Stereoselective synthesis of novel ptilomycalin a analogs via successive 1,3-dipolar cycloaddition reactions and their Ca2+-ATPase inhibitory activity

Article abstract of DOI:10.1055/s-2003-40195

The pentacyclic guanidine compounds 4 and 5 were stereoselectively synthesized as novel ptilomycalin A and crambescidin analogs. The synthetic method involves successive 1,3-dipolar cycloaddition reactions which effectively access the key intermediates, t

Full text of DOI:10.1055/s-2003-40195

SPECIAL TOPIC
1427
Stereoselective Synthesis of Novel Ptilomycalin A Analogs via Successive 1,3-
2
+
Dipolar Cycloaddition Reactions and their Ca -ATPase Inhibitory Activity
c
b
a
c
b
a
S
A
tereoselective
S
y
n
nthesis of No
g
vel
P
tilomyc
e
alinAAna
l
logs ina Georgieva, Manabu Hirai, Yuichi Hashimoto, Tadashi Nakata, Yasushi Ohizumi, Kazuo Nagasawa*
a
b
c
Institute of Molecular and Cellular Biosciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
E-mail: nagasawa@iam.u-tokyo.ac.jp
Department of Pharmaceutical Molecular Biology, Faculty of Pharmaceutical Sciences, Tohoku University, Aoba, Aramaki, Aoba-ku,
Sendai 980-8578, Japan
Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan
Received 5 May 2003
H
H
H
H
O
Abstract: The pentacyclic guanidine compounds 4 and 5 were
stereoselectively synthesized as novel ptilomycalin A and crambes-
cidin analogs. The synthetic method involves successive 1,3-dipo-
lar cycloaddition reactions which effectively access the key
intermediates, trans- and cis-2,5-disubstituted pyrrolidine 8 having
hydroxyl groups at the -positions on their side chains. Among the
analogs synthesized, 4b and 5b exhibited significant inhibitory ac-
R1
R2
N
14
N
7
N
N
6
7
N
N
6
O H
H
O
O H
H
X
X
Me
Me
Me
Me
2
+
O
O
tivity against Ca -ATPase.
R1
=
Key Words: ptilomycalin A, 1,3-dipolar cycloaddition, nitrone,
pentacyclic guanidine, Ca -ATPase inhibitory activity
O
14
N
NH2
2
+
NH2
Ptilomycalin A (1)
O
O
1
2
Ptilomycalin A (1) and related crambescidins [e.g.,
isocrambescidin (2)] are characteristic of a family of ma-
rine guanidine alkaloids, which consist of unique pentacy-
clic guanidine units (so-called ‘vessel part’) and a
spermidine or hydroxyspermidine unit (so-called ‘anchor
part’) linked by a linear long-chain fatty acid. They show
significant antitumor, antiviral, and antifungal activi-
R2
=
O
14
N
NH2
NH2
13,14,15-
Isocrambescidin 800 (2) OH
R1 = H: Crambescidin 359 (3)
OR3
3
R O
1
a,b
2+
2b,3
+
+
ties,
Ca channel blocker activity,
and Na -, K -
2
+
H
H
H
H
O
and Ca -ATPase inhibitory activity that is competitive
4
N
N
with respect to ATP. Because of the unique structure and
diverse biological activities of ptilomycalin A (1) and its
N
N
6
N
N
H
6
7
7
analogs, many synthetic studies have been reported.5 In
–8
O H
H
O
O H
Cl
Cl
2
000, a new member of the pentacyclic guanidine alka-
4
5
loids, crambescidin 359 (3), which lacks the carboxylate
side chain at C14 of ptilomycalin A (1), was reported for
4a, 5a: R3 = H
O
O
9
the first time. The key structural feature of ptilomycalin
b, 5b: R3
4
=
N
NH2
NH2
12
A and its derivatives in terms of biological activities is be-
lieved to be the pentacyclic guanidine moiety (vessel
1
0
part), which would be expected to play a key role in Figure 1 Marine pentacyclic guanidine alkaloids ptilomycalin A
(
1), 13,14,15-isocrambescidin 800 (2), crambescidine 359 (3), and
binding to anionic substrates such as carboxylate and/or
phosphate-containing compounds. Thus, the biological
activities of crambescidin 359 (3), i.e., the ‘vessel part’
alone, as well as the structure-activity relationships of 1
and 2, and the role of the spermidine-containing long fatty
acid chain of 1 in the biological activities, are of great in-
terest.
their novel analogs 4 and 5.
pentacyclic guanidine 6 could be prepared by double N,O-
acetalization of the guanylated dihydroxy-diketone 7,
which can be synthesized from the 2,5-disubstituted pyr-
rolidine 8 having hydroxyl groups at the -positions of its
side chains. There have been various synthetic studies on
the stereocontrolled synthesis of 2,5-disubstituted pyrro-
Recently, we have developed stereoselective synthetic
methods for trans- and cis-fused pentacyclic guanidine
1
1
compounds. The concept is illustrated in Scheme 1. The
12
lidines. A powerful approach is the successive 1,3-di-
polar cycloaddition protocol originally developed by
1
3
Synthesis 2003, No. 9, Print: 03 07 2003.
Art Id.1437-210X,E;2003,0,09,1427,1432,ftx,en;C01803SS.pdf.
Tuffariello et al. and subsequently evaluated by Ali and
1
4
Wazeer (Scheme 2). Treatment of the isoxazolidine 11,
obtained through the 1,3-dipolar cycloaddition reaction of
©
Georg Thieme Verlag Stuttgart · New York

1
428
A. Georgieva et al.
SPECIAL TOPIC
1
-pyrroline 1-oxide (9) and the alkene 10, with MCPBA to give the isoxazolidine 17b stereoselectively in 78%
results in the regioselective formation of the aldonitrone yield. The resulting isoxazolidine 17b was subjected to
13
1
2. The obtained aldonitrone 12 can be subjected to a sec- MCPBA oxidation in dichloromethane at 0 °C to gener-
ond 1,3-dipolar cycloaddition reaction with another alk- ate the nitrone 18b regioselectively with opening of the
ene 10 to generate the isoxazolidine 13, which can be isoxazolidine ring. The second 1,3-dipolar cycloaddition
further transformed to the trans-2,5-disubstituted pyrroli- reaction of 18b with the olefin 16a took place regio- and
dine 2,5-trans-8 with excellent selectivity. On the other stereoselectively from the less hindered side in the ‘exo-
hand, the corresponding cis-isomer (2,5-cis-8) can be se- mode’ to give the isoxazolidine 19b in 66% yield from
1
6
lectively obtained from the common intermediate 13 by 17b. Hydrogenation of 19b in the presence of 10% Pd/C
MCPBA oxidation to give the nitrone 14. During this suc- exclusively gave the trans-2,5-disubstituted pyrrolidine
cessive 1,3-dipolar cycloaddition process, hydroxyl 20b in 73% yield. Reaction of 20b with bis-N-Boc-thio-
groups at the -positions on the side chains of pyrrolidine urea and HgCl217 gave the N-protected guanidine 21b,
are also introduced simultaneously. In this paper, we de- which was then subjected to oxidation of the two hydroxyl
scribe the stereoselective synthesis of the new pentacyclic groups on the side chains by tetra-n-propylammonium
guanidines 4 and 5, novel analogs of ptilomycalin A (1) perruthenate (TPAP)–NMO, followed by removal of the
and isocrambesdcidin (2), via successive 1,3-dipolar cy- three kinds of protective groups, i.e., tert-butyldimethyls-
cloaddition reactions, and we present the results of assays ilyl, triisopropylsilyl and Boc groups, with CSA7 in tol-
,16
of their biological activities.
uene at 100 °C. Under these conditions, double N,O-
acetalization simultaneously occurred to give the desired
pentacyclic guanidine 5a in 40% yield from 20b after
counter-anion exchange to chloride with methanolic hy-
drogen chloride.
Synthesis of the trans-fused analog 5a is shown in
Scheme 3. The optically active nitrone 15, prepared from
(
S)-malic acid by the method reported by Brandi and et
15
al., was reacted with the alkene 16b in toluene at 100 °C
H
O
H
O
H
H
N,O-acetalization
N
N
O
N
N
O
N
NH
H
H
n
n
n
OH
HO
n
P
P
X
R1
R2
R1
R2
6
P: protective group
7
successive 1,3-dipolar
cycloaddition reaction
H
H
2
5
N
N
H
β
β
O
OP
PO
PO
PO
9
OP
n
n
n
OP
n
R2
R2
R1
R2
10
8
Scheme 1 Synthetic analysis of pentacyclic guanidine compound 6.
9, 10
2,5-cis 8
2
5
2
N
OP
N
β
O
β
O
2,5-trans 8
R2
β
OH HO
1
1
14
MCPBA
MCPBA
2
2
5
OP
N
O
OH
N
OP
O
OH
R2
β
β
R2
β
12
13
Scheme 2 Synthesis of 2,5-disubstituted pyrrolidine 8 from 9 and
0 via successive 1,3-dipolar cycloaddition reactions.
1
Scheme 3 Synthesis of 5a.
Synthesis 2003, No. 9, 1427–1432 ISSN 1234-567-89 © Thieme Stuttgart · New York

SPECIAL TOPIC
Stereoselective Synthesis of Novel Ptilomycalin A Analogs
1429
The cis-fused pentacyclic guanidine 4a, which is a ptilo-
mycalin A analog, was also synthesized as shown in
Schemes 3 and 4. Successive 1,3-dipolar cycloaddition
1) 27, EDCI, DMAP
) 10% Pd/C, H2
4
b (37%)
4a or 5a
5b (32%)
2
reactions of the chiral nitrone 15 with the olefins 16a and Scheme 6 Synthesis of 4b and 5b.
6b gave the isoxazolidine 19a in 49% yield. Oxidation of
1
1
4
19
the isoxazolidine 19a with MCPBA in dichloromethane zumi et al. (Table 1). The IC value of ptilomycalin A
effected regioselective cleavage to give the nitrone 22a. (1) in this assay system is reported to be 5 M. The syn-
Hydrogenation of the nitrone 22a with PtO2 and the re- thetic analogs 4b and 5b showed IC50 values of 3 and 1
duction of the resulting N-hydroxypyrrolidine with
M, respectively. Compounds 4a and 5a, which lack the
5
0
4
1
4
1
8
Mo(CO)6 gave the 2,5-cis-pyrrolidine 23a stereoselec- ‘anchor part’ of 4b and 5b, did not show any inhibitory ac-
tively in 40% yield from 19a. The same four steps as those tivity. More interestingly, crambescidine 359 (3)16
applied in the synthesis of 5a from 20b effectively gave showed weak inhibitory activity with an IC value of 100
5
0
the pentacyclic guanidine 4a in 42% yield.
M. These results suggested that, i) both the ‘vessel part’
and the ‘anchor part’ of ptilomycalin A (1) and its synthet-
ic analogs are necessary, and ii) the stereochemistry of the
pentacyclic guanidine moiety is not important for the
OTIPS
H
MCPBA
°C
1) PtO2, H2
19a
2
+
N
Ca -ATPase inhibitory activity.
(n = 1, m = 2)
0
H
2) Mo(CO)6
O
OH HO
2+
Table 1 Ca -ATPase Inhibitory Activities of Pentacyclic
m
n
40% (3 steps)
H
Guanidines
2
2a (n = 1, m = 2)
Compound
IC50 Value ( M)
OTIPS
1
) bis-N-Boc thiourea
HgCl2, Et3N
Ptilomycalin A (1)
5
6
H
H
H
N
4a
4
b
H
2) TPAP, NMO
OH HO
3) CSA
4) HCl-MeOH
m
n
5b
4a
1
H
42% (4 steps)
23a (n = 1, m = 2)
>100
>100
100
Scheme 4 Synthesis of 4a.
5
a
Crambescidien 359 (3)
Spermidine containing the long chain fatty acid 27 was
synthesized as shown in Scheme 5. Protection of spermi-
dine (24) with benzyl cyanoformate and coupling reaction In conclusion, we have successfully synthesized novel
of the thus obtained 25 with hexadecanedioic acid (26) ptilomycalin A analogs 4 and 5 using successive 1,3-dipo-
gave 27 in 59% yield in two steps.
lar cycloaddition reactions as a key step. This simple and
powerful method for construction of the pentacyclic
guanidine skeleton has potential in the preparation of var-
ious types of ptilomycalin A analogs. Since the novel an-
Introduction of the side chain fatty acid 27 into the penta-
cyclic guanidine alcohols 4a and 5a was performed using
1
-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydro-
2+
alogs, 4b and 5b, show potent Ca -ATPase inhibitory
activity, we intend to synthesize a series of pentacyclic
guanidine compounds for detailed structure-activity rela-
tionship studies, and also to develop some of these com-
pounds as chemical probes to investigate the ATP binding
chloride (EDCI) and DMAP to give the corresponding es-
ter, whose Cbz groups were removed with H over Pd/C
to furnish the 4b and 5b in 37% and 32% yield, respec-
tively (Schemes 5 and 6).
2
2+
site of Ca -ATPase. Further progress will be reported in
due course.
BnCO2CN
NH2
NH2
NHCbz
NHCbz
HN
HN
95%
Spermidine (24)
2
5
Optical rotations were recorded with a JASCO DIP-370 polarime-
ter. IR spectra were measured with a JASCO VALOR-III FT-IR
1
13
spectrophotometer. H and C NMR were recorded on JEOL
DELTA-NMR-ECP-500 and JNM-EX-300 instruments, and mass
spectra on JEOL JMA-HX110 spectrometers. Flash column chro-
matography was performed using silica gel 60 (230–400 mesh; E.
Merck, Darmstadt, Germany).
HO2C
CO2H
NHCbz
NHCbz
12
26
N
HO2C
12
EDCI, DMAP
2%
O
2
7
6
Scheme 5 Synthesis of the ‘anchor part’ 27.
Compound 17b
A mixture of the nitrone 15 (2.45 g, 9.53 mmol) and olefin 16b
(
1
4.35 g, 19.1 mmol) in toluene (110 mL) was heated at 100 °C for
2 h, then allowed to cool to the r.t. The solvent was evaporated in
vacuo and the residue was purified by silica gel chromatography
2
+
Next the Ca -ATPase inhibitory activity, one of the char-
4
acteristic biological activities of ptilomycalin A (1), of 4
and 5 was examined, using the method described by Ohi-
Synthesis 2003, No. 9, 1427–1432 ISSN 1234-567-89 © Thieme Stuttgart · New York

1
430
A. Georgieva et al.
SPECIAL TOPIC
(
hexanes–EtOAc, 50:1) to give 17b (3.60 g, 78%); [ ] –1.7 (c 1.7,
N-Boc protected guanidine 21b (1.74 g, 70%). To the guanidine 21b
D
CHCl3).
(1.74 g, 1.81 mmol) in CH Cl (35 mL) was added 4-methylmor-
2
2
–
1
pholine-N-oxide (848 mg, 7.25 mmol) and a catalytic amount of
TPAP. The resultant mixture was stirred at r.t. for 1 h. The reaction
IR (neat): 2950, 1470, 1400, 1260, 1110, 1050 cm .
1
H NMR (CDCl , 300 MHz): = 4.10 (m, 1 H), 3.89 (m, 1 H), 3.56
m, 3 H), 3.33 (m, 1 H), 3.16 (m, 1 H), 2.06 (m, 3 H), 1.48 (m, 12
3
mixture was then directly loaded on a short silica gel column (Et O)
2
(
to give the diketone (1.25 g, 72%). To the diketone (1.25 g, 1.31
mmol) in toluene (100 mL) was added D-10-camphorsulfonic acid
(303 mg, 1.31 mmol) and the mixture was stirred for 12 h at 100 °C.
The reaction mixture was concentrated in vacuo, and the residue
H), 1.03 (s, 18 H), 0.86 (s, 9 H), 0.016 (s, 6 H).
1
3
C NMR (CDCl , 75 MHz): = 79.08, 74.36, 63.13, 55.67, 40.48,
4.61, 34.03, 32.74, 31.56, 26.17, 25.94, 25.82, 22.62, 17.94, 12.05,
5.30.
3
3
–
was purified by column chromatography (CHCl –MeOH, 100:1,
3
1
00:2, 100:5, 100:8, 100:10) to give 5a as the D-10-camphorsulfon-
HRMS (FAB): m/z calcd for C H NO Si (M + H), 486.3799;
2
6
56
3
2
ic acid salt. The counter-anion was exchanged to chloride with
HCl–MeOH at r.t. for 12 h to give 5a as the hydrogen chloride salt
found, 486.3805.
(
380 mg, 40%, 4 steps); [ ] –67.4 (c 0.4, CHCl ).
D
3
Compound 19b
–
1
IR (neat): 3400, 2950, 1750, 1660, 1620, 1180, 1110, 1050 cm .
To a solution of 17b (3.60 g, 7.42 mmol) in CH Cl (100 mL) was
added MCPBA (1.92 g, 11.1 mmol) at 0 °C, and the resulting mix-
ture was stirred for 20 min. To the reaction mixture was added an
2
2
1
H NMR (CDCl , 500 MHz): = 9.60 (s, 1 H), 9.56 (s, 1 H), 4.14
3
(
m, 1 H), 3.84 (m, 3 H), 3.62 (m, 2 H), 2.53 (d, J = 10 Hz, 1 H), 1.70
excess of solid Ca(OH) and this was stirred at r.t. for another 10
2
(m, 19 H).
1
min. The resultant mixture was filtered through a pad of Celite, and
the filtrate was concentrated in vacuo to give the nitrone 18b as a
clear brown oil. A mixture of the nitrone 18b and the olefin 16a
3
C NMR (CDCl , 125 MHz): = 149.03, 85.43, 80.77, 73.65,
3
6
2
3.13, 61.74, 56.70, 48.38, 42.73, 39.14, 38.33, 36.30, 35.09, 30.75,
7.01, 19.89, 19.88, 18.03.
(3.18 g, 14.8 mmol) in toluene (70 mL) was heated at 100 °C for 12
h. After removal of the solvent in vacuo, the residue was purified by
column chromatography (hexanes–EtOAc, 20:1) to give 19b (3.50
g, 66%, 2 steps) as a clear brown oil; [ ]D –6.7 (c 1.5, CHCl3).
HRMS (FAB): m/z calcd for C H N O (M +H), 336.2287; found,
18 30 3 3
336.2292.
–
1
Compound 17a
IR (neat): 3350 (br), 2900, 1720, 1460, 1390, 1250, 1020 cm .
A mixture of the nitrone 15 (2.45g, 9.53 mmol) and olefin 16a (4.00
g, 18.7 mmol) in toluene (110 mL) was heated at 100 °C for 12 h.
After cooling, the reaction mixture was concentrated in vacuo and
the residue was purified by silica gel chromatography (hexanes–
EtOAc, 50:1) to give 17a (3.68 g, 82%); [ ] –1.5 (c 0.6, CHCl ).
1
H NMR (CDCl , 300 MHz): = 4.43 (m, 1 H), 4.15 (m, 1 H), 4.01
m, 1 H), 3.91 (m, 1 H), 3.71 (m, 1 H), 3.57 (m, 3 H), 3.15 (m, 1 H),
.30 (m, 1 H), 2.02 (m, 1 H), 1.90 (m, 1 H), 1.79 (m, 1 H), 1.43 (m,
9 H), 1.03 (s, 9 H), 0.87 (s, 18 H), 0.02 (s, 12 H).
3
(
2
2
D
3
1
3
C NMR (CDCl , 75 MHz): = 77.20, 73.27, 68.92, 63.24, 62.88,
IR (neat): 2950, 1470, 1390, 1260, 1110, 1050 cm–1.
3
6
2
–
2.83, 43.87, 41.78, 40.64, 37.48, 37.06, 32.87, 32.75, 32.47, 32.22,
5.94, 25.54, 25.43, 22.84, 21.86, 18.31, 17.97, 17.67, 12.26, 12.20,
5.28, –5.31 –5.33.
1
H NMR (CDCl , 300 MHz): = 4.10 (m, 1 H), 3.89 (m, 1 H), 3.57
3
(
m, 3 H), 3.34 (m, 1 H), 3.17 (m, 1 H), 2.08 (m, 3 H), 1.48 (m, 10
H), 1.03 (s, 18 H), 0.86 (s, 9 H), 0.013 (s, 6 H).
HRMS (FAB): m/z calcd for C H NO Si (M – OH), 698.5395;
found, 698.5403.
3
8
80
4
3
13
C NMR (CDCl , 75 MHz): = 79.06, 74.33, 63.02, 55.69, 40.52,
3
3
3.82, 33.52, 32.61, 31.64, 26.04, 22.71, 18.05, 14.20, 12.18, –5.15.
Compound 20b
HRMS (FAB): m/z calcd for C H NO Si (M + H), 472.3642;
2
5
54
3
2
To a solution of 19b (3.50 g, 4.90 mmol) in EtOH (50 mL) was add-
ed 10% Pd/C (30 mg) and the mixture was stirred for 12 h at r.t. un-
der hydrogen. It was then filtered through a pad of Celite and the
filtrate was concentrated in vacuo. The residue was purified by sil-
ica gel chromatography (EtOAc–MeOH, 9:1) to give the pyrroli-
dine 20b (2.56 g, 73%); [ ] +6.3 (c 0.9, CHCl ).
found, 472.3650.
Compound 19a
To a solution of 17a (3.68 g, 7.81 mmol) in CH Cl (100 mL) was
added MCPBA (2.01g, 11.7 mmol) at 0 °C and the reaction mixture
was stirred for 20 min. To the reaction mixture was added an excess
2
2
D
3
of solid Ca(OH) , and the resulting mixture was stirred at r.t. for an-
2
IR (neat): 3350 (br), 2900, 1700, 1600, 1560, 1470, 1400, 1260,
–
1
other 10 min. The mixture was filtered through a pad of Celite, and
the filtrate was concentrated in vacuo to give the nitrone 18a as a
clear brown oil. A mixture of the nitrone 18a and the olefin 16b
1
110 (br) cm .
1
H NMR (CDCl , 300 MHz): = 4.10 (m, 2 H), 3.80 (m, 2 H), 3.56
3
(
m, 4 H), 3.37 (m, 1 H), 2.23 (m, 1 H), 2.02 (m, 2 H), 1.45 (m, 32
(3.48g, 15.3 mmol) in toluene (70 mL) was heated at 100 °C for 12
H), 1.04 (s, 9 H), 0.86 (s, 18 H), 0.02 (s, 12 H).
h. After removal of the solvent in vacuo, the residue was purified by
silica gel column chromatography (hexanes–EtOAc, 20:1) to give
1
3
C NMR (CDCl , 75 MHz): = 77.20, 69.63, 68.88, 63.41, 63.24,
3
1
9a (3.35 g, 60%, 2 steps) as a clear brown oil; [ ] –2.8 (c 1.0,
6
2
–
3.11, 60.38, 53.27, 41.16, 40.87, 37.25, 36.90, 35.94, 32.88, 32.75,
5.97, 25.90, 25.83, 21.99, 21.03, 18.34, 17.97, 14.17, 12.15, 12.04,
5.28.
D
CHCl3).
IR (neat): 3350 (br), 2900, 1720, 1480, 1400, 1260, 1020 cm–1.
HRMS (FAB): m/z calcd for C H NO Si (M – OH), 700.5552;
found, 700.5561.
1
3
8
82
4
3
H NMR (CDCl , 300 MHz): = 4.43 (m, 1 H), 4.15 (m, 1 H), 4.01
m, 1 H), 3.91 (m, 1 H), 3.71 (m, 1 H), 3.57 (m, 3 H), 3.15 (m, 1 H),
3
(
2
2
.30 (m, 1 H), 2.02 (m, 1 H), 1.90 (m, 1 H), 1.79 (m, 1 H), 1.43 (m,
9 H), 1.03 (s, 9 H), 0.87 (s, 18 H), 0.02 (s, 12 H).
Compound 5a
To a mixture of the pyrrolidine 20b (1.86 g, 2.60 mmol), bis-N-Boc-
thiourea (858 mg, 3.11 mmol) and Et N (1.2 mL, 9.10 mmol) in
DMF (18 mL) was added HgCl (842 mg, 3.11 mmol) at 0 °C, and
the resulting mixture was stirred for 30 min. The reaction mixture
was diluted with EtOAc, and the mixture was filtered through a pad
of Celite. The filtrate was concentrated in vacuo and the residue was
purified by chromatography (hexanes–EtOAc, 10:1) to give the bis-
1
3
C NMR (CDCl , 75 MHz): = 75.24, 73.22, 70.74, 68.89, 63.21,
3
3
6
2
–
3.05, 61.28, 41.87, 40.68, 37.28, 37.17, 32.99, 32.65, 32.46, 31.55,
6.35, 25.94, 25.86, 22.61, 21.95, 18.31, 17.99, 17.97, 14.08, 12.20,
5.30.
2
+
HRMS (FAB): m/z calcd for C H NO Si (M – OH), 698.5395,
found, 698.5400.
3
8
80
4
3
Synthesis 2003, No. 9, 1427–1432 ISSN 1234-567-89 © Thieme Stuttgart · New York

SPECIAL TOPIC
Compound 23a
Stereoselective Synthesis of Novel Ptilomycalin A Analogs
1431
Compound 27
To a solution of 19a (3.35 g, 4.68 mmol) in CH Cl (70 mL) was
To a solution of spermidine (24) (1g, 6.88 mmol) in CH Cl (30 mL)
2
2
2 2
added MCPBA (1.21g, 7.03 mmol) at 0 °C and the reaction mixture
was stirred for 20 min. To the reaction mixture was added excess of
was added benzylcyanoformate (2 mL, 13.7 mmol) at 0 °C, and the
mixture was stirred for 2 h. The reaction mixture was concentrated
in vacuo, and the residue was purified by silica gel column chroma-
solid Ca(OH) , and the resulting mixture was stirred at r.t. for anoth-
2
er 10 min. The mixture was filtered through a pad of Celite, and the
tography (CHCl –MeOH, 5:1) to give 25 (2.71 g, 95%) as a white
3
filtrate was concentrated in vacuo to give the nitrone 22a as a clear
solid. A mixture of 25 (152 mg, 0.37 mmol), hexadecanedioic acid
(157 mg, 0.55 mmol), EDCI (70 mg, 0.37 mmol) and a catalytic
amount of DMAP in CH Cl (16 mL) was stirred at r.t. for 24 h. To
brown oil. A mixture of the nitrone 22a and PtO (500 mg) in EtOH
2
(200 mL) was stirred for 12 h at r.t. under hydrogen. The reaction
2
2
mixture was filtered through a pad of Celite and the filtrate was con-
centrated in vacuo. The residue was purified by silica gel column
chromatography (hexanes–EtOAc, 2:1) to give hydroxylamine
the reaction mixture was added H O (5 mL) and the resulting mix-
ture was extracted with EtOAc (100 mL). The extracts were dried
2
over MgSO and the filtrates were concentrated in vacuo. The resi-
4
(2.61 g, 76%, 2 steps) as a clear brown oil. To the emulsion of hy-
due was purified by silica gel column chromatography (hexanes–
droxylamine (2.61 g, 3.55 mmol) in CH CN (200 mL) and H O (30
EtOAc, 1:1, 1:3, 1:5) to give 27 (155 mg, 62%) as a white solid.
3
2
mL) was added Mo(CO) (939 mg, 3.55 mmol), and the mixture
1
6
H NMR (CDCl , 500 MHz): = 7.33 (br s, 10 H), 5.08 (br s, 4 H),
.38 (br s, 2 H), 3.22 (br s, 4 H), 3.10 (br s, 2 H), 2.27 (t, J = 8 Hz,
H), 2.23 (m, 2 H), 1.80–1.40 (m, 10 H), 1.24 (br s, 20 H).
3
was heated at 100 °C for 15 min. The reaction mixture was concen-
trated in vacuo, and the residue was purified by silica gel column
chromatography (EtOAc–MeOH, 9:1) to give the pyrrolidine 23a
3
2
1
3
C NMR (CDCl , 125 MHz): = 177.86, 173.83, 156.55, 156.47,
(
1.27 g, 40%, 3 steps) as a clear brown oil; [ ] 2.0 (c 0.4, CHCl ).
3
D
3
1
1
36.65, 136.35, 128.36, 128.24, 127.99, 127.90, 127.78, 127.78,
27.73, 66.55, 66.24, 47.28, 42.22, 40.24, 37.61, 33.94, 32.92,
–
1
IR (neat): 3350, 2900, 1740, 1480, 1400, 1260, 1020 cm .
1
H NMR (CDCl , 300 MHz): = 4.37 (m, 1 H), 4.18 (m, 1 H), 3.78
29.40-28.93, 27.25, 25.44, 24.66.
3
(
1
m, 3 H), 3.56 (m, 5 H), 2.50 (m, 1 H), 2.21 (m, 1 H), 1.97 (m, 1 H),
.75 (m, 2 H), 1.47 (m, 26 H), 1.03 (s, 9 H), 0.86 (s, 9 H), 0.85 (s, 9
HRMS (FAB): m/z calcd for C H N O (M + H), 682.4431; found,
3
9
60
3
7
6
82.4428.
H), 0.01 (s, 12 H).
1
3
C NMR (CDCl , 75 MHz): = 77.20, 73.91, 71.26, 68.54, 67.34,
Compound 4b
3
6
3
1
–
3.58, 63.23, 63.10, 53.86, 40.55, 38.68, 37.94, 37.68, 35.65, 32.93,
2.86, 30.32, 29.66, 28.88, 26.16, 25.96, 25.74, 25.49, 22.94, 21.74,
8.33, 18.01, 17.89, 17.86, 14.02, 12.20, 12.04, 11.81, –4.92, –5.28,
5.67.
A mixture of 4a (5 mg, 13 mol), carboxylic acid 27 (10 mg, 15
mol) and EDCI (7 mg, 36 mol) in CH Cl (1 mL) in the presence
2
2
of a catalytic amount of DMAP was stirred at r.t. for 24 h. The re-
action mixture was concentrated in vacuo, and the residue was pu-
+
rified by silica gel column chromatography (MeOH–CHCl , 3:97)
3
HRMS (FAB): m/z calcd for C H NO Si (M – OH), 700.5552;
found, 700.5561.
3
8
82
4
3
to give the ester (6 mg, 46%). A mixture of the ester (6 mg) and 10%
Pd/C (2 mg) in EtOH (5 mL) was stirred at r.t. for 4 h under hydro-
gen. The reaction mixture was filtered through a pad of Celite and
the filtrates were concentrated in vacuo to give 4b (3.5 mg, 80%);
Compound 4a
To a mixture of the pyrrolidine 23a (1.27 g, 1.78 mmol), bis-N-Boc-
thiourea (589 mg, 2.14 mmol) and Et N (1 mL, 7.20 mmol) in DMF
16 mL) was added HgCl (579 mg, 2.14 mmol) at 0 °C, and the re-
[
] –35.7 (c 0.7, CHCl ).
D
3
3
–
1
(
IR (neat): 2927, 1736, 1635, 1457, 1042 cm .
2
sulting mixture was stirred for 30 min. The reaction mixture was di-
luted with EtOAc and the mixture was filtered through a pad of
Celite. The filtrate was concentrated in vacuo, and the residue was
purified by silica gel column chromatography (hexanes–EtOAc,
1
H NMR (CD OD, 500 MHz): = 5.42 (br s, 1 H), 4.14 (m, 2 H),
3
3
(
8
.78 (t, J = 11, 1 H), 3.69 (m, 2 H), 3.64 (d, J = 10.8 Hz, 1 H), 3.14
m, 1 H), 3.03 (m, 2 H), 2.92 (m, 1 H), 2.70 (m, 1 H), 2.43–2.22 (m,
H), 2.14 (dd, J = 12.9, 4.9 Hz, 1 H), 1.28 (br s, 30 H).
1
0:1) to give the bis-N-Boc protected guanidine (1.17 g, 70%). To
1
3
C NMR (CD OD, 125 MHz): = 147.10, 149.82, 85.58, 81.31,
the bis-N-Boc protected guanidine (1.17 g, 1.22 mmol) in CH Cl
3
2
2
7
3
4.73, 64.08, 62.78, 57.48, 52.06, 44.09, 44.04, 40.53, 39.85, 37.32,
4.96, 34.88, 33.56, 32.08, 30.08-30.23, 25.95, 25.90, 23.59, 19.56.
(
35 mL) was added 4-methylmorpholine-N-oxide (570 mg, 4.86
mmol) and a catalytic amount of TPAP. The mixture was stirred for
h at r.t., and the reaction mixture was directly loaded onto a short
1
HRMS (FAB): m/z calcd for C H N O (M + H), 731.5799; found,
731.5794.
4
1
75
6
5
silica gel column with Et O to give the diketone (923 mg, 78%). To
2
the diketone (923 mg, 0.96 mmol) in toluene (100 mL) was added
D-10-camphorsulfonic acid (224 mg, 0.96 mmol), and the mixture
was heated at 100 °C for 12 h. The reaction mixture was concentrat-
ed in vacuo, and the residue was purified by column chromatogra-
Compound 5b
As described above for 4a, 5a (5 mg) was also converted to 5b (3
mg, 32%, 2 steps).
phy (CHCl –MeOH, 100:1, 100:2, 100:3, 100:8, 100:10) to give 4a
3
1
H NMR (CDCl , 500 MHz): = 5.08 (br s, 1 H), 3.87 (m, 2 H), 3.80
3
as the D-10-camphorsulfonic acid salt. The counter anion was ex-
changed to chloride with HCl–MeOH at r.t. for 12 h to give 4a as
(m, 2 H), 3.63 (m, 2 H), 3.15–2.95 (m, 4 H), 2.55 (m, 1 H), 2.42 (d,
J = 12 Hz, 1 H), 2.35 (t, J = 8.2 Hz, 2 H), 2.27 (m, 4 H), 2.20 (d,
J = 12 Hz, 1 H), 1.25 (br s, 30 H).
the hydrogen chloride salt (190 mg, 42%, 4 steps); [ ] –14.3 (c 1.3,
D
CHCl3).
–
1
HRMS (FAB): m/z calcd for C41
H N O (M + H), 731.5799; found,
75 6 5
IR (neat): 3250, 3120, 1655, 1610, 1440, 1280, 1120, 1060 cm .
7
31.5797.
1
H NMR (CDCl , 500 MHz): = 8.94 (s, 1 H), 8.77 (m, 1 H), 4.36
3
(
1
m, 1 H), 3.99 (m, 1 H), 3.80 (m, 2 H), 3.57 (m, 2 H), 2.71 (m, 1 H),
.70 (m, 19 H).
Acknowledgment
1
3
C NMR (CDCl , 125 MHz): = 148.86, 84.32, 80.27, 70.56,
3
Toray Co., Ltd. Award in Synthetic Organic Chemistry, Japan and
the funds from the Pharmacy Research Encouragement Foundation
are greatly acknowledged for the financial support. This research
was supported in part by Grant-in-Aid for Scientific Research from
6
2
2.73, 58.53, 50.83, 47.32, 42.86, 39.14, 38.30, 34.14, 32.72, 30.82,
9.11, 27.05, 20.15, 19.84.
HRMS (FAB): m/z calcd for C H N O (M + H), 336.2287; found,
1
8
30
3
3
3
36.2296.
Synthesis 2003, No. 9, 1427–1432 ISSN 1234-567-89 © Thieme Stuttgart · New York

1
432
A. Georgieva et al.
SPECIAL TOPIC
the Ministry of Education, Culture, Sports, Science and Technology
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Synthesis 2003, No. 9, 1427–1432 ISSN 1234-567-89 © Thieme Stuttgart · New York