Total syntheses of bengamides B and E

Article abstract of DOI:10.1021/jo0017133

Total syntheses of the cytotoxic marine natural products bengamides B and E are described. Both bengamides are prepared via amide coupling of a protected polyhydroxylated lactone intermediate 9 with a suitably substituted aminocaprolactam intermediate. Lactone 9 is prepared in five steps from commercially available α-D-glucoheptonic γ-lactone. The key reactions are a selective deprotection of a 1,2-acetonide in the presence of a 1,3-acetonide and an (E)-selective olefination of an unstable aldehyde using a gem-dichromium reagent. The bengamide B lactam intermediate 10 is prepared in seven steps from commercially available (5R)-5-hydroxy-L-lysine (12). The desired S-configuration at the γ-OH lactam position is established using the Mitsunobu reaction.

Full text of DOI:10.1021/jo0017133

2118
J . Org. Chem. 2001, 66, 2118-2122
Tota l Syn th eses of Ben ga m id es B a n d E
Frederick R. Kinder, J r.,* Sompong Wattanasin,* Richard W. Versace,* Kenneth W. Bair,
J ohn Bontempo, Michael A. Green, Yansong J . Lu, H. Rao Marepalli, Penny E. Phillips,
Didier Roche, Long D. Tran, RunMing Wang, Liladhar Waykole, David D. Xu, and
Sonya Zabludoff
Oncology Department, Novartis Pharmaceuticals Corporation, 556 Morris Avenue,
Summit, New J ersey 07901
frederick.kinder@pharma.novartis.com
Received December 5, 2000
Total syntheses of the cytotoxic marine natural products bengamides B and E are described. Both
bengamides are prepared via amide coupling of a protected polyhydroxylated lactone intermediate
9 with a suitably substituted aminocaprolactam intermediate. Lactone 9 is prepared in five steps
from commercially available R-D-glucoheptonic γ-lactone. The key reactions are a selective
deprotection of a 1,2-acetonide in the presence of a 1,3-acetonide and an (E)-selective olefination of
an unstable aldehyde using a gem-dichromium reagent. The bengamide B lactam intermediate 10
is prepared in seven steps from commercially available (5R)-5-hydroxy-L-lysine (12). The desired
S-configuration at the γ-OH lactam position is established using the Mitsunobu reaction.
Ta ble 1. Rep r esen ta tive Ben ga m id es Isola ted fr om
J a sp id a e Sp on ges
In tr od u ction
The bengamides are marine natural products first
isolated by Crews et al. from J aspidae sponges indigenous
to the coral reefs that surround the Fiji islands.1 These
cyclolysine derivatives are potent antiproliferative agents
against both transformed and nontransformed cells.2
Bengamides that possess a lipophilic ester substituent
on the caprolactam (e.g., bengamides A, B, M, and O)
inhibit tumor cell growth at 10-100 nM (IC50 range) and
are >100-fold more potent than their nonlactam ester-
bearing counterparts (e.g., bengamides E, F, P, and Z).3
We recently reported that bengamides B, E, and Z
significantly inhibit MDA-MB-435 human breast carci-
noma cells implanted as xenografts in athymic mice at
well-tolerated doses.2a The mechanism of action of the
bengamides is under investigation. To continue profiling
the antitumor properties of the bengamides, additional
supplies of these natural products were needed. Since a
continued supply of bengamides from sponge extraction
was not a practical option, we required an efficient
synthesis capable of producing gram quantities of these
compounds. Herein we report concise total syntheses of
bengamides B and E that meet this need. Several
syntheses of bengamides A, B, and E have been previ-
ously published.4 However, all of these syntheses are long
(14-15 steps for bengamide E and 30-32 steps for
bengamide B) which render them impractical for prepa-
bengamide
R1
R2
R3
A (1)
B (2)
E (3)
F (4)
M (5)
O (6)
P (7)
Z (8)
O2C(CH2)12CH3
O2C(CH2)12CH3
H
Me
H
Me
Me
Me
H
H
H
H
H
H
H
H
H
O2C(CH2)11CH(CH3)2
O2C(CH2)10CH(CH3)2
H
OH
O2C(CH2)12CH3
H
Me
ration of grams of material.5 The present synthesis relies
on the coupling of two key intermediates: lactone 9 and
aminocaprolactam 10. Although every reported synthesis
takes advantage of a similar coupling strategy, the
syntheses of intermediates corresponding to 9 and 10
require a prohibitive number of protection/deprotection
steps. The utilization of two commercially available
natural products, R-D-glucoheptonic γ-lactone (11) and
(5R)-5-hydroxy-L-lysine (12), makes a much shorter ben-
gamide synthesis possible. Lactone 11 contains the same
(4) (a) Chida, N.; Ogawa, N. ChemComm. 1997, 807. (b)Mukai, C.;
Hanaoka, M. Synlett 1996, 11. (c) Mukai, C.; Moharram, S. M.;
Kataoka, O.; Hanaoka, M. J . Chem. Soc., Perkin Trans. 1 1995, 2849.
(d) Mukai, C.; Kataoka, O.; Hanaoka, M.; J . Org. Chem. 1995, 60, 5910.
(e) Chida, N.; Tobe, T.; Murai, K.; Yamazaki, K.; Ogawa, S. Heterocycles
1994, 38, 2383. (f) Mukai, C.; Kataoka, O.; Hanaoka, M. Tetrahedron
Lett. 1994, 35, 6899. (g) Marshall, J . A.; Luke, G. P. J . Org. Chem.
1993, 58, 6229. (h) Marshall, J . A.; Luke, G. P. Synlett 1992, 1007. (i)
Chida, N.; Tobe, T.; Okada, S.; Ogawa, S. J . Chem. Soc., Chem.
Commun. 1992, 1064. (j) Kishimoto, H.; Ohrui, H.; Meguro, H. J . Org.
Chem. 1992, 57, 5042. (k) Broka, C. A.; Ehrler, J . Tetrahedron Lett.
1991, 32, 5907. (l) Chida, N.; Tobe, T.; Ogawa, S. Tetrahedron Lett.
1991, 32, 1063.
(1) (a) Quin˜oa`, E.; Adamczeski, M.; Crews, P.; Bakus G. J . J . Org.
Chem. 1986, 51, 4494. (b) Adamczeski, M.; Quin˜oa`, E.; Crews, P. J .
Am. Chem. Soc. 1989, 111, 647. (c) Adamczeski, M.; Quin˜oa`, E.; Crews,
P. J . Org. Chem. 1990, 55, 240.
(2) (a) Kinder, F. R.; Bair, K. W.; Bontempo, J .; Crews, P.; Czuchta,
A. M.; Nemzek, R. Thale, Z.; Vattay. A.; Versace, R. W.; Weltchek, S.;
Wood, A.; Zabludoff, S. D.; Phillips, P. E. Proc. Am. Assoc. Cancer Res.
2000, 41, 600. (b) Phillips, P. E.; Bair, K. W.; Bontempo, J .; Crews, P.;
Czuchta, A. M.; Kinder, F. R.; Vattay, A.; Versace, R. W.; Wang, B.;
Wang, J .; Wood, A. Proc. Am. Assoc. Cancer Res. 2000, 41, 59.
(3) (a) Bengamide B was evaluated in the NCI 60 cell line screen.
The data can be obtained at the NCI website (http://dtp.nci.nih.gov/).
(b) Thale, Z.; Kinder, F. R.; Bair, K. W.; Czuchta, A. M.; Versace, R.
W.; Phillips, P. E.; Sanders, M. L.; Wattanasin, S.; Crews, P.,
unpublished results.
(5) A 10-step synthesis of bengamide E was recently reported at the
219th National ACS meeting: see Clark, T. J .; Boeckman, R. K.; J r.
Book of Abstracts; 219th American Chemical Society National Meeting,
San Francisco, CA, Mar 26-31, 2000, Abstr ORGN-58.
10.1021/jo0017133 CCC: $20.00 © 2001 American Chemical Society
Published on Web 02/24/2001

Total Syntheses of Bengamides B and E
J . Org. Chem., Vol. 66, No. 6, 2001 2119
F igu r e 1. Retrosynthesis of bengamide B.
methyl iodide provided methyl ether 14 in 82% yield.7
The key step in the transformation of 11 to the advanced
intermediate 9 was the selective removal of the 1,2-
acetonide in the presence of the 1,3-acetonide. This was
accomplished by the treatment of bis(acetonide) 14 with
acetic acid. The desired vicinal diol 15 was produced in
68% yield.8 Every step up to this point did not require
chromatographic purification. Oxidative cleavage of the
diol with NaIO4 produced aldehyde 16. This aldehyde was
prone to hydration and required repeated rotary evapo-
ration with CHCl3 or toluene to remove all traces of
water. Aldehyde 16 was then olefinated with the low-
valent organochromium species generated in situ from
1,1-diodoisobutane (prepared in two steps from isobu-
tyraldehyde9) and Cr(II)Cl2 to produce a nearly 3:1
mixture of E and Z isomers in 39% yield.10 The desired
E isomer, 9, was isolated in 29% yield using preparative
normal phase HPLC. None of aldehyde 16 was recover-
able from the reaction mixture. Alternative olefination
attempts including the Wittig reaction and the S. J ulia
olefination11 produced <10% of the olefin 9. Two steps
remained in order to complete the synthesis of bengamide
E. Commercially available L-(-)-R-amino-ꢀ-caprolactam
and lactone 9 were stirred at reflux in i-PrOH to give
the protected bengamide E adduct in 85% yield. Finally,
TFA-promoted acetonide hydrolysis produced bengamide
E in 54% yield after reverse phase HPLC purification.
Once a feasible route to lactone 9 was established, the
remaining challenge to produce bengamide B resided in
the preparation of the substituted aminocaprolactam 10
(Scheme 2). Cyclization of (5R)-5-hydroxy-L-lysine (12)
followed by N-Boc carbamoylation of the free amine was
performed in one pot using standard peptide synthesis
conditions (58% yield for two steps). The secondary
alcohol was inverted using Mitsunobu conditions to give
a 78% yield of p-NO2-benzoate 18 in the desired S-
configuration.12 Selective methylation of the lactam
nitrogen with MeI/NaHMDS produced lactam intermedi-
ate 19 in 83% yield. LiOH-promoted ester hydrolysis of
19 generated the corresponding alcohol 20 in 97% yield.
Sch em e 1. Syn th esis of Ben ga m id e E (3)a
a
Reagents: (a) acetone, cat. I2 (86%); (b) MeI, Ag2O (82%); (c)
HOAc (68%); (d) NaIO4, MeOH (85%); (e) (CH3)2CHI2, CrCl2, THF,
DMF (29%); (f) L-(-)-R-amino-ꢀ-caprolactam, i-PrOH, reflux (85%);
(g) TFA, THF, H2O (54%).
sequence of chiral hydroxy groups present on the poly-
hydroxylated portion common to the bengamide class.
Hydroxylysine 12 contains all the functionality required
to prepare bengamides that bear a caprolactam oxygen
substituent. However, 12 has the opposite configuration
at the γ-OH position which made an inversion reaction
necessary. The retrosynthetic analysis of bengamide B
in Figure 1 is representative of the present bengamide
synthesis strategy.
Discu ssion
(6) Kartha, K. P. R. Tetrahedron Lett. 1986, 27, 3415.
(7) Gurjar, M. K.; Srinivas, N. R. Tetrahedron Lett. 1991, 32, 3409.
(8) Shing, T. K. M.; Zhou, Z. H.; Mak, C. W. J . Chem. Soc., Perkin
Trans. 1 1992, 1907.
(9) Friedrich, E. C.; Falling, S. N.; Lyons, D. E. Synth. Commun.
1975, 33.
(10) Okazoe, T.; Takai, K.; Utimoto, K. J . Am. Chem. Soc. 1987, 109,
951.
(11) (a) Baudin, J . B.; Hareau, G.; J ulia, S. A.; Ruel, O. Tetrahedron
Lett. 1991, 32, 1175. (b) Blakemore, P. R.; Cole, W. J .; Kocienski, P.
J .; Morley, A. Synlett 1998, 26.
The synthesis of bengamide E (3) is outlined in Scheme
1. R-D-Glucoheptonic γ-lactone (11) was converted to the
bis(acetonide) 13 by treatment of an acetone solution of
11 with catalytic I2.6 The reaction also produced ap-
proximately 10% of another bis(acetonide) that could be
removed through crystallization. Methylation of the
remaining unprotected hydroxyl group using Ag2O with

2120 J . Org. Chem., Vol. 66, No. 6, 2001
Sch em e 2. Syn th esis of Ben ga m id e B (2)a
Kinder et al.
a
Reagents: (a) EDCI, HOBT, DMF; (b) (Boc)2O (58% for two steps); (c) DEAD, PPh3, p-nitrobenzoic acid (78%); (d) MeI, NaHMDS
(83%); (e) LiOH (97%); (f) EDCI, DMAP, myristic acid (94%); (g) TFA, (99%); (h) 9, i-PrOH, 80 °C; (i) TFA, THF, H2O (61% for two steps).
Flash column chromatography was performed with silica
(Merck EM9385, 230-400 mesh). 1H and 13C NMR spectra
were recorded at 500 or 300 and at 125 and 75 MHz,
respectively, in CDCl3 unless otherwise mentioned. Proton and
carbon chemical shifts are expressed in ppm relative to
internal tetramethylsilane, coupling constants (J ) are ex-
pressed in hertz.
Esterification of 20 with myristic acid in the presence of
EDCI and DMAP produced the bengamide B lactam
intermediate 21 in 94% yield. Treatment of 21 with TFA
removed the BOC protecting group. Neutralization (NH4-
OH) of the crude TFA salt and chromatographic purifica-
tion gave the amine 10 in 99% yield. Condensation of
lactone 9 with aminocaprolactam 10 in refluxing i-PrOH
provided the corresponding amide without competing
amine attack on the acyclic ester moiety. Subsequent
acetonide hydrolysis with TFA generated bengamide B
(2) in 61% yield (two steps).
In conclusion, a synthetic route has been established
that is capable of providing gram amounts of two
members of the bengamide natural product class starting
from two commercially available natural products. The
benefits of the present synthesis are 2-fold: 1) multigram
quantities of these relatively scarce natural products
facilitate further biological testing in animal models, and
2) several series of bengamide analogues can be prepared
through modification of both the lactone and aminoca-
prolactam intermediates.13
Ben ga m id e B (2). A solution consisting of 9 (1.0 g, 3.7
mmol), 10 (1.2 g, 3.4 mmol), and i-PrOH (5 mL) was stirred
at 80 °C for 16 h. The i-PrOH was removed on a rotary
evaporator, and the crude product was chromatographed (2%
MeOH/CH2Cl2) to yield 1.82 g (83%) of acetonide which was
used directly in the next step. To the acetonide (precooled in
a 0 °C bath) was added a solution of 6 mL of TFA, 6 mL of
THF, and 4 mL of H2O precooled to ca. 0 °C. The reaction was
stirred at 0 °C for 20 min. The solvents were removed using a
rotary evaporator under high vacuum (<5 Torr) at 0 °C. The
residue was dissolved in 20 mL of MeOH and neutralized with
the dropwise addition of concentrated NH4OH at 0 °C. The
solution was evaporated to dryness and chromatographed (2%
MeOH/CH2Cl2). The product was further purified by prepara-
tive reverse phase HPLC (C18 column, isocratic 20% CH3CN/
H2O) to yield 1.25 g (73%) of waxy white solid: R20 +63.6° (c
D
1
2.9, CHCl3) (lit.1a R20 +34.6 ° (c 0.075, MeOH)); H NMR δ
D
8.11 (d, J ) 6.2; 1H), 5.79 (ddd, J ) 15.5, 6.5, 0.9, 1H), 5.46
(ddd, J ) 15.6, 7.3, 1.3, 1H), 4.65 (m, 2H), 4.28 (s, 1H), 4.22 (t,
J ) 6.3, 1H), 3.80 (m, 2H), 3.67 (dd, J ) 14.6, 10.1, 1H), 3.60
(s, 1H), 3.55 (s, 3H), 3.22 (m, 2H), 3.11 (s, 3H), 3.07 (s, 1H),
2.31 (t, J ) 7.4, 2H), 2.15 (m, 2H), 1.97 (m, 1H), 1.63 (m, 4H),
1.26 (m, 20H), 1.00 (dd, J ) 6.8, 2.7, 6H), 0.88 (t, J ) 6.8, 3H);
13C NMR 173.02, 172.15, 171.78, 141.48, 125.40, 80.83, 74.32,
72.86, 72.33, 69.17, 60.06, 53.36, 51.33, 36.40, 34.35, 32.68,
31.92, 30.80, 29.68, 29.65, 29.60, 29.45, 29.35, 29.24, 29.10,
29.00, 24.78, 22.69, 22.22, 22.11, 14.12. Anal. Calcd for
Exp er im en ta l Section
Gen er a l Meth od s. All chemicals were obtained from
commercial suppliers and used without further purification.
(12) (a) Mitsunobu, O. Synthesis 1981, 1. (b) The Mitsunobu reaction
was not attempted with myristic acid. p-NO2-benzoate ester 18 was a
convenient intermediate for the synthesis of bengamide B analogues.
(13) The synthesis and antitumor activity of bengamide analogues
will be published elsewhere.

Total Syntheses of Bengamides B and E
J . Org. Chem., Vol. 66, No. 6, 2001 2121
C32H58N2O8: C, 64.19; H, 9.76; N, 4.68. Found: C, 63.91; H,
9.87; N, 4.50.
reaction mixture was concentrated in vacuo. The residue was
dissolved in 100 mL of CH3CN and neutralized with NH4OH.
The solution was conentrated using a rotary evaporator and
chromatographed (2.5% MeOH/CH2Cl2) to yield 2.8 g (99%) of
Ben ga m id e E (3). A solution of 9 (98 mg, 0.37 mmol), L-
(-)-R-amino-ꢀ-caprolactam (142 mg, 1.11 mmol), and i-PrOH
(2 mL) was stirred at reflux for 18 h. The i-PrOH was removed
on a rotary evaporator, and the crude product was chromato-
graphed (3% MeOH/CH2Cl2) to yield 123.8 mg (85%) of
acetonide. To 150 mg of this acetonide (precooled to 0 °C) was
added a solution of TFA (3 mL), THF (3 mL), and H2O (2 mL)
precooled to 0 °C. The reaction was stirred at 0 °C for 20 min.
The solvents were removed using a rotary evaporator under
high vacuum (<5 Torr) at 0 °C. The residue was dissolved in
MeOH (10 mL) and neutralized with concentrated NH4OH at
0 °C. The solvents were removed using a rotary evaporator
and chromatographed (3% MeOH/CH2Cl2). The product was
further purified by preparative reverse phase HPLC (C18
column, isocratic 30% CH3CN/H2O) to yield 73 mg (54%) of 3
as a white solid: R20D +57.9° (c 0.75, CH2Cl2) (lit.1b R20D +36.9
1
10 as a white solid. H NMR δ 5.69 (s, 2H), 4.61 (t, J ) 9.4,-
1H), 4.13 (d, J ) 10.9, 1H), 3.64 (dd, J ) 10.2 and 14.7, 1H),
3.20 (d, J ) 14.7, 1H), 3.06 (s, 3H), 2.30 (t, J ) 7.5, 2H), 2.14
(m, 2H), 1.83 (m, 2H), 1.61 (t, J ) 6.8, 2H), 1.26 (m, 20H),
0.88 (t, J ) 6.8, 3H); 13C NMR 179.87, 179.52, 76.06, 60.03,
59.68, 43.32, 41.26, 39.27, 38.85, 36.57, 36.37, 35.39, 31.77,
29.61, 21.06. HRMS calc. for
391.2936, found 391.2926.
C
21H40N2O3Na (M + Na)+
3,5:6,7-Bis-O-(1-m et h ylet h ylid en e)-R-D-glu coh ep t on ic
γ-La cton e (13). R-D-Glucoheptonic γ-lactone (11) (500 g, 2.4
mol) was added into 9 L of acetone in a 5 gal plastic drum.
The mixture was agitated mechanically until most of the solid
dissolved (15-20 min). Iodine (60 g, 0.236 mol) was added
portionwise to the lactone solution over 5-10 min. The
resulting mixture was stirred overnight. A saturated solution
of Na2S2O3 (1.3 L) was added to the iodine solution to quench
the reaction. The resulting solution was conentrated to about
half of its original volume in vacuo, and brine solution (5 L)
was added. The resulting mixture was extracted with 3 × 1.2
L EtOAc. All organic layers were combined and evaporated to
dryness. The solid was slurried with a mixture of ether and
hexane (3:7), and filtered. The filter cake was washed with
Et2O (50 mL) and air-dried to produce 599 g of the desired
compound as a white powder (86.5%): mp 150-152 °C (lit.14
1
° (c 0.043, MeOH)); H NMR δ 7.91 (d, J ) 6.5; 1H), 6.17 (t,
J ) 5.7; 1H), 5.72 (ddd, J ) 15.5, 6.5, and 0.8, 1H), 5.39 (ddd,
J ) 15.6, 7.3, and 1.4, 1H), 4.48 (ddd, J ) 11.2, 6.5, and 1.3,
1H), 4.16 (t, J ) 6.2, 1H), 3.76 (dd, J ) 6.9 and 1.3, 1H), 3.72
(d, J ) 6.9, 1H), 3.54 (d, J ) 4.6, 1H), 3.47 (s, 3H), 3.22 (m,
2H), 2.25 (m, 1H), 1.99 (m, 2H), 1.78 (m, 2H), 1.51 (m, 1H),
1.36 (m, 1H), 0.94 (d, J ) 2.5, 3H), 0.93 (d, J ) 2.7, 3H); 13C
NMR δ 172.18, 169.47, 139.22, 122.79, 78.42, 71.64, 70.14,
69.82, 57.31, 49.41, 39.50, 28.42, 28.20, 26.23, 25.34, 19.52.
Anal. Calcd for C17H30N2O6: C, 56.97; H, 8.44; N, 7.82.
Found: C, 56.61; H, 8.09; N, 7.59.
1
mp 153-154 °C), H NMR δ 4.62 (m, 1H), 4.50 (m, 1H), 4.35
(6E)-6,7,8,9-Tetr a d eoxy-8-m eth yl-2-O-m eth yl-3,5-O-(1-
m eth yleth ylid en e)-gu lon on -6-en on ic Acid La cton e (9).
15 (100 g, 0.382 mol) was dissolved into a 1:1 mixture of
methanol/H2O (2 L). The stirred mixture was cooled in an ice-
water bath to about 8 °C. Solid NaIO4 (98 g, 0.458 mol) was
added portionwise. The reaction was complete within 40 min
as indicated by TLC (silica gel, 5% MeOH/15% EtOAc/CH2-
Cl2). Solid NaCl was added into the reaction mixture to
saturate the methanolic solution. The solid was filtered and
washed with 2 L CH2Cl2. The filtrate was extracted with 3 ×
200 mL CH2Cl2. The combined organic layers were dried over
Na2SO4, filtered, and conentrated to a syrup, which formed a
precipitate upon addition of hexane. The solid was filtered and
rinsed with Et2O. The crude product was chromatographed
(3%MeOH/CH2Cl2) to give 75 g (85%) 16 as a white solid. This
solid readily hydrated on standing. Prior to use in the next
step, 16 was dissolved in CHCl3 then concentrated in vacuo
(m, 2H), 4.07 (m, 1H), 3.93 (m, 1H), 3.82 (dd, J ) 4.0 and 8.9,
1H), 3.08 (dd, J ) 2.0 and 8.5, 1H), 1.51 (s, 3H), 1.44 (s, 3H),
1.39 (s, 3H), 1.35 (s, 3H); 13C NMR δ 174.4, 109.4, 98.6, 72.8,
71.4, 69.3, 68.4, 67.8, 66.7, 28.6, 26.7, 24.6, 19.3.
2-O-Meth yl-3,5:6,7-bis-O-(1-m eth yleth ylid en e)-R-D-glu -
coh ep ton ic γ-La cton e (14). 13 (719 g, 2.49 mol) was added
into 4.5 L of CH2Cl2 in a 5 gal plastic drum. The mixture was
stirred under N2. Iodomethane (2500 g, 17.6 mol) was added
immediately followed by addition of silver(I) oxide (1750 g, 7.58
mol). H2O (30 mL) was added to the reaction mixture. An ice
bath was used to maintain the reaction temperature at 15-
30 °C. The reaction was stirred in the absence of light for 18
h. After diluting the reaction mixture with 1.5 L of CH2Cl2,
the solid was filtered and washed with an additional 2.2 L of
CH2Cl2. The undesired solid was discarded, and the filtrate
was evaporated to dryness. The residue was slurried in Et2O
(1.5 L), filtered, and dried to give 618 g of product (82%): mp
1
1
several times. Mp 125-127 °C; H NMR δ 9.62 (s, 1H), 4.78
139-141 °C; H NMR δ 4.70 (dd, J ) 5 and 6, 1H), 4.35 (m,
(t, J ) 6, 1H), 4.46 (s, 2H), 4.15 (d, J ) 6, 1H), 3.67 (s, 3H),
1.59 (s, 3H), 1.57 (s, 3H); 13C NMR δ 198.8, 171.9, 99.0, 78.4,
74.4, 72.9, 68.4, 67.4, 59.2, 28.7, 19.0. To a 1 L round-bottom
flask, under N2, was added anhydrous THF (300 mL) and
anhydrous DMF (13 mL). Anhydrous CrCl2 (20 g, 0.16 mol)
was added and stirred for 1 h. A solution of 16 (4.6 g 20 mmol)
and 1,1-diiodo-2-methylpropane (12.4 g 40 mmol) in THF (200
mL) and DMF (4 mL) was added over 5 min. The resulting
slurry was stirred for 1.5 h then quenched with a 100 mL
solution of saturated aq NH4Cl containing 2 g Na2S2O3 and
10 g NH4HCO3 followed by solid NH4HCO3 (30 g). The
resulting slurry was filtered through a bed of Na2SO4 and silica
gel and evaporated to give an oil. The oil was chromatographed
on silica gel (25% EtOAc/CH2Cl2) to give 2.1 g (39%) of a
mixture of 9 and the corresponding Z isomer. The mixture was
purified by preparative normal phase HPLC (silica column,
1H); 4.27 (s, 1H) 1.35 (s, 3H), 4.13 (d, J ) 5, 1H), 4.10 (d, J )
6, 1 H), 3.92 (dd, J ) 4.5 and 9, 1H), 3.82 (dd, J ) 2 and 9,
1H), 3.65 (s, 3H), 1.48 (s, 3H), 1.42 (s,6 H); 13C NMR δ 172.5,
109.6, 98.5, 79.0, 73.1, 69.5, 68.6, 67.5, 66.9, 59.1, 28.9, 26.9,
24.9, 19.4. HRMS calcd for C14H22O7Na (M + Na)+ 325.1258,
found 325.1264.
2-O-Meth yl-3,5-O-(1-m eth yleth ylid en e)-R-D-glu coh ep -
ton ic γ-La cton e (15). 14 (618 g, 2.05 mol) was dissolved in 8
L of a mixture of HOAc and H2O (1:1) over 30 min. The solution
was stirred at ambient temperature overnight. The solution
was evaporated to dryness in vacuo. The solid was slurried in
3-5 L of hot acetone and filtered. After oven drying at 20-30
°C, 363 g of the desired compound was obtained (67.6%): mp
1
177-178 °C; H NMR δ 4.92 (bt, 1H), 4.80 (dd, J ) 2 and 4,
1H), 4.50 (d, J ) 5.5, 1H), 4.42 (bd, 1H), 4.38 (s, 1H), 3.95 (dd,
J ) 2 and 9, 1H), 3.55 (bdd, J ) 2 and 9, 2H), 3.42 (s, 3H),
3.38 (m, 1H), 1.42 (s, 3H), 1.22 (s, 3H); 13C NMR δ 173.3, 97.5,
78.3, 68.8, 68.5, 67.2, 67.1, 62.2, 57.4, 28.9, 19.2. Anal. Calcd
for C11H18O7: C, 50.38; H, 6.92. Found: C, 50.14; H, 6.91.
isocratic 50% EtOAc/hexane) to give 1.54 g (28.5%) of 9 as a
1
white solid: [R]25 -132.7 ° (c 1.036 CHCl3); H NMR δ 5.85
D
(dd, J ) 15.6 and 6.2, 1H), 5.64 (ddd, J ) 15.6, 7.5, and 1.3,
1H), 4.74 (dd, J ) 3.8 and 2.1, 1H), 4.48 (dd, J ) 7.5 and 1.8,
1H), 4.12 (d, J ) 3.9, 1H), 4.02 (t, J ) 2.0, 1H), 3.68 (s, 3H),
2.36 (m, 1H), 1.56 (s, 3H), 1.51 (s, 3H), 1.04 (d, J ) 1.9, 3H),
1.03 (d, J ) 1.9, 3H); 13C NMR δ 172.8, 143.2, 122.0, 98.7, 79.0,
71.7, 70.0, 67.6, 59.2, 30.7, 29.2, 21.9, 21.8, 19.2. HRMS calcd
for C14H22O5Na (M+Na)+ 293.1365, found 293.1355.
(3S,6R)-3-(ter t-Bu toxyca r bon yl)a m in oh exa h yd r o-6-h y-
d r oxy-2H-a zep in -2-on e (17). (5R)-5-Hydroxy-L-lysine (12)
(10 g, 0.040 mol), 1-hydroxybenzotriazole hydrate (8.2 g, 0.060
mol), and 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide‚
HCl (EDCI) (11.6 g, 0.060 mol) were added sequentially to 500
mL of DMF with stirring. After 0.5 h, Et3N (16.8 mL, 0.120
(3S,6S)-3-Am in oh exa h yd r o-6-(t r id ecylca r b on yl)oxy-
2H-a zep in -2-on e (10). A solution of 20 (3.6 g, 7.7 mmol), TFA
(5 mL), and CH2Cl2 (10 mL) was stirred at 25 °C for 2 h. The
(14) Cram, D. J .; Elhafez, F. A. J . Am. Chem. Soc. 1952, 74, 5828.

2122 J . Org. Chem., Vol. 66, No. 6, 2001
Kinder et al.
mol) was added. The reaction was stirred at 25 °C for 48 h.
Di-tert-butyl dicarbonate (17.6 g, 0.080 mol) and Et3N (16.8
mL, 0.120 mol) were then sequentially added. Stirring was
continued for 16 h. The reaction mixture was filtered to remove
Et3N-HCl, and the solvent was removed by rotary evaporation
under high vacuum to give a thick oil. The oil was dissolved
in 150 mL of CH2Cl2 and applied to a silica gel column (150 g,
40 × 250 mm). The column was eluted with 3% MeOH/CH2-
Cl2 to give the crude product as a solid. The crude solid was
dissolved in 120 mL of CH2Cl2 with heating and then cooled
to -20 °C for 1 h. The resulting solid was filtered and washed
with 50 mL of CH2Cl2. The combined filtrates were evaporated
to dryness. CH2Cl2 (40 mL) was added to this residue, and the
resulting slurry was stirred for 0.5 h at 25 °C. The slurry was
filtered and the solid washed with 25 mL of CH2Cl2. The solids
were combined to give 5.57 g (58%) of 17: 1H NMR (d6-DMSO)
δ 7.42 (t, J ) 5.1, 1H), 6.38 (d, J ) 6.6, 1H), 4.60 (d, J ) 4.2,
1H), 4.07 (m, 1H), 3.74 (m, 1H), 3.32 (m, 1H), 3.03 (m, 1H),
1.8-1.5 (m, 4H), 1.39 (s, 9H); 13C NMR (d6-DMSO) δ 173.8,
154.5, 77.9, 63.7, 52.4, 45.1, 34.2, 28.1, 24.9. Anal. Calcd for
C11H20N2O4: C, 54.08; H, 8.25; N, 11.47. Found: C, 54.06; H,
8.11; N, 11.41.
(3S,6S)-3-(ter t-Bu toxyca r bon yl)a m in oh exa h yd r o-6-(4-
n itr op h en ylca r bon yl)oxy-2H-a zep in -2-on e (18). To a 500
mL flask were added 17 (6 g, 0.025 mol), 4-nitrobenzoic acid
(8.25 g, 0.05 mol), and triphenylphosphine (12.9 g, 0.05 mol).
The flask was purged with N2, and 200 mL of freshly distilled
THF (Na metal) was added. The mixture was cooled in a -20
°C bath, and diethyl azodicarboxylate (7.8 mL, 0.05 mol) was
added at a rate to maintain e10 °C. The reaction was allowed
to warm to room temperature (∼2 h) and stirred for 14 h. The
solvent was evaporated, and the residue dissolved in 200 mL
of EtOAc. This was washed with 5% NaHCO3 (3 × 150 mL)
and brine (1 × 150 mL) and then dried with Na2SO4 and
evaporated to give an oil. To this oil was added 100 mL of
ether. The resulting solid was filtered and washed with ether
(3 × 50 mL), acetone (2 × 50 mL), and MeOH (2 × 50 mL) to
give 6.2 g of 18. The combined filtrate and washes were
evaporated, and the residue was chromatographed on a silica
gel column with CH2Cl2:hexane (1:1) and then ether to give
1.34 g of 18 for a combined yield of 7.54 g (78%): 1H NMR δ
8.29 (d, J ) 8.4, 1H), 8.18 (d, J ) 8.4, 2H), 6.44 (m, 1H), 5.90
(d, J ) 5.7, 1H), 4.91 (m, 1H), 4.42 (m, 1H), 3.58-3.41 (m,
2H), 2.36-2.25 (m, 2H), 2.16-2.03 (m, 1H), 1.82-1.65 (m, 1H),
1.45 (s, 9H); 13C NMR δ 174.9, 163.6, 155.2, 150.8, 134.9, 130.8,
123.6, 79.8, 72.8, 52.8, 45.0, 33.0, 29.8, 28.4. Anal. Calcd for
C18H23N3O7: C, 54.96; H, 5.86; N, 10.68. Found: 54.97; H, 5.88;
N, 10.60.
The reaction was quenched with 50 mL of H2O. The mixture
was extracted with 2 × 100 mL of EtOAc. The organic layers
were dried over Na2SO4, conentrated, and chromatographed
(40% EtOAc/hexane) to yield 4.3 g (83.0%) of 19 as a white
solid: 1H NMR δ 8.31 (d, J ) 9.1, 2H), 8.20 (d, J ) 8.7, 2H),
6.00 (d, J ) 5.7, 1H), 4.88 (t, J ) 10.6, 1H), 4.50 (dd, J ) 6.0
and 10.2, 1H), 3.82 (dd, J ) 9.8 and 17.7, 1H), 3.38 (d, J )
14.7, 1H), 3.15 (s, 3H), 2.21 (m, 3H), 1.68 (m, 1H), 1.46 (s, 9H);
13C NMR δ 172.94, 164.16, 155.59, 151.18, 135.37, 131.19,
124.05, 80.06, 71.59, 53.66, 52.99, 36.76, 33.15, 30.38, 28.78.
HRMS calcd for C19H25N3O7Na (M + Na)+ 430.1585, found
430.1597.
(3S,6S)-1-Meth yl-3-(ter t-bu toxycar bon yl)am in oh exah y-
d r o-6-h yd r oxy-2H-a zep in -2-on e (20). To a solution of 19 (4.1
g, 9.8 mmol), MeOH (40 mL), and H2O (10 mL) was added
LiOH/H2O (0.83 g, 20 mmol) at 25 °C. After being stirred at
this temperature for 1h, the reaction was quenched with dry
ice (CO2) and evaporated to dryness. To the residue was added
a solution consisting of CH2Cl2 (45 mL) and MeOH (5 mL).
The solution was filtered through Celite. The filtrate was
evaporated to dryness and chromatographed (10% EtOAc/CH2-
Cl2) to yield 2.52 g (97.0%) of 20 as a white solid: 1H NMR δ
6.00 (d, J ) 5.6, 1H), 4.38 (dd, J ) 6.4 and 10.2, 1H), 3.61 (m,
2H), 3.21 (dd, J ) 1.9 and 12.4, 1H), 3.06 (s, 3H), 2.66 (d, J )
4.5, 1H), 2.21 (d, J ) 12.4, 1H), 2.08 (d, J ) 14.3, 1H), 1.82
(m, 1H), 1.60 (td, J ) 2.3 and 13.9,1H), 1.44(s, 9H); 13C NMR
δ 174.53, 157.04, 81.46, 69.80, 58.37, 54.63, 38.78, 38 41, 32.14,
30.21. HRMS calcd for C12H22N2O4Na (M+Na)+ 281.1472,
found 281.1475.
(3S,6S)-1-Meth yl-3-(ter t-bu toxycar bon yl)am in oh exah y-
d r o-6-(tr id ecylca r bon yl)oxy-2H-a zep in -2-on e (21). To a
solution of myristic acid (2.97 g, 13.0 mmol) and CH2Cl2 (50
mL) were added EDCI (2.62 g, 13.65 mmol) and DMAP (1.67
g, 13.65 mmol) at 25 °C. After being stirred at 25 °C for 30
min, a solution of 19 (2.4 g, 9.3 mmol) and CH2Cl2 (50 mL)
was added portionwise. The reaction was stirred for 16 h at
25 °C. After being stirred, the reaction was quenched with 50
mL of H2O. The mixture was extracted with EtOAc (2 × 100
mL). The organic layers were dried (Na2SO4), conentrated, and
chromatographed (2.5% EtOAc/CH2Cl2) to yield 4.1 g (94.2%)
of 21 as a white solid: 1H NMR δ 5.97 (d, J ) 5.6, 1H), 4.60
(tt, J ) 3.4 and 10.6, 1H), 4.43 (dd, J ) 6.0 and 10.6, 1H),
3.63 (dd, J ) 10.2 and 14.7, 1H), 3.20 (d, J ) 14.7, 1H), 3.24
(s, 3H), 2.30 (t, J ) 7.5, 2H), 2.13 (d, J ) 10.6, 2H), 1.92 (m,
1H), 1.61 (m, 3H), 1.45 (s, 9H), 0.93 (m, 20H), 0.88 (t, J ) 6.4,
3H); 13C NMR (CDCl3) δ 173.42, 172.98, 155.58, 79.94, 69.75,
53.79, 53.00, 36.68, 34.73, 33.23, 32.30, 30.49, 30.02, 29.98,
29.83, 29.73, 29.62, 29.47, 28.78, 25.25, 23.07,14.50. HRMS
calcd for C26H48N2O5Na (M + Na)+ 491.3455, found 491.3470.
(3S,6S)-1-Meth yl-3-(ter t-Bu toxycar bon yl)am in oh exah y-
d r o-6-(4-n itr op h en ylca r bon yl)oxy-2H-a zep in -2-on e (19).
To a solution of 17 (5.0 g, 12.7 mmol) and THF (50 mL) at -7
°C was added KHMDS (15.3 mL, 15.3 mmol, 1 M solution in
THF) within 5 min. After the mixture was stirred at -78 °C
for 30 min, MeI (3.6 g, 25 mmol) was added dropwise to the
reaction mixture. The reaction was stirred at 25 °C for 18 h.
Su p p or tin g In for m a tion Ava ila ble: Copies of 1H and 13C
NMR spectra of 9, 14, 19, 20, and 21 are available free of
charge via the Internet at http://pubs.acs.org.
J O0017133