 3H),
6.95 (d, 1H, J ) 8.7 Hz, 2H), 7.10 (d, J ) 8.7 Hz, 2H), 7.29 (d,
J ) 2.1 Hz, 1H), 7.46 (dd, J ) 8.7 Hz, 2.1 Hz, 1H), 7.46 (s,
1H), 7.51 (m, 2H), 7.55 (d, J ) 7.2 Hz, 2H), 7.92 (d, J ) 13.5
Hz, 2H), 7.97 (d, J ) 13.5 Hz, 2H); 13C NMR (75.4 MHz, CDCl3)
δ 56.1 (CH3), 113.2 (CH), 117.0 (2 CH), 121.9 (CH), 123.3 (C),
124.4 (C), 128.5 (CH), 131.0 (2 CH), 135.8 (CH), 135.8 (CH),
137.9 (CH), 138.4 (CH), 143.7 (C), 154.8 (C), 160.8 (C);
HRCIMS found m/z 360.1210 (M + NH4+), C17H18N3O6 requires
360.1196.
The above bis-nitrostyrene (1.3 g, 3.8 mmol) in THF (10 mL)
was added over 10 min to a solution of LiAlH4 (2.9 g, 77.0
mmol) in THF (40 mL) at reflux under an atmosphere of N2,
and heating was continued for 11 h. The mixture was cooled
to 0 °C and quenched with excess 6 M NaOH (aq, 400 mL)
and stirred for 40 min to produce a clear solution. The alkaline
solution was extracted with EtOAc (3 × 200 mL), and the
organic extracts were washed with brine and dried over
Na2SO4. The volatiles were removed to afford the air-sensitive,
hygroscopic diamine 7 as a yellow oil (1.1 g, 98%). IR (NaCl,
1
neat) ν 1505 cm-1 (NH2); H NMR (300 MHz, CDCl3) δ 1.56
(bs), 2.64 (t, J ) 6.6 Hz, 2H), 2.71 (t, J ) 6.6 Hz, 2H), 2.89 (t,
J ) 7.2 Hz, 2H), 2.95 (t, J ) 6.9 Hz, 2H), 3.83 (s, 3H), 6.80 (s,
1H), 6.87 (d, J ) 6.6 Hz, 2H), 6.93 (s, 2H), 7.11 (d, J ) 6.6 Hz,
2H); 13C NMR (75.4 MHz, CDCl3) δ 39.0 (CH2), 39.1 (CH2),
43.4 (2 × CH2), 56.2 (CH3), 113.3 (CH), 117.1 (CH), 121.2 (CH),
121.3 (CH), 124.6 (CH), 129.7 (CH), 132.9 (C), 133.7 (C), 144.1
(C), 149.9 (C). ESI found (MH+) m/z 287, C17H23N2O2 requires
287.1760.
concentrated to a brown glass. The residue was purified by
chromatography (silica, 1:4 n-hexane/CHCl3) and recrystallized
from EtOAc/n-hexane to give colorless crystals of 5 (5.7 g, 83%).
mp 83-85 °C; IR (NaCl, neat) ν 1710 (CHdO), 1605 (CdC)
cm-1; UV (CHCl3) λmax 273 nm (ꢀ 16600); 1H NMR (300 MHz,
CDCl3) δ 3.90 (s, 3H), 7.00 (d, 2H, J ) 8.7 Hz), 7.18 (d, 1H, J
) 8.4 Hz), 7.79 (d, 1H, J ) 8.4 Hz), 7.83 (d, 2H, J ) 8.7 Hz),
9.87 (s, 1H), 9.90 (s, 1H); 13C NMR (75.4 MHz, CDCl3) δ 56.0
(CH3), 112.5 (CH), 116.4 (CH), 122.0 (CH), 129.4 (CH), 130.2
(C), 131.2 (C), 131.7 (CH), 143.55 (C), 156.6 (C), 162.5 (C), 189.7
(CH), 190.4 (CH); HREIMS found m/z 256.0742 (M+), C15H12O4
requires 256.0736. Anal. Calcd for C15H12O4: C, 70.30; H, 4.71.
Found: C, 69.97; H, 4.69.
Bis-oxa zolon e (6). Dialdehyde 5 (512 mg, 2.0 mmol) in
Ac2O (10 mL) under atmospheric N2 was added to a 50 mL
RBF. In a separate 25 mL flask, a mixture of Pb(OAc)2 (650
mg, 2.0 mmol) and hippuric acid (2.15 g, 12.0 mmol) in Ac2O
(5 mL) was heated with stirring until a clear orange solution
was obtained. The resultant solution was cannulated into the
Ma cr ola cta m (8). Bis-oxazolone 6 (50.0 mg, 0.09 mmol)
was stirred in pyridine (18 mL, 5 mM) at 60 °C for 15 min. A
solution of (1R,2R)-(+)-1,2-diphenylethylene-1,2-diamine di-
hydrochloride in pyridine (2.0 mL) was added and stirring
continued for 20 h. The reaction mixture was concentrated to
a yellow solid, dissolved in CHCl3 and washed with brine, dried
over Na2SO4, and concentrated to a yellow glass which was
purified by flash chromatography (SiO2, 3:97 MeOH/CHCl3)
followed by HPLC (silica, Dynamax, 2:98 MeOH/CH2Cl2, 4 mL/
min) to afford chiral macrolactam 8 (3.8 mg, 6%). [R]24D +1.43°
(c 0.14, MeOH); UV (MeOH) λmax 306 (ꢀ 24000); CD (MeOH):
λ 252 nm (∆ꢀ -8.9), 278 (+0.9), 316 (+4.8), 327 (+5.1), IR
(NaCl, neat) ν 1655 (CO), 1505 (CdC) cm-1 1H NMR (300
;
MHz, CDCl3) δ 3.74 (bs, 3H), 5.33 (bs, 1H), 5.50 (bs, 1H), 6.59
(d, J ) 7.5 Hz, 2H), 6.80 (d, J ) 7.5 Hz, 2H), 7.17 (m, 10H),
7.35 (m, 2H), 7.56 (m, 2H), 7.83 (m, 2H), 8.05 (bs, 1H), 8.23

2504 J . Org. Chem., Vol. 64, No. 7, 1999
Bailey and Molinski
(bs, 1H); 13C NMR (150.8 MHz, CDCl3) 53.4 (CH2), 55.9 (CH2),
59.8 (CH3), 112.7, 116.2, 122.3, 127.5, 127.7, 127.6, 128.6,
128.9, 131.1, 132.3, 133.1, 138.4, 143.2, 152.5, 158.7, 166.8;
MALDI MS, found m/z 737.2786 (MH+ - H2O), C47H38N4O6
requires 754.2791.
14 min, 22.0 mg, 30%). Three late-eluting peaks (rt, 16-30
min) were shown to be higher MW oligomeric products
(MALDI MS) and were not investigated further. 11a ,b, mp
213-217 °C; IR (NaCl, neat) ν 1652-1634 cm-1; UV (CHCl3)
λ
max 287 (ꢀ 35000); 1H NMR (300 MHz, CDCl3) δ 2.54 (m, 4H),
Ma cr ola cta m (9). Bis-oxazolone 6 (25.0 mg, 0.05 mmol)
was stirred in pyridine (98 mL, 0.5 mM) at 50 °C for 15 min.
To the solution was added 3-oxapentane-1,5-diamine dihydro-
chloride 2 (9.7 mg, 0.06 mmol) in pyridine (2 mL). The reaction
was cooled and concentrated after 3 days. The subsequent
yellow residue was taken up in CHCl3, washed with 0.1 N HCl
and brine, dried over Na2SO4, and concentrated to a pale
yellow glass. HPLC (silica, Dynamax, 2:98 MeOH/CH2Cl2)
afforded unreacted 6 (5 mg) and macrolactam 9 (2.3 mg, 7%);
IR (NaCl, neat) 1648 (CO), 1506 (CdC) cm-1; UV λmax 305 (ꢀ
27000); 1H NMR (300 MHz, CDCl3) δ 3.82 (bs, 4H), 3.88 (s,
3H), 6.80 (d, J ) 8.7 Hz, 2H), 6.94 (d, J ) 8.4 Hz, 2H), 7.19 (s
1H), 7.22 (s, 1H), 7.30 (bs,1H), 7.34 (s, 1H), 7.45 (m, 10H), 7.65
2.89 (m, 4H), 3.47 (m, 4H), 3.59 (s, 3H), 3.63 (s, 3H), 3.72 (m,
4H), 3.92 (s, 6H), 6.31 (bs), 6.42 (bs), 6.54 (m, 6H), 6.65 (m, 8
H), 6.72 (m, 4H), 6.92 (m, 12H), 7.12 (m, 6H), 7.20 (s, 1H),
7.30 (m, 3H), 7.43 (m, 4H), 7.54 (m, 4H), 7.93 (m, 8H), 8.28
(bs), 8.63 (bs); 13C NMR (100 MHz, CDCl3) δ 33.8, 34.0, 34.4,
40.1, 40.3, 40.4, 41.0, 52.7, 55.7, 55.9, 56.0, 111.8, 111.9, 112.2,
113.5, 114.3, 114.6, 116.0, 117.4, 122.0, 122.0, 122.5, 124.5,
124.9, 125.6, 125.7, 126.2, 127.4, 127.7, 127.9, 128.4, 128.5,
128.7, 128.8, 129.7, 130.1, 130.2, 130.5, 130.9, 131.3, 131.8,
132.1, 132.2, 132.3, 132.4, 132.6, 133.3, 143.6, 145.0, 149.4,
149.7, 149.9, 150.2, 154.7, 154.8, 156.2, 157.0, 164.7, 165.2,
165.9, 166.3, 166.8, 167.1; MALDI, m/z 851 (M + Na+, 100%),
829 (M + H+, 8); HRFABMS found m/z 829.3219 (MH+),
(bs, 1H), 7.73 (d, J ) 7.8 Hz, 2H), 7.86 (d, J ) 8.1 Hz, 2H); 13
C
C
50H45N4O8 requires 829.3237.
NMR (150.2 MHz, CDCl3) 52.7 (CH2), 53.4 (CH2), 55.9 (CH3),
111.5, 112.38, 117.46, 122.2, 122.7, 127.3, 127.4, 127.6, 128.3,
128.7, 128.8, 128.9, 131.5, 132.2, 132.3, 132.4, 132.5, 133.7,
152.2, 158.3, 163.6, 165.9; MALDI MS found m/z 629.1865
(MH+ - H2O), C37H34N4O7 requires 646.2427.
Isod ityr osin e P ep tid es (12). A sample of 11a ,b (4 mg)
was hydrogenated in MeOH over H2 (1 atm) and 10% Pd-C
for 16 h. The mixture was filtered through Celite and evapo-
rated to give the peptide 12 as a mixture of isomers (∼95%).
1H NMR (300 MHz, CDCl3) δ 2.70 (m), {3.38 (m), 3.81 (s), 3.84
(s), 3.86 (s) ) 4 × OMe}, 4.63 (m), 5.10 (m), 5.84 (m), 6.89 (m),
7.00 (m), 7.44 (m), 7.68 (m); MALDI FTMS found m/z 855.3324
(M + Na+, C50H48N4O8Na requires 855.3370.
Ma cr ola cta m (10). Macrolactam 10 was prepared as for
9, but CHCl3 was used as solvent instead of pyridine. Workup
and HPLC as before gave macrolactam in 7% yield. IR 1638
1
(CdO), 1508 (CdC) cm-1; H NMR (300 MHz, CDCl3) δ 1.17
Ack n ow led gm en t. We are very grateful to Profes-
sor Carlito Lebrilla, Mark Cancilla, and Ken Tseng (UC
Davis) for MALDI MS spectra, Jimmy Orjala (Agraquest,
Inc.) for ESI MS spectra, and J oyce J ames (Bruker,
Fremont, CA) and Roger Mulder for some 13C NMR
spectra. This research was supported by the NIH (GM
57560). The 600 MHz NMR spectrometer was partially
funded through NIH RR11973.
(m, 2H), 1.34 (m, 4H), 1.55 (m, 2H), 1.62 (m, 2H), 3.27 (m,
2H), 3.47 (m, 2H), 3.96 (s, 3H), 6.03 (s, 1H), 6.22 (m, 2H), 6.54
(m, 2H), 6.62 (s, 1H), 6.94 (s, 1H), 7.60 (m, 15H), 8.00 (d, 2H,
J ) 7.8 Hz,), 8.85 (bs, 1H); MALDI found m/z 695.2843 (M +
Na+), C40H40N4O6 requires 672.2948.
Ma cr ola cta m s (11a ,b). A solution of diamine 2 (29.0 mg,
0.10 mmol) and bis-oxazolone 6 (50.0 mg, 0.09 mmol) in
pyridine (200.0 mL, 0.5 mM) was stirred at 50 °C. Reaction
was complete after 4 days as visualized by TLC. The pale
yellow solution was cooled and concentrated under vacuum
to afford a yellow amorphous solid. The residue was purified
by flash chromatography (silica, 3:97 MeOH/CH2Cl2), followed
by HPLC with the same solvent (silica, Dynamax 25 × 300
mm, 4.0 mL/min) to obtain 11a ,b eluting as a single peak (rt
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
and MS of 5-12 and 13C NMR of 5-7 and 11a ,b. This material
is available free of charge via the Internet at http://pubs.acs.org.
J O9825198