A facile synthesis of naturally occurring aminopeptidase inhibitor tyromycin A

Full text of DOI:10.1021/jo010260e

J . Org. Chem. 2001, 66, 5259-5261
5259
a new facile synthetic route to this bioactive natural
product, 1, is a task of current interest, and its first
synthesis has been completed by Samadi et al.13 by using
the well-known decarboxylative Barton-radical coupling
reaction. Recently we reported the first coupling reaction
of citraconimide 6 and triphenylphosphine (TPP) adduct
with aliphatic aldehydes to complete the most efficient
synthesis of chaetomellic acid A,8 and herein we report
the extension of this coupling reaction to complete a
practical synthesis of tyromycin A via a double Wittig
reaction and hydrolysis pathway starting from juniperic
acid.14
A F a cile Syn th esis of Na tu r a lly Occu r r in g
Am in op ep tid a se In h ibitor Tyr om ycin A†
Sivaprakasam Mangaleswaran and
Narshinha P. Argade*,‡
Division of Organic Chemistry (Synthesis), National
Chemical Laboratory, Pune 411008, India
argade@dalton.ncl.res.in
Received March 9, 2001
The PCC oxidation15a of 1,16-hexadecanediol (4) in
dichloromethane gave the desired dialdehyde 515b in 77%
yield (Scheme 1). The reaction of dialdehyde 5 with an
excess of citraconimide-TPP adduct in refluxing glacial
acetic acid followed by removal of acetic acid in vacuo
furnished a mixture of bis-condensed exo Wittig products
7 (E,E major), 8 (E,Z minor), and 9 (Z,Z minor) in 70%
yield with an 85:15 ratio of E:Z geometry of the carbon-
carbon double bond. In the above reaction, when the
acetic acid was distilled off under normal atmospheric
pressure and the residue was heated for 30 min at 140-
150 °C, the reaction directly furnished the endo bisimide
10 in 72% yield. The mixture of 7 + 8 + 9 in refluxing
tetralin underwent a smooth trisubstituted exocyclic to
tetrasubstituted endocyclic double bond isomerization to
yield the bismaleimide derivative 10 in quantitative yield.
The mixture of exo-isomers 7 + 8 + 9 upon treatment
with sodium methoxide in methanol followed by acidifi-
cation gave tyromycin A in 60% yield. The reaction of
bisimide 10 upon treatment with KOH in water + THF
+ CH3OH (1:1:1) followed by acidification, ethyl acetate
extraction, and silica gel column chromatographic puri-
fication16 gave tyromycin A in 98% yield. The spectral
and analytical data obtained for tyromycin A (1) were in
agreement with reported data.5,13
Several structurally interesting and bioactive com-
pounds with disubstituted maleic anhydride moieties,
such as CP-225,917/CP-263,114,1 byssochlamic acid,2
tautomycin,3 chaetomellic acid A,4 and tyromycin A5 have
been recently (except byssochlamic acid) isolated as
natural products. Recently we completed the synthesis
of the 2,3-disubstituted maleic anhydride segment of
antibiotic tautomycin6 and three alternate syntheses of
ras farnesyl protein transferase inhibitor chaetomellic
acid A.7-9 A number of FPTase inhibitors are in human
clinical trails by several companies.10 Work on the total
synthesis of byssochlamic acid is in progress in our
laboratories,11 and recently we planned for the synthesis
of tyromycin A (1). It has been isolated from mycelial
cultures of the basidiomycete Tyromyces lacteus (Fr.)
Murr,5 and its structure was established as 1,16-bis[4-
methyl-2,5-dioxo-3-furanyl]hexadecane (1) by using spec-
tral and analytical data and by transformation into the
corresponding tetramethyl ester and diimide derivatives.5
Among the enzymes bound to surfaces of mammalian
cells, aminopeptidases have been recognized as a poten-
tial target for the immunomodulating drugs.12 Tyromycin
A was found to inhibit the leucine and cysteine amino-
peptidases bound to the outer surface of HeLa S3 cells,
and it also exhibits cytostatic activity.5 Development of
In summary, we have demonstrated yet another ap-
plication of our recently reported citraconimide-TPP
adduct coupling reaction with aliphatic aldehydes to
complete the practical two-step synthesis of bioactive
natural product tyromycin A in 71% overall yield, and
our method also offers potentially easy access to tyro-
mycin congeners for structure-activity relationship stud-
ies. A one-pot double Wittig reaction has been used
previously in the synthesis of â-carotene.17
† NCL Communication No. 6606.
‡ Fax: +91-20-5893153.
(1) (a) Dabrah, T. T.; Harwood, H. J ., J r.; Huang, L. H.; J ankovich,
N. D.; Kaneko, T.; Li, J .-C.; Lindsey, S.; Moshier, P. M.; Subashi, T.
A.; Therrien, M.; Watts, P. C. J . Antibiot. 1997, 50, 1. (b) Nicolaou, K.
C.; Baran, P. S.; Zhong, Y.-L.; Choi, H.-S.; Yoon, W. H.; He, Y.; Fong,
K. C. Angew. Chem., Int. Ed. 1999, 38, 1669. (c) Nicolaou, K. C.; Baran,
P. S.; Zhong, Y.-L.; Fong, K. C.; He, Y.; Yoon, W. H.; Choi, H.-S. Angew.
Chem., Int. Ed. 1999, 38, 1676 and references cited therein.
(2) (a) Raistrick, H.; Smith, G. Biochem. J . 1933, 27, 1814. (b) White,
J . D.; Kim, J .; Drapela, N. E. J . Am. Chem. Soc. 2000, 122, 8665 and
references cited therein.
(3) Cheng, X.-C.; Kihara, T.; Kusakabe, H.; Magae, J .; Kobayashi,
Y.; Fang, R.-P.; Ni, Z.-F.; Shen, Y.-C.; Ko, K.; Yamaguchi, I.; Isono, K.
J . Antibiot. 1987, 40, 907.
(4) Singh, S. B.; Zink, D. L.; Liesch, J . M.; Goetz, M. A.; J enkins, R.
G.; Nallin-Omstead, M.; Silverman, K. C.; Bills, G. F.; Mosley, R. T.;
Gibbs, J . B.; Albers-Schonberg, G.; Lingham, R. B. Tetrahedron 1993,
49, 5917.
(13) Poigny, S.; Guyot, M.; Samadi, M. J . Org. Chem. 1998, 63, 1342.
(14) Hiroaki, O.; Koichi, O. Mokuzai Gakkaish 2000, 46, 54 and
references cited therein.
(15) (a) Sharma, A.; Chattopadhyay, S. J . Org. Chem. 1999, 64, 8059.
(b) McMurry, J . E.; Fleming, M. P.; Kees, K. L.; Krepski, L. R. J . Org.
Chem. 1978, 43, 3255.
(5) Weber, W.; Semar, M.; Anke, T.; Bross, M.; Steglich, W. Planta
Med. 1992, 58, 56.
(6) Deshpande, A. M.; Natu, A. A.; Argade, N. P. Synthesis 2001,
702.
(7) Deshpande, A. M.; Natu, A. A.; Argade, N. P. J . Org. Chem. 1998,
63, 9557.
(8) Desai, S. B.; Argade, N. P. J . Org. Chem. 1997, 62, 4862.
(9) Argade, N. P.; Naik, R. H. Bioorg. Med. Chem. 1996, 4, 881.
(10) Singh, S. B.; J ayasuriya, H.; Silverman, K. C.; Bonfiglio, C. A.;
Williamson, J . M.; Lingham, R. B. Bioorg. Med. Chem. 2000, 8, 571.
(11) Mangaleswaran, S.; Argade, N. P. Unpublished results.
(12) Aoyagi, T.; Suda, H.; Nagai, M.; Okagawa, K.; Suzuki, J .;
Kakeuchi, T.; Umezawa, H. Biochim. Biophys. Acta 1976, 452, 131.
(16) Samadi et al.13 believe that the tyromycin A during the silica
gel column chromatographic purification undergoes a ring opening to
form the corresponding di- and tetracarboxylic acids. We chromato-
graphed 100 mg of pure tyromycin A over silica gel column (60-120
mesh) using a petroleum ether (60-80 fraction)-ethyl acetate mixture
(9:1), obtained more than 98 mg of tyromycin A, and proved that it is
fairly stable to silica gel column purification conditions. The disubsti-
tuted maleic anhydrides under neutral and acidic conditions stay in a
ring-closed form, while in basic medium they exist in dianionic form.4
To our knowledge, the conditions needed to obtain them in the cis-
dicarboxylic acid form are still elusive.
(17) Wittig, G.; Pommer, H. Ger. Patent 954,247, 1959; Chem. Abstr.
1959, 53, 2279.
10.1021/jo010260e CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/23/2001

5260 J . Org. Chem., Vol. 66, No. 15, 2001
Notes
Sch em e 1a
a
(i) CH2N2, Et2O, 0 °C, 2 h (95%); (ii) LAH, Et2O, rt, 2 h (98%); (iii) PCC, CH2Cl2, rt, 10 h (77%); (iv) TPP, AcOH, 5, reflux, 10 h (70%);
(v) (a) TPP, AcOH, 5, reflux, 10 h, (b) ∆, 140-150 °C, 30 min (72%); (vi) Tetralin, reflux, 1 h (98-100%); (vii) (a) CH3ONa, CH3OH, reflux,
2 h, (b) H+/HCl (60%); (viii) (a) KOH, H2O, THF, CH3OH, reflux, 2 h, (b) H+/HCl (98%).
30 min. The supernatant of the reaction mixture was filtered
through a small pad of silica gel and concentrated in vacuo. The
silica gel column purification of the residue using a petroleum
ether and ethyl acetate mixture (9:1) gave pure 5: 978 mg (77%
yield); mp 52-53 °C; 1H NMR (CDCl3, 200 MHz) δ 1.26 (bs, 20H),
1.63 (quintet, J ) 6 Hz, 4H), 2.43 (dt, J ) 6 and 2 Hz, 4H), 9.77
(s, 2H); MS (m/e) 254, 236, 192, 136, 108, 95, 81, 68, 57; IR
Exp er im en ta l Section
Melting points are uncorrected. Column chromatographic
separations were carried out on ACME silica gel (60-120 mesh).
Triphenylphosphine, citraconic anhydride, and juniperic acid
were obtained from Aldrich Chemical Co. 1,16-Hexadecanediol
(4) is commercially available and is a more suitable starting
material for the synthesis of tyromycin A (1). We began our
synthesis with juniperic acid (2) as it was immediately available
to us from our polymer chemistry division. The citraconimide 6
was obtained in quantitative yield from citraconic anhydride via
dehydration of a mixture of the corresponding regioisomers of
maleanilic acids.18
(Nujol) νmax 2748, 1713 cm-1
.
(E/Z)-1,16-Bis[4-m eth yl-2,5-d ioxo-1-p-tolylp yr r olid in -3-
yl]-1,15-h exa d eca d ien e (7/8/9). A mixture of citraconimide 6
(3.01 g, 15 mmol), triphenylphosphine (3.93 g, 15 mmol), and
1,16-hexadecanedial (762 mg, 3 mmol) in glacial acetic acid (40
mL) was refluxed with stirring for 10 h. Acetic acid was distilled
off in vacuo at 45-50 °C, and the residue was dissolved in ethyl
acetate (50 mL). The organic layer was washed with water and
brine and dried over Na2SO4. Concentration of the organic layer
followed by silica gel column chromatographic purification of the
residue using a mixture of petroleum ether and ethyl acetate
Meth yl Ester of J u n ip er ic Acid (3). A solution of acid 2
(2.72 g, 10 mmol) in ether (30 mL) was treated with a solution
of diazomethane in ether at 0 °C until the starting material was
completely consumed (2 h). Excess diazomethane was quenched
with acetic acid, and the reaction mixture was concentrated in
vacuo. Silica gel column purification of the residue using a
petroleum ether and ethyl acetate mixture (8:2) gave pure 3:
2.71 g (95% yield); mp 60-62 °C; 1H NMR (CDCl3, 200 MHz) δ
1.28 (bs, 22H), 1.45-1.75 (bm, 5H), 2.35 (t, J ) 8 Hz, 2H), 3.65
(t, J ) 8 Hz, 2H), 3.68 (s, 3H); MS (m/e) 286, 268, 256, 236, 199,
1
(85:15) gave a mixture of 7, 8, and 9 (E:Z ) 85:15 by H NMR):
1
1.31 g (70% yield); mp 96-100 °C; H NMR (CDCl3, 200 MHz)
δ 1.29 (bs, 20H), 1.48 (d, J ) 8 Hz, 0.9H) (Z-isomer), 1.53 (d, J
) 8 Hz, 5.1H), 1.40-1.60 (m, 4H), 2.00-2.40 (m, 3.4H), 2.39 (S,
6H), 2.70-2.90 (m, 0.6H) (Z-isomer), 3.35 (q, J ) 8 Hz, 0.3H)
(Z-isomer), 3.46 (q, J ) 8 Hz, 1.7 H), 6.23 (dt, J ) 8 and 2 Hz,
0.3 H) (Z-isomer), 6.93 (dt, J ) 8 and 2 Hz, 1.7 H), 7.21 (d, J )
8 Hz, 4H), 7.29 (d, J ) 8 Hz, 4H); MS (m/e) 624, 518, 423, 396,
312, 242, 228, 215, 202, 186, 133, 118, 107, 95, 81, 68, 55; IR
(Nujol) νmax 1770, 1710, 1672 cm-1. Anal. Calcd for C40H52N2O4:
C, 76.88; H, 8.38; N, 4.48. Found: C, 77.11; H, 8.12; N, 4.32.
143, 112, 98, 87, 74, 69, 55; IR (CHCl3) νmax 3400, 1712 cm-1
.
1,16-Hexa d eca n ed iol (4). A solution of 3 (2.29 g, 8 mmol)
in ether (25 mL) was added dropwise to a suspension of lithium
aluminum hydride (379 mg, 10 mmol) in ether (20 mL) at room
temperature over a period of 10 min. The reaction mixture was
stirred at room temperature for 2 h, and excess reagent was
decomposed by cautious addition of moist ether (30 mL) and
stirring for 30 min. To this mixture was added dilute HCl (20
mL), and the reaction mixture was extracted with ether (3 × 25
mL). The organic layer was washed with brine, dried over
Na2SO4, concentrated, and dried in vacuo. Silica gel column
chromatographic purification of the residue using petroleum
ether-ethyl acetate (1:1) gave pure 4: 2.02 g (98% yield); mp
91-92 °C (lit.19 mp 89-90 °C); 1H NMR (CDCl3, 200 MHz) δ
1.30 (bs, 24H), 1.58 (q, J ) 6 Hz, 4H), 3.65 (t, J ) 6 Hz, 4H); MS
(m/e) 258, 240, 228, 222, 210, 194, 180, 166, 152, 137, 123, 109,
1,16-Bis[4-m et h yl-2,5-d ioxo-1-p -t olylp yr r ol-3-yl]h exa -
d eca n e (10). The imide 10 was prepared using the same
procedure as described for the preparation of 7 + 8 + 9 except
that the acetic acid was distilled off slowly over a period of 15
min at 140-150 °C bath temperature and the oily residue was
further heated with stirring for 30 min at same temperature.
10: 1.34 g (72% yield); mp 96-98 °C; 1H NMR (CDCl3, 200 MHz)
δ 1.29 (bs, 20H), 1.35 (bs, 4H), 1.60 (quintet, J ) 4 Hz, 4H),
2.07 (s, 6H), 2.40 (s, 6H), 2.48 (t, J ) 6 Hz, 4H), 7.24 (d, J ) 6
Hz, 4H), 7.28 (d, J ) 6 Hz, 4H); 13C NMR (CDCl3, 75 MHz) δ
8.2, 20.5, 23.2, 27.6, 28.7, 29.1 (5 × CH2), 125.1 (2-carbons) 129.0
(2-carbons), 136.5, 140.7, 170.2, 170.5; MS (m/e) 624, 438, 242,
228, 215, 202, 154, 136, 120, 106, 91, 81, 55; IR (Nujol) νmax 1770,
1713 cm-1. Anal. Calcd for C40H52N2O4: C, 76.88; H, 8.38; N,
4.48. Found: C, 77.01; H, 8.22; N, 4.57.
95, 82, 67, 54; IR (Nujol) νmax 3415, 3356, 1462 cm-1
.
1,16-Hexa d eca n ed ia l (5). To a stirred suspension of PCC
(3.24 g, 15 mmol) in CH2Cl2 (35 mL) at 0 °C was added a solution
of 1,16-hexadecanediol (1.29 g, 5 mmol) in CH2Cl2 (15 mL) over
a period of 20 min, and the reaction mixture was further stirred
for 10 h at room temperature. The reaction mixture was diluted
with anhydrous ether (40 mL) and then stirred vigorously for
Isom er iza tion of Exo Isom er s (7 + 8 + 9) to En d o Isom er
(10). A solution of the 7, 8, and 9 mixture (500 mg) in tetralin
(10 mL) was refluxed for 1 h with stirring. The reaction mixture
was then cooled to room temperature, and silica gel column
purification of the reaction mixture using a petroleum ether and
ethyl acetate mixture (9:1) gave pure 10: 490 mg (98% yield).
(18) Mangaleswaran, S.; Argade, N. P. J . Chem. Soc., Perkin Trans.
1 2000, 3290.
(19) Saotome, K.; Komoto, H.; Yamazaki, T. Bull. Chem. Soc. J pn.
1966, 39, 480.

Notes
1,16-Bis[4-m eth yl-2,5-d ioxo-3-fu r a n yl]h exa d eca n e (Ty-
J . Org. Chem., Vol. 66, No. 15, 2001 5261
29.4, 29.6 (4 × CH2), 140.4, 144.7, 165.8, 166.2; MS (m/e) 446,
428, 400, 373, 210, 196, 149, 126, 98, 55; IR (Nujol) νmax 1855,
1767, 1670 cm-1. Anal. Calcd for C26H38O6: C, 69.95; H, 8.52.
Found: C, 70.08; H, 8.28.
r om ycin A, 1). (a) A mixture of 7 + 8 + 9 (500 mg) in a solution
of sodium methoxide (500 mg) in methanol (20 mL) was refluxed
for 2 h with stirring and then the methanol was distilled off in
vacuo. The residue was acidified with dilute HCl and extracted
with ether (30 mL × 2), and the organic layer washed with water
and brine and dried over Na2SO4. Concentration of the organic
layer in vacuo followed by silica gel column chromatographic
purification of the residue furnished pure 1: 214 mg (60% yield).
(b) To a solution of imide 10 (500 mg) in a THF-methanol
mixture (12 mL, THF:MeOH ) 1:1) was added a solution of KOH
(1.2 g) in water (6 mL), and the reaction mixture was refluxed
for 2 h with stirring. The solvent mixture was removed in vacuo,
and the residue was acidified with dilute HCl. Repetition of the
above workup procedure followed by silica gel column chromato-
graphic purification furnished pure 1: 350 mg (98% yield); mp
60 °C (lit.5 mp 59-60 °C); 1H NMR (CDCl3, 200 MHz) δ 1.23
(bs, 24H), 1.55 (quintet, J ) 8 Hz, 4H), 2.05 (s, 6H), 2.43 (t, J )
8 Hz, 4H); 13C NMR (CDCl3, 75 MHz) δ 9.5, 24.4, 27.5, 29.2,
Ack n ow led gm en t. S.M. thanks CSIR, New Delhi,
for the award of a research fellowship. N.P.A. thanks
D.S.T., New Delhi, for financial support under the
Young-Scientist scheme. We thank Dr. K. N. Ganesh,
Head, Division of Organic Chemistry (synthesis), for
constant encouragement.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
1, 3, 4, 5, 7 + 8 + 9 mixture, and 10 and 13C NMR spectra of
1 and 10. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O010260E