On the synthesis of pyrinodemin A. Part 1: The location of the olefin

Article abstract of DOI:10.1016/j.tet.2004.11.051

The elucidation of the structure of the cytotoxic marine sponge alkaloid pyrinodemin A by synthesis is described. Based on the ¹³C NMR spectra of three double bond positional isomers and the natural product, it is concluded the C14′-C15′ isomer

Full text of DOI:10.1016/j.tet.2004.11.051

Tetrahedron 61 (2005) 1127–1140
On the synthesis of pyrinodemin A.
Part 1: The location of the olefin
*
Stuart P. Romeril, Victor Lee, Jack E. Baldwin and Timothy D. W. Claridge
*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
Received 30 September 2004; revised 28 October 2004; accepted 18 November 2004
Available online 10 December 2004
Abstract—The elucidation of the structure of the cytotoxic marine sponge alkaloid pyrinodemin A by synthesis is described. Based on the
13C NMR spectra of three double bond positional isomers and the natural product, it is concluded the C140–C150 isomer best represents the
true structure of pyrinodemin A. In addition, the structural assignment of pyrinodemin C is evaluated.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
within the research group, we communicated the synthesis
of three double bond positional (D-) isomers (1, 2, 3) of
pyrinodemin A (Fig. 1).6,7 The interesting structure of the
natural product has attracted the attention of others and
synthetic studies have also been reported by both the Snider
group8 and more recently Morimoto et al.9 Herein we
describe in full the syntheses and characterisation of these
three molecules and give our rationalisation for the true
identity of the natural product.
The bioassay-guided isolation of new compounds from
marine sponges has led to the discovery of a diverse array of
important biologically active alkaloids.1 They are usually
obtained in very small quantities, which makes accurate
structural determination challenging, as attested by the
instances of structural revisions in the literature.2 With the
unfeasible or unacceptable possibility of harvesting signifi-
cant quantities from the natural source, it often falls to the
synthetic chemist to confirm or revise the structure of these
natural products.3
It was proposed that structure 1 could be biosynthetically
formed via intramolecular cycloaddition of alkenyl-nitrone
4 (Scheme 1). This nitrone can be derived from the
condensation of aldehyde 5 with hydroxylamine 6, which
in turn can be derived from aldehyde 7, therefore the
proposed structure of pyrinodemin A can be assembled from
two 3-alkylpyridine aldehydes in a biomimetic synthesis.
The retrosynthetic strategy towards aldehyde 5 (correspond-
ing to the left-hand half common to all pyrinodemins)
involved installation of the 3-alkylpyridine moiety using
lithiated 3-picoline (Scheme 2). The alkyl chain derives
from two further sections, a protected alkynol and an a,u-
dibromoalkane to act as electrophile. The modular nature of
the convergent synthesis towards 1 allows the individual
preparation of the left-hand and the right-hand sides, and
thus potentially the synthesis of all the pyrinodemin
alkaloids.
Pyrinodemin A was isolated from an unidentified marine
sponge Amphimedon sp. collected off Nakijin, Okinawa,
Japan by Kobayashi and co-workers.4 The natural product
exhibited cytotoxicity against murine leukaemia L1210
(IC50Z0.058 mg/mL) and KB epidermoid carcinoma cells
(IC50Z0.5 mg/mL) in vitro, and the structure was proposed
to be 1 based on electron impact mass spectrometry (EIMS)
and NMR correlations. Although macrocyclic and oligo-
meric 3-alkylpyridines have been isolated,1 the cis-cyclo-
pent[c]-isoxazolidine structural motif is unique to the
pyrinodemin family of alkaloids. Pyrinodemin A was
isolated along with pyrinodemins B–D, cytotoxic bis-3-
alkylpyridines containing the same bicyclic ring system
showing minor structural variations in the right-hand side
chain, and three monomeric 3-alkylpyridine alkaloids.5
1.1. Synthesis of aldehyde 5
As part of our ongoing studies into marine sponge alkaloids
Commercially available 5-hexyn-1-ol 8 was protected as its
tert-butyldiphenylsilyl ether 9 using tert-butyldiphenyl-
chlorosilane and imidazole in 96% yield (Scheme 3).
Deprotonation of 9 with n-butyllithium followed by
Keywords: Sponge; Pyrinodemin; Alkaloids; Nitrone; EIMS.
* Corresponding authors. Tel.: C44 1865 275693; fax: C44 1865 275632;
e-mail addresses: victor.lee@chem.ox.ac.uk;
jack.baldwin@chem.ox.ac.uk
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.11.051

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S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
Figure 1. The three isomers of pyrinodemin A synthesised in this work.
Scheme 1. Retrosynthetic analysis of pyrinodemin A isomers 1, 2 and 3. For 1, 4, 6, 7 RZPy(CH2)8 and R0Z(CH2)2HC]CH(CH2)9Py; for 2, 23, 22, 5 R0Z
(CH2)3HC]CH(CH2)8Py; for 3, 36, 25, 24 R0Z(CH2)4HC]CH(CH2)7Py.
addition of the acetylide anion to an excess of 1,7-
dibromoheptane (prepared from 1,7-heptanediol and conc.
HBr at reflux)10 in 1,3-dimethyl-3,4,5,6-tetrahydro-2-(1H)-
pyrimidinone (DMPU)11 gave 10 in 68% yield along with
recovered starting material and dialkyation product (Section
1.5). Lindlar semi-hydrogenation revealed the Z-alkene 11
in 94% yield.12 Displacement of the primary bromine using
lithiated 3-picoline (generated using LDA in THF/DMPU)13
gave 12 in 63% yield. Due to concerns over the work up and
purification of the polar alcohol 13 in the presence of the
tetra-n-butyl ammonium fluoride cation, ammonium
fluoride in methanol14 was used in preference to TBAF,
and the desilylation proceeded in 97% yield. Oxidation
using 2-iodoxybenzoic acid (IBX) in DMSO and THF
delivered aldehyde 5 in 92% yield.15
1.2. Synthesis of aldehyde 7
The synthesis commenced with the protection of the
homologous 4-pentyn-1-ol 14 as its silyl ether 15 in 93%
yield (Scheme 3). Deprotonation, followed by alkylation
with excess 1,8-dibromooctane delivered 16 in 77% yield,
which was subjected to Lindlar hydrogenation to give
alkene 17 in 97% yield. Treatment with lithiated 3-picoline
produced alkylpyridine 18 in 59% yield, deprotection with
ammonium fluoride gave alcohol 19 in 97% yield, and
subsequent IBX oxidation afforded the aldehyde 7 in 93%
yield.
1.3. Synthesis of the C160–C170 isomer of pyrinodemin A
(1)
With both aldehyde components in hand, the next step
involved the biomimetic coupling of both aldehydes with a
molecule of hydroxylamine. Aldehyde 7 was condensed
Scheme 2. Retrosynthetic analysis of aldehyde 5.

S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
1129
Scheme 3. Synthesis of aldehydes 5 and 7. Reagents and conditions: (a) TBDPSCI, imidazole, THF, 96% for 9, 93% for 15; (b) n-BuLi, THF, then
Br(CH2)yC3Br, DMPU, 68% for 10, 77% for 16; (c) Lindlar catalyst, quinoline, H2, PhH, 94% for 11, 97% for 17; (d) 3-Picoline, LDA, THF, DMPU, 63% for
12, 59% for 18; (e) NH4F, MeOH, 97% for 13, 97% for 19; (f) IBX, DMSO, THF, 92% for 5, 93% for 7.
Scheme 4. Synthesis of isomer 1. RZ(CH2)8Py, R0Z(CH2)9Py. Reagents and conditions: (a) NH2OH$HCl, MeOH, NaOAc, 93%; (b) (i) NaCNBH3, MeOH,
pH 3; (ii) 5, Na2SO4, DCM, 89% over two steps; (c) PhH, reflux, 41%.
with hydroxylamine hydrochloride using sodium acetate as
base in methanol to give oxime 20 in 93% yield (Scheme 4).
The product was identified as a ca. 1:1 mixture of Z:E
oxime isomers from 1H NMR, however this ratio was
inconsequential as subsequent reduction with sodium
cyanoborohydride delivered hydroxylamine 6. 4-Ene-1-
hydroxylamines have been shown to be thermally
unstable,16 decomposing via a reverse-Cope mechanism to
give secondary hydroxylamines,17 so the product was
condensed immediately (without purification) with 1 equiv
of aldehyde 5 in the presence of sodium sulphate to afford
nitrone 4 in 89% yield over two steps. Heating nitrone 4
under reflux in benzene at high dilution (to promote
intramolecular cyclisation) delivered a less-polar product
in 41% yield. Mass-spectrometry indicated that the product
was isomeric with nitrone 4 and 1H NMR showed the
disappearance of the distinctive triplet of the nitrone proton
indicating that cyclisation had taken place.
C-170; HSQC-TOCSY and DQF-COSY confirmed the ring
sizes in the bicyclic core; and 1D DPFGSE-NOESY19 (tmZ
400 ms) confirmed the cis-relationship of H-15 and the ring-
junction protons H-16 and H-20. The product was thus
assigned unambiguously as the C-160, C-170 isomer of
pyrinodemin A (1).20
The cyclised product of the reaction could be potentially any
of four isomers of 1 (cycloaddition of the nitrone with either
olefin and with either regioselectivity), therefore high-field
(500 MHz) NMR experiments were required to confirm the
structure (Fig. 2). HSQC-TOCSY18 (tmZ80 ms) indicated
that C-200 correlates with H-190, H-180 and H-170 (in the
olefinic region), thus locating the olefin between C-160 and
Figure 2. Structural determination of structure 1.

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S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
Scheme 5. Synthesis of isomer 2. RZ(CH2)8Py, R0Z(CH2)8Py. Reagents and conditions: (a) NH2OH$HCl, MeOH, NaOAc, 84%; (b) (i) NaCNBH3, MeOH,
pH 3; (ii) 5, Na2SO4, DCM, 71% over two steps; (c) PhH, heat, 63%.
The spectra of synthetic 1 and pyrinodemin A were similar
and analysis of the 1H and 13C NMR spectra suggested that
the gross structure (i.e., the central 5,5-bicyclic core and the
3-alkylpyridine chains) had been correctly assigned,
however the olefinic and allylic regions showed some
anomalies. Kobayashi reported that both the olefinic
carbons and the allylic carbons appeared as coincidental
peaks at 129.3 and 27.1 ppm, respectively. For synthetic 1
the olefinic carbons (C-160 and C-170) occur as distinct
peaks at 129.2 and 130.3 ppm (DdZ1.1), and the allylic
carbons C-150 and C-180 at 27.1 and 24.8 ppm, respectively.
The typical allylic carbon chemical shift for an E-olefin is
ca. 31 ppm, and that for a Z-olefin is ca. 27 ppm.21 Hence
the observed spectral discrepanci0es did not originate from a
mistakenly assigned C-160-C17 doub0le bond geometry.
The chemical shift deviation of C-18 can be attributed
to the proximity of the isoxazolidine nitrogen exerting a
g-shielding effect. Based on these data it was concluded that
the proposed structure for the natural product was incorrect:
structure 1 was not pyrinodemin A but rather a D-isomer. It
was also concluded that the olefin must lie towards the
centre of the chain, away from the isoxazolidine in a more
magnetically symmetrical environment.
sodium acetate to produce oxime 21 in 84% yield
(Scheme 5). Reduction with sodium cyanoborohydride
gave hydroxylamine 22 that was immediately condensed
with a further equivalent of aldehyde 5 to form nitrone 23 in
71% yield over two steps. Thermal cyclisation of this
nitrone gave a less-polar product in 63% yield: the structure
of which was established as 2 by the same NMR
experiments indicated above. The 1H NMR and EIMS
spectra were very similar to those of pyrinodemin A,
however the 13C NMR spectrum did not show coincidental
olefinic or allylic carbon peaks: the olefinic carbons
resonated at dC 130.0 and 130.4 (DdZ0.4) and the allylic
carbons at dC 27.0 and 27.1. In spite of the apparent
similarities between pyrinodemin A and 2, we observed two
distinct and fully resolved peaks for both the allylic and
olefinic carbons. Therefore, the critical regions of the
spectra were inconsistent and we concluded that the
C150–C160 isomer 2 was not the correct structure for
pyrinodemin A.
Independently and concurrently, Snider and Shi prepared
structures 1 and 2. Their results were identical (within a
small experimental error) to those presented here (Table 1).
They observed, but did not rationalise the non-coincident
olefinic peaks and concluded that the double bond position
in natural pyrinodemin A was at C150–C160. They described
isomer 2 as ‘probably’ the structure of pyrinodemin A.8
1.4. Synthesis of the C150–C160 isomer of pyrinodemin A
(2)
The requirement for the olefin to reside further from the
isoxazolidine would be satisfied by structure 2, which
derives from 2 equiv of aldehyde 5 (Scheme 1). This isomer
is a more plausible candidate from a biosynthetic perspec-
tive, as it involves the coupling of two identical aldehyde
units. This hypothesis was further encouraged by the
isolation of oxime 21 from the same sponge extract as
pyrinodemin A,5 and we speculated that this oxime could be
a biosynthetic precursor to pyrinodemin A. The proposed
synthesis was put into practice and hydroxylamine hydro-
chloride was condensed with aldehyde 5 in the presence of
1.5. Synthesis of aldehyde 24
We concluded that the magnitude of the difference in the
chemical shifts of the olefinic carbons diminished as the
olefin was moved further away from the central0 core, and
therefore, set about the synthesis of the C140–C15 isomer of
pyrinodemin A (3) This isomer can be derived from
aldehyde 5 (as prepared above) and aldehyde 24 (via
hydroxylamine 25) according to our modular strategy
(Scheme 1). It was envisaged that aldehyde 24 could be
Table 1. Comparison of the assignments of Snider and this work with pyrinodemin A
Isomer
dC Olefinic C (ppm)
Dd (ppm)
dC Allylic C (ppm)
Pyrinodemin A4
129.3 (2C)
0
27.1 (2C)
24.8, 27.1
24.9, 27.0
27.0, 27.1
27.1, 27.2
C160–C170 1 (Baldwin)6
C160–C170 1 (Snider)8
C150–C160 2 (Baldwin)6
C150–C160 2 (Snider)8
129.2, 130.3
129.3, 130.3
129.5, 129.9
129.6, 130.0
1.1
1.0
0.4
0.4

S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
1131
Scheme 6. Synthesis of aldehyde 24. Reagents and conditions: (a) HBr(aq.), toluene, reflux, 60%; (b)TBDPSCl, imidazole, THF, 96%; (c) LiChCH$eda,
DMSO, THF, 84%; (d) n-BuLi, THF, DMPU, then Cl(CH2)6I, 85%; (e) Lindlar catalyst, H2, quinoline, benzene, 83%; (f) NaI, acetone, reflux, 95%; (g) LiBr,
butanone, reflux, 96%; (h) 3-picoline, LDA, DMPU, THF, 79% for 31a, 63% for 31b, 36% for 31c; (i) NH4F, MeOH, 95%; (j) IBX, DMSO, THF, 93%.
assembled using a similar synthetic route to the isomeric
aldehydes 5 and 7.
the desilylation was avoided and the terminal alkyne 30 was
delivered in 84% yield.
The corresponding alkynol (6-heptyn-1-ol) was not com-
mercially available, so 5-bromopentan-1-ol 26 (obtained
from 1,5-pentanediol 27 by selective monobromination)22
was protected as its tert-butyldiphenylsilyl ether 28 in 96%
yield, before conversion to the terminal alkyne (Scheme 6).
The displacement of the bromide with lithium acetylide
(stabilised as the ethylenediamine complex) at room
temperature in DMSO was attempted,23 however the yields
were poor and inconsistent. Purification of the crude
revealed the presence of tert-butyldiphenylsilyl ethyne
29,24 leading us to speculate that desilylation occurred due
to the inefficient heat dissipation in the viscous liquid
resulting in localised exotherms. In order to reduce the
reaction temperature and decrease the viscosity, THF was
added as a co-solvent. With precise temperature control at
K5 8C and a slow addition of alkylbromide to the acetylide,
In the syntheses of the two previous fragments (aldehydes 5
and 7), alkylation of a lithiated acetylene with a dibromide
had been a key reaction. The starting material and the two
products (mono and dialkylation of the dibromide) all had
very similar Rf values and therefore the purification of the
desired product was technically demanding. Although the
reaction conditions were optimised, a small yet significant
amount of dialkylation was observed (Table 2). It was
decided to employ the commercially available 1-chloro-6-
iodohexane instead, which gave a faster more efficient
reaction. The alkylation was completely regioselective and
no dialkylation product was detected. Deprotonation of
acetylene 30 with n-butyllithium in THF/DMPU followed
by addition of 2 equiv of 1-chloro-6-iodohexane afforded 31
in 85% yield, and subsequent Lindlar hydrogenation
produced alkene 32a in 83% yield.
Table 2. Comparison of alkyne-anion alkylations
Alkynol
Electrophile
Alkynol (%)
4
Product (%)
77
Dialkylation (%)
4
Br(CH2)8Br
4 equiv
15
Br(CH2)7Br
4 equiv
9 (est.)a
5 (est.)a
68
85
4
9
I(CH2)6Cl
2 equiv
—
29
a Yields of alkynol were estimated from the 1H NMR of mixed fractions.
Table 3. Comparison of strategies towards 3-alkylpyridine 32
Sequence X
Yield of Finkelstein reaction (%)
Yield of displacement reaction (%)
Overall yield (%)
Cl/I/CH2Py
Cl/Br/CH2Py
Cl/CH2Py
95
96
—
36
63
79
34
60
79

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S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
Scheme 7. Synthesis of isomer 3. RZ(CH2)8Py, R0Z(CH2)7Py. Reagents and conditions: (a) NH2OH$HCl, MeOH, NaOAc, 90%; (b) (i) NaCNBH3, MeOH,
pH 3; (ii) 5, Na2SO4, DCM, 79% over two steps; (c) PhH, heat, 87%.
It had been proposed to transform the alkylchloride 32a to
the alkyliodide 32c via a Finkelstein reaction25 to improve
the yield of the subsequent nucleophilic substitution with
lithiated 3-picoline. Although halogen exchange was
efficient, the yield of the subsequent SN2 displacement
reaction by lithiated 3-picoline was poor, proceeding at best
in 36% yield, and typically in the range 10–20% yield. This
was surprising given the efficient conversion observed by
others for this reaction on similar substrates.12,26 Conver-
sion of 32a to the alkylbromide 32b and subsequent lithiated
3-picoline displacement gave moderate yields, consistent
with an alkylation of this nature (vide supra), however using
the original alkylchloride 32a as a substrate the transform-
ation proceeded cleanly in good yield, providing a superior
route towards 33 (Table 3). Ammonium fluoride desilyl-
ation of 33 was achieved in 95% yield and subsequent
oxidation with IBX in DMSO/THF delivered aldehyde 24 in
93% yield.
sample of the natural product using more reliable physical
methods.
2. Morimoto’s results
Morimoto et al. recently prepared isomers 2, 3 and the
C130–C140 isomer of pyrinodemin A, and based on the 13C
NMR Dd values shown in Table 4, concluded that isomer 3
was the correct structure of pyrinodemin A.9 Although the
absolute 13C NMR values do vary slightly, the Dd values
appear to be highly consistent between 0the synthetic groups.
Morimoto’s results rule-out the C13 –C140 isomer as a
candidate for the structure of pyrinodemin A, however it is
curious that this isomer with the olefin in the exact centre of
the chain should have such a high Dd value. The result was
not rationalised by the authors, however is presumably due
to a conformational effect0 and it follows that other D-
isomers (e.g., the C120–C13 isomer) could possess spectro-
scopic properties indistinguishable from the natural product.
1.6. Synthesis of the C140–C150 isomer of pyrinodemin A
(3)
Table 4. Morimoto’s data in comparison to pyrinodemin A
Isomer
dC Olefinic C
(ppm)
Dd
dC Allylic C
(ppm)
Condensation of aldehyde 24 with hydroxylamine hydro-
chloride in the presence of sodium acetate in methanol gave
oxime 35 in 90% yield (Scheme 7) Reduction with sodium
cyanoborohydride in methanol at pH 3 gave hydroxylamine
25 and subsequent condensation with aldehyde 5 afforded
nitrone 36 in 79% yield over two steps. Thermal cyclisation
of nitrone 36 at high dilution delivered the C140–C150
isomer 3 in 87% yield. The compound was fully
characterised:27 the olefinic carbons were observed as two
partially resolved peaks at 129.90 and 129.92 ppm (Dd
0.02),28 the allylic carbons exhibited a single resonance at
27.1 ppm and the signal distribution between 20 and 40 ppm
appeared to be a better match with the published data than
the two isomers previously prepared. As the available 13C
assignments for pyrinodemin A have been reported to only
one decimal place, we conclude that this isomer is
indistinguishable from the natural product. It is necessary
to qualify that we cannot be absolutely certain that 3 is the
true structure of pyrinodemin A until all other possible
isomers have been discounted by synthesis or preferably by
the re-isolation and characterisation of a pure authentic
Pyrinodemin A
C150–C160 (2)
C140–C150 (3)
C130–C140
129.3 (2C)
0
27.1 (2C)
129.6, 130.0
129.77, 129.79
129.6, 129.9
0.4
0.02
0.3
Unassigned
Unassigned
Unassigned
Data taken from Ref. 9.
3. EIMS analysis
Kobayashi assigned the location of the olefin in pyrino-
demin A based on the EIMS fragmentation pattern shown in
Figure 3.4 The use of EIMS alone to ascertain the position of
the olefin in an aliphatic chain is not a reliable technique
(vide supra). It is known that alkene ions show a tendency to
isomerise under EIMS conditions, and that the spectra of
D-isomers are similar irrespective of double bond
position.29 The standard method to locate an olefin in an
aliphatic chain is to functionalise the olefin, then examine
the derivative using chemical ionisation.30,31 More recently,
collision activated decomposition in tandem mass spec-
trometry has been applied to natural products, without the

S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
1133
Figure 3. EIMS fragmentation pattern of the proposed structure of pyrinodemin A taken from Ref. 4. The fragments assigned as cleavage adjacent to the olefin
are highlighted.
need for derivitisation.32,33 In spite of this, the EIMS
spectrum is the only other piece of indicative data available
from the natural product, and it would be inadequate to
neglect an analysis.
73% yield. High-resolution NMR experiments showed the
presence of the 5,5-bicyclic isoxazolidine confirming the
structure of the product as 37.
The EIMS spectrum of any pyrinodemin A isomer is
complicated by a contribution to intensity of peaks at
m/z%190 from fragmentation of the left-hand side of the
molecule. Using the saturated analogue as a reference, it
was possible to identify those peaks arising from the
fragmentation of the right-hand side, and compare the
intensities of these peaks for the different isomers (Table 5).
Kobayashi’s EIMS spectrum of pyrinodemin A shows an
(MC2)C peak at a higher intensity to the (MC1)C isotope
peak.34 This observation strongly suggested that the natural
sample was contaminated with the dihydro analogue of
pyrinodemin A 37, possibly a natural product in its own
right, inseparable from pyrinodemin A by the HPLC method
used. In order to identify the contaminant peaks, and to
provide a reference sample for the unsaturated isomers,
analogue 37 was synthesised. It was hoped that the EIMS
spectra of 37 and the three isomers already prepared would
enable us to conduct a proper analysis of the EIMS data of
the natural product.
None of the EIMS spectra of the synthetic samples m0atched
exactly that 0of the0 natural product but both the C15 –C160
and the C14 –C15 isomers (2 and 3) showed a reasonable
fit. It should be noted that the natural product and synthetic
samples were recorded on different instruments, which
generates an experimental error. This is exemplified by the
EIMS spectra of the C150–C160 isomer (2) recorded by
Snider, Morimoto and ourselves where even significant
peaks show a three-fold variation in intensity (e.g., m/z 231:
Snider, 15%;8 Morimoto, 48%;9 this work, 29%). Given
the experimental error inherent in this comparison, we
conclude that anything more than this broad analysis is
unjustified.
The synthesis of 37 commenced from unsaturated oxime 35
which was selectively hydrogenated over palladium (5% on
carbon) to give oxime 38 in 94% yield and subsequently
reduced to the hydroxylamine 39 with sodium cyano-
borohydride in 74% yield (Scheme 8). Condensation with
aldehyde 5 gave nitrone 40 in 67% yield, and cyclisation
produced the saturated analogue of pyrinodemin A (37) in
Scheme 8. Synthesis of saturated analogue 35. RZ(CH2)8Py, R00Z(CH2)12Py. Reagents and conditions: (a) Pd (5% on C), H2, MeOH, 94%; (b) (i) NaCNBH3,
MeOH, pH 3, 74%; (ii) 5, Na2SO4, DCM, 67% over two steps; (c) PhH, heat, 73%.
Table 5. EMIS data for pyrinodemin A and synthetically prepared D-isomers
C160–C170
isomer (1)
C150–C160
isomer (2)
C140–C150
isomer (3)
C130–C140 isomer
(Morimoto)a
m/z
Pyrinodemin Aa
231
244
259
270
285
20
25
10
17
42
2, (232) 6
16
15, (258) 40
11
43
29
43
6
18
49
30
18
27
23
82
0
12
37
17
75
a Data taken from Ref. 9.

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S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
Figure 4. The EIMS fragmentation peaks used to assign the position of the olefin in pyrinodemin C (taken from Ref. 5).
4. A note on the structure of pyrinodemin C
re-isolated and characterised using unambiguous tech-
niques. Until these 0endea0vours have been undertaken, we
believe that the C14 –C15 isomer (3) should be accepted as
the structure of pyrinodemin A, and we have used this as a
target for the asymmetric synthesis of the natural product.38
In addition, analysis of the EIMS spectrum of pyrinodemin
C also revealed that there may be a fundamental flaw in its
structural assignment.
Pyrinodemin C is a homologue of pyrinodemin A shorter by
one-carbon in the right-hand alkyl chain. The position of the
olefin was deduced by the application of the same EIMS
analytical method (Fig. 4) as for pyrinodemin A (in this case
from fragment ions m/z 190 and 217)35 and assigned three
methylenes from the isoxazolidine nitrogen. The only
published 13C NMR data for this compound are the allylic
carbon chemical shifts (deduced from HMQC cross peaks),
both of which are assigned as dC ca. 27 ppm. The results and
rationalisation presented above suggest that the position of
the olefin has been incorrectly assigned in pyrinodemin C
and that a structural revision may be necessary for this
natural product.
6. Experimental
6.1. General procedures
Proton magnetic resonance spectra were recorded on Bru¨ker
AC200 (200 MHz), Bru¨ker DPX400 (400 MHz), Bru¨ker
DQX400 (400 MHz), Bru¨ker AMX500 (500 MHz), and
Bru¨ker DRX500 (500 MHz), spectrometers at ambient
temperature. Proton spectra assignments are supported by
1H–1H correlations (COSY) and by 1H–13C correlations
(HMQC) where necessary. Chemical shifts (dH) are reported
in parts per million (ppm) and are referenced to the residual
solvent peak. Coupling constants (J) are reported to the
nearest 0.5 Hz. Carbon magnetic resonance spectra were
recorded on Bru¨ker AC200 (50.3 MHz), Bru¨ker DPX400
(100.6 MHz), Bru¨ker DQX400 (100.6 MHz), Bru¨ker
5. Conclusion
Prior to our communication on the synthesis of isomer 3,7
Snider proposed that the observed 13C spectral discrepancy
between natural pyrinodemin A and isomer 2 was unlikely
to be due to the position of the olefin, but instead caused by
concentration, pH or different parameters in the acquisition
of the NMR spectra and maintained that isomer 2 was
probably the correct structure of natural pyrinodemin A.36
Experiments have shown that the olefinic 13C NMR Dd
value of isomer 3 remains unchanged at low concentrations
(1 mg), and furthermore our work on monomeric 3-alkyl-
pyridine alkaloids has demonstrated that the chemical shifts
of the pyridine aromatic protons are very sensitive to the
presence of acid in the solution.37 The spectra of
pyrinodemin A and its synthetic isomers are not consistent
with the presence of acid in the sample. If the olefinic 13C
chemical shifts of (natural) pyrinodemin A were sensitive to
NMR acquisition parameters, then it would be difficult to
explain the consistency of the olefinic Dd13C as observed by
the Baldwin, Morimoto and Snider groups for compounds 1
and 2. In light of the smaller Dd value observed with isomer
3 we believe that the 13C spectral difference between natural
pyrinodemin A and isomer 2 is due to the position of the
olefin rather than the aforementioned factors or parameters.
AMX500
(125.8 MHz),
and
Bru¨ker
DRX500
(125.8 MHz), spectrometers at ambient temperature.
Chemical shifts (dC) are reported in parts per million
(ppm) and are referenced to the residual solvent peak.
Carbon spectra assignments are supported by DEPT or APT
analysis and 13C–1H correlations (HSQC) where necessary.
The 13C spectra of the 5,5-bicyclic isoxazolidine structures
synthesised showed some broad peaks particularly those
proximate to the ring nitrogen. The chemical shift dC of
those assigned from HSQC and HSQC-TOCSY analysis are
indicated with the symbol (z) and are quoted to the nearest
ppm, those not observed using either technique are indicated
as ‘not observed’. Superscript ‘a’ denotes one of a pair of
diastereotopic protons.
Infrared spectra were recorded on a Perkin–Elmer Paragon
1000 Fourier Transform spectrometer between NaCl plates.
Absorption maxima (nmax) of the major peaks are reported
in wavenumbers (cmK1). Low-resolution mass spectra were
recorded using a TRIO-1 GCMS spectrometer, a Micromass
Platform (APCI) spectrometer, Micromass Autospec spec-
trometer (CIC) and a micromass ZAB spectrometer (CIC,
EI). Only molecular ions (MC), protonated molecular ions
(MHC), fragments from molecular ions and other major
peaks are reported. High-resolution mass spectra were
recorded on a Micromass Autospec spectrometer and are
In summary we have synthesised and characterised three
D-isomers of pyrinodemin A. Based on comparisons of the
1H and 13C NMR data wit0h those of the natural product, we
believe that the C140–C15 isomer 3 is the best candidate for
the structure of pyrinodemin A. There may however, be
other isomers possessing spectroscopic properties indis-
tinguishable from pyrinodemin A. In order to ascertain the
true structure of the natural product all possible D-isomers
would have to be synthesised or ideally, an authentic sample

S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
1135
accurate to G10 ppm. Electrospray mass spectra were
recorded on a Waters Micromass LCT spectrometer.
Microanalyses were carried out by Elemental Microanalysis
Limited, and are reported to three significant figures.
Melting points were measured using a Cambridge Instru-
ments GallenTM III hot stage melting point apparatus and
are uncorrected. Thin layer chromatography (TLC) was
performed using Merck aluminium foil backed plates pre-
coated with silica gel 60 F254 (1.05554). Visualisation was
by the quenching of UV fluorescence (lmaxZ254 nm);
staining with 10% w/v ammonium molybdate in 1 M
sulphuric acid, 20% w/v phosphomolybdic acid in ethanol,
3% w/v ninhydrin in 97:3 n-BuOH/AcOH, followed by
heating; or iodine on silica. Retention factors (Rf) are
reported to 2 decimal places. Flash chromatography was
125.6 (2C, Py C-5*), 130.7, 131.9 (2CH, C-160, C-170),
138.4 (2C, Py C-4*), 140.6 (2C, Py C-3*), 148.0, 150.5 (4C,
Py C-2*, C-6*).
dH (500 MHz, CDCl3) 1.22–1.34 (20H, H-9 to H-12, H-90 to
H-140), 1.34–1.49 (4H, m, 0H-13, H-18), 1.49–1.80 (12H, m,
H-8,H-14, H-17, H-19, H-8 , H-190), 1.91–2.16(4H, m, H-150,
H-180), 2.53–2.65 (1H, m, H-200), 2.59 (4H, t, JZ7.7 Hz, H-7,
a
H-70), 2.78–2.87 (2H, m, H-16, H-200 ), 3.41–3.51 (1H, m,
H-20), 4.01–4.08 (1H, m, H-15), 5.28–5.39 (2H, m, H-160,
H-170), 7.16–7.22 (2H, m, Py-H), 7.43–7.50 (2H, m, Py-H),
8.38–8.50 (4H, br, s, Py-H); dC (125.8 MHz, CDCl3) 24.8
(1C, C-180), 26.2, 26.4 (2C, C-17, C-18), 26.9 (1C, C-13),
27.1 (1C, C-150), 27.9, 028.7, 29.0, 29.2, 29.3, 29.4, 29.6
(13C, C-9 to C-14, C-9 to C-140, C-190), 31.0 (2C, C-8,
C-80)0, 32.9 (2C, C-7, C-70), 49.8 (1C, C-16), z57 (1C,
C-20 ), z73 (1C, C-20), z78 (1C, C-15), 123.1 (2C, Py
C-5*), 129.2, 130.3 (2CH, C-160, C-170), 135.6 (2C, Py
C-4*), 137.8 (2C, Py C-3*), 148.0, 149.8 (4C, Py C-2*, C-6*).
˚
performed using ICN silica 32–63, 60 A. All reactions were
carried out under a positive atmosphere of argon at room
temperature unless otherwise specified.
Anhydrous diethyl ether, and THF were obtained by
distillation from sodium/benzophenone ketyl under nitro-
gen, anhydrous DCM was distilled from calcium hydride
under nitrogen. PE refers to the fraction of light petroleum
ether boiling between 40 and 60 8C, and was distilled before
use. Benzene, diisopropylamine, hexane, 3-methylpyridine,
pyridine, triethylamine, and 1,3-dimethyl-3,4,5,6-tetra-
hydro-2(1H)-pyrimidinone (DMPU) were distilled from
calcium hydride under argon or reduced pressure and stored
6.1.2. Preparation of the C150–C160 isomer of pyrino-
demin A 2. A solution of nitrone 22 (0.142 g, 0.25 mmol) in
benzene (100 mL) was heated at reflux for 18 h. The solvent
was removed in vacuo to afford the crude product which was
purified by flash chromatography (100% EtOAc) to yield 2
(0.089 g, 0.16 mmol, 63%) as a colourless oil; RfZ0.30
(100% EtOAc); nmax/cmK1 (thin film) 2928 (s), 2855 (s),
1575 (m), 1478 (m), 1465 (m), 1422 (m), 1337 (w), 1189
(w), 1026 (m), 793 (w), 714 (s); m/z Probe APCIC (NH3)
574.6 (MHC, 100%); m/z Probe EIMS (Cve ion) 572 (2%),
555 (3%), 365 (55%), 355 (10%), 327 (8%), 315 (4%), 301
(9%), 285 (49%), 270 (18%), 259 (6%), 244 (43%), 231
(29%), 220 (38%), 204 (5%), 190 (21%), 176 (37%), 162
(16%), 148 (18%), 134 (13%), 120 (26%), 106 (100%), 93
(97%); HRMS found MHCZ574.4721, C38H60N3O
requires 574.4736; dH (500 MHz, CDCl3) 1.28–1.42 (18H,
m, H-9 to H-12, and H-90 to H-130), 1.34 (1H, m, H-13),
1.44 (2H, m, H-180), 1.46 (1H, m, H-18), 1.47 (1H, m, H-13a0),
1.49 (1H, m, H-17), 1.49 (1H, m, H-14), 1.59 (2H, m, H-19 ),
1.59 (1H, m, H-14a), 1.64 (4H, m, H-8, H-80), 1.69 (1H, m,
H-17a), 1.70 (1H, m, H-18a), 1.72 (1H, m, H-19), 1.80 (1H,
m, H-19a), 2.04 (2H, m, H-140), 2.07 (2H, m, H-170), 2.60–
2.72 (1H, m, H-200), 2.60 (4H, t, JZ7.7 Hz, H-7, H-70),
˚
over 4 A molecular sieves under argon until used. Methanol
˚
was distilled from 4 A molecular sieves under reduced
˚
pressure and stored over 4 A molecular sieves under argon
˚
until used. Dimethyl sulphoxide was dried over 4 A
molecular sieves. Imidazole was dried under vacuum before
use.
6.1.1. Preparation of the C160–C170 isomer of pyrino-
demin A 1. A solution of nitrone 4 (0.286 g, 0.50 mmol) in
benzene (250 mL) was heated at reflux for 24 h. The solvent
was removed in vacuo, and the crude product was purified
by flash chromatography (100% EtOAc) to yield 1 (0.118 g,
0.21 mmol, 41%) as a colourless oil; RfZ0.13 (100%
EtOAc); nmax/cmK1 (thin film) 2927 (s), 2854 (s), 1574 (m),
1478 (m), 1464 (m), 1422 (m), 1026 (m); m/z Probe APCIC
(NH3) 574 (MHC, 100%); HRMS found 574.4735,
C38H60N3O requires 574.4736; m/z Probe EIMS (Cve
ion) 574 (1%), 556 (2%), 530 (9%), 515 (6%), 365 (28%),
355 (10%), 327 (9%), 315 (5%), 299 (15%), 285 (43%), 270
(11%), 259 (15%), 258 (40%), 244 (16%), 232 (6%), 231
(2%), 220 (20%), 218 (11%), 204 (6%), 190 (28%), 176
(44%), 162 (17%), 148 (20%), 136 (20%), 134 (14%), 120
(27%), 106 (100%), 93 (89%); dH (500 MHz, CD3OD)
1.27–1.37 (24H, H-8 to H-12, H-80 to H-140), 1.33, 1.42
(2H, m, H-13), 1.46 (2H, m, H-18), 1.48 (1H, m, H-17), 1.50
(2H, m, H-14), 1.57 (2H, m, H-190), 1.63 (1H, m, H-17),
1.65,01.80 (2H, m, H-19), 2.03 (2H, m, H-150), 2.10 (2H, m,
H-18 ),2.65(1H, m,H-200), 2.65(4H,t, JZ7.5 Hz, H-7,H-70),
a
2.78–2.89 (2H, m, H-16, H-200 ), 3.40–3.51 (1H, m, H-20),
4.00–4.08 (1H, m, H-15), 5.28–5.38 (2H, m, H-150, H-160),
7.14–7.21 (2H, m, Py-H), 7.43–7.50 (2H, m, Py-H), 8.36–
8.49 (4H, br, s, Py-H); dC (125.8 MHz, CDCl3) 26.2, 26.3
(2C, C-17, C-18), 26.9 (1C,0 C-13), 27.0 (1C, C-170), 27.1
(1C, C-140), 27.4 (1C, C-18 ), 27.7 (1C, C-190), 28.6 (1C,
C-14), 29.0, 29.1,029.2, 29.3, 29.5, 29.6,0 (9C, C-9 to C-12
and0 C-90 to C-13 ), 31.0 (2C, C-8, C-8 ), 32.9 (2C, C-07,
C-7 ), 34.1, (1C, C-19), 49.8 (1C, C-16), 56.8 (1C, C-20 ),
72.5 (1C, C-20), 77.6 (1C, C-15), 123.1 (2C, Py C-5*),
129.5, 129.9 (2CH, C-150, C-160), 135.7 (2C, Py C-4*),
137.9 (2C, Py C-3*), 147.0, 149.8 (4C, Py C-2*, C-6*).
a
2.85-2.95 (2H, m, H-16, H-200 ), 3.50–3.60 0(1H, m, H-20),
6.1.3. Preparation of 1-(tert-butyldiphenylsilyloxy)-5-
bromopentane 28. To a solution of 5-bromopentan-1-ol
26 (3.00 g, 18.0 mmol) and imidazole (3.06 g, 45.0 mmol)
in THF (40 mL) at 0 8C was added tert-butyldiphenyl-
chlorosilane (5.20 mL, 19.9 mmol) dropwise. The mixture
was allowed to warm to room temperature over 3 h, then
was quenched with NH4Cl(aq) (sat., 90 mL) and extracted
4.10–4.20 (1H, m, H-15), 5.40 (2H, m, H-17 , H-160), 7.30–
7.40(2H, m, Py-H), 7.65–7.75 (2H, d, JZ8.0 Hz, Py-H), 8.30–
8.40 (4H, br, s, Py-H); dC (125.8 MHz, CD3OD) 26.4, 27.8,
27.9, 28.7, 29.38, 30.8, 30.9, 31.0, 31.1, 31.2, 31.3, 31.4
(18CH2), 32.8, 34.3 (4C, C-13, C-14, C130, C140), 51.5 (1C,
C-16), 58.1 (1C, C-200), 74.5 (1C, C-20), 79.6 (1C, C-15),

1136
S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
with 1:1 Et2O:PE (4!30 mL). The organic phases were
washed with NaCl(aq) (sat., 30 mL) and dried over Na2SO4.
Removal of solvent in vacuo afforded the crude product
which was purified by flash chromatography (15% benzene,
85% PE) to yield 28 (6.96 g, 17.2 mmol, 96%) as a
solution was stirred for 3 h from K78 8C to room
temperature. The mixture was quenched with H2O
(25 mL) and NH4Cl(aq) (sat., 25 mL), then extracted into
EtOAc (4!60 mL). The organic phases were washed with
NaCl(aq) (sat., 50 mL) and dried over Na2SO4. Removal of
solvent in vacuo afforded the crude product which was
purified by flash chromatography (15% toluene, 85% PE) to
yield 31 (1.24 g, 2.64 mmol, 85%) as a colourless oil; RfZ
0.13 (15% toluene, 85% PE); nmax/cmK1 (thin film) 3071
(m), 2933 (s), 2858 (s), 1590 (w), 1472 (m), 1462 (m), 1428
(s), 1389 (w), 1361 (w), 1112 (s), 1009 (w), 824 (m), 740
(w), 702 (s); m/z Probe CIC (NH3) 469.4 (M[35Cl]HC,
100%), 411.3 (21%), 213.1 (72%), 178.9 (29%); HRMS
found MHCZ469.2698, C29H42OSi35Cl requires 469.2693;
dH (200 MHz, CDCl3) 1.15 (9H, s, C(CH3)3), 1.40–1.75
(12H, m, H-2 to H-4 and H-9 to H-11), 1.75–1.90 (2H, m,
H-12), 2.15–2.30 (4H, m, H-5, H-8), 3.58 (2H, t, JZ7.0 Hz,
H-13), 3.78 (2H, t, JZ6.0 Hz, H-1), 7.40-7.55 (6H, m,
Ph-H), 7.70–7.85 (4H, m, Ph-H); dC (50.3 MHz, CDCl3)
18.8 (2C, C-5, C-8), 19.3 (1C, C(CH3)3), 25.2, 26.5 (2CH2),
27.0 (3C, C(CH3)3), 28.1, 29.0 (3CH2), 32.2, 32.6 (2C, C-2,
C-12), 45.0 (1C, C-13), 63.9 (1C, C-1), 80.0, 80.3 (2C, C-6,
C-7), 127.7 (4CH, Ph), 129.6 (2CH, Ph), 134.1 (2C, C-Si),
135.6 0 (4CH, Ph).
colourless oil; RfZ0.18 (15% benzene, 85% PE); nmax
/
cmK1 (thin film) 3071 (m), 2932 (s), 2858 (s), 1590 (w),
1473 (m), 1428 (s), 1390 (w), 1362 (w), 1253 (w), 1189 (w),
1112 (s), 1008 (w), 823 (m), 740 (m), 702 (s); m/z Probe
CIC (NH3) 424.2 (M[81Br]NHC4 , 100%), 407.2
(M[81Br]HC, 84%); HRMS found MHCZ405.1249, C21-
H30OSi79Br requires 405.1249; microanalysis found C,
62.3; H, 7.44; C21H29OSiBr requires C, 62.2; H, 7.21; dH
(200 MHz, CDCl3) 1.20 (9H, s, C(CH3)3), 1.55–1.80 (4H,
m, H-2, H-3), 1.95 (2H, quin., JZ7.0 Hz, H-4), 3.45 (2H, t,
JZ7.0 Hz, H-5), 3.80 (2H, t, JZ5.5 Hz, H-1), 7.40–7.57
(6H, m, Ph-H) 7.75–7.85 (4H, m, Ph-H); dC (50.3 MHz,
CDCl3) 19.3 (1C, C(CH3)3), 24.6 (1C, C-3), 27.0 (3C,
C(CH3)3), 31.7 (1C, C-2), 32.6 (1C, C-5), 33.9 (1C, C-4),
63.6 (1C, C-1), 127.7 (4CH, Ph), 129.7 (2CH, Ph), 134.0
(2C, ArC-Si), 135.7 (4CH, Ph).
6.1.4. Preparation of 1-(tert-butyldiphenylsilyloxy)-hept-
6-yne 30. To a suspension of lithium acetylide-ethylene
diamine complex (2.44 g, 90%, 23.9 mmol, 1.85 equiv) in
DMSO (15 mL) and THF (5 mL) at K5 8C, was added a
solution of 1-(tert-butyldiphenylsilyloxy)-5-bromopentane
28 (5.22 g, 12.9 mmol) in THF (5 mL) cooled to K40 8C
via cannula dropwise over 30 min. The reaction was then
stirred at room temperature for 1 h. The mixture was
quenched with NH4Cl(aq) (sat., 100 mL) and H2O (20 mL),
then extracted into 1:1 Et2O:PE (3!100 mL). The organic
phases were washed with NaCl(aq) (sat., 2!50 mL), and
dried over Na2SO4. Removal of solvent in vacuo afforded
the crude product which was purified by flash chromato-
graphy (20% benzene, 80% PE) to yield 30 (3.83 g,
10.9 mmol, 84%) as a colourless oil; RfZ0.34 (20%
benzene, 80% PE); nmax/cmK1 (thin film) 3309 (m), 3071
(w), 2933 (s), 2859 (s), 1459 (m), 1428 (s), 1371 (w), 1335
(w), 1112 (s), 823 (w), 740 (w), 702 (s); m/z Probe CIC
(NH3) 351.1 (MHC, 100%); HRMS found MHCZ
351.2148, C23H31OSi requires 351.2144; microanalysis
found C, 78.9; H, 9.02; C23H30OSi requires C, 78.8; H,
8.62; dH (200 MHz, CDCl3) 1.10 (9H, s, C(CH3)3), 1.45–
1.70 (6H, m, H-2 to H-4), 1.95 (1H, t, JZ2.5 Hz, H-7),
2.15–2.27 (2H, m, H-5), 3.70 (2H, t, JZ6.0 Hz, H-1), 7.35–
7.50 (6H, m, Ph-H), 7.65–7.75 (4H, m, Ph-H); dC
(50.3 MHz, CDCl3) 18.4 (1C, C-5), 19.2 (1C, C(CH3)3),
25.0 (1C, C-3), 26.9 (3C, C(CH3)3), 28.2 (1C, C-4), 32.0
(1C, C-2), 63.7 (1C, C-1), 68.2 (1C, C-7), 84.6 (1C, C-6),
127.6 (4CH, Ph), 129.5 (2CH, Ph), 134.1 (2C, C-Si), 135.6
(4CH, Ph).
6.1.6. Preparation of Z-13-chloro-1-(tert-butyldiphenyl-
silyloxy)-tridec-6-ene 32a. To a solution of 13-chloro-1-
(tert-butyldiphenylsilyloxy)-tridec-6-yne 31 (2.13 g,
4.54 mmol) and benzene (30 mL) were added Lindlar
catalyst (0.640 g) and quinoline (58 mL). The mixture was
stirred under hydrogen gas (1 atm, balloon) for 1 h. The
reaction had not reached completion, so additional Lindlar
catalyst (0.410 g) was added, and the mixture stirred for a
further 3 h. The mixture was filtered through cellulose and
washed with benzene (150 mL). The organic phase was
washed with KHSO4(aq) (1%, 30 mL), neutralised with
NaHCO3(aq) (sat., 30 mL), then with NaCl(aq) (sat., 50 mL)
and dried over Na2SO4. Removal of solvent in vacuo
afforded the crude product which was purified by flash
chromatography (15% toluene, 85% PE) to yield 32a
(1.77 g, 3.76 mmol, 83%) as a colourless oil; RfZ0.20 (15%
toluene, 85% PE); nmax/cmK1 (thin film) 3071 (m), 3001
(m), 2931 (s), 2857 (s), 1656 (w), 1590 (w), 1472 (m), 1428
(m), 1390 (w), 1361 (w), 1188 (w), 1112 (s), 824 (m), 739
(w), 702 (s); m/z Probe CIC (NH3) 471.4 (M[35Cl]HC,
100%), 256.2 (19%), 196.3 (33%), 179.9 (20%), 123.1
(21%), 95.1 (27%); HRMS found MHC 471.2848, C29H44-
OSi35Cl requires 471.2850; microanalysis found C, 73.8; H,
9.42; C29H43OSiCl requires C, 73.9; H, 9.21; dH (200 MHz,
CDCl3) 1.10 (9H, s, C(CH3)3), 1.30–1.55 (10H, m, H-3, H-4,
H-9 to H-11), 1.55-1.70 (2H, m, H-2), 1.80 (2H, quin., JZ
7.0 Hz, H-12), 2.00–2.15 (4H, m, H-5, H-8), 3.55 (2H, t, JZ
7.0 Hz, H-13), 3.72(2H, t, JZ6.5 Hz, H-1), 5.30–5.50 (2H, m,
H-6, H-7), 7.35–7.55(6H, m, Ph-H), 7.65–7.80(4H, m, Ph-H);
dC (50.3 MHz, CDCl3) 19.3(1C, C(CH3)3), 25.5, 26.8(2CH2),
26.9 (3C, C(CH3)3), 27.1, 27.2, 28.5, 29.5, 29.6 (5CH2), 32.5,
32.6 (2C, C-2, C-12), 45.1 (1C, C-13), 64.0 (1C, C-1), 127.6
(4CH, Ph), 129.5 (2CH, Ph), 129.7, 130.0 (2C, C-6, C-7),
134.2 (2C, C-Si), 135.6 (4CH, Ph).
6.1.5. Preparation of 13-chloro-1-(tert-butyldiphenyl-
silyloxy)-tridec-6-yne 31. To a solution of 1-(tert-butyl-
diphenylsilyloxy)-hept-6-yne 30 (1.09 g, 3.11 mmol) in
THF (10 mL) cooled to K16 8C was added n-BuLi
(2.03M in hexanes, 1.54 mL, 3.13 mmol). After stirring at
K16 8C for 1 h, the solution was cooled to K78 8C, and
DMPU (3.77 mL, 31.2 mmol, 10 equiv) was added. After a
further 15 min stirring, the yellow solution was transferred
via cannula to a solution of 1-chloro-6-iodohexane (1.55 g,
6.29 mmol, 2 equiv) in THF (4 mL) at K78 8C. The
6.1.7. Preparation of Z-13-bromo-1-(tert-butyldiphenyl-
silyloxy)-tridec-6-ene 32b. A solution of Z-13-chloro-1-
(tert-butyldiphenylsilyloxy)-tridec-6-ene 32a (0.099 g,

S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
1137
0.21 mmol), and LiBr (0.623 g, 7.18 mmol) in butanone
(2 mL) was heated at reflux for 24 h. The butanone was
removed in vacuo, and H2O (25 mL) was added. The
product was extracted into EtOAc (3!30 mL). The organic
phases were washed with Na2S2O3(aq) (sat., 20 mL), then
NaCl(aq) (sat., 30 mL) and dried over Na2SO4. Removal of
solvent in vacuo afforded the crude product which was
purified by flash chromatography (15% benzene, 85% PE)
to yield 32b (0.104 g, 0.20 mmol, 96%) as a colourless oil;
RfZ0.20 (15% benzene, 85% PE); nmax/cmK1 (thin film)
3071 (m), 3000 (m), 2932 (s), 2857 (s), 1590 (w), 1462 (m),
1428 (m), 1389 (w), 1361 (w), 1260 (w), 1112 (s), 824 (m),
740 (m), 702 (s); 534.5 (10%, MNHC3 ), 517.5 (100%,
MHC), 471.5 (18%), 455.4 (33%), 437.6 (30%), 375.5
(64%), 256.3 (35%), 196.2 (60%); HRMS found MHC
515.2337 C29H44OSiBr79 requires 515.2345 dH (200 MHz,
CDCl3) 1.10 (9H, br, s, C(CH3)3), 1.30–1.53 (10H, m, H-3,
H-4, H-9 to H-11), 1.53–1.70 (2H, m, H-2), 1.88 (2H, quin,
JZ7.5 Hz H-12), 1.98-2.16 (4H, m, H-5, H-8), 3.42 (2H, t,
JZ7.0 Hz, H-13), 3.70 (2H, t, JZ6.5 Hz, H-1), 5.30–5.48
(2H, m, H-6, H-7), 7.35–7.52 (6H, m, Ph-H), 7.67–7.75 (4H,
m, Ph-H); dC (50.3 MHz, CDCl3) 19.2 (1C, C(CH3)3), 25.5
(1CH2), 26.9 (3C, C(CH3)3), 27.1, 27.2, 28.1, 28.4, 29.5,
(6CH2), 32.5, 32.8 (2C, C-2, C-12), 34.0 (1C, C-13), 64.0
(1C, C-1), 127.6 (4CH, Ph), 129.5 (2CH, Ph), 129.6, 130.0
(2C, C-6, C-7), 134.2 (2C, C-Si), 135.6 (4CH, Ph).
0.390 mL, 0.79 mmol, 3 equiv). The solution was stirred at
K10 8C for 30 min then DMPU (0.094 mL, 0.78 mmol,
3 equiv) was added. After 15 min stirring, 3-methylpyridine
(0.077 mL, 0.79 mmol) was added dropwise. After a further
60 minutes stirring at K10 8C, the solution was cooled to
K78 8C. This solution was added via cannula to a solution
of halide 32a, 32b, or 32c (0.26 mmol) in THF (2 mL)
cooled to K78 8C. The reaction was stirred for 22 h from
K78 8C to room temperature. The reaction was quenched
with NH4Cl(aq) (sat., 10 mL) and H2O (10 mL) and
extracted with EtOAc (3!30 mL). The organic phases
were washed with NaCl(aq) (sat., 20 mL) and dried over
Na2SO4. Removal of solvent in vacuo afforded the crude
product which was purified by flash chromatography (25%
EtOAc, 75% benzene) to yield 33 (79% from 32a, 63% from
32b, 36% from 32c) as a pale yellow oil; RfZ0.33 (25%
EtOAc, 75% benzene); nmax/cmK1 (thin film) 3000 (w),
2930 (s), 2856 (s), 1575 (w), 1462 (w), 1428 (m), 1389 (w),
1111 (s), 1026 (w), 824 (m), 740 (m), 702 (s); m/z Probe
CIC (NH3) 528.4 (MHC, 100%), 470.3 (23%); HRMS
found MHC 528.3668, C35H50NOSi requires 528.3662; dH
(200 MHz, CDCl3) 1.13 (9H, s, C(CH3)3), 1.30–1.55 (12H,
m, H-3, H-4, H-9 to H-12), 1.55–1.70 (4H, m, H-2, H-13),
2.00–2.20 (4H, m, H-5, H-8), 2.68 (2H, t, JZ7.5 Hz, H-14),
3.74 (2H, t, JZ6.5 Hz, H-1), 5.32–5.52 (2H, m, H-6, H-7),
7.22–7.32 (1H, m, Py H-5*), 7.40–7.60 (7H, m, 6H Ph-H,
1H Py H-4*), 7.70–7.80 (4H, m, Ph-H), 8.50–8.55 (2H, m,
Py H-2*, H-6*); dC (50.3 MHz, CDCl3) 19.7 (1C, C(CH3)3),
25.9 (1CH2), 27.3 (3C, C(CH3)3), 27.7, 29.6, 29.7, 29.8,
30.0, 30.2, 31.6, 33.0, 33.5 (10CH2), 64.4 (1C, C-1), 123.7
(1C, Py C-5*) 128.0 (4CH, Ph), 129.9 (2CH, Ph), 130.3 (2C,
C-6, C-7), 134.6 (2C, ArC-Si), 136.0 (4CH, Ph), 136.2 (1C, Py
C-4*), 138.4 (1C, Py C-3*), 147.7, 150.4 (2C, Py C-2*, C-6*).
6.1.8. Preparation of Z-13-iodo-1-(tert-butyldiphenyl-
silyloxy)-tridec-6-ene 32c. A solution of Z-13-chloro-1-
(tert-butyldiphenylsilyloxy)-tridec-6-ene 32a (0.835 g,
1.77 mmol), and NaI (2.69 g, 17.9 mmol, 10 equiv), in
acetone (15 mL), was heated at reflux for 24 h. The acetone
was removed in vacuo, and H2O (50 mL) was added. The
product was extracted into EtOAc (3!50 mL). The organic
phases were washed with Na2S2O3(aq) (sat., 30 mL), then
NaCl(aq) (sat., 50 mL) and dried over Na2SO4. Removal of
solvent in vacuo afforded the crude product which was
purified by flash chromatography (15% benzene, 85% PE)
to yield 32c (0.948 g, 1.68 mmol, 95%) as a colourless oil;
RfZ0.32 (15% benzene, 85% PE); nmax/cmK1 (thin film)
3071 (m), 3001 (m), 2930 (s), 2856 (s), 2362 (w), 2344 (w),
1655 (w), 1590 (w), 1472 (m), 1428 (m), 1389 (w), 1361
(w), 1190 (w), 1112 (s), 824 (m), 740 (m), 701 (s); m/z Probe
CIC (NH3) 580.3 (MNHC4 , 67%), 563.2 (MHC, 100%),
437.3 (35%), 256.1 (27%), 196.0 (30%); HRMS found
MHC 563.2209, C29H44OSiI requires 563.2206; micro-
analysis found C, 61.8; H, 7.62; C29H43OSiI requires C,
61.9; H, 7.71; dH (200 MHz, CDCl3) 1.08 (9H, s, C(CH3)3),
1.25–1.50 (10H, m, H-3, H-4, H-9 to H-11), 1.50–1.67 (2H,
m, H-2), 1.83 (2H, quin, JZ7.5 Hz, H-12), 1.95–2.13 (4H,
m, H-5, H-8), 3.20 (2H, t, JZ7.0 Hz, H-13), 3.68 (2H, t, JZ
6.5 Hz, H-1), 5.27–5.47 (2H, m, H-6, H-7), 7.35–7.50 (6H,
m, Ph-H), 7.65–7.75 (4H, m, Ph-H); dC (50.3 MHz, CDCl3)
7.3 (1C, C-13), 19.2 (1C, C(CH3)3), 25.5 (1CH2), 26.9 (3C,
C(CH3)3), 27.1, 27.2, 28.2, 29.5, 30.4 (6CH2), 32.5, 33.5
(2C, C-2, C-12), 63.9 (1C, C-1), 127.6 (4CH, Ph), 129.5
(2CH, Ph), 129.6, 130.0 (2C, C-6, C-7), 134.1 (2C, C-Si),
135.6 (4CH, Ph).
6.1.10. Preparation of Z-14-(pyridin-3-yl)-tetradec-6-en-
1-ol 34. To a solution of 33 (1.44 g, 2.73 mmol) in MeOH
(30 mL) was added NH4F (1.43 g, 38.6 mmol, 14 equiv).
The mixture was heated at 60 8C for 6.5 h. The reaction was
quenched with NaHCO3(aq) (sat., 30 mL) and H2O (30 mL)
and extracted with EtOAc (3!100 mL). The organic phases
were washed with NaCl(aq) (sat., 50 mL) and dried over
Na2SO4. Removal of solvent in vacuo afforded the crude
product which was purified by flash chromatography (30%
Et3N, 15% EtOAc, 55% PE) to yield 34 (0.754 g,
2.60 mmol, 95%) as a pale yellow oil; RfZ0.22 (30%
Et3N, 15% EtOAc, 55% PE); nmax/cmK1 (thin film) 3339
(br, m), 3003 (m), 2928 (s), 2855 (s), 1578 (w), 1479 (w),
1461 (w), 1424 (m), 1065 (m), 713 (m); m/z Probe APCIC
(NH3) 290.4 (MHC, 100%); HRMS found MHCZ
290.2496, C19H32NO requires 290.2484; dH (200 MHz,
CDCl3) 1.15–1.45 (12H, m, H-3, H-4, and H-9 to H-12),
1.45–1.70 (4H, m, H-2, H-13), 1.85–2.10 (4H, m, H-5, H-8),
2.57 (2H, t, JZ7.5 Hz, H-14), 2.90–3.30 (1H, br s, OH),
3.60 (2H, t, JZ6.5 Hz, H-1), 5.20–5.42 (2H, m, H-6, H-7),
7.17 (1H, dd, J1Z8.0 Hz, J2Z5.0 Hz Py H-5*) 7.46 (1H, br,
d, JZ8.0 Hz Py H-4*), 8.34–8.45 (2H, m, Py H-2*, H-6*);
dC (50.3 MHz, CDCl3) 25.5, 27.1, 29.0, 29.1, 29.2, 29.5,
29.6, 31.0, 32.5, 32.7, 32.9 (11CH2), 62.5 (1C, C-1), 123.3
(1C, Py C-5*), 129.7, 129.9 (2C, C-6, C-7), 135.9 (1C, Py
C-4*), 138.0 (1C, Py C-3*), 146.9, 149.7 (2C, Py C-2*, C-6*).
6.1.9. Preparation of Z-1-(tert-butyldiphenylsilyloxy)-14-
(pyridin-3-yl)-tetradec-6-ene 33. To a solution of diiso-
propylamine (0.111 mL, 0.79 mmol, 3 equiv) in THF
(2 mL) at K10 8C was added n-BuLi (2.03 M in hexanes,
6.1.11. Preparation of Z-14-(pyridin-3-yl)-tetradec-6-en-
1-al 24. To a solution of IBX (0.454 g, 1.62 mmol,

1138
S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
1.5 equiv) in DMSO (5 mL) was added a solution of 34
(0.310 g, 1.07 mmol) in THF (1 mL) via cannula. The
reaction mixture was stirred for 5 h after which time it was
diluted by H2O (100 mL), filtered and extracted with EtOAc
(3!30 mL). The organic phases were washed with NaCl(aq)
(sat., 30 mL) and dried over Na2SO4. Filtration and removal
of solvent in vacuo afforded the crude product which was
purified by flash chromatography (50% EtOAc, 50% PE) to
yield 24 (0.285 g, 0.99 mmol, 93%) as a pale yellow oil;
RfZ0.27 (50% EtOAc, 50% PE); nmax/cmK1 (thin film)
3004 (w), 2928 (s), 2855 (s), 2718 (w), 1725 (s), 1575 (m),
1478 (m), 1461 (m), 1422 (m), 1190 (w), 1027 (m), 794 (w),
714 (m); m/z APCIC (NH3) 288.3 (MHC, 100%); HRMS
found MHCZ288.2328, C19H30NO requires 288.2327; dH
(200 MHz, CDCl3) 1.15–1.45 (10H, m, H-4 and H-9 to H-12),
1.45–1.70 (4H, m, H-3, H-13), 1.85–2.10 (4H, m, H-5, H-8),
2.38 (2H, dt, J1Z7.5 Hz, J2Z2.0 Hz, H-2), 2.55 (2H, t, JZ
7.5 Hz, H-14), 5.20–5.40 (2H, m, H-6, H-7), 7.15 (1H, dd,
J1Z8.0 Hz, J2Z5.0 Hz, Py H-5*) 7.44 (1H, dd, JZ8.0 Hz,
J2Z2.0 Hz, Py H-4*), 8.39 (2H, apparent broad s, Py, H-2*,
H-6*), 9.71 (0.5H, t, JZ2.0 Hz, H-1); dC (50.3 MHz,
CDCl3) 22.0 (1C, C-3), 26.4, 27.2, 29.1, 29.2, 29.3, 29.6,
31.1, 33.0, (10CH2, C-3 to C-5 and C-7 to C-14), 43.2 (1C,
C-2), 123.2 (1C, Py C-5*), 128.2, 131.3 (2CH, C-5, C-6)
135.8 (1C, Py C-4*), 137.9 (1C, Py C-3*), 147.1, 149.9 (2C,
Py C-2*, C-6*), 202.6 (1C, C-1).
6.1.13. Preparation of 1-[N-Z-14-(pyridin-3-yl)-tetradec-
6-enylideneamino]-Z-14-(pyridin-3-yl)-tetradec-5-ene
N-oxide 36. To a solution of 35 (0.0552 g, 0.18 mmol) in
MeOH (10 mL) at 0 8C was added of methyl orange
(indicator, 2 mg) and conc. HCl (6 M) turning the indicator
red (approx. pH 3). NaBH3CN (0.0473 g, 0.75 mmol,
4 equiv) in MeOH (3 mL) was added dropwise with
concurrent addition of conc. HCl to keep the mixture at
pH 3. The mixture was stirred for 2 h at 0 8C. The mixture
was basified (dropwise, tested with pH paper) with
NaOH(aq) (6 N), and worked up using solvents chilled to
0 8C. The mixture was diluted with NaCl(aq) (sat., 20 mL)
and H2O (20 mL) and extracted with DCM (3!30 mL).
The organic phases were washed with NaCl(aq) (sat., 30 mL)
and dried over Na2SO4. Concentration in vacuo (without
heating) gave a solution of hydroxylamine 25 in DCM (ca.
50 mL). To the hydroxylamine solution, was added Na2SO4
(0.512 g), and aldehyde 5 (0.0524 g, 0.18 mmol, 1 equiv) in
DCM (5 mL) via cannula. The flask was stirred for 18 h at
room temperature. The crude reaction mixture was filtered,
the solvent removed in vacuo and was purified by flash
chromatography (30% Et3N, 50% EtOAc, 20% PE) to yield
nitrone 36 (0.0829 g, 0.14 mmol, 79%) as a yellow oil; RfZ
0.12 (30% Et3N, 50% EtOAc, 20% PE); nmax/cmK1 (thin
film) 3292 (br, m), 3003 (m), 2927 (s), 2855 (s), 2361 (m),
2342 (w), 1670 (m), 1575 (m), 1478 (m), 1463 (m), 1422
(m), 1027 (w), 794 (w), 714 (m); m/z Probe APCIC (NH3)
574.6 (MHC, 100%); HRMS found MHCZ574.4730,
C38H60N3O requires 574.4736; dH (200 MHz, CDCl3) 1.35
(22H, br, s, H-8 to H-12, and H-30, 40, H-90 to H-120), 1.50-
1.80 (6H, m, H0-3, H-10 3, H-130), 1.80–2.20 (10H, m, H-4,
H-7, H-20, H-5 , H-8 ), 2.45 (2H, apparent q, JZ7.5 Hz,
H-2), 2.62 (04H, t, JZ7.5 Hz, H-14, H-140), 3.76 (2H0, t, JZ
7.0 Hz, H-1 ), 5.25–5.50 (4H, m, H-5, H-6, H-60, H-7 ), 6.70
(1H, t, JZ6.0 Hz, H-1), 7.22 (2H, dd, J1 7.5 Hz, J2 5.0 Hz,
Py H-5*), 7.51 (2H, d, JZ8.0 Hz, Py H-4*), 8.40–8.50 (4H,
m, Py H-2*, H-6*); dC (50.3 MHz, CDCl3) 26.1, 26.5, 26.7,
27.4, 27.6, 27.8, 29.5, 29.7, 29.8, 30.1, 31.5 (18CH2), 33.4
(4CH2, C-13, C-14, C-130, C-140), 65.7 (1C, C-10), 123.6
(2C, Py C-5*), 128.8, 129.7, 130.7, 131.4 (4C, C-5, C-6,
C-60, C-70), 136.2 (2C, Py C-4*), 138.3 (2C, Py C-3*), 139.4
(1C, C-1), 147.6, 150.3 (4C, Py C-2*, C-6*).
6.1.12. Preparation of Z-14-(pyridin-3-yl)-tetradec-6-en-
1-oxime 35. To a solution of 24 (0.138 g, 0.48 mmol) in
MeOH (6 mL) were added NaOAc (0.119 g, 1.45 mmol,
3 equiv), then hydroxylamine hydrochloride (0.100 g,
1.44 mmol, 3 equiv). The mixture was stirred for 4.5 h at
room temperature. The solvent was removed in vacuo and
DCM (4 mL) and H2O (4 mL) with NaHCO3(s) (0.146 g,
1.74 mmol, 3.5 equiv) were added to neutralise the acetic
acid produced. The mixture was diluted with H2O (20 mL)
and extracted with EtOAc (3!30 mL). The organic phases
were successively washed with NaHCO3(aq) (sat., 20 mL),
H2O (20 mL), and NaCl(aq) (sat., 20 mL), and dried over
Na2SO4. Removal of solvent in vacuo afforded the crude
product which was purified by flash chromatography (50%
EtOAc, 50% PE) to yield 35 (0.131 g, 0.43 mmol, 90%) as a
colourless oil; RfZ0.20, 0.29 (E/Z isomers, 50% EtOAc,
50% PE); nmax/cmK1 (thin film) 3214 (br, m), 3086 (br, m),
3005 (m), 2927 (s), 2855 (s), 1655 (w), 1580 (m), 1462 (m),
1426 (m), 1334 (br, w), 1191 (w), 1030 (w), 903 (w), 795
(w), 712 (m); m/z Probe APCIC (NH3) 303.3 (MHC, 30%),
285.3 ([MHKH2O]C, 100%); HRMS found MHCZ
303.2444, C19H31N2O requires 303.2436. The subscripts E
and Z differentiate between the E and Z isomers.39 dH
(200 MHz, CDCl3) 1.20–1.70 (14H, m, H-3, H-4 and H-9 to
H-13), 1.90–2.10 (4H, m, H-5, H-8), 2.20 (1H, apparent q,
JZ7.0 Hz, 2H !0.5H-2E), 2.40 (1H, apparent q, JZ6.5 Hz,
2H !0.5H-2Z), 2.59 (2H, t, JZ7.5 Hz, H-14), 5.23–5.45
(2H, m, H-6, H-7), 6.70 (0.5H, t, JZ5.5 Hz, H-1Z), 7.21
(1H, dd, J1Z5.0 Hz, J2Z7.5 Hz, Py H-5*) 7.40–7.55 (1.5H,
m, 0.5H H-1E, 1H Py H-4*), 8.35–8.50 (2H, m, Py H-2*,
H-6*); dC (50.3 MHz, CDCl3) 24.9, 25.7, 26.3, 26.8, 27.1,
29.0, 29.1, 29.2, 29.4, 29.6, 31.0, 32.9 (11CH2), 123.4, (1C,
Py C-5*), 129.3, 130.2 (2C, C-6, C-7), 136.2 (1C, Py C-4*),
138.1 (1C, Py C-3*), 146.7, 149.6 (2C, Py C-2*, C-6*), 151.5
(1C, C-1 Z-oxime), 152.3 (1C, C-1 E-oxime).
6.1.14. Preparation of the C140–C150 isomer of pyrino-
demin A 3. A solution of nitrone 36 (0.0682 g, 0.12 mmol)
in benzene (80 mL) was heated at reflux for 24 h. The
solvent was removed in vacuo, to afford the crude product
which was purified by flash chromatography (100% EtOAc)
to yield 3 (0.0598 g, 0.10 mmol, 87%) as a pale yellow oil;
RfZ0.16 (100% EtOAc); nmax/cmK1 (thin film) 2928 (s),
2855 (s), 1575 (m), 1478 (m), 1465 (m), 1422 (m), 1339 (w),
1189 (w), 1026 (m), 794 (w), 714 (m); m/z Probe APCIC
(NH3) 574.4 (MHC, 50%), 289.4 (67%), 286.4 (100%),
220.2 (67%); m/z Probe EIMS (Cve ion) 572 (3%), 555
(7%), 383 (14%), 365 (88%), 355 (15%), 327 (14%), 315
(9%), 299 (27%), 285 (82%), 270 (23%), 259 (27%), 244
(18%), 231 (30%), 220 (56%), 204 (6%), 190 (21%), 176
(34%), 162 (21%), 148 (19%), 134 (14%), 120 (28%), 106
(100%), 93 (84%); HRMS found 574.4729, C38H60N3O
requires 574.4736; dH (500 MHz, CDCl3) 1.22–1.38 (16H,
m, H0-9 to H-12, and H-90 to H-120), 1.41 (4H, m, H-170,
H-18 ), 1.49 (2H, m, H-17, H-18), 1.51 (2H, m, H-13), 1.59
(2H, m, H-190), 1.62 (2H, m, H-14), 1.68 (4H, m, H-8, H-80),

S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
1139
1.72 (2H, m, H-17a, H-18a), 1.73 (1H, m, H-19), 1.80 (1H,
m, H-19a), 1.90–2.05 (4H, m, H-130, H-160), 2.53-2.61 (5H,
(0.0341 g, 0.11 mmol, 74%) as a white waxy solid; RfZ
0.13 (33.3% Et3N, 33.3% EtOAc, 33.3% PE); mpZ70–
71 8C; m/z Probe CIC (NH3) 307.2 (MHC, 36%), 291.2
(100%, MHC–H2O); HRMS found MHCZ307.2754,
C19H35N2O requires 307.2749; dH (200 MHz, CDCl3) 1.24
(20H, br, s, H-3 to H-12), 1.43–1.70 (4H, m, H-2, H-13),
2.59 (2H, t, JZ7.5 Hz, H-14), 2.93 (2H, t, JZ7.0 Hz, H-1),
7.19 (1H, dd, J1Z5.0 Hz, J2Z7.5 Hz, Py H-5*) 7.42–7.52
(1H, m, Py H-4*), 8.40–8.45 (2H, m, Py H-2*, H-6*); dC
(50.3 MHz, CDCl3) 27.0, 27.1, 29.1, 29.4, 29.6 (11C, C-2 to
C-12), 31.1, 33.0 (2C, C-13, C-14), 54.0 (1C, C-1) 123.2,
(1C, Py C-5*), 135.8 (1C, Py C-4*), 138.0 (1C, Py C-3*),
147.1, 149.9 (2C, Py C-2*, C-6*).
a
m, H-7, H-70, H-200), 2.77–2.88 (2H, m, H-16, H-200 ),
3.40–3.50 (1H, m, H-20)0, 4.00–4.08 (1H, m, H-15), 5.30–
5.38 (2H, m, H-140, H-15 ), 7.15–7.20 (2H, m, Py-H), 7.45–
7.50 (2H, m, Py-H), 8.38–8.45 (4H, br, s, Py-H); dC
(125.8 MHz, CDCl3) 26.2 (1C, C-17), 26.4 (1C, C-18), 26.9
(2C, C-13, and C-170 or C-180), 27.1 (2C, C-130, C-160),
28.0 (1C, C-190), 28.7 (1C, C-14), 29.0, 29.1, 29.2†, 29.3,
29.5,029.6‡, (9C, C-9 to C-012 and C-90 to C-120 and C-180 or
C-17 ), 31.0 (2C, C-8, C-8 ), 32.9 (2C, C-7, C-70), 34.5, (1C,
C-19), 49.8 (1C, C-16), 57.4 (1C, C200), 72.8 (1C, C-20),
77.5 (1C, C-15), 123.1 (2C, Py C-5*), 129.70, 129.72 (2CH,
C-150, C-160), 135.6 (2C, Py C-4*), 137.8 (2C, Py C-3*),
147.1, 149.9 (4C, Py C-2*, C-6*).
6.1.17. Preparation of 1-[N-14-(pyridin-3-yl)-tetradecyl-
ideneamino]-Z-14-(pyridin-3-yl)-tetradec-5-ene N-oxide
40. To a solution of 39 (0.0328 g, 0.11 mmol) in DCM
(5 mL) was added Na2SO4 (1.16 g), and aldehyde 5
(0.0360 g, 0.13 mmol) in DCM (2 mL) via cannula. The
reaction was stirred for 20 h at room temperature. The crude
reaction mixture was filtered, the solvent removed in vacuo
to afford the crude product which was purified by flash
chromatography (40% Et3N, 40% EtOAc, 20% PE) to yield
nitrone 40 (0.0415 g, 0.072 mmol, 67%) as a pale yellow
oil; RfZ0.28 (40% Et3N, 40% EtOAc, 20% PE); nmax/cmK1
(CHCl3) 3306 (br, m), 2929 (s), 2856 (s), 1657 (m), 1578
(w), 1480 (w), 1464 (m), 1424 (m), 1028 (w), 713 (m); m/z
Probe CIC (NH3) 576.5 (MHC, 100%), 367.2 (13%), 287.1
(5%); HRMS found MHCZ576.4897, C38H62N3O requires
576.4893; dH (200 MHz, CDCl3) 1.10–1.40 (30H, m, H-8 to
H-120 and H-30 to H-120), 1.40–1.70 (6H, m, H-3, H-13,
H-13 ), 1.80–2.12 (6H, m, H-4, H-7, H-20), 2.48 (2H,
apparent q, JZ6.5 Hz, H-2), 2.58 (4H, t, JZ7.5 Hz, H-14,
H-140), 3.71 (2H, t, JZ7.0 Hz, H-10), 5.22–5.46 (2H, m,
H-5, H-6), 6.66 (1H, t, JZ5.0 Hz, H-1), 7.18 (2H, dd, J1Z
8.0 Hz, J2Z5.0 Hz, Py H-5*), 7.47 (2H, d, JZ8.0 Hz, Py
H-4*), 8.35–8.45 (4H, m, Py H-2*, H-6*); dC (50.3 MHz,
CDCl3) 25.6, 26.3, 26.4, 27.0, 27.2, 27.4, 29.1, 29.4, 29.6,
31.1, 33.0, 34.4 (24CH2), 65.4 (1C, C-10), 123.2 (2C, Py
C-5*), 128.4, 131.0 (2C, C-5, C-6), 135.8 (2C, Py C-4*),
138.0 (2C, Py C-3*), 139.1 (1C, C-1), 147.0, 149.8 (4C, Py
C-2*, C-6*).
6.1.15. Preparation of 14-(pyridin-3-yl)-tetradecan-1-
oxime 38. A solution of 35 (0.0492 g, 0.16 mmol) and
catalyst (5% Pd on C, 5.9 mg) in MeOH (2 mL) was stirred
under hydrogen (1 atm, balloon) for 5 h. Removal of
solvent in vacuo afforded the crude which was purified by
flash chromatography (60% EtOAc, 40% PE) to yield 14-
(pyridin-3-yl)-tetradecan-1-oxime 38 (0.0465 g, 0.15 mmol,
94%) as a white waxy solid; RfZ0.23, 0.35 (E/Z isomers,
60% EtOAc, 40% PE); mpZ81–85 8C; nmax/cmK1 (CHCl3)
3020 (br, w), 2929 (s), 2856 (s), 2361 (w), 2343 (w), 1578
(w), 1466 (w), 1425 (w), 1029 (w); m/z Probe APCIC (NH3)
305.3 (MHC, 44%), 287.3 ([MHKH2O]C, 100%); HRMS
found MHCZ305.2607, C19H33N2O requires 305.2593;
m/z Probe EIMS (Cve ion) 304.2 (5%), 287.2 (14%), 246.2
(62%), 232.2 (13%), 218.2 (16%), 204.1 (18%), 190.1
(14%), 176.1 (10%), 162.1 (13%), 148 (14%), 134.1 (8%),
120.1 (16%), 106.1 (100%), 93.0 (70%). The subscripts
and
E
differentiate between the E and Z isomers.39 dH
Z
(200 MHz, CDCl3) 1.25 (18H, br, s, H-4 to H-12), 1.40–
1.70 (4H, m, H-3, H-13), 2.11–2.27 (1H, m, 2H ! 0.5H-2E),
2.31–2.45 (1H, m, 2H !0.5H-2Z), 2.59 (2H, t, JZ7.5 Hz,
H-14), 6.67–6.76 (0.5H, m, H-1Z), 7.16–7.29 (1H, m, Py
H-5*) 7.39–7.55 (1.5H, m, 0.5H H-1E, 1H Py H-4*), 8.38–
8.51 (2H, m, Py H-2*, H-6*); dC (50.3 MHz, CDCl3) 25.0,
26.1, 26.7, 29.1, 29.3, 29.5 (11C, C-2 to C-12), 31.0, 33.0
(2C, C-13, C-14), 123.3, (1C, Py C-5*), 136.1 (1C, Py C-4*),
138.2 (1C, Py C-3*), 146.8, 149.6 (2C, Py C-2*, C-6*), 151.8
(1C, C-1 Z-oxime), 152.5 (1C, C-1 E-oxime).
6.1.18. Preparation of a saturated analogue of pyrino-
demin A 37. A solution of nitrone 40 (0.0415 g,
0.072 mmol) in benzene (100 mL) was heated at reflux for
24 h. Removal of solvent in vacuo afforded the crude
product which was purified by flash chromatography (100%
EtOAc) to yield 37 (0.0304 g, 0.053 mmol, 73%) as a
colourless oil; RfZ0.23 (100% EtOAc); nmax/cmK1 (thin
film) 2927 (s), 2854 (s), 1676 (w), 1575 (m), 1465 (m), 1422
(m), 1026 (m), 714 (s); m/z Probe APCIC (NH3) 576.5
(MHC, 100%), 291.4 (42%); EIMS (Cve ion) 575 (12%),
557 (10%), 483 (5%), 385 (24%), 367 (100%), 357 (24%),
329 (13%), 315 (16%), 301 (23%), 287 (80%), 274 (23%),
270 (20%), 246 (35%), 232 (13%), 231 (1%), 220 (59%),
218 (25%), 204 (12%), 190 (26%), 176 (30%), 162 (16%),
148 (18%), 134 (10%), 120 (21%), 106 (77%), 93 (73%);
HRMS found 576.4897, C38H62N3O requires 576.4893; dH
(400 MHz, CDCl3) 1.18–1.84 (44H, m, H-8 to H-14, H-17,
H-18, H-19, H-80 to H-190), 2.60–2.75 (1H, m, H-200), 2.60
(4H, t, JZ8.0 Hz, H-7, H-70), 2.80–2.90 (2H, m, H-16,
6.1.16. Preparation of 14-(pyridin-3-yl)-tetradecane-1-
hydroxylamine 39. To a stirred solution of 38 (0.0453 g,
0.15 mmol) in MeOH (10 mL) at 0 8C was added of methyl
orange (indicator, 2 mg) and conc. HCl (6 M) turning the
indicator red (ca. pH 3). NaBH3CN (0.0354 g, 0.56 mmol,
4 equiv) in MeOH (1 mL) was added dropwise with
concurrent addition of conc. HCl to keep the mixture at
pH 3. The mixture was stirred for 3.5 h at room temperature.
The mixture was basified (dropwise and tested with pH
paper) with NaOH(aq) (6 N), diluted with NaCl(aq) (sat.
20 mL) and extracted with DCM (3!30 mL). The organic
phases were washed with NaCl(aq) (sat., 20 mL) and dried
over Na2SO4. Removal of solvent in vacuo to afford the
crude product which was purified by flash chromatography
(33.3% Et3N, 33.3% EtOAc, 33.3% PE) to yield 39
† This data point can be resolved into two signals at 29.18 and 29.21 ppm.
‡ This data point can be resolved into two signals at 29.58 and 29.63 ppm.
a
H-200 ), 3.42–3.51 (1H, m, H-20), 4.02–4.10 (1H, m, H-15),

1140
S. P. Romeril et al. / Tetrahedron 61 (2005) 1127–1140
7.20 (2H, dd, J1Z5.0 Hz, J2Z7.5 Hz, Py H-5*), 7.48 (2H, d,
JZ8.0 Hz, Py H-4*), 8.40–8.48 (4H, m, Py H-2*, H-6*); dC
(100.6 MHz, CDCl3) 26.3, 26.5, 27.0, 27.4, 28.1, 28.8,
29.1§, 29.3, 29.4, 29.5, 29.6¶, 29.7, 31.1, 33.0 (CH2), 49.9
(1C, C-16), 123.2 (2C, Py C-5*), 135.8 (2C, Py C-4*), 137.9
(2C, Py C-3*), 147.1, 149.9 (4C, Py C-2*, C-6*); C-15, C-20
and C-200 were not observed.
16. House, H. O.; Manning, D. T.; Melillo, D. G.; Lee, L. F.;
Haynes, O. R.; Wilkes, B. E. J. Org. Chem. 1976, 41, 855–863.
17. Ciganek, E. J. Org. Chem. 1990, 55, 3007–3009.
18. John, B. K.; Plant, D.; Heald, S. L.; Hurd, R. E. J. Magn.
Reson. 1991, 94, 664–669.
19. Stott, K.; Keeler, J.; Van, Q. N.; Shaka, A. J. J. Magn. Reson.
1997, 125, 302–324.
20. Throughout this article, we have used this terminology as a
descriptor for the olefin position.
21. Vysotskii, M. V.; Imbs, A. B.; Popkov, A. A.; Latyshev, N. A.;
Svetashev, V. I. Tetrahedron Lett. 1990, 31, 4367–4370.
22. Chong, J. M.; Heuft, M. A.; Rabbat, P. J. Org. Chem. 2000, 65,
5837–5838.
Acknowledgements
We thank the States of Jersey Education Committee for a
scholarship (to S. P. R.) and Professor Jun’ichi Kobayashi
for providing us with the spectra of natural pyrinodemin A.
23. Novis Smith, W.; Beumel, O. F. Jr. Synthesis 1974, 441–442.
24. dH (200 MHz, CDCl3) 1.15 (9H, s, C(CH3)3), 2.75 (1H, s,
ChCH), 7.40–7.55 (6H, m, Ph-H) 7.75–7.85 (4H, m, Ph-H);
dC (50.3 MHz, CDCl3) 18.4 (1C, C(CH3)3), 26.9 (3C,
C(CH3)3), 85.4, 97.3 (2C, ChC), 127.8 (4CH, Ph), 129.7
(2CH, Ph), 132.7 (2C, ArC-Si), 135.5 (4CH, Ph).
25. Lalonde, M.; Chan, T. H. Synthesis 1985, 817–845.
26. Morimoto, Y.; Yokoe, C.; Kurihara, H.; Kinoshita, T.
Tetrahedron 1998, 54, 12197–12214.
References and notes
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28. Dd 0.02, exponential line broadening 0.50 Hz, referenced to
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supporting information of Ref. 6.
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35. A typographical error appears in Ref. 5 where ion fragments
m/z 190 and 217 were reported as (C14H22N)C and
(C16H25N)C, respectively. We presume that Kobaysahi et al.
attempted to assign m/z 190 and 217 as (C13H20N)C and
(C15H23N)C, respectively, that is, cleavage on either side of
the olefin as depicted in Figure 4.
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1
39. For the assignment of H and 13C signals of E and Z oximes,
see Pretsch, E.; Clerc, T.; Seibl, J.; Simon, W. Spectral Data
for Structure Determination of Organic Compounds, 2nd ed.;
Springer-Verlad: Berlin, 1981; p C195 and H175.
§ This data point can be resolved into two signals at 29.09 and 29.13 ppm.
¶ This data point can be resolved into two signals at 29.57 and 29.60 ppm.