Modular synthesis of pantetheine and phosphopantetheine

Article abstract of DOI:10.1021/ol048853+

(Chemical Equation Presented) D-Pantetheine and D-phosphopantetheine, precursors to coenzyme A, have been synthesized though a linear sequence from three modules (M1-M3) in 9 and 10 steps, respectively. These routes provide access to analogues of coenzyme A containing modified cystamines, β-alanines, and pantoic acid residues. All three modules were joined using conventional methods of peptide synthesis. The chiral component, M3, was derived from D-pantolactone.

Full text of DOI:10.1021/ol048853+

ORGANIC
LETTERS
2004
Vol. 6, No. 26
4801-4803
Modular Synthesis of Pantetheine and
Phosphopantetheine
Alexander L. Mandel, James J. La Clair, and Michael D. Burkart*
Department of Chemistry and Biochemistry, UniVersity of California-San Diego,
9500 Gilman DriVe, La Jolla, California 92093-0358
mburkart@ucsd.edu
Received June 17, 2004
ABSTRACT
D
-Pantetheine and
(M1 M3) in 9 and 10 steps, respectively. These routes provide access to analogues of coenzyme A containing modified cystamines,
and pantoic acid residues. All three modules were joined using conventional methods of peptide synthesis. The chiral component, M3, was
derived from -pantolactone.
D
-phosphopantetheine, precursors to coenzyme A, have been synthesized though a linear sequence from three modules
−
â-alanines,
D
Coenzyme A (CoA), one of the most utilized cofactors in
Nature, mediates the activation and transfer of acyl groups
in fatty acid biosynthesis, secondary metabolite biosynthesis,
primary metabolic pathways, and regulatory processes.1-4
CoA plays an important role in cellular development, aging,
and cancer.5 Studies directed at the biosynthesis and process-
ing of CoA remain vital to the understanding of metabolic
disease.
CoA can be dissected into four modules as outlined in
Figure 1. The first module, cystamine (M1), presents a
terminal thiol that serves as the linkage point for acyl
transport. The cystamine moiety is connected via an amide
linkage to â-alanine (M2) that is further joined through an
amide bond to pantoic acid (M3). In CoA, pantetheine, M1-
M3, is joined to a 3′-adenosyl phosphate (M4) through a
5′-pyrophosphate bridge.
The first synthesis of CoA was unveiled in 1961, through
the coupling of pantethenic acid, cystamine, and a 5′-
phosphoromorpholidate.6 Further modifications by Michelson
provided an enhanced route to M4 through addition of an
adenosine diphosphate.7 Both syntheses use pantolactone, the
highly stable product of pantethenic acid hydrolysis, to
increase versatility. However, low yields, racemization at the
R-carbon of pantolactone, and unusual side reactions have
limited the viability of schemes beginning with pantolactone.
As a result, derivatives varying at the â-alanine moiety have
generally been avoided,4 and the â-alanine (M2) and pantoic
acid (M3) modules are installed from pantothenate. Here we
describe a modular route that permits individual derivatiza-
tion at each module (Figure 1).
While pantolactone (4) can be coupled directly onto
â-alanine to afford the necessary pantethenic acid analogue,
such strategies depend solely on the nucleophilicity of the
â-alaninylamine. Several disadvantages such as adverse
effects from protecting groups and low-yielding reactions
discourage variations that must be installed in this early stage
(1) Dewick, P. Medicinal Natural Products: A Biosynthetic Approach;
Wiley: West Sussex, England, 2001; Chapter 1.
(2) Engel, C.; Wierenga, R Curr. Opin. Struct. Biol. 1996, 6, 790-797.
(3) Knudsen, J.; Jensen, M. V.; Hansen, J. K.; Faergeman, N. J.;
Neergaard, T. B. F.; Gaigg B. Mol. Cell. Biochem. 1999, 192, 95-103.
(4) Mishra, P. K.; Drueckhammer, D. G. Chem ReV. 2000, 100, 3283-
3309.
(6) Moffatt, J. G.; Khorana, H. G. J. Am. Chem.. Soc. 1961, 83, 663-
675.
(7) Michelson, A. M. Biochim. Biophys. Acta 1964, 93, 71-77.
(5) Brownell, J. E.; Allis, C. D. Curr. Opin. Gene. DeV. 1996, 6, 176-
184.
10.1021/ol048853+ CCC: $27.50
© 2004 American Chemical Society
Published on Web 11/25/2004

Scheme 1
While both chemical and chemoenzymatic methods exist
to convert pantetheine (3) to CoA, established procedures
require 4′-phosphopantethiene (2).6,7,10,11 Chemical phos-
phorylation of pantetheine (3) has been reported to give 2,
albeit in poor yield. Some alterations in the pantethiene
backbone such as reversing the pantoic acid stereocenter from
R to S12 will hinder the biosynthetic pathway to CoA. For
access to a wider range of CoA derivatives, it would be useful
to build CoA chemically. Therefore, we developed a route
to directly couple a 4′-phosphorylated pantoic acid to amide
11 (Scheme 2).
Figure 1. A modular view of coenzyme A, including a retrosyn-
thetic breakdown to 4′-phosphopantetheine and pantetheine.
of the synthesis. In addition, pantolactone is extremely stable
to hydrolysis and contains a sensitive R-hydroxyl group that
enhances the potentional for R-carbon racemization under
acidic or basic conditions.8 Accordingly, a scheme for
opening pantolactone was developed (Scheme 1).9 D-Pan-
tolactone 4 was reduced with lithium aluminum hydride to
afford triol 5 in high yield. Subsequent conversion to
p-anisaldehyde acetal 6 selectively protected the 1,3-diol,
permitting Swern oxidation followed by mild chlorite oxida-
tion to protected pantoic acid 7.
In parallel, cystamine (8) was S-protected with trityl
chloride under acidic conditions and then neutralized with
sodium hydroxide to amine 9 (Scheme 1). Subsequent
coupling with Fmoc-â-alanine provided amide 10 through
standard carbodiimide conditions. The protected M1-M2
block 10 was deprotected with piperidine and immediately
coupled with 7 to provide 12. Global deprotection was
achieved with iodine in methanol to afford pantetheine (3)
as a disulfide in 41% overall yield from cystamine or 28%
from D-pantolactone (4).
The R-hydroxyl of D-pantolactone (4) was protected by
benzylation under mildly basic conditions. Careful control
of pH is necessary to prevent epimerization. Benzyl panto-
lactone 13 was reduced to lactol 14 with DIBAL-H. Several
conditions were attempted to open the lactol, but it was found
that masking the aldehyde as olefin 15 using Wittig condi-
tions13,14 provided a facile means to open the ring. A sample
of 15 was esterified with (R)-2-phenylbutyric acid and
verified that enantiomeric purity had been maintained.15 From
this point, the phosphate was added by incubation with
(10) Strauss, E.; Begley, T. J. Biol. Chem. 2002, 277, 48205-48209.
(11) Nazi, I.; Koteva, K. P.; Wright, G. D. Anal. Biochem. 2004, 324,
100-105.
(12) Bibart, R. T.; Vogel, K. W.; Drueckhammer, D. G. J. Org. Chem.
1999, 64, 2903-2909.
(13) Hart, D. J.; Patterson, S.; Zakarian, A. Heterocycles 2000, 52, 1025-
1028.
(8) Dueno, E. E.; Chu, F.; Kim, S.; Jung, K. W. Tetrahedron Lett. 1999,
40, 1843-1846.
(9) Shiina, I.; Shibata, J.; Ibuka, R.; Imai, Y.; Mukaiyama, T. Bull. Chem.
Soc. Jpn. 2001, 74, 113-122.
(14) Miyaoka, H.; Sagawa, S.; Nagaoka, H.; Yamada, Y. Tetrahedron:
Asymmetry 1995, 6, 587-594.
(15) Dale, J. A.; Mosher, H. S. J. Am. Chem. Soc. 1968, 90, 3732-
3738. See Supporting Information for more details.
4802
Org. Lett., Vol. 6, No. 26, 2004

Scheme 2
Scheme 3
yields ranging from 30 to 88%. Low yields in couplings of
19e and 19f were due to extended reaction times. Alternate
coupling reagents could be screened to increase the yield of
these reactions. Amides 20a-f provided access to analogues
of pantetheine and phosphopantetheine through conversion
to 21a-f or 23a-d. Once coupled, 21a-f could be depro-
tected with a variety of conditions.19,20,21 As shown in Scheme
3, the deprotection of 21b,d,f with iodine in methanol offered
22b,d,f in unoptimized yields of 7, 71, and 11%, respectively,
from 19b,d,f. Comparable schemes were also available for
the modification of 23a-d.15,22
Schemes 1-3 provide access to the three-component
modular synthesis of pantetheine, 4′-phosphopantetheine, and
analogues therein. With this approach, modifications may
be introduced at any of three peptoid modules M1, M2, and
M3, accessing full synthetic flexibility within the pantetheine
structure. We are currently following various avenues of
parallel chemical and chemoenzymatic synthesis to inves-
tigate novel analogues of CoA in primary and secondary
metabolic pathways.
dibenzyl-N,N-diisopropylphosphoramidite followed by im-
mediate ozonolysis to provide aldehyde 16 in 62% yield from
15.16
As in Scheme 1, mild chlorite oxidation of 16 completes
the synthesis. After isolation, 17 was coupled to 11 using
standard peptide coupling conditions to provide 18. Final
conversion to phosphopantetheine (2) was achieved through
reduction with lithium naphthalenide.17 The 1H NMR spec-
trum of 2 matched the published spectra18 with the exception
of a downfield shift in the methylene group adjacent to the
thiol (δ ) 2.83 found vs δ ) 2.64 reported by Sarma). This
was attributed to a different state of thiol oxidation, as we
suspect that Sarma examined the disulfide of 2.
Both 7 and 17 were used to generate a set of pantetheine
and phosphopantetheine analogues bearing an internal amino
acid residue in place of â-alanine (Scheme 3). Using methods
established in Scheme 1, S-trityl cystamine was coupled to
Fmoc-protected amino acids 19a-f to provide 20a-f in
Supporting Information Available: Experimental pro-
cedures and spectral data. This material is available free of
charge via the Internet at http://pubs.acs.org.
OL048853+
(16) Variations of this scheme can also be used to isolate the dibenzyl
phosphite of 15. Partial ozonolysis or oxidation with oxygen can also be
used to generate the dibenzyl phosphate of olefin 15. The phosphate oxidizes
easily in the presence of ozone, whereas olefin cleavage takes several
minutes of exposure.
(17) Liu, H.; Yip, J. Tetrahedron Lett. 1997, 38, 2253-2256.
(18) Lee, C.; Sarma, R. H. J. Am. Chem. Soc. 1975, 97, 1225-1235.
(19) Szarek, W. A.; Zamojski, A.; Tiwari, K. N.; Ison, E. R. Tetrahedron
Lett. 1986, 33, 3827-3830.
(20) Zervas, L.; Photaki, I. J. Am. Chem. Soc. 1962, 84, 3887-3897.
(21) Riley, A. M.; Guedat, P.; Schlewer, G.; Spiess, B.; Potter, B. V. L.
J. Org. Chem. 1998, 63, 295.
(22) Kitas, E. A.; Knorr, A.; Trzeciak, A.; Bannwarth, W. HelV. Chim.
Acta 1991, 74, 1314.
Org. Lett., Vol. 6, No. 26, 2004
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