Total synthesis of motuporin (nodularin-v)

Article abstract of DOI:10.1021/ja9811243

The serine/threonine phosphatase (protein phosphatase 1 and 2A) inhibitors constitute a biologically and structurally interesting class of natural products. Among this class of inhibitors are cyclic pentapeptides (nodularins) and cyclic heptapeptides (mic

Full text of DOI:10.1021/ja9811243

J. Am. Chem. Soc. 1999, 121, 6355-6366
6355
Total Synthesis of Motuporin (Nodularin-V)
Shawn M. Bauer1 and Robert W. Armstrong*,2
Contribution from the Department of Chemistry and Biochemistry, UniVersity of California at Los Angeles,
Los Angeles, California 90095
ReceiVed April 3, 1998
Abstract: The serine/threonine phosphatase (protein phosphatase 1 and 2A) inhibitors constitute a biologically
and structurally interesting class of natural products. Among this class of inhibitors are cyclic pentapeptides
(nodularins) and cyclic heptapeptides (microcystins), both of which inhibit at the nanomolar level and are the
only peptide inhibitors of these enzymes. Described herein is the total synthesis of motuporin, which utilizes
an Ugi four-component condensation (4CC) reaction to synthesize the 2-(N)-methylaminobutenyl residue,
Matteson’s dihalomethyllithium insertion methodology for the construction of a key fragment, and an overall
synthetic strategy amenable to the synthesis of analogues.
Introduction
methylaminobutenyl moiety as this is known to be contained
within the active site in the microcystin class of inhibitors from
a microcystin‚protein phosphatase-1 cocrystal structure.11 With
this in mind, we hypothesized that in the corresponding
pentapeptide structure this residue should also be in the active
site and hence would be a good choice for modification and
analogue studies.
Inhibitors of protein phosphatase 1 and 2A (PP1 and PP2A)
comprise a structurally diverse class of natural products includ-
ing the calyculins,3 tautomycin,4 okadaic acid,5 the micro-
cystins,6 and the nodularins (Figure 1).7 The last two examples
are both cyclic peptides of seven and five residues, respectively,
and contain similar functionality including the (2S,3S,8S,9S)-
3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadieno-
ic acid (ADDA) residue that is unique to this class of peptides.
Motuporin was isolated in 1992 by Andersen and co-workers
from the Paupa New Guinea sponge Theonella swinhoei Gray
and is one of the most potent inhibitors of PP1 known, inhibiting
at subnanomolar concentrations and showing strong in vitro
cytotoxicity against a number of cancer cell lines.8 It had also
received attention from the synthetic community prior to our
efforts in the form of a completed total synthesis from the
laboratory of Stuart Schreiber.9 The work herein describes the
successful total synthesis of motuporin, a member of the
nodularin class of inhibitors.
Retrosynthetic Analysis
Motuporin contains three sites of functionality which require
protection for chemical synthesis: two carboxylic acids and a
dehydroamino acid. For the protection of the carboxylic acid
functionality we chose a methyl ester protection strategy based
on the variety of conditions available for deprotection.12 Base-
catalyzed saponification requires a minimum of reagents which
would interfere with the purification of the highly polar natural
product, a further benefit of this choice. It was also shown by
Schreiber and Valentekovich8 in their total synthesis of motu-
porin that the saponification conditions also result in dehydration
of threonine to afford the dehydroamino acid residue and the
natural product.
With the protection scheme decided upon it was proposed to
effect cyclization of the 19-membered pentapeptide macrocycle
at the ADDA (S)-valine amide bond (Scheme 1). This point of
cyclization was based on the reported isolation of a similar
acyclic peptide by Reinhart and co-workers and subsequent
feeding studies which support the theory that this is the point
of cyclization in the biosynthesis of the natural product.13 For
Our interest in the total synthesis of motuporin was motivated
not only by the varied functionality of the molecule, but also
by the synthetic and biological studies of a number of the
inhibitors in this class currently ongoing in our laboratory.10
Thus, we planned a synthetic route that was amenable to
analogue studies of the molecule, specifically near the 2-(N)-
(1) Current Address: Berlex Biosciences; 15049 San Pablo Ave; P.O.
Box 4099; Richmond, CA 94804.
(2) Current Address: Amgen, Inc.; One Amgen Center Drive; Mail Stop
99-1-B.; Thousand Oaks, CA 91320.
(3) Kato, Y.; Fusetani, N.; Matsunaga, S.; Hashimoto, K.; Fujita, S.;
Furuya, T. J. Am. Chem. Soc. 1986, 108, 2780-2781.
(4) Cheung, X. C.; Kihara, T.; Kusakabe, H.; Magae, J.; Kobayashi, Y.;
Fang, R. P.; Ni, Z. F.; Shen, Y. C.; Ko, K.; Yamaguchi, I.; Kono, K. J.
Antibiotics 1987, 40, 907-909.
(10) Total synthesis of calyculin C: (a) Scarlato, G. R.; Demattei J. A.;
Chong L. S.; Ogawa A. K.; Lin, M. R.; Armstrong R. W. J Org. Chem.
1996, 61, 6139-6152. (b) Ogawa A. K.; DeMattei, J. A.; Scarlato, G. R.;
Tellew, J. E.; Chong, L. S.; Armstrong, R. W. J. Org. Chem. 1996, 61,
6153-6161. (c) Ogawa, A. K.; Armstrong, R. W. J. Am. Chem. Soc. 1998,
120, 12435-12442. Synthetic efforts toward Tautomycin: (d) Maurer K.
W.; Armstrong R. W. J. Org. Chem. 1996, 61, 3106-3116. Biological
activity and binding: (e) Gupta, V.; Ogawa, A. K.; Du, X. H.; Houk, K.
N.; Armstrong, R. W. J. Med. Chem. 1997, 40, 3199-3206.
(11) Goldberg, J.; Huang, H.; Kwon, Y.; Greengard, P.; Nairn, A. C.;
Kuriyan, J. Nature, 1995, 36, 745-753.
(5) Tachibana, K.; Scheuer, J.; Tsukitani, Y.; Kikuchi, H.; Van Egan,
D.; Clardy, J.; Gopichand, Y.; Schmita, F. J. J. Am. Chem. Soc. 1981, 103,
2469-2471.
(6) Honkanen, R. E.; Zwiller, J.; Moore, R. E.; Daily, S. L.; Khatra, B.
S.; Dukelow, M.; Boynton, A. L. J. Biol. Chem. 1990, 265, 19401-19404..
(7) Hankanen, R. E.; Dukelow, M.; Zwiller, J.; Moore, R. E.; Khatra,
B. S.; Boynton, A. L. Mol. Pharm. 1991, 40, 577-583.
(8) Dilip de Silva, E.; Williams, D. E.; Andersen, R. J.; Klix, H.; Holmes,
C. F. B.; Allen, T. M. Tetrahedron Lett. 1992, 33, 1561-1564.
(9) Valentekovich, R. J.; Schreiber, S. L. J. Am. Chem. Soc. 1995, 117,
9069-9070.
(12) Greene, T. W.; Wuts, P. G. M. ProtectiVe Groups in Organic
Synthesis, 2nd ed.; Wiley: New York, 1991.
(13) Choi, B. W.; Namikoshi, F. S.; Rinehart, K. L.; Carmichael, W.
W.; Kaup, A. M.; Evans, W. R.; Beasley, V. R. Tetrahedron Lett. 1993,
34, 7881-7884.
10.1021/ja9811243 CCC: $18.00 © 1999 American Chemical Society
Published on Web 06/26/1999

6356 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Bauer and Armstrong
Scheme 1
protection of the amine and acid functionality involved in the
cyclization we chose the tert-butoxycarbonyl carbamate (Boc)
and the tert-butyl ester, respectively, because of the relatively
mild trifluoroactic acid (TFA) deprotection conditions and the
generally high purity and minimum of epimerization of the crude
product from these reactions.
Further disconnection of linear peptide 1 affords Boc-
protected ADDA (2) and a tetrapeptide which can be further
disconnected to give dipeptides 3 and 4. The ADDA synthesis
was envisioned from the coupling of a Wittig or Horner-
Emmons reagent derived from bromide 5 with aldehyde 6.14
While this method for constructing the diene moiety of this
molecule has been reported previously,13b,c our studies and final
success represents a considerable improvement over the earlier
attempts. This same intermediate, 6, can be elaborated by
manipulation of the terminal groups to afford the 3-methyl-
aspartyl (MeAsp) residue in dipeptide 3.
of the resulting cyclohexenamide to the free acid has been shown
previously18 and provides a means of incorporating the valuable
MeAsp and ADDA residues late in the synthesis. The use of
Ugi technology overcomes the difficulty of coupling a secondary
amine and carboxylic acid using standard peptide coupling
techniques, which is often a low yielding process. Additionally,
the Ugi reaction makes it possible to vary the functionality at
the dehydroaminoamide position easily, thus offering another
degree of flexibility in the synthesis of analogues. In practice,
while this route was quite successful in providing material, the
mixture of diastereomers (and resulting rotamers from the
tertiary amide) made characterization difficult. Thus, we also
synthesized dipeptide 4 using protected amino acids and
conventional coupling technology. It is worth noting that the
mixture of diastereomers at this center is inconsequential for
purposes of synthesizing motuporin as this carbon becomes part
of the dehydroamino residue.
For the synthesis of aldehyde 6 we proposed to use the
dihalomethyllithium insertion method of Matteson.15 This
methodology offers a unique approach to the construction of a
series of contiguous stereocenters and proceeds with extremely
high stereoselectivity resulting in material that is enantiomeri-
cally and diastereomerically pure. From previous work in our
laboratories we have found this method is amenable to large-
scale synthesis, a necessity as it affords four of the eight
stereogenic centers in the molecule.
Synthesis of Aldehyde 6
The synthesis of 6 began with the transmetalation of
chloroiodomethane with n-butyllithium in the presence of
triisopropyl borate 11 to give diisopropyl chloromethylborate.19
This was then transesterified with (1R,2R,3S,5R)-(+)-pinanediol
and the chloride displaced in SN2 fashion with lithium p-
methoxybenzyloxide (LiOPMB) in tetrahydrofuran (THF) to
produce protected alcohol 13 ready for the first insertion. Chain
extension of 13 with dichloromethyllithium followed by addition
of 3.7 equiv of ZnCl2 to affect rearrangement of the ate-complex
gave R-chloroborate ester 13 as a single diastereomer. Ste-
reospecific displacement of the chloride with methylmagnesium
chloride afforded the R-methyl borate ester ready for the next
iteration.
Finally, we proposed that dipeptide 4 could be made from
the Ugi 4CC of monoprotected glutamic acid 9,16 aldehyde 10,
methylamine, and cyclohexenyl isocyanide.17 The conversion
(14) For other syntheses of ADDA see: (a) Namakoshi, M.; Rinehart,
K. L.; Dahlem, A. M.; Beasley, V. R.; Carmichael, W. W. Tetrahedron
Lett. 1989, 30, 4349. (b) Chakraborty, T. K.; Joshi, T. P. Tetrahedron Lett.
1990, 31, 2043. (c) Beatty, M. F.; Jennings-White, C.; Avery, M. A. J.
Chem. Soc., Perkin Trans. 1 1992, 1637. (d) Kim, H. Y.; Toogood, P. L.
Tetrahedron Lett. 1996, 37, 2349-2352. (e) Sin, N.; Kallmerten, J.
Tetrahedron Lett. 1996, 37, 5645-5648. (f) D’Aniello, F.; Mann, A.;
Taddei, M. J. Org. Chem. 1996, 61, 4870. (g) D’Aniello, F.; Mann, A.;
Schoenfelder, A.; Taddei, M. Tetrahedron 1997 53, 1447-1456. (h) Panek,
J. S.; Hu, T. J. Org. Chem. 1997, 62, 4914-4915.
(16) (a) Adams, D. R.; Bailey, P.; Collier, I.; Hefferman, J. D.; Stokes,
S. Chem. Commun. 1996, 7, 349-350. (b) Adams, D. R.; Bailey, P.; Collier,
I.; Hefferman, J. D.; Stokes, S. Chem. Commun. 1996, 7, 886.
(17) Gokel, G.; Lu¨dke, G.; Ugi, I. In Isonitrile Chemistry; Ugi, I., Ed.;
Academic Press: New York, 1971; pp 145-199.
(18) Keating, T. A.; Armstrong, R. W. J. Am. Chem. Soc. 1995, 117,
7842-7843.
(19) Matteson, D. S.; Sadhu, K. M. Organometallics 1984, 3, 614-618.
(15) Matteson D. S. Pure Appl. Chem. 1991, 63, 339-344.

Total Synthesis of Motuporin (Nodularin-V)
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6357
Scheme 2
Scheme 3
Butylcarbamate (Boc) with the pyrocarbonate, and oxidation
of the alcohol with the Dess-Martin reagent24 gave aldehyde
6 in 54% yield for the four steps.
During the course of the synthesis we required a large amount
of precursor 6, and found it could be made quite easily by
carrying through material in 20-30 mmol batches, run in
parallel. While it is possible to work with larger amounts, the
initial deprotonation is exothermic and maintaining a bath
temperature of -100 °C was difficult above this quantity.
Beyond this minor difficulty, the procedure was quite efficient
and afforded a large amount of material in a short period of
time.
Synthesis of Val-Methylaspartyl Dipeptide
Elaboration of aldehyde 6 to dipeptide 3 was accomplished
as follows: the aldehyde was oxidized with sodium chlorite25
and the resulting acid protected as the methyl ester (18) with
methyl iodide in N,N-dimethylformamide (DMF). The protected
primary alcohol was then deprotected with 2,3-dichloro-5,6-
dicyano-1,4-diquinone (DDQ)26 and oxidized with the same two-
step protocol as before affording acid 19 in 86% yield. Coupling
of the acid to (D)-valine with benzotriazol-1-yloxy tris(dimeth-
ylamino)phosphonium hexafluorophosphate (BOP reagent) and
diisopropylethylamine (DIPEA) was performed uneventfully,
affording the fully protected dipeptide. Given the acid lability
of two protecting groups, we anticipated difficulties with the
selective deprotection of the Boc-protected amine in the presence
of the acid labile tert-butyl ester. However, we found that the
transformation could be accomplished easily using the conditions
of Rapoport27 affording the aminodipeptide 3 as a single
diastereomer, ready to be coupled to dipeptide 4.
The next stepsowing to the comparatively low nucleophi-
licity of azide and the steric bulk of the substrateswas per-
formed with dibromomethyllithium20 affording the R-bromo
borate (14) instead of the usual chloride.21 Bromide 14 was then
converted cleanly to the azide by treatment with sodium azide
in CH2Cl2/H2O under phase transfer catalyst conditions.22
Notably, this was the only reaction in any of our trials using
this methodology which has given any detectable amount of
the diastereomer. This observation is in agreement with Mat-
teson, who also reports a small percentage of the undesired
diastereomer when performing azide displacements.23
The final chain extension was effected through the use of
the transmetalation conditions of the first step and afforded the
azido borate in 74% yield from the bromide (3 steps). Oxidative
removal of the boron by addition of hydrogen peroxide followed
by sodium hydroxide gave amino alcohol 17. Interestingly,
reversing the order of addition resulted in a large amount of
alkene 16 (presumably by elimination of the azide from the ate-
complex) and the desired alcohol as the minor product.
Reduction of the azide to amine 17 with standard hydrogenation
conditions gave the amine with no concomitant loss of the PMB
protecting group. Amine 17 was then protected as the tert-
Synthesis of the γ-(D)-Glutamyl-Threonine Dipeptide (4)
As a means of providing diversity for later studies we
proposed to use an Ugi 4CC to synthesize the protected threonyl
residue which would later be converted to the dehydroamino
acid. Thus, Ugi reaction of the carboxylbenzyloxy (Z) protected
acid 9, aldehyde 10,28 methylamine 20, and cyclohexenyl
(20) Matteson, D. S.; Kandil, A. A.; Soundararajan, R. J. Am. Chem.
Soc. 1990, 112, 3964-3969.
(21) Initial attempts with the chloride were successful; however, the
reaction only progressed to ca. 50% completion. Given the potential for
explosion afforded by the reaction conditions we were reluctant to continue
the reaction for a longer duration.
(22) Matteson, D. S.; Beedle, E. C. Tetrahedron Lett. 1987, 28, 4499-
4502.
(23) Matteson, D. S.; Beedle, E. C. J. Labeled Compd. Radiopharm. 1988,
25, 675-683.
(24) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155-4156.
(25) Bal, B. S.; Childers, W. E.; Pinnick, H. W. Tetrahedron 1981, 37,
2091-2096.
(26) Tanaka, T.; Oikawa, Y.; Hamada, T.; Yonemitsu, O. Tetrahedron
Lett. 1986, 27, 3651-3654.
(27) Gibson, F. S.; Bergmeier, S. C.; Rapoport, H. J. Org. Chem. 1994,
59, 3216-3218.

6358 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Bauer and Armstrong
Scheme 4
Scheme 5
Scheme 6
isocyanide 21 afforded cyclohexenamide dipeptide 22 as a
mixture of separable diastereomers in reasonable yield. To our
surprise, attempted hydrolysis of the cyclohexenyl moiety with
standard conditions resulted in exclusive conversion to primary
amide 23. Upon further study of the hydrolysis conditions we
found that by increasing the amount of acid and preheating the
reaction mixture to 60 °C free carboxylic acid 4 was the major
product, with only a small amount of the aforementioned amide
present.
Initially, we noted that the heated conditions also resulted in
epimerization of the R-stereocenter, presumably due to formation
of the azalactone intermediate. Upon closer observation, how-
ever, we realized that the reaction was in fact proceeding through
the primary amide that was simply hydrolyzed to the carboxylic
acid under the more stringent conditions. This was verified by
treating the amide 23 with the revised conditions and obtaining
acid 24. The two diastereomers 4(R) and 4(S) were inseparable
by flash chromatography and were carried on as a mixture.
Synthesis of Boc-Protected ADDA (2)
Synthesis of the remaining two stereocenters was accom-
plished by Brown crotylboration30 of phenylacetaldehyde with
the reagent derived from (+)-B-(methoxy)diisopinocampheyl-
borane and cis-2-butene. This was then converted to the methyl
ether 27 and elaborated by using standard conditions to give
enoate 28 and finally allylic bromide 29.
Conversion of 29 to Wittig reagent 30 and deprotonation with
n-butyllithium in THF afforded 33 in a rather disappointing 17%
yield of the desired trans-trans product, an observation in
agreement with other attempts to form this bond with similar
technology.13b,c An almost 4-fold increase product was realized
when the base was changed to lithium diisopropylamide (LDA).
Further attempts at optimization with the tributylphosphonium
ylide 31 and LDA as base resulted in coupled material in higher
yield, but material which was found to be a 1:1 mixture of
diastereomers. Finally, the attempted coupling with Horner-
Emmons reagent 32 showed even less success, affording only
epimerized aldehyde and recovered 32.
Because of the complexity of the intermediates beyond this
point and the fact that many of the compounds exist as a mixture
of rotamers we decided to develop a diastereoselective route
using standard coupling methods for purposes of characteriza-
tion. Thus, commercially available diprotected (S)-threonine,
24, was converted to the 2,2,2-trichloroethyl ester with dicy-
clohexylcarbodiimide (DCC) and catalytic N,N-(dimethylami-
no)pyridine (DMAP). The Boc group was then removed with
TFA in dichloromethane giving amine 26, which was then
coupled to the aforementioned acid (24) with use of the BOP
reagent. Finally, the acid was deprotected with Zn dust in
aqueous acetic acid (HOAc)29 overnight affording 4(S) in
diastereomerically pure form. This sequence, in addition to
providing material for characterization, illustrates the improve-
ment possessed by the Ugi reaction in forming the synthetically
challenging tertiary amide bond.
With the diene in hand, attempted deprotection of the PMB
ether with DDQ resulted in deprotection of the primary alcohol
and allylic oxidation of the protected amine to the ketone. We
(28) Prepared in two steps by protecting methyl lactate with benzyl
bromide and sodium hydride in DMF followed by reducing the ester to the
aldehyde with diisobutylaluminum hydride in toluene at -78 °C.
(29) Woodward, R. B.; Heusler, K.; Gosteli, J.; Naegeli, P.; Oppolzer,
W.; Ramaga, R.; Ranganathan, S.; Vorbru¨ggen J. Am. Chem. Soc. 1966,
88, 852-853.
(30) Brown, H. C.; Jadhav, P. K.; Bhat, S. K. J. Am. Chem. Soc. 1988,
110, 1535-1538.

Total Synthesis of Motuporin (Nodularin-V)
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6359
Table I
Scheme 8
Scheme 7
reagent affording the fully protected tetrapeptide as a mixture
of separable diastereomers, presumably epimerized at the
threonyl R-center.34,35 The protected tetrapeptide was then
converted to amino alcohol 35 by hydrogenolysis of the
carboxybenzyloxy carbamate and the benzyl ether. This was
then immediately coupled to Boc-ADDA, 2, using O-(7-
azabenzotriazol-1-yl)-1,1-3,3-tetramethyluronium pentafluo-
rophosphate (HATU), with DIPEA as base.36 Notably, both BOP
reagent and bis-oxazolidinonyl phosphoryl chloride (BOP
chloride)37 failed in this transformation, though they were
successful in model couplings of acid 2 to glutamic acid diesters.
The protected pentapeptide was then deprotected with neat TFA,
and cyclized with HATU in THF under dilute conditions. This
afforded the cyclized material as a mixture of rotamers which
were then deprotected by using the conditions of Schreiber and
Valentekovich38 to afford motuporin as a 1:3 mixture of epimers
separable by High Performance Thin Layer Chromatography.
During the course of the synthesis, we noted that the yield
of the cyclization step varied dramatically with respect to the
stereochemistry of the threonyl residue. When material was
diastereomeric at this center (derived from the Ugi synthetic
route to 4) the cyclization proceeded in nearly twice the yield
were surprised at this result as allylic oxidation under DDQ
conditions is known in the case of allylic alcohols,31 but to our
knowledge unprecedented for amines. Attempts at deprotecting
the alcohol with borontrifluoride etherate/ethanethiol 32 or TFA/
dichloromethane33 conditions gave concomitant deprotection of
the Boc groupsa result that could not be overcome by altering
reagent equivalents or varying the temperaturesthus necessitat-
ing a deprotection/reprotection strategy for this transformation.
Oxidation of the alcohol to the acid afforded Boc protected
ADDA 2 in 87% yield from the protected alcohol. Notably,
initial attempts at oxidation of the aldehyde to the acid afforded
only a small amount of the acid, the remainder of the material
being baseline by thin-layer chromatography. However, we
found that when the amount of 2-methyl-2-butene was increased
from 20 to 100+ equiv the yield increased to nearly quantitative,
supporting the postulate that the byproducts generated during
the reaction was decomposing the more reactive diene rather
than reacting with the 2-methyl-2-butene.
(34) Bodansky, M. Principles of Peptide Synthesis; (Reactivity and
Structure, Vol. 16; Springer-Verlag: Berlin, Heidelberg, 1984.
(35) The R-center of the threonyl residue was postulated as the site of
epimerization as the diastereomers showed opposite but nearly equal optical
rotations. This was in agreement with the optical rotations for the separate
Ugi derived cyclohexenamide dipeptides 4(R) and 4(S) which were known
to be epimers at this center and showed similar optical rotations. While the
coupling gave a major and a minor component (presumably due to
epimerization via the azalactone), the figures and Experimental Section show
the manipulations of the minor diastereomer.
Final Coupling and Deprotection
Completion of the synthesis was accomplished as shown in
Scheme 8. Amine 3 and acid 4(S) were coupled by using BOP
(31) Trost, B. M.; Chung, J. Y. L. J. Am. Chem. Soc. 1985, 107, 4586-
(36) Jou, G.; Gonzalez, I.; Albericio, F.; Lloyd-Williams, P.; Giralt, E.
J. Org. Chem. 1997, 62, 354-366.
4588.
(32) Daly, S. M.; Armstrong, R. W. Tetrahedron Lett. 1989, 30, 5713-
5715.
(33) Yan, L.; Kahne, D. Synlett 1995, 523-524.
(37) Diego-Moseguer, J.; Palomo-Coll, A. L.; Fernandez,-Lizarbe, J. R.;
Zugaza-Bilbao, A. Synthesis 1980, 547-551.
(38) Valentekovich, R. J. Personal communication.

6360 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Bauer and Armstrong
Figure 1.
distilled under Ar from calcium hydride. n-Butyllithium (2 M in
pentane), N,N-dimethylformamide, and methylmagnesium chloride (1
M in THF) were purchased from Aldrich in Sure Seal bottles. All
moisture-sensitive reactions were performed in oven-dried glassware
under an Ar atmosphere unless otherwise noted. Reactions were
monitored with Merck Silica Gel 60 thin-layer chromatography plates.
Flash chromatography was performed with use of flash chromatography
silica gel (60A) from ICN Biomedical. Thin Layer Chromatography
plates were Merck silica gel 60 and High Performance Thin Layer
Chromatography plates were from Bodman Scientific.
as reported for the above sequence. This seems to suggest that
this stereocenter has a strong effect on the overall conformation
of the molecule, a result that is in agreement with the drastically
different optical rotations of intermediates epimeric at this center
(Vide supra).
Conclusion
The total synthesis of motuporin provides quantities of the
natural product for testing and also proof of our synthetic plan
for the synthesis of analogues. In completing the synthesis we
showed the utility of Matteson’s synthetic methodology through
its success in generating the large amount of stereochemically
pure material required for the synthesis. By using an Ugi 4CC
to synthesize the (N)-methyl dehydroamino acid residue we
demonstrated the utility of this reaction in forming a tertiary
amide bond which proved difficult using standard coupling
techniques. Additionally, this strategy also allows for the
introduction of varied functionality at this site of the molecule
by using different inputs in the 4CC. This synthetic plan affords
a novel method of constructing structurally varied dehydroamino
acids, and should prove valuable in analogue studies of
motuporin.
(1S,2R,3S,5S)-Pinanediol chloromethyl borate. Triisopropylborate
(11; 24.9 mL (106 mmol) was placed in a flame-dried round-bottom
flask under Ar and diluted with 80 mL of THF. The mixture was cooled
to -78 °C, and 7.9 mL (110 mmol) of chloroiodomethane was added
followed by 50 mL (100 mmol) of n-butyllithium (added to the vortex
of the stirring solution via syringe pump) over 40 min. The resulting
beige suspension was warmed to room temperature and titrated with
etherial HCl to the methyl orange endpoint, then concentrated and
vacuum distilled (20 Torr, 60-80 °C) affording the diisopropyl
chloromethyl borate as a faint orange liquid containing diisopropyl butyl
borate as the major impurity.
The above distillate was diluted with diethyl ether and (1R,2R,3S,5R)-
(+)-pinanediol (7.6 g, 45 mmol) was added slowly to the reaction until
a small amount of the diol persisted (TLC). At this time the reaction
was concentrated in vacuo and purified by flash chromatography (10%
diethyl ether/pentane) affording 9.2 g (40 mmol, 90%) of the title
compound as a colorless oil: 1H NMR (400 MHz, CDCl3) δ 0.79 (s,
3H), 1.15 (d, J ) 11.1 Hz, 1H), 1.24 (s, 3H), 1.36 (s, 3H), 1.50 (m,
1H), 1.85, (m, 2H), 2.03 (t, J ) 5.1 Hz, 1H), 2.18 (m, 1H), 2.30 (m,
1H), 2.93 (s, 2H), 4.31 (dd, J ) 1.9, 8.96 Hz, 1H); 13C NMR (100.6
MHz, CDCl3) δ 23.7, 26.1, 26.8, 28.2, 35.0, 38.0, 39.2, 50.9, 78.4,
86.8; IR (thin film) 2920, 1360, 1029, 846 cm-1; [R] -30.6 (c 0.1711,
CH2Cl2).
Experimental Section
All reagents were obtained from commercial suppliers and used
without further purification with the following exceptions. ZnCl2 was
dried at 100 °C under vacuum overnight then fused, powdered, and
placed in sealed ampules. Tetrahydrofuran (THF) was distilled under
Ar from sodium benzophenone ketyl. Dichloromethane was distilled
from phosphorus pentoxide. Toluene, acetonitrile, dimethyl sulfoxide
(DMSO), diisopropylamine, and diisopropylethylamine (DIPEA) were

Total Synthesis of Motuporin (Nodularin-V)
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6361
(1S,2R,3S,5S)-Pinanediol p-Methoxybenzyloxymethyl Borate (12).
n-Butyllithium (15.1 mL, 30.2 mmol) was slowly added to a stirring
solution of p-methoxybenzyl alcohol (3.65 mL, 30.3 mmol) in 40 mL
of THF at -78 °C. After the addition was complete the mixture was
stirred for 15 min, then 2.10 mL (30.2 mmol) of DMSO and 5.393 g
(23.4 mmol) of pinanediol chloromethyl borate were added and the
mixture was warmed to room temperature until completely dissolved
affording a pale yellow solution. The mixture was then warmed to 50
°C, forming a thick white suspension as the reaction progressed, and
was stirred until the reaction was complete as shown by TLC. The
reaction was cooled to room temperature, diluted with diethyl ether
and 0.6 M aqueous HCl, and separated. The aqueous layer was extracted
twice with diethyl ether, and the combined organic extracts were dried
with saturated NaCl and Na2SO4. After concentration in vacuo the crude
material was purified by flash chromatography (250 mL of SiO2, 20%
diethyl ether/pentane) affording 5.39 g of a slightly yellow oil: 1H
NMR (360 MHz, CDCl3) δ 0.86 (d, J ) 10.8 Hz, 1H), 1.30 (s, 3H),
1.44 (s, 3H), 2.24 (m, 1H), 2.35 (m, 1H), 3.31 (d, J ) 1.5 Hz, d), 3.82
(s, 3H), 4.33 (dd, J ) 1.8, 8.8 Hz, 1H), 4.46 (d, J ) 11.9 Hz, 1H),
1.89-1.95 (m, 2H), 2.09 (dd, J ) 4.9, 4.1 Hz, 1H), 6.8 (d, 2H), 7.3 (d,
2H); 13C NMR (91 MHz, CDCl3) δ 23.9, 26.4, 27.0, 28.5, 35.1, 38.0,
39.4, 51.0, 53.4, 55.2, 78.1, 86.4, 113.6, 129.8, 130.2, 159.0; IR (thin
film) 2911, 1743, 1613, 822 cm-1 ; HRMS (FAB, NBA) found
329.1923 (M - H)+, calcd for C19H26BO4 329.1924.
(FAB, NBA) found 357.2237 (M-H)+, calcd for C21H30BO4; [R] -14.9
(c 0.1585, CH2Cl2).
(1S,2R,3S,5S)-Pinanediol (1R,2R)-1-Bromo-3-(p-methoxybenzyl-
oxy)-2-methylpropyl Borate (14). The R-methyl borate ester was
azeotroped with toluene, dissolved in 70 mL of THF, and cooled to
-78 °C. Dibromomethane (11.3 mL, 161 mmol) was added to the
solution followed by 35 mmol of freshly prepared LDA in 20 mL of
THF down the side of the flask, the reaction becoming orange as
addition progressed. After 1 h of stirring 15.4 g (113 mmol) of ZnCl2
in 95 mL of THF were added directly to the stirring solution and the
mixture was allowed to warm to room temperature overnight. The
reaction was purified by aqueous workup with saturated ammonium
chloride and chromatographed (200 mL of SiO2, 20% diethyl ether/
pentane) to give 11.76 g (96%) of the desired compound as a pale
yellow syrup: 1H NMR (360 MHz, CDCl3) δ 0.88 (s, 3H), 1.09 (d, J
) 6.7 Hz, 3H), 1.33 (s, 3H), 1.38 (s, 3H), 1.38 (d, J ) 20.7 Hz, 1H),
1.92, m, 2H), 2.10 (m, 1H), 2.25 (m, 1H), 2.36 (m, 1H), 3.34 (t, J )
8.6 Hz, 1H), 3.44 (dd, J ) 5.2, 9.3 Hz, 1H), 3.63 (d, J ) 6.6, 1H),
3.82 (s, 3H), 4.37 (dd, J ) 2.0, 8.9 Hz, 1H), 4.47 (d, J ) 11.8 Hz,
1H), 4.52 (d, J ) 11.8 Hz, 1H), 6.92 (d, J ) 8.6 Hz, 2H), 7.31 (d, J
) 8.6 Hz, 2H); 13C NMR (90 MHz, CDCl3) δ 15.7, 23.8, 26.0, 26.8,
28.0, 35.1, 36.1, 38.1, 39.1, 51.1, 53.3, 55.0, 72.5, 72.9, 78.0, 86.1,
113.6, 129.1, 130.1, 159.0; HRMS (FAB, NBA) found 449.1503 (M-
H)+, calcd for 449.1517; [R] -19.07 (c 0.1448, CH2Cl2).
(1S,2R,3S,5S)-Pinanediol (1R)-2-(p-Methoxybenzyloxy)-1-chlo-
roethyl Borate (13). THF (80 mL) was placed in a flame-dried round-
bottom flask purged with Ar that was then cooled to -100 °C and
charged with 2.10 mL (33.4 mmol) of dichloromethane. n-Butyllithium
(15.3 mL, 30.6 mmol) was then added slowly down the side of the
flask resulting in the formation of a cloudy yellow suspension. After
30 min of stirring borate ester 12 was added in 17 mL of THF down
the side of the flask resulting in a clear yellow solution. After the
mixture was stirred for 30 min, a solution of 10.24 g (75.2 mmol) of
ZnCl2 in 60 mL of THF was added directly to the solution and the
reaction mixture allowed to warm to room temperature until all of the
ate-complex had rearranged to 13 as determined by TLC (ca. 17 h).
The reaction mixture was diluted with saturated ammonium chloride
and diethyl ether and separated, the aqueous layer was extracted twice
with diethyl ether, and the combined organic layers were then dried
over Na2SO4. After concentration of the organic layers the material
was purified by flash chromatography (250 mL of SiO2, 10% diethyl
ether/pentane) to afford 7.23 g (70%) of the desired compound as a
colorless oil: 1H NMR (360 MHz, CDCl3) δ 0.83 (s, 3H), 1.23 (d, J
) 11 Hz, 1H), 1.29 (s, 3H), 1.41 (s, 3H), 1.80-1.94 (m, 2H), 2.80 (m,
1H), 2.21 (m, 1H), 2.35 (m, 1H), 3.65, dd, J ) 5.8, 6.6 Hz, 1H), 3.79
(m, 1H), 3.78 (m, 3H), 4.35 (dd, J ) 1.7, 9.1 Hz, 1H), 4.50 (d, J )
11.9 Hz, 2H), 4.55 (d, J ) 11.9 Hz, 2H), 6.88 (d, J ) 8.5 Hz, 2H),
7.27 (d, J ) 8.5 Hz, 2H);13C NMR (90 MHz, CDCl3) δ 23.8, 26.1,
26.8, 28.3, 35.0, 38.0, 39.1, 50.9, 55.0, 71.5, 72.6, 78.5, 86.8, 113.6,
129.1, 129.9, 159.0; IR (thin film) 2934, 2061, 1613, 823 cm-1; HRMS
(FAB, NBA) found 378.1767 (M+), calcd for C20H28BClO4 378.1769;
[R] 21.8 (c 0.1159, CH2Cl2).
(1S,2R,3S,5S)-Pinanediol (1R)-2-(p-Methoxybenzyloxy)-1-meth-
ylethyl Borate. Chloroborate ester 13 (10.25 g) was azeotroped with
5 mL of toluene, then diluted with 120 mL of THF and cooled to -78
°C. Methylmagnesium chloride (9.9 mL, 29.6 mmol) was added slowly
to the vortex of the stirring solution until no starting material remained
as determined by TLC. The cold bath was then removed and the mixture
warmed to room temperature. After 2 h all material had rearranged to
the product (TLC) and the mixture was purified via aqueous workup
as described above. The organic layers were then concentrated and
chromatographed (200 mL of SiO2, 30% diethyl ether/pentane) affording
a quantitative amount (9.7 g) of the desired product as a colorless oil:
1H NMR (360 MHz, CDCl3) δ 0.82 (s, 3H), 1.06 (d, J ) 7.4 Hz, 3H),
1.15 (d, J ) 10.9 Hz, 1H), 1.28 (s, 3H), 1.37 (s, 3H), 1.50 (m, 1H),
1.85, (m, 1H), 2.03 (dd, J ) 5.2, 5.7 Hz, 1H), 2.15 (m, 1H), 2.31 (m,
1H), 3.45 (t, J ) 8.0 Hz, 1H), 3.57 (dd, J ) 6.3, 8.7 Hz, 1H), 3.77 (s,
3H), 4.24 (dd, J ) 1.6, 8.8 Hz, 1H), 4.43 (s, 3H), 6.85 (d, J ) 8.6 Hz,
2H), 7.25 (d, J ) 8.6 Hz, 2H); 13C NMR (90 MHz, CDCl3) δ 12.5,
23.8, 26.1, 26.9, 28.5, 35.3, 37.9, 39.3, 51.0, 55.0, 72.1, 73.1, 85.3,
113.3, 130.8, 158.8; IR (thin film) 2916, 1613, 1512, 818 cm-1; HRMS
(1S,2R,3S,5S)-Pinanediol (1S,2S)-1-azido-3-(p-methoxybenzyloxy)-
2-methylpropyl Borate. Bromoborate 12 (5.86 g, 12.9 mmol) was
diluted with 200 mL of dichloromethane, then 50 mL of water, sodium
azide (8.40 g, 129 mmol), and 0.60 mL of Aliquot 336 (1.3 mmol)
were added. The biphasic mixture was sealed with a plastic cap and
Teflon tape and stirred vigorously overnight. The reaction mixture was
then diluted with saturated ammonium chloride and dichloromethane
and separated, and the organic layer was dried over Na2SO4. The
solution was then filtered, concentrated, and chromatographed (220 mL
of SiO2, dichloromethane) affording 5.05 g (94%) of the desired product
as a pale yellow oil containing a trace amount of the undesired
diastereomer: 1H NMR (360 MHz, CDCl3) δ 0.81 (s, 3H), 0.99 (d, J
) 6.9 Hz, 3H), 1.21 (d, J ) 10.9 Hz, 1H), 1.28 (s, 3H), 1.32 (s, 3H),
1.78-1.90 (m, 2H), 2.08 (t, J ) 5.2 Hz, 1H), 2.13-2.39 (m, 2H), 3.16
(d, J ) 4.1 Hz, 1H), 3.32 (m, 1H), 3.80 (s, 3H), 4.29 (dd, J ) 2.0, 9.0
Hz, 1H), 4.42 (d, J ) 12.0 Hz, 1H), 4.44 (d, J ) 12.0 Hz, 1H), 6.88
(d, J ) 8.7 Hz, 2H), 7.26 (d, J ) 8.5 Hz, 2H); 13C NMR (90 MHz,
CDCl3) δ 15.6, 24.0, 26.3, 27.0, 28.4, 35.3, 36.0, 38.1, 39.4, 51.1, 55.2,
71.4, 72.6, 78.2, 86.6, 113.7, 129.3, 130.4, 158.9; IR (thin film) 2871,
2096, 1513, 755 cm-1; HRMS (FAB, NBA) found 414.2564 (M +
H)+, calcd for C22H33BN3O4; [R] 3.38 (c 0.0893, CH2Cl2).
(2R,3S)-2-Azido-4-(p-methoxybenzyloxy)-3-methyl-1-butanol (14).
A 5.07 g (12.2 mmol) sample of the purified R-azidoborate was
azeotroped with toluene. It was then diluted with 50 mL of THF and
cooled to -78 °C, and 1.10 mL (14.6 mmol) of chloroiodomethane
was added. To this was added n-butyllithium (6.50 mL, 12.9 mmol),
dropwise, directly to the stirring solution taking care to keep the color
of the mixture faint yellow (if the addition is too fast it results in a
darker color and a significantly lower yield). After the addition was
complete the mixture was warmed to room temperature by removal of
the bath and stirred until all material had rearranged to the title
compound (overnight). It was then worked up as above (saturated
ammonium chloride and diethyl ether) and chromatographed (200 mL
SiO2, 10% diethyl ether/pentane) giving 4.11 g (78%) of the desired
product as a faint yellow oil that was used immediately for the next
step.
(2R,3S)-2-Azido-4-(p-methoxybenzyloxy)-3-methyl-1-butanol. To
a solution of 15 (3.868 g, 9.01 mmol) in 90 mL of THF were added
aqueous 30% hydrogen peroxide (1.12 mL, 9.91 mmol) followed by 3
N aqueous sodium hydroxide (3.3 mL, 9.91 mmol). The addition of
hydrogen peroxide resulted in a cloudy white suspension and evolution
of heat. After the reaction was complete (TLC) the mixture was
partitioned between diethyl ether and water and separated, the aqueous
phase was extracted twice with ether, and the combined organic extracts
were dried over Na2SO4. After concentration of the crude solution it
was chromatographed (150 mL of SiO2, 66% diethyl ether/pentane)
giving 1.866 g (75%) of the desired azido alcohol as a colorless oil:

6362 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Bauer and Armstrong
1H NMR (400 MHz, CDCl3) δ 0.99 (d, J ) 7.0 Hz, 3H), 2.00 (m, 1H),
3.27 (broad s, 1H), 3.38 (dd, J ) 4.8, 9.4 Hz, 1H), 3.45 (dd, J ) 6.1,
9.4 Hz, 1H), 3.52 (m, 1H), 3.63 (m, 1H), 3.73 (dd, J ) 4.2, 11.1 Hz,
1H), 3.77 (s, 3H), 4.42 (s, 2H), 6.88 (ddd, J ) 2.1, 2.8, 8.7 Hz, 2H),
7.25 (ddd, 2.1, 2.8, 8.7 Hz, 2H); 13C NMR (101 MHz, CDCl3) δ 14.3,
35.3, 54.9, 62.9, 66.5, 71.2, 72.6, 113.5, 129.1, 129.7, 159.0; IR (thin
film) 3410, 2935, 1613, 820 cm -1; [R] 8.29, (c 0.0607, CH2Cl2).
(2R,3S)-2-Amino-4-(p-methoxybenzyloxy)-3-methyl-1-butanol. The
azido alcohol (0.723 g, 2.6 mmol) was dissolved in 20 mL of methanol.
Palladium on carbon (10%) was added (0.621 g, 0.52 mmol) and the
mixture purged and pressurized with H2 (balloon). After the reaction
was complete (ca. 40 min) it was filtered through a short plug of Celite
and concentrated to afford a quantitative amount of the polar amino
alcohol (17) as a colorless oil that was used without purification for
the next step.
Methyl (2R,3S)-2-tert-butoxycarbonylamino-4-(p-methoxyben-
zyloxy)-3-methylbutanoate (18). The crude carboxylic acid (0.0676
g, 0.192 mmol) and potassium carbonate (0.029 g, 0.211 mmol) were
diluted with DMF (10 mL) and cooled to 0 °C. Iodomethane (0.024
mL, 0.384 mmol) was added slowly to the suspension, which was then
stirred for 40 min, partitioned between diethyl ether and water, and
separated. The aqueous layer was then extracted thrice with ether and
the combined organic extracts were dried with Na2SO4. The crude
reaction mixture was then concentrated in vacuo and the yellow residue
chromatographed (30 mL of SiO2, 20% ethyl acetate/hexanes) affording
the protected product as a colorless syrup (0.0406 g, 60%).
Methyl (2R,3S)-2-tert-butoxycarbonylamino-4-hydroxy-3-meth-
ylbutanoate. PMB ether 18 was diluted with 18 mL of 100:1
dichloromethane/water. To this was added DDQ (0.730 g, 0.20 mmol),
which resulted in a dark emerald-green solution. The mixture was stirred
75 min over which time it changed to a rust-colored suspension. It
was then partitioned between saturated NaHCO3 and dichloromethane
and separated. The aqueous phase was then extracted thrice with
dichloromethane and the combined organic layers were dried over Na2-
SO4. Concentration of the crude extracts afforded material that was
purified by chromatography (40 mL of SiO2, 40% ethyl acetate/hexanes)
yielding the alcohol as a pale yellow syrup (0.4172 g, 96%): 1H NMR
(500 MHz, CDCl3) δ 0.87 (d, J ) 7.0 Hz, 3H), 1.32 (s, 9H), 2.03 (m,
1H), 3.21 (broad s, 1H), 3.39 (dd, J ) 5.6, 11.1 Hz, 1H), 3.49 (dd, J
) 4.1, 11.3 Hz, 1H), 3.62 (s, 3H), 4.17 (t, J ) 7.2 Hz, 1H), 5.61 (d,
J ) 8.6 Hz, 1H); 13C NMR (126 MHz, CDCl3) δ 20.7, 34.1, 43.4,
56.4, 60.2, 67.5, 82.3, 153.6, 169.3; IR (thin film) 3390, 2978, 1694,
734 cm-1; HRMS (FAB, NBA) found 248.1501 (M + H)+, calcd for
C11H22NO5 248.1498; [R] -15.13 (c 0.1156, CDCl3).
(2R,3S)-2-(tert-Butyloxycarbonylamino)-4-(p-methoxybenzyloxy)-
3-methyl-1-butanol. To a solution of amino alcohol 17 (2.09 mmol
from the previous step) in 20 mL of dichloromethane were added 2
equiv of Boc anhydride (0.96 g, 4.18 mmol). The resulting solution
was stirred overnight, then concentrated and chromatographed (75 mL
of SiO2, 30-50% ethyl acetate/hexanes) giving 0.559 g (88%, two
steps) of the carbamate as a colorless oil: 1H NMR (360 MHz, CDCl3)
δ 0.98 (d, J ) 7.0 Hz, 3H), 1.40 (s, 9H), 1.99 (m, 1H), 3.38 (m, 1H),
3.57 (m, 1H), 3.74 (s, 3H), 4.38 (d, J ) 11.5 Hz, 1H), 4.40 (d, J )
11.5, 1H), 5.42 (broad d, 1H), 6.83 (d, J ) 8.6 Hz, 2H), 7.19 (d, J )
8.6 Hz, 2H); 13C NMR (91 MHz, CDCl3) δ 15.2, 28.2, 34.5, 55.0,
55.5, 64.1, 71.8, 72.8, 78.9, 113.6, 129.1, 129.7, 156.5, 159.1; IR (thin
film) 3409, 2974, 1514, 823 cm -1; HRMS (CI) found 340.2132 (M +
H)+, calcd for C18H30NO5 340.2124; [R] -18.4 (c 0.0488, CDCl3).
Methyl (2S,3R)-3-tert-butoxycarbonylamino-4-methoxycarbonyl-
3-methylbutanoic Acid (19). The PMB deprotected alcohol (0.4162
g, 1.80 mmol) was oxidized by using the same two-step procedure as
above affording a quantitative amount of the acid (0.40 g) as a colorless
foaming syrup: 1H NMR (360 MHz, CDCl3) δ 1.29 (d, J ) 7.2 Hz,
3H), 1.46 (s, 9H), 3.31 (m, 1H), 4.54 (dd, J ) 3.6, 9.7 Hz, 1H), 5.56
(d, J ) 9.7 Hz, 1H), 11.00 (broad s, 1H); 13C NMR (91 MHz, CDCl3)
δ 13.4, 28.0, 41.1, 52.4, 54.9, 80.1, 156.1, 171.4, 178.4; IR (thin film)
3436, 2982, 1715, 1505 cm-1; HRMS (FAB, NBA) found 262.1291
(M + H)+, calcd for C11H20NO6 262.1291; [R] -19.44 (c 0.1451,
CDCl3).
tert-Butyl (2S,3R,2′S)-3-tert-butyloxycarbonylamino-2-methyl-4-
methoxycarbonyl-3′-methyl-2′-aminobutanoate. Acid 19 (0.1115 g,
0.43 mmol) and t-Bu-Val-NH2 (0.23 g, 0.51 mmol) were combined in
a flask and azeotroped from toluene. The resulting white solid was
dissolved in acetonitrile (5 mL) and DIPEA (0.15 mL, 0.86 mmol)
was added followed by BOP reagent (0.23 g, 0.514 mmol). The solution
was stirred for 70 min, then partitioned between brine and ethyl acetate
and separated. The aqueous phase was then extracted thrice with ethyl
acetate and the combined organic layers dried with Na2SO4. Concentra-
tion of the crude extracts and flash chromatography (20 mL of SiO2,
0-10% methanol/dichloromethane) afforded 0.1557 g (85%) of a white
solid: 1H NMR (360 MHz, CDCl3) δ 0.78 (d, J ) 7.2 Hz, 3H), 0.81
(d, J ) 7.7 Hz, 3H), 1.34 (s, 9H), 1.36 (s, 9H), 3.02 (dq, J ) 6.8, 11.7
Hz, 1H), 4.06 (dq, J ) 7.0, 11.1 Hz, 1H), 4.61 (s, 3H), 5.26 (dd, J )
4.7, 8.5 Hz, 1H), 5.30 (dd, J ) 3.8, 9.7 Hz, 1H), 6.81 (d, J ) 9.6 Hz,
1H), 7.30 (d, J ) 8.5 Hz, 1H); 13C NMR (91 MHz, CDCl3) δ 15.1,
17.4, 18.6, 27.7, 28.0, 31.0, 41.3, 52.2, 55.8, 57.0, 79.3, 81.8, 156.1,
170.7, 171.8, 173.5; IR (thin film) 3287, 1740, 1699, 1652 cm-1; HRMS
(FAB, NBA) found 417.2603 (M + H)+, calcd for C20H36N2O7
417.2601; [R] -3.80 (c 0.0300, CH2Cl2).
(2R,3S)-2-tert-Butoxycarbonylamino-4-(p-methoxybenzyloxy)-3-
methylbutanal (6). The Boc protected amino alcohol (1.38 g, 4.57
mmol) was diluted with 20 mL of dichloromethane and oxidized by
addition of the Dess-Martin reagent (2.10 g, 5.02 mmol). During the
course of the reaction the mixture changed from an opaque white
solution to a thick white suspension. After 1 h it was partitioned between
saturated NaHCO3 (10 mL), saturated Na2S2O3 (30 mL), and diethyl
ether (40 mL), then stirred vigorously until both layers became clear
(ca. 5-7 min). The phases were then separated and the aqueous phase
extracted twice with ether, dried over Na2SO4, and concentrated
affording 1.28 g (94%) of the pure aldehyde as a single diastereomer:
1H NMR (360 MHz, CDCl3) δ 0.94 (d, J ) 7.0 Hz, 3H), 1.41 (s, 9H),
2.52 (m, 1H), 3.19 (distorted t, J ) 9.0 Hz, 1H), 3.35 (dd, J ) 4.2, 9.5
Hz, 1H), 3.76 (s, 3H), 4.15 (d, J ) 4.9 Hz, 1H), 4.27 (d, J ) 11.6 Hz,
1H), 4.35 (d, J ) 11.4 Hz, 1H), 5.28 (d, J ) 7.2, 1H), 6.84 (d, J ) 8.5
Hz, 2H), 7.16 (d, J ) 8.4 Hz, 2H), 9.52 (s, 1H); 13C NMR (101 MHz,
CDCl3) δ 14.0, 28.2, 34.6, 55.1, 62.8, 70.7, 72.7, 79.7, 113.7, 129.2,
129.6, 156.1, 159.2, 200.2; IR (thin film) 3340, 2975, 1710, 1514 cm-1
;
HRMS (CI) found 338.1967 (M + H)+, calcd for C18H28NO5 338.1967;
[R] -82.2 (c 0.037, CDCl3).
(2R,3S)-2-tert-Butoxycarbonylamino-4-(p-methoxybenzyloxy)-3-
methylbutanoic Acid. Aldehyde 6 (1.103 g, 3.66 mmol) was placed
in a flask with 75 mL of tert-butyl alcohol to which was added
2-methyl-2-butene (2.0 M in THF, 36 mL, 73 mmol) followed by a
solution of sodium chlorite (2.98 g, 32.9 mmol) and monobasic sodium
phosphate (3.07 g, 25.6 mmol) in 30 mL of water. As the oxidant was
added the solution became bright yellow and evolved heat. The reaction
was stirred overnight, changing from yellow to colorless. It was then
concentrated under vacuum, diluted with saturated NaHCO3, and
extracted once with hexanes. The aqueous phase was then acidified
with 2 M HCl and extracted twice with ether, the combined ether
extracts then dried over Na2SO4. The product was concentrated in vacuo
affording a quantitative amount of the product as a pale yellow syrup:
1H NMR (360 MHz, CDCl3) δ 1.10 (d, J ) 6.9 Hz, 3H), 1.51 (s, 9H),
2.52 (m, 1H), 3.43 (m, 1H), 3.83 (s, 3H), 4.40 (m, 2H), 4.51 (d, J )
11.4 Hz, 1H), 5.76 (d, J ) 8.6 Hz, 1H), 6.93 (d, J ) 8.4 Hz, 2H), 7.30
(d, J ) 8.5 Hz, 2H), 11.3 (s, 1H); 13C NMR (101 MHz, CDCl3) δ14.3,
28.2, 30.7, 35.3, 55.0, 56.7, 71.5, 72.8, 79.7, 113.6, 129.1, 156.1, 159.0,
176.7; IR (thin film) 2977, 1715, 1613, 1249 cm-1; HRMS (FAB, NBA)
found 354.1913 (M + H)+, calcd for C18H28NO6 354.1917; [R] -2.35
(c 0.2554, CH2Cl2).
tert-Butyl (2S,3R,2′S)-3-amino-2-methyl-4-methoxycarbonyl-3′-
methyl-2′-aminobutanoate (3). The fully protected Val-MeAsp dipep-
tide (0.092 g, 0.217 mmol) was dissolved in 2 mL of 1 M HCl/ethyl
acetate and the reaction vessel was sealed with a plastic cap and Teflon
tape. After 2 h the reaction mixture was concentrated in vacuo,
partitioned between 0.6 M aqueous HCl and dichloromethane, and
separated. The aqueous phase was then basified with saturated NaHCO3
and extracted twice with dichloromethane, which was then dried over
Na2SO4 and concentrated affording 0.046 g (70%) of the desired product
as a colorless film. Concentration of the initial organic extract afforded
0.029 g (30%) of recovered starting material. 1H NMR (500 MHz,

Total Synthesis of Motuporin (Nodularin-V)
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6363
CDCl3) δ 0.86 (d, J ) 6.9 Hz, 3H), 0.88 (d, J ) 6.9 Hz, 3H), 1.41 (s,
9H), 1.96 (broad s, 2H), 2.12 (m, 1H), 2.79 (dq, J ) 6.0, 7.2 Hz, 1H),
3.61 (m, 1H), 3.70 (s, 3H), 4.37 (dd, J ) 4.3, 8.7 Hz, 1H), 7.55 (d, J
) 8.5, 1H); 13C NMR (126 MHz, CDCl3) δ 15.2, 17.4, 18.9, 27.9,
31.0, 56.7, 57.1, 81.6, 171.1, 173.6, 173.8; IR (thin film) 3309, 1738,
1651, 1538 cm-1; HRMS (FAB, NBA) found 317.2076 (M + H)+,
calcd for C15H28N2O5 317.2076; [R] -11.0 (c 0.0911, CH2Cl2).
Methyl (R)-2-Benzyloxypropionate. (R)-Methyl lactate (1.0 mL,
10 mmol) and benzyl bromide (1.7 mL, 0.015 mmol) were diluted with
20 mL of DMF and cooled to 0 °C. NaH (0.24 g, 0.011 mmol) was
added over 2 min resulting in a cloudy suspension. This was stirred
for 10 min, then warmed to room temperature which resulting in a
slightly green cloudy solution that was stirred until all starting material
was consumed (TLC). The reaction mixture was quenched with 2 M
aqueous HCl and extracted with hexanes, then dried over Na2SO4. The
dried extracts were then concentrated and the crude residue purified
by chromatography (30 mL of SiO2, 5-15% ether/pentane) affording
1.10 g of the desired product as a colorless oil: 1H NMR δ 1.41 (d, J
) 6.84 Hz, 3H), 3.69 (s, 3H), 4.04 (q, J ) 6.9 Hz, 1H), 4.40 (d, J )
11.7 Hz, 1H), 4.66 (d, J ) 11.7 Hz, 1H), 7.20-7.36 (m, 5H); 13C NMR
(91 MHz, CDCl3) δ 18.2, 51.4, 71.5, 73.5, 127.4, 127.5, 128.0, 137.2,
173.1; IR (thin film) 3032, 2873, 1749, 739 cm-1; HRMS (EI) found
194.0941 (M)+, calcd for C11H14O3 194.0921; [R] 78.5 (c 0.3653,
CDCl3).
(R)-2-Benzyloxypropanal (10). Benzyl ether protected methyl
lactate (1.10 g, 5.70 mmol) was diluted with 10 mL of toluene and
cooled to -78 °C. To this was added DIBAL (1.0 M in hexane, 11
mmol), dropwise, to the stirring solution. After 90 min the reacton was
quenched with 2 mL of ice-cold methanol, then partioned with 100
mL of 1 M HCl and hexanes. The biphasic mixture was then separated,
washed twice with hexanes, and dried over Na2SO4. Concentration at
reduced temperature and pressure afforded the aldehyde as a colorless
liquid (0.83 g, 5.1 mmol): 1H NMR (400 MHz, CDCl3) δ 1.39 (d, J )
7.0 Hz, 3H), 3.95 (dq, J ) 1.7, 7.0 Hz, 1H), 4.65 (d, J ) 11.8 Hz,
1H), 4.71 (d, J ) 11.8 Hz, 1H), 7.30-7.49 (m, 5H); 13C NMR (101
MHz, CDCl3) δ 15.1, 76.8, 79.2, 127.7, 128.3, 137.2, 203.2; IR (thin
film) 2935, 2871, 2712, 1733, 739 cm -1; HRMS (FAB, NBA) found
163.0761 (M - H)+, calcd for C10H11O2 163.0759; [R] 34.93 (c 0.0875,
CH2Cl2).
Cyclohexenyl (4R,2′R,3′R)-4-Amino-5-methoxycarbonylpentanoyl-
3′-benzyloxy-2′-N-methylaminobutanamideandCyclohexenyl(4R,2′S,3′R)-
4-Amino-5-methoxycarbonylpentanoyl-3′-benzyloxy-2′-N-methyl-
aminobutanamide (22(R) + 22(S)). (D)-Z-glutamic acid methyl ester
9 (0.114 g, 0.386 mmol) was placed in a flask followed by aldehyde
8 (0.100 g, 0.386 mmol), methylamine (20) (2.0 M in methanol, 0.19
mL, 0.39 mmol), and cyclohexenyl isocyanide (21) (1.0 M in hexanes,
0.38 mmol). The flask was sealed with a plastic cap and Teflon tape
and stirred overnight. The following day the reaction mixture was
concentrated by high vacuum and chromatographed (40 mL of SiO2,
50-100% ether/pentane) affording 0.130 g of the desired product (59%)
as a 1.4:1 mixture of diastereomers. Major diastereomer: 1H NMR
(360 MHz, CDCl3) δ 1.23 (d, J ) 6.1 Hz, 3H), 1.54 (m, 2H), 1.63 (m,
2H), 1.81 (m, 1H), 2.10 (m, 4H), 2.30 (m, 2H), 2.51 (m, 1H), 3.73 (s,
3H), 4.25 (m, 3H), 4.47 (d, J ) 11.5 Hz, 1H), 4.50 (m, 1H), 4.59 (d,
J ) 11.6, 1H), 5.04 (d, J ) 12.3, 1H), 5.09 (d, J ) 12.3, 1H), 5.12 (m,
1H), 5.72 (d, J ) 7.7, 1H), 6.03 (m, 1H), 7.21-7.38 (m, 10H), 7.48
(broad s, 1H); 13C NMR (91 MHz, CDCl3) δ 16.6, 17.0, 21.9, 22.4,
24.0, 27.8, 28.1, 28.9, 32.5, 52.5, 53.1, 61.7, 62.7, 66.9, 70.8, 72.3,
83.1, 114.2, 127.4, 127.5, 127.6, 127.8, 127.9, 128.1, 128.2, 128.3,
128.4, 132.8, 136.2, 138.6, 156.2, 167.1, 172.7, 173.3; IR (thin film)
3307, 2934, 1716, 1634 cm-1; HRMS (FAB, NBA) found 580.3018
(M + H)+, calcd for C32H41N3O7 580.3023; [R] -34.4 (c 0.062, CDCl3).
Minor diastereomer: 1H NMR (360 MHz, CDCl3) δ 1.09 (distorted d,
3H), 1.40-1.59 (m, 4H), 1.89 (m, 3H), 2.00 (m, 2H), 2.18 (m, 1H),
2.31 (m, 3H), 2.88 (s, 3H), 3.66 (s, 3H), 4.08 (m, 1H), 4.30 (m, 1H),
4.41 (d, J ) 11.1 Hz, 1H), 4.57 (d, J ) 11.2 Hz, 1H), 4.71 (d, J ) 9.5
Hz, 1H), 5.01 (s, 2H), 5.68 (d, J ) 7.5 Hz, 1H), 6.01 (s, 1H), 7.20-
7.31 (m, 10H); 13C NMR (91 MHz, CDCl3) δ 16.4, 16.5, 21.8, 22.3,
23.8, 27.3, 27.6, 27.8, 29.4, 32.5, 52.4, 53.4, 62.1, 66.8, 66.9, 71.6,
71.8, 71.9, 73.5, 73.7, 112.9, 127.7, 127.8, 128.0, 128.3, 128.4, 132.3,
136.2, 137.8, 156.0, 167.2, 172.5, 173.0; IR (thin film) 3316, 1720,
1534, 1453 cm-1; HRMS (FAB, NBA) found 580.3015 (M + H)+,
calcd for C32H41N3O7 580.3023; [R] +30.1 (c 0.071, CDCl3).
2,2,2-Trichloroethyl (2S,3R)-3-Benzyloxy-2-[tert-butoxycarbonyl-
(N)-methylamino]butanoate. Acid 24 (282.0 mg, 0.872 mmol) and
2,2,2-trichloroethanol (108 µL, 1.13 mmol) were combined with 2 mL
of dichloromethane. Dicyclohexylcarbodiimide (216 mg, 1.05 mmol)
was added followed by a few crystals of DMAP resulting in an opaque
solution that became a white suspension over a few minutes. The
mixture was stirred overnight, filtered through a cotton plug, concen-
trated, then chromatographed (40 mL of SiO2, 10% ethyl acetate/
hexanes) yielding the fully protected ester (262.4 mg, 66%) as a
1
colorless oil. H NMR (500 MHz, CDCl3) δ 1.25 (m, 3H), 1.48 (s,
2.5H), 1.50 (s, 6.5H), 3.10 (s, 3H), 4.39 (qt, J ) 6.2 Hz, 0.8H), 4.31
(qt, J ) 5.7 Hz, 0.2H), 4.41 (d, J ) 11.6 Hz, 1H), 4.68 (m, 2H), 4.79
(d, J ) 11.9 Hz, 1H), 4.81 (m, 1H), 5.14 (d, J ) 4.4 Hz, 1H), 7.20-
7.31 (m, 5H); 13C NMR (126 MHz, CDCl3) 15.7, 16.0, 28.1, 28.2,
32.8, 33.2, 62.1, 63.4, 71.3, 74.1, 74.2, 74.5, 75.2, 80.0, 80.2, 94.4,
126.9, 127.0, 127.2, 127.3, 128.0, 138.0, 138.2, 155.3, 156.6, 168.3,
168.6; IR (thin film) 3010, 1766, 1694, 723 cm-1; HRMS (FAB, NBA)
found 454.0945 (M + H)+, calcd for C19H27NO5Cl3 454.0955; [R]
+15.25 (c 0.2624, CH2Cl2).
2,2,2-Trichloroethyl (2S,3R)-3-Benzyloxy-2-(N)-methylaminobu-
tanoate (25). The fully protected Boc threonyl ester (0.3431 g, 0.754
mmol) was diluted with 2 mL of 20% TFA in CH2Cl2, the solution
immediately changing to pale yellow. The mixture was stirred for 90
min, then concentrated in Vacuo, azeotroped with toluene (2 × 3 mL),
and placed on a vacuum line overnight to give a quantitative amount
of the free amine as a colorless oil: 1H NMR (400 MHz, CDCl3) δ
1.45 (d, J ) 5.5 Hz, 3H), 2.83 (s, 3H), 4.14 (m, 1H), 4.24 (s, 1H),
4.46 (d, J ) 11.5 Hz, 1H), 4.63 (d, J ) 11.5 Hz, 1H), 4.76 (s, 2H),
7.24-7.36 (m, 5H); 13C NMR (101 MHz, CDCl3) δ 15.9, 32.8, 64.6,
70.6, 71.8, 74.5, 93.1, 127.3, 127.6, 127.9, 136.1, 164.6; IR (thin film)
2877, 1770, 1682, 799 cm-1; HRMS (CI) found 354.04460 (M + H)+,
calcd for C14H19NO2Cl3 354.04305; [R] -21.20 (c 0.1757, CDCl3).
2,2,2-Trichloroethyl (4R,2′S,3′R)-4-Amino-5-methoxycarbonyl-
pentanoyl-3′-benzyloxy-2′-(N)-methylaminobutanoate. Acid 9 (260
mg, 0.72 mmol) and the amine derived from threonine (164 mg, 0.56
mmol) were combined with 2 mL of acetonitrile. To the stirring solution
was added DIPEA (250 µL, 1.4 mmol) followed by BOP reagent (370
mg, 0.84 mmol), which resulted in a dark yellow color. This solution
was stirred overnight, the color changing from yellow to orange, at
which time it was determined to have progressed to completion (TLC).
The reaction mixture was then partitioned between saturated aqueous
NaCl and dichloromethane, separated, and the aqueous phase extracted
thrice with dichloromethane. The combined organic layers were dried
over Na2SO4, then concentrated and chromatographed (60 mL SiO2,
40% ethyl acetate/hexanes), which gave the product as a slightly brown
foam (170.9 mg, 48%): 1H NMR (500 MHz, CDCl3) δ 1.17 (d, J )
6.3 Hz, 3H), 2.09 (m, 1H), 2.21 (m, 1H), 2.47 (m, 1H), 2.52 (m, 1H),
3.17 (s, 3H), 3.73 (s, 3H), 4.36 (m, 1H), 4.42 (d, J ) 11.3 Hz, 1H),
4.43 (m, 1H), 4.60 (d, J ) 11.4 Hz, 1H), 4.61 (d, J ) 11.9 Hz, 1H),
4.82 (d, J ) 11.9 Hz, 1H), 5.08 (d, J ) 12.2 Hz, 1H), 5.11 (d, J )
12.3 Hz, 1H), 5.60 (d, J ) 4.1 Hz, 1H), 5.60 (d, J ) 4.1 Hz, 1H), 5.76
(d, J ) 7.6 Hz, 1H), 7.21-7.40 (m, 10H); 13C NMR (126 MHz, CDCl3)
δ 15.8, 27.0, 29.2, 34.3, 52.3, 43.8, 60.4, 66.8, 71.5, 74.3, 75.2, 94.4,
127.0, 127.5, 128.2, 128.3, 128.4, 136.2, 138.1, 156.0, 168.2, 172.4,
173.7; IR (thin film) 3318, 1748, 1722, 698 cm-1; [R] -25.47 (c 0.043,
CDCl3).
(4R,2′R,3′R)-4-Amino-5-methoxycarbonylpentanoyl-3′-benzyloxy-
2′-(N)-methylaminobutanoic Acid and (4R,2′S,3′R)-4-Amino-5-
methoxycarbonylpentanoyl-3′-benzyloxy-2′-(N)- methylaminobu-
tanoic Acid (4(R) and 4(S)). 4(R) and 4(S) were synthesized as a
mixture of diastereomers by combining cyclohexenamides (22(R) and
22(S)) (0.133 g, 0.24 mmol) with 8.5 mL of THF and warming to 60
°C. To this solution was added concentrated HCl (0.22 mL, 2.64 mmol)
in one portion and the mixture was stirred for 20 min. After the reaction
was determined to be complete (TLC) it was cooled to room
temperature, concentrated by high vacuum, and chromatographed (30
mL of SiO2, 0-10% methanol/dichloromethane) affording 0.090 g of
the desired product as a 1:1 mixture of diastereomers (75%).

6364 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Bauer and Armstrong
Synthesized as diastereomerically pure material by reduction of the
trichloroethyl ester as follows: the trichloroethyl ester dipeptide (80
mg, 0.13 mmol) was placed in a 10 mL flask and dissolved in 2 mL of
90% aqueous acetic acid. Once the starting material had dissolved
completely, Zn dust was added and the resulting gray suspension was
stirred overnight. The cloudy silver-gray mixture was partitioned
between dichloromethane and water and separated, and the aqueous
phase was extracted twice with ethyl acetate. The combined organic
phases were then dried over MgSO4, concentrated, and chromatographed
(10 mL of SiO2, 0-10% methanol/dichloromethane) affording the acid
disappeared as shown by TLC. The mixture was concentrated and
purified by flash chromatography (100 mL of SiO2, 10% ethyl acetate/
hexanes) affording 1.717 g (85%) of the aldehyde as a clear oil: 1H
NMR (360 MHz, CDCl3) δ 1.26 (d, J ) 7.1 Hz, 3H), 2.45 (dddd, J )
3.4, 7.1, 14.2, 21.2 Hz, 1H), 2.80 (dd, J ) 7.3, 13.7 Hz, 1H), 3.10 (dd,
J ) 6.5, 13.7 Hz, 1H), 3.38 (s, 3H), 3.98 (m, 1H), 7.25-7.42 (m, 5H),
9.75 (s, 1H); 13C NMR (91 MHz, CDCl3) δ 7.2, 37.2, 48.7, 57.6, 81.3,
126.3, 128.3, 129.0, 137.8, 203.8; IR (thin film) 2827, 2719, 1726,
701 cm-1; HRMS (EI) found 192.1075 (M+), calcd for C12H16O2
192.1150; [R] -24.61 (c 0.138, CDCl3).
1
(38.2 mg, 60%) as a colorless film. H NMR (400 MHz, CDCl3) δ
Ethyl (2E,4S,5S)-5-Methoxy-2,4-dimethyl-6-phenyl-2-hexenoate
(28). The methoxy aldehyde derived from 27 (1.71 g, 8.93 mmol) was
diluted with 50 mL of toluene and Ph3PCH(CH3)CO2CH2CH3 (3.74 g,
10.3 mmol) was added resulting in a yellow suspension that persisted
until heating. The mixture was refluxed overnight, affording a slightly
darker yellow solution that was partitioned between diethyl ether and
water, and the organic phase was separated. The aqueous phase was
then extracted with ether and the combined organic extracts dried with
Na2SO4. After concentration the crude yellow residue was chromato-
graphed (70 mL of SiO2, 20% ethyl acetate/hexanes) affording 2.102
g (85%) of the desired product as a faint yellow oil: 1H NMR (360
MHz, CDCl3) δ 1.22 (d, J ) 6.8 Hz, 3H), 1.43 (t, J ) 7.1 Hz, 3H),
1.88 (s, 3H), 2.76 (m, 1H), 2.85 (dd, J ) 7.2, 13.9 Hz, 1H), 2.95 (dd,
J ) 4.9, 14.0 Hz, 1H), 3.39 (s, 3H), 3.40 (m, 1H), 4.33, (q, J ) 7.2
Hz, 2H), 6.84 (d, J ) 10.2 Hz, 1H), 7.29-7.43 (m, 5H); 13C NMR (91
MHz, CDCl3) δ 12.2, 14.0, 15.0, 36.8, 37.8, 56.3, 60.2, 85.8, 125.9,
127.3, 128.0, 129.2, 143.8, 167.8; IR (thin film) 2827, 1714, 1455,
1241 cm-1; HRMS (FAB, NBA) found 277.1805 (M + H)+, calcd for
C17H25O3 277.1804; [R] -28.86 (c 0.1465, CDCl3).
(2S,3S,4E)-2-Methoxy-3,5-dimethyl-1-phenyl-4-hexen-6-ol. Ester
28 (2.102 g, 7.60 mmol) was diluted with 10 mL of THF and added to
a suspension of LiAlH4 (0.29 g, 7.6 mmol) in 40 mL of THF in a
round-bottom flask equipped with a reflux condenser. After the mixture
was stirred at room temperature for 60 min the reaction was quenched
by slow addition of 0.3 mL of water (caution, exothermic), followed
by 0.3 mL of 15% aqueous NaOH, and finally 0.9 mL of water. The
suspension was stirred until a fine gray suspension formed, which was
then vacuum filtered, and the supernatant was dried over Na2SO4. The
solution was filtered, concentrated, and chromatographed (150 mL of
SiO2, 20% ethyl acetate/hexanes) affording 1.540 g (86%) of a clear
oil: 1H NMR (500 MHz, CDCl3) δ 1.04 (d, J ) 6.8 Hz, 3H), 1.59 (s,
3H), 2.60 (m, 1H), 2.70 (dd, J ) 7.8, 14.0 Hz, 1H), 2.83 (dd, J ) 4.4,
14.0 Hz, 1H), 3.22 (m, 1H), 3.23 (s, 3H), 3.97 (s, 2H), 5.35 (d, J )
9.9 Hz, 1H), 7.16-7.30 (m, 5H); 13C NMR (126 MHz, CDCl3) δ 13.6,
16.2, 35.6, 37.7, 58.2, 68.2, 86.9, 125.7, 127.9, 129.1, 134.7, 139.3;
IR (thin film) 3396, 2928, 1453, 700 cm-1; HRMS (CI) found 252.1959
(M + NH4)+, calcd for C15H26NO2 262.1964; [R] -11.94 (c 0.1057,
CDCl3).
1.13 (d, J ) 6.2 Hz, 3H), 2.04 (m, 1H), 2.20 (m, 1H), 2.43 (m, 1H),
2.50 (m, 1H), 3.08 (s, 3H), 3.71 (s, 3H), 4.34 (m, 1H), 4.43 (d, J )
11.6 Hz, 1H), 4.57 (d, J ) 11.5 Hz, 1H), 5.09 (s, 2H), 5.40 (d, J ) 3.9
Hz, 1H), 5.84 (d, J ) 7.8 Hz, 1H), 7.19-7.38 (m, 10H); 13C NMR
(101 MHz, CDCl3) δ 16.3, 27.1, 29.4, 34.6, 52.5, 53.9, 60.9, 67.1,
71.8, 75.0, 127.4, 127.6, 128.2, 128.3, 128.5, 136.2, 138.3, 156.3, 172.7,
173.4, 174.1; IR (thin film) 3321, 2952, 1720, 1637 cm-1; HRMS (CI)
found 501.2235 (M + H)+, calcd for C26H33N2O8 501.2237; [R] 20.68
(c 0.0382, CH2Cl2).
(2S,3S)-3-Methyl-1-phenyl-4-penten-2-ol. Freshly sublimed potas-
sium tert-butoxide (1.467 g, 12 mmol) was placed in a flame-dried
round-bottom flask charged with Ar and containing a large magnetic
stir-bar. THF (20 mL) was added and the suspension cooled to -78
°C followed by addition of cis-2-butene (1 mL). n-Butyllithium was
slowly added resulting in a bright yellow suspension that was stirred
30 min. At this time, (+)-B(OCH3)(iPc)2 (4.94 g, 15.6 mmol) in 15
mL of THF was added to the stirring mixture resulting in a clear yellow
solution. After 30 min, borontrifluoride etherate (1.92 mL, 12.0 mmol)
was added followed immediately by phenylacetaldehyde (1.4 mL, 12.0
mmol) in 10 mL of THF. The reaction became very viscous and was
stirred 2 h at -78 °C, then slowly warmed to room temperature and
quenched by adding 10 mL of 30% H2O2 (slowly) and 15 mL of 3 N
NaOH. The resulting white biphasic mixture was stirred vigorously
for 2 h, until all of the alcohol had been liberated by oxidation. The
mixture was then partitioned between brine and dichloromethane and
separated, and the aqueous phase was extracted twice with dichlo-
romethane and the combined organic extracts dried over Na2SO4. After
concentration of the extracts, the crude syrup was chromatographed
(170 mL of SiO2, 0-10% ethyl acetate/hexanes) affording 1.685 g of
the desired compound (80%) as a colorless oil: 1H NMR (360 MHz,
CDCl3) δ 1.14 (d, J ) 6.8 Hz, 3H), 1.58 (broad s, 1H), 2.63 (dd, J )
9.4, 13.8 Hz, 1H), 2.91 (dd, J ) 3.6, 13.8 Hz, 1H), 3.74 (ddd, J ) 3.7,
5.5, 9.3 Hz, 1H), 5.11-5.19 (m, 2H), 5.90 (ddd, J ) 7.4, 10.6, 18.0
Hz, 1H), 7.20-7.38 (m, 5H); 13C NMR (91 MHz, CDCl3) δ 14.5, 40.8,
43.0, 75.7, 115.4, 126.4, 128.6, 129.3, 138.9, 140.9; IR (thin film) 3425,
2919, 1604, 914 cm-1; HRMS (EI) found 176.1199 (M+), calcd for
C12H16O 176.1201; [R] -43.55 (c 0.1233, CH2Cl2).
(2S,3S)-2-Methoxy-3-methyl-1-phenyl-4-pentene (27). The alcohol
derived from the crotylboration of phenylacetaldehyde (0.376 g, 2.13
mmol) was diluted with DMF (8 mL) and cooled to 0 °C. NaH (0.43
g, 5.3 mmol) was added slowly to the mixture resulting in a gray
suspension. After 20 min of stirring iodomethane (0.33 mL, 5.3 mmol)
was added and the mixture warmed to room temperature. After 60 min
the reaction was quenched by careful addition of water, then the solution
was partitioned between dichloromethane, separated, dried with Na2-
SO4, and purified by chromatography (60 mL SiO2, dichloromethane)
affording 0.387 g of clear oil (95%): 1H NMR (500 MHz, CDCl3) δ
1.15 (d, J ) 6.9 Hz, 3H), 2.46 (m, 1H), 2.76 (dd, J ) 8.0, 14.0 Hz,
1H), 2.85 (dd, J ) 4.4, 14.0 Hz, 1H), 3.29 (s, 3H), 3.31 (m, 1H), 5.12
(m, 2H), 5.93 (m, 1H), 7.21-7.38 (m, 5H); 13C NMR (126 MHz,
CDCl3) δ 15.0, 37.8, 40.8, 58.2, 86.4, 114.5, 125.9, 128.1, 129.2, 139.6,
141.0; IR (thin film) 3028, 2929, 1605, 700 cm-1; HRMS (EI) found
190.1360 (M+), calcd for C13H18O 190.1358; [R] -23.6 (c 0.1480, CH2-
Cl2).
(2S,3S,4E)-6-Bromo-2-methoxy-3,5-dimethyl-1-phenyl-4-hex-
ene (29). The alcohol from reduction of ethyl ester 28 (1.08 g, 4.61
mmol) was diluted with 25 mL of THF. To this was added carbon
tetrabromide (3.05 g, 9.21 mmol) followed by triphenylphosphine (2.66
g, 10.1 mmol) in 30 mL of THF, which resulted in an orange solution.
The mixture was stirred for 60 min, and the insoluble triphenylphos-
phine oxide which precipitated from the solution was then removed
by vacuum filtration. The solution was then concentrated and chro-
matographed (75 mL of SiO2, 0-5% ethyl acetate/hexanes) affording
0.819 g (60%) of the allylic bromide as a colorless oil: 1H NMR (360
MHz, CDCl3) δ 1.02, d, J ) 6.8 Hz, 3H), 1.64 (d, J ) 1.3 Hz, 3H),
2.45 (m, 1H), 2.68 (dd, J ) 7.2, 13.9 Hz, 1H), 2.80 (dd, J ) 4.7, 13.9
Hz, 1H), 3.19 (ddd, J ) 4.8, 6.5, 11.2 Hz, 1H), 3.24 (s, 3H), 3.93 (d,
J ) 9.4 Hz, 1H), 3.97 (d, J ) 9.4 Hz, 1H), 5.51 (d, J ) 9.8 Hz, 1H),
7.14-7.30 (m, 5H); 13C NMR (91 MHz, CDCl3) δ 14.8, 15.6, 36.5,
37.9, 41.5, 58.4, 86.4, 125.9, 128.0, 129.4, 131.7, 134.0, 139.0; IR (thin
film) 2966, 1930, 1206, 701 cm-1; HRMS (CI) found 314.1130 (M +
NH4)+, calcd for C15H25BrNO 314.1120; [R] -4.35 (c 0.1159, CH2-
Cl2).
(2S,3S)-3-Methoxy-2-methyl-4-phenylbutanal. Alkene 27 (2.01 g,
10.5 mmol) was diluted with 30 mL of dichloromethane and cooled to
-78 °C. Ozone was then bubbled into the solution until a faint blue
color persisted, the solution was then purged with air, and triphen-
ylphosphine (2.90 g, 11.1 mmol) was added in one portion. The cooling
bath was then removed and the solution stirred until all of the ozonide
(2S,3S,8S,9S,4E,6E)-3-tert-Butoxycarbonylamino-9-methoxy-2,6,8-
trimethyl-1-p-methoxybenzyloxy-4, 6-decadiene (30). The allylic
bromide 29 (0.073 g, 0.25 mmol) was diluted with toluene (20 mL)
and treated with triphenylphosphine (0.065 g, 0.25 mmol). The mixture

Total Synthesis of Motuporin (Nodularin-V)
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6365
was refluxed overnight, then concentrated in vacuo and used im-
mediately for the next step.
The solution was stirred for 2 h, changing from pale yellow to light
orange over the course of the reaction. The mixture was then partitioned
between saturated aqueous NaCl and ethyl acetate and separated, the
aqueous phase was extracted twice with ethyl acetate, and the combined
organic layers were dried over MgSO4. The suspension was filtered,
concentrated to a brown oil, then chromatographed (15 mL SiO2, 50-
100% ethyl acetate/hexanes) to give the tetrapeptide (40 mg, 85%) as
two diastereomers, both slightly yellow oils. Minor diastereomer: 1H
NMR (500 MHz, CDCl3) δ 0.88 (t, J ) 6.8 Hz, 6H), 1.12 (d, J ) 6.8
Hz, 6H), 1.48 (s, 9H), 2.15 (m, 2H), 2.31 (m, 1H), 2.42 (m, 1H), 2.60
(m, 1H), 3.04 (s, 3H), 3.10 (ddd, J ) 4.1, 6.9, 7.0 Hz, 1H), 3.63 (s,
3H), 3.72 (s, 3H), 4.34 (m, 3H), 4.49 (d, J ) 11.6 Hz, 1H), 4.56 (d, J
) 11.5 Hz, 1H), 4.68 (dd, J ) 3.8, 8.8 Hz, 1H), 5.09 (s, 2H), 5.32 (d,
J ) 5.4 Hz, 1H), 5.90 (d, J ) 7.7 Hz, 1H), 6.20 (d, J ) 8.3 Hz, 1H),
7.20-7.40 (m, 10H), 7.48 (d, J ) 8.9 Hz, 1H); 13C NMR (126 MHz,
CDCl3) δ 15.4, 16.9, 17.5, 18.7, 26.7, 27.9, 29.2, 31.2, 33.3, 41.1, 52.3,
52.4, 53.6, 54.2, 57.1, 60.9, 66.7, 71.2, 73.2, 82.1, 127.2, 127.3, 127.7,
128.1, 128.4, 136.4, 138.7, 156.1, 169.7, 170.7, 171.1, 172.5, 173.6;
IR (thin film) 2936, 1732, 1660, 1506 cm-1; HRMS (FAB, NBA/NaI)
found 821.3902 (M + Na)+, calcd for C41H58N4O12Na 821.3949; [R]
-67.6 (c 0.0306, CDCl3). Major diastereomer: 1H NMR (500 MHz,
CD3OD) δ 0.88-0.91 (m, 6H), 1.12 (d, J ) 7.2 Hz, 3H), 1.16 (d, J )
6.1 Hz, 3H), 1.43 (s, 9H), 2.10-1.73 (m, 4H), 2.47 (m, 1H), 2.91 (s,
3H), 3.18 (m, 1H), 3.64 (s, 3H), 3.69 (s, 3H), 4.11 (d, 6.2, 1H), 4.08
(m, 1H), 4.25 (m, 1H), 4.57 (m, 1H), 4.60 (d, J ) 7.4 Hz, 1H), 4.68
(d, J ) 5.8 Hz, 1H), 4.93 (d, J ) 8.3 Hz, 1H), 5.04 (d, 12.6 Hz, 1H),
5.08 (d, J ) 12.5 Hz, 1H), 7.18-7.36 (m, 10H); 13H NMR (126 MHz,
CD3OD) δ 44.5, 15.5, 17.0, 18.0, 26.6, 26.8, 28.2, 30.3, 32.0, 51.3,
51.5, 53.2, 54.1, 58.0, 61.3, 66.2, 70.8, 73.4, 81.3, 127.0, 127.2, 127.3,
127.5, 127.7, 128.0, 138.2, 139.4, 155.4, 170.1, 170.7, 170.8, 171.6,
173.0, 174.6; IR (thin film) 2977, 1727, 1650, 848 cm-1; [R] -2.6 (c
0.0325, CDCl3).
The above phosphonium salt was evaporated from toluene (1 × 3
mL), dissolved in 2 mL of THF, and cooled to 0 °C. Freshly prepared
lithium diisopropylamide (0.25 mmol) in 1 mL of THF was added
slowly to the stirring solution, which became dark red as the addition
progressed. After the mixture was stirred for 10 min, aldehyde 6 was
added in 1 mL of THF resulting in a pale yellow solution after the
addition was complete. After the solution was stirred for 10 min the
ice bath was removed and the reaction partitioned between ether and
water and separated, and the organic layer was dried over Na2SO4.
The mixture was then concentrated by rotary evaporation and chro-
matographed (20 mL of SiO2, 10% ethyl acetate/hexanes) affording
0.075 g (67%) of the desired trans-trans diene and 0.014 g (16%) of
the undesired trans-cis diene both as clear oils: 1H NMR (360 MHz,
CDCl3) 1.03 (d, J ) 7.1 Hz, 3H), 1.06 (d, J ) 6.8 Hz, 3H), 1.47 (s,
9H), 1.61 (s, 3H), 1.93 (m, 1H), 2.61 (m, 1H), 2.69 (dd, J ) 7.4, 13.8
Hz, 1H), 2.82 (dd, J ) 4.3, 13.9 Hz, 1H), 3.20 (m, 1H), 3.24 (s, 3H),
3.36, dd, J ) 5.2 9.0 Hz, 1H), 3.48, (dd, J ) 5.0, 8.9 Hz, 1H), 6.17 (d,
J ) 15.6 Hz, 1H), 6.88 (d, J ) 8.7 Hz, 2H), 7.15-7.30 (m, 7H); 13C
NMR (91 MHz, CDCl3) δ 12.6, 14.4, 16.1, 28.3, 36.5, 37.7, 38.1, 55.0,
58.4, 72.0, 72.7, 78.8, 86.9, 113.6, 125.8, 126.4, 128.0, 129.0, 129.3,
130.2, 132.5, 135.0, 135.1, 139.2, 155.3, 159.0; IR (thin film) 3412,
2974, 1514, 701 cm-1; HRMS (FAB, NBA) found 538.3527 (M +
H)+, calcd for C33H46NO5 538.3532; [R] -17.1 (c 0.0830, CDCl3).
(2S,3S,8S,9S,4E,6E)-3-tert-Butoxycarbonylamino-9-methoxy-2,6,8-
trimethyl-4,6-decadien-1-ol. The protected alcohol 33 (0.247 g, 0.47
mmol) was diluted with 2 mL of dichloromethane. Ethanethiol (1 mL)
was added followed by borontrifluoride etherate (0.46 mL, 3.76 mmol),
which resulted in a pale yellow solution. After 30 min, all material
had been totally deprotected and the mixture was partitioned between
water and dichloromethane and separated, and the aqueous phase was
then extracted with ethyl acetate. The combined organic layers were
then concentrated in vacuo and diluted with dichloromethane. Boc
anhydride (0.13 mL, 0.56 mmol) was added to the solution and the
mixture was stirred until all starting material was consumed, then
concentrated and chromatographed (50 mL of SiO2, 20% ethyl acetate/
hexanes) affording the desired alcohol (0.106 g, 60%) as a colorless
oil: 1H NMR (500 MHz, CDCl3) δ 0.99 (d, J ) 6.9 Hz, 3H), 1.03 (d,
J ) 6.8 Hz, 3H), 1.44 (s, 9H), 1.62 (s, 3H), 2.59 (m, 1H), 2.68 (dd, J
) 9.09, 16.5 Hz, 1H), 2.79 (dd, J ) 4.6, 14.0 Hz, 1H), 3.19 (ddd, J )
4.9, 7.0, 11.3 Hz, 1H), 3.23 (s, 3H), 3.25 (dd, J ) 2.9 14.9 Hz, 1H),
3.47 (m, 1H), 3.71 (d, J ) 10.6 Hz, 1H), 4.09 (q, J ) 7.3 Hz, 1H),
4.97 (d, J ) 7.9 Hz, 1H), 5.40 (d, J ) 9.9 Hz, 1H), 5.43 (dd, J ) 7.3,
15.6 Hz, 1H), 6.20 (d, J ) 15.6 Hz, 1H), 7.15-7.29 (m, 5H); 13C NMR
(126 MHz, CDCl3) δ 12.6, 14.2, 16.1, 22.1, 18.33, 28.3, 36.6, 58.8,
79.8, 87.2, 124.1, 125.3, 128.1, 129.1, 129.3, 132.4, 135.7, 136.7, 139.2,
156.3; IR (thin film) 3377, 2931, 1682, 1014 cm-1; HRMS (FAB, NBA)
found 418.2956 (M + H)+, calcd for C25H39NO4 418.2957; [R] -13.6
(c 0.0719, CDCl3).
(2S,3S,8S,9S,4E,6E)-3-tert-Butoxycarbonylamino-9-methoxy-2,6,8-
trimethyl-4, 6-decadienoic Acid (2). The Boc protected amino alcohol
(0.0883 g, 0.22 mmol) was oxidized by using the two-step procedure
above affording a quantitative amount (0.0907 g, 0.22 mmol) of the
desired acid as a colorless foam: 1H NMR (500 MHz, CDCl3) δ 1.02
(d, J ) 6.7 Hz, 3H), 1.25 (d, J ) 6.1 Hz, 3H), 1.45 (s, 9H), 1.61 (s,
3H), 2.60 (m, 1H), 2.68 (dd, J ) 7.3, 21.3 Hz, 1H), 2.79 (dd, J ) 4.5,
14.0 Hz, 1H), 3.19 (m, 2H), 3.23 (s, 3H), 4.40 (m, 1H), 5.35 (m, 1H),
5.39 (d, J ) 9.8 Hz, 1H), 5.49 (m, 1H), 6.20 (d, J ) 15.6 Hz, 1H),
7.10-7.30 (m, 5H); 13C NMR (126 MHz, CDCl3) δ 12.7, 14.5, 16.1,
21.1, 23.4, 28.3, 36.6, 38.2, 44.2, 54.2, 58.5, 87.1, 125.1, 125.9, 128.1,
129.3, 132.5, 135.9, 136.4, 139.3; IR (thin film) 3425, 2977, 1715,
701 cm-1; HRMS (FAB, NBA) found 432.2743 (M + H)+, calcd for
C25H37NO5 432.2750; [R] -19.10 (c 0.0547, CDCl3).
tert-Butyl (4R,2′R,3′R,2′′S,3′′R,2′′′S)-4-benzyloxycarbonylamino-
5-methoxycarbonylpentanoyl-3′-benzyloxy-2′-(N)-methylaminobu-
tanoyl-3′′-amino-4′′-methoxycarbonyl-2′′methylbutanoyl-2′′′-amino-
3′′′-methylbutanoate. Amine 3 (19 mg, 0.059 mmol) and acid 4 (R)
(38.2 mg, 0.076 mmol) were azeotroped with 2 mL of toluene. The
resulting foam was then dissolved in 1 mL of acetonitrile and DIPEA
(26 µL, 0.15 mmol) and BOP reagent (39 mg, 0.088 mmol) were added.
tert-Butyl (2S,3S,8S,9S,4E,6E,4′R,2′′R,3′′R,2′′′S,3′′′R,2′′′′S)-3-tert-
Butoxycarbonylamino-9-methoxy-2,6,8-trimethyl-4, 6-decadienoyl-
4′-benzyloxycarbonylamino-5′-methoxycarbonylpentanoyl-3′′-ben-
zyloxy-2′′-(N)-methylaminobutanoyl-3′′′-amino-4′′′-methoxycarbonyl-
2′′′-methylbutanoyl-2′′′′-amino-3′′′′-methylbutanoate (1). The protected
tetrapeptide was diluted with methanol (7 mL) and 20 mg of 10% Pd/C
was added to the solution. The black suspension was then purged and
pressurized with H2 (balloon), and stirred for 16 h. After stirring, the
reaction mixture was filtered through a short pad of Celite (0.4 mL)
that was then washed exhaustively with methanol. The filtrate was then
concentrated affording 0.013 g (82%) of amine 3 as a clear film, which
was used immediately for the next step.
Boc-ADDA (2; 0.024 g, 0.057 mmol) and tetrapeptide 35 (0.0291
g, 0.052 mmol) were evaporated from toluene (containing a few drops
of dichloromethane for solubility), then diluted in 0.5 mL of DMF.
The stirring solution was treated with HATU (0.025 g, 0.062 mmol)
followed by DIPEA (0.022 mL, 0.124 mmol) which resulted in a faint
yellow-green solution. The mixture was stirred overnight, then parti-
tioned between water and ethyl acetate (with a small amount of brine
to break the emulsion) and separated, and the aqueous phase was
extracted thrice with ethyl acetate. The combined organic layers were
dried over MgSO4, filtered, and concentrated to a pale brown oil that
was then chromatographed (10 mL of SiO2, 0-10% methanol/
dichloromethane) affording 0.030 g (61%) of the desired compound
(colorless film) as rotamers: (500 MHz, CD3OD) 0.92 (m, 6H), δ 1.02
(d, J ) 6.7 Hz, 3H), 1.10 (d, J ) 6.8 Hz, 1.4H), 1.13 (d, J ) 6.8 Hz,
1.6H), 1.19 (m, 6H), 1.42 (s, 9H), 1.45 (s, 9H), 1.61 (s, 3H), 1.90-
2.20 (m, 2H), 2.20-2.50 (m, 2H), 2.61 (m, 2H), 2.70-3.00 (m, 2H),
3.07 (s, 1.6 H), 3.08 (s, 1.4H), 3.19 (m, 2H), 3.21 (s, 1.6H), 3.22 (s,
1.4H), 3.66 (s, 1.5H), 3.68 (s, 1.5H), 3.69 (s, 1.5H), 3.70 (s, 1.5), 4.14
(d, J ) 6.1 Hz, 1H), 4.15 (m, 1H), 4.29 (q, J ) 6.0 Hz, 1H), 4.44 (dd,
J ) 5.3, 9.0 Hz, 1H), 4.57 (t, J ) 5.8 Hz, 1H), 5.00 (m, 1H), 5.39 (d,
J ) 9.8 Hz, 1H), 5.51 (m, 1H), 6.18 (d, J ) 15.5 Hz, 1H), 7.10-7.30
(m, 5H); 13C NMR (126 MHz, CD3OD) δ 11.5, 12.9, 14.6, 15.0, 16.9,
18.0, 19.3, 19.4, 26.8, 27.6, 29.1, 30.3, 31.9, 32.0, 35.4, 36.1, 37.5,
39.3, 40.1, 51.1, 51.2, 51.4, 51.7, 53.2, 54.2, 57.2, 58.0, 60.0, 61.6,
64.5, 81.2, 86.9, 125.5, 127.7, 129.0, 132.3, 135.3, 135.4, 159.0, 156.1,
170.5, 170.8, 171.1, 172.1, 174.2, 174.4, 174.6, 174.7, 175.7, 176.4;
IR (thin film) 2975, 1738, 1651, 1248 cm-1; HRMS (FAB, NBA, Ultra)

6366 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Bauer and Armstrong
found 1010.5736 (M + Na)+, calcd for C51H81N5O14Na 1010.5678; [R]
-30.5 (c 0.0084, EtOAc).
Motuporin. The protected motuporin diester (2.8 mg) was depro-
tected by using 0.2 mL of saturated Ba(OH)2 in 1 mL of 9:1 water/
methanol. The solution was stirred overnight resulting in no visible
change, then acidified with 2 M aqueous HCl and extracted thrice with
ethyl acetate; the combined organic extracts were dried over MgSO4.
After concentration, the material was purified by high performance prep
plate (50% methanol/dichloromethane) affording 1.0 mg of motuporin
as a white solid and ca. 0.4 mg of epimeric material: 1H NMR (500
MHz, CD3OD) δ 0.74 (d, J ) 6.9 Hz, 3H), 0.82 (d, J ) 6.9 Hz, 3H),
0.97 (d, J ) 7.1 Hz, 3H), 1.00 (d, J ) 6.5 Hz, 3H), 1.08 (d, J ) 6.5
Hz, 3H), 1.18 (d, J ) 7.0 Hz, 3H), 1.60 (d, J ) 1.0 Hz, 3H), 1.72 (d,
J ) 7.2 Hz, 3H), 2.03 (m, 1H), 2.29 (m, 1H), 2.48 (m, 1H), 2.55 (m,
1H), 2.64 (dd, J ) 7.3, 14.0 Hz, 1H), 2.75 (m, 1H), 2.79 (dd, J ) 4.6,
9.2 Hz, 1H), 3.04 (dd, J ) 6.2, 10.9 Hz, 1H), 3.05 (s, 3H), 3.18 (m,
1H), 3.21 (s, 3H), 4.16 (m, 1H), 4.17 (d, J ) 3.0, 1H), 4.40 (m, 1H),
4.46 (t, J ) 4.2 Hz, 1H), 4.59 (dd, J ) 8.9, 10.6 Hz, 1H), 5.37 (d, J
) 9.5 Hz, 1H), 5.60 (dd, J ) 8.9, 15.5 Hz, 1H), 6.01 (d, J ) 15.6 Hz,
1H), 6.90 (q, J ) 7.2 Hz, 1H), 7.20-7.31 (m, 5H), 7.35 (m, 2H), 7.70
(dd, J ) 1.6, 7.5 Hz, 1H), 8.60 (s, 1H); IR (thin film) 2924, 1734,
1458, 656 cm-1; HRMS (FAB, NBA/NaCl) found 790.3967 (M +
Na)+, calcd for C40H57NO10Na 790.400313; [R] -51 (c 0.0009, CD3-
OD).
cyclo (2S,3S,8S,9S,4E,6E,4′R,2′′R,3′′R,2′′′S,3′′′R,2′′′′S)-3-amino-
9-methoxy-2,6,8-trimethyl-4,6-decadienoyl-4′-benzyloxycarbonyl-
amino-5′-methoxycarbonylpentanoyl-3′′-benzyloxy-2′′-(N)-methyl-
aminobutanoyl-3′′′-amino-4′′′-methoxycarbonyl-2′′′methylbutanoyl-
2′′′′amino-3′′′′-methylbutanamide. Pentapeptide 1 (0.024 g, 0.025
mmol) was dissolved in 1 mL of TFA and stirred for 60 min over
which time the appearance changed from colorless to faint orange. It
was then concentrated by high vacuum and azeotroped from toluene
(2 mL) affording a white solid.
The pentapeptide amino acid was then dissolved in 25 mL of THF
and treated with DIPEA (0.013 mL, 0.075 mmol) followed by HATU
(0.014 g, 0.075 mmol). The slightly cloudy solution was stirred
overnight, then partitioned between water (10 mL), brine (5 mL), and
ethyl acetate (20 mL). The layers were separated and the aqueous phase
extracted twice with ethyl acetate; the combined organic layers were
then dried over MgSO4. After filtration, the organic layers were
concentrated and chromatographed (5 mL of SiO2, 20% acetone/
dichloromethane), then purified by High Performance TLC (using 5%:
5%:90% ethyl acetate/methanol/dichloromethane) affording ca. 5.0 mg
of the desired product as a white solid. 1H NMR (500 MHz, CD3OD)
δ 0.88 (m, 6H), 0.98 (d, J ) 6.7 Hz, 2H), 0.99 (d, J ) 5.7 Hz, 1H),
1.07 (d, J ) 7 Hz, 2H), 1.08 (d, J ) 7.0 Hz, 1H), 1.16-1.25 (m, 6H),
1.60 (s, 3H), 1.97-2.20 (m, 5H), 2.20-2.42 (m, 2H), 2.58 (m, 1H),
2.66 (m, 1H), 2.80 (m, 1H), 2.88 (s, 1H), 3.03 (s, 2H), 3.18-3.25 (m,
3H), 3.20 (s, 1H), 3.21 (s, 2H), 3.70 (s, 3H), 3.72 (s, 3H), 4.00-4.70
(m, 10H), 5.32 (m, 0.3H), 5.41 (m, 1H), 5.60 (dd, J ) 8.6, 15.7 Hz,
0.7H), 5.67 (dd, J ) 8.1, 15.8 Hz, 0.3H), 6.22 (d, J ) 15.6 Hz, 1H),
7.10-7.40 (m, 5H); IR (thin film) 2928, 1738, 1653, 845 cm-1; HRMS
(FAB, NBA/NaCl) found 836.4441 (M + Na)+, calcd for C42H63N5O11-
Na 836.4422; [R] -16 (c 0.0028, CDCl3).
Acknowledgment. Support from the NIH (Grant GM 69674)
is gratefully acknowledged.
Supporting Information Available: 1H and 13C spectra for
all compounds (PDF). This material is available free of charge
via the Internet at http://pubs.acs.org.
JA9811243