Studies toward the synthesis of pinolidoxin, a phytotoxic nonenolide from the fungus Ascochyta pinodes. Determination of the configuration at the C-7, C-8, and C-9 chiral centers and stereoselective synthesis of the C6- C18 fragment

Article abstract of DOI:10.1021/jo991722f

The absolute stereochemistry at the C-7, C-8, and C-9 chiral centers of pinolidoxin (1) has been determined by chemical and spectral methods. First, the synthesis of four stereoisomeric fully benzoylated 2,3-erythro-1,2,3,4- heptanetetrols, corresponding to the C₆-C₁₈ portion of the natural substance, has been accomplished starting from meso-tartaric acid. As next step, the selection of the synthetic tetrabenzoate possessing 'natural' stereochemistry (10a') suitable for absolute configuration determination, has been carried out by correlation with its 'natural' homologue derived from degradation of pinolidoxin. Determination of the stereochemistry at the title chiral centers has been carried out by application of the Mosher's method both to 7a', a compound stereochemically related to 10a', and to pinolidoxin itself. The stereoselective synthesis of a protected form of the C₆-C₁₈ portion of pinolidoxin, to be used in its total synthesis, has also been accomplished starting from commercially available D-erythronolactone.

Full text of DOI:10.1021/jo991722f

3432
J . Org. Chem. 2000, 65, 3432-3442
Stu d ies tow a r d th e Syn th esis of P in olid oxin , a P h ytotoxic
Non en olid e fr om th e F u n gu s Ascoch yta pin od es. Deter m in a tion of
th e Con figu r a tion a t th e C-7, C-8, a n d C-9 Ch ir a l Cen ter s a n d
Ster eoselective Syn th esis of th e C6-C18 F r a gm en t
Lorenzo de Napoli, Anna Messere, Daniela Palomba,1 and Vincenzo Piccialli*
Dipartimento di Chimica Organica e Biologica, Universita` degli Studi di Napoli “Federico II”,
Via Mezzocannone 16, 80134 Napoli, Italy
Antonio Evidente
Dipartimento di Scienze Chimico-Agrarie, Universita` degli Studi di Napoli "Federico II”
Via Universita` 100, 80055 Portici, Italy
Gennaro Piccialli
Universita` del Molise, Facolta` di Seienze Via Mazzini 8, 86170 Isernia, Italy
Received November 4, 1999
The absolute stereochemistry at the C-7, C-8, and C-9 chiral centers of pinolidoxin (1) has been
determined by chemical and spectral methods. First, the synthesis of four stereoisomeric fully
benzoylated 2,3-erythro-1,2,3,4-heptanetetrols, corresponding to the C6-C18 portion of the natural
substance, has been accomplished starting from meso-tartaric acid. As next step, the selection of
the synthetic tetrabenzoate possessing “natural” stereochemistry (10a ′), suitable for absolute
configuration determination, has been carried out by correlation with its “natural” homologue
derived from degradation of pinolidoxin. Determination of the stereochemistry at the title chiral
centers has been carried out by application of the Mosher’s method both to 7a ′, a compound
stereochemically related to 10a ′, and to pinolidoxin itself. The stereoselective synthesis of a protected
form of the C6-C18 portion of pinolidoxin, to be used in its total synthesis, has also been accomplished
starting from commercially available D-erythronolactone.
In tr od u ction
Fungi of Aschochyta species have considerable phyto-
patological and agrarian relevance because they are
responsible for diseases of important crops used for
animal and human feed, such as legumes and cereals.2
Some years ago, one of us undertook a study aimed at
isolating the toxic metabolites produced by Ascochyta
pinodes, the causal agent of anthracnose of pea (Pisum
sativum L.) causing severe lesions and necrosis of
leaves and pods of the host plant. The main phytotoxin,
named pinolidoxin (1, Figure 1), was isolated and char-
acterized as a new tetrasubstituted nonenolide, namely
2-(2,4-hexadienoiloxy)-7,8-dihydroxy-9-propyl-5-nonen-9-
olide.3 Later, from the same fungus three new toxic
nonenolides closely related to pinolidoxin, namely 7-epi-
(2), 5,6-dihydro-, and 5,6-epoxypinolidoxin (Figure 1),
were isolated in lower amounts.4 Among the isolated
substances pinolidoxin showed high phytotoxicity toward
host (pea) and nonhost (bean) plants. This finding
stimulated structure-activity relationship studies, which
were carried out both on the natural pinolidoxins and
on some unnatural derivatives of 1 by assaying their
(1) Part of the present work is taken from the degree thesis of D.P.
performed under the supervision of V.P. and G.P., Universita` di Napoli
“Federico II”, 1996.
(2) Vurro, M.; Zonno, M. C.; Evidente, A.; Capasso R.; Bottalico A.
Mycotox. Res. 1992, 8, 17-20.
(3) Evidente, A.; Capasso, R.; Abouzeid, M. A.; Lanzetta, R.; Vurro,
M.; Bottalico, A. J . Nat. Prod. 1993, 56, 1937-1943.
(4) Evidente, A.; Lanzetta, R.; Capasso, R.; Vurro, M.; Bottalico A.
Phytochemistry 1993, 34, 999-1003.
F igu r e 1.
phytotoxicity on weeds and crop plants, zootoxicity, and
antifungal activity.5 The results obtained indicated in
(5) Evidente, A.; Capasso, R.; Andolfi, A.; Vurro, M.; Zonno, M. C.
Nat. Toxins 1998, 6, 183-188.
10.1021/jo991722f CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/29/2000

Studies toward the Synthesis of Pinolidoxin
J . Org. Chem., Vol. 65, No. 11, 2000 3433
Sch em e 1
particular that primarily important structural features
for the phytotoxicity of pinolidoxin are the unmodified
C-7/C-8 diol system and the C-5/C-6 double bond (7-epi-
and 5,6-epoxypinolidoxins as well as C-7,C-8-protected
derivatives of 1 exhibited low or no phytotoxicity) while
the sorbic acid side chain does not seem to affect the
activity (hexahydropinolidoxin is also strongly phytotoxic
possibly due to its increased lipophilicity and, therefore,
the easier cell penetration).
that could not be determined by previous NMR studies
and X-ray experiments.3 In particular, the stereochemical
information on the molecule, comprising four chiral
centers, was confined to the knowledge of the E config-
uration of the C5/C6 double bond, deduced from the large
value (15.8 Hz) of the coupling constant between the
pertinent protons. In addition, the easy formation of an
acetonide derivative involving the C-7/C-8 diol system
was suggestive of a syn relationship between the hy-
droxyl groups at these carbons. Though the acetonide
formation could not conclusively secure the syn relation-
ship within the C-7/C-8 diol system (due to the confor-
mational freedom of the 10-membered ring also an anti
diol system at C-7/C-8 could form an acetonide deriva-
tive), as a first approximation we decided to assume this
stereochemical feature to be correct. This assumption,
that strongly semplified the synthetic work we have
accomplished, was later demonstrated to be indeed
correct.
The present paper deals with the determination of the
configuration at the C-7, C-8, and C-9 chiral centers of
pinolidoxin, carried out along the general lines detailed
below and schematically shown in Scheme 1, as well as
the stereoselective synthesis of its C6-C18 portion, start-
ing from commercially available D-erythronolactone. In
particular:
(1) Four of the eight possible stereoisomers correspond-
ing to the C6-C18 fragment of pinolidoxin, namely those
displaying a syn relationship between the C-7 and C-8
hydroxyl groups, were synthesized in the form of fully
benzoylated 2,3-erythro-1,2,3,4-heptanetetrols. These ma-
terials appeared to be easily accessible both by synthesis
(see Scheme 2) and from degradation of natural pinoli-
doxin (see Scheme 3), whose amount at disposal was very
limited (few milligrams);
The possible direct use of toxins produced by plant
pathogens as natural herbicides has been reviewed.6
Recently, Vurro and Ellis7 have shown the ability of some
phytotoxins, including pinolidoxin, to strongly suppress
PAL (phenylalanine-ammonia lyase) induction in poplar
cells, suggesting a role of these substances in suppressing
specific defense responses in plant cells during patho-
genesis. From a practical point of view, these results
suggest the use of phytotoxins in an integrated weed
control program in which subtoxic amounts of these
substances could be administered in combination with
weed pathogens in order to induce reduction of defense
mechanisms of the undesired weed, thus helping the
pathogen to cause its disease. Therefore, in view of the
possible use of pinolidoxin in the biocontrol of noxious
plants, we embarked on its total synthesis.8 This would
allow us to obtain sufficient amounts of the toxin, isolated
at low levels from the fungal culture filtrates, to test its
activity also in greenhouse or field experiments and to
prepare suitably modified derivatives and analogues of
the natural metabolite for further structure-activity
relationship studies. In this paper, we report the results
of a preliminary study that sets the basis for the
accomplishment of the stereoselective total synthesis of
pinolidoxin (1).9
Str a tegy
(2) The synthetic tetrabenzoate possessing the “natu-
ral” stereochemistry was selected via correlation with its
“natural” equivalent derived from degradation of pinoli-
doxin (see Scheme 4);
As a first step toward the synthesis of pinolidoxin, we
had to cope with the elucidation of its stereochemistry
(6) (a) Strobel, G. A.; Kenfield, D.; Bunkers, G.; Sugawara, F.;
Clardy, J . Phytotoxins as potential herbicides. In Phytotoxins and their
involvement in plant diseases; Ballio, A., Graniti, A., Eds. Experientia
1991, 47, 819-826. (b) Evidente, A. Bioactive metabolites from
phytopathogenic fungi and bacteria. In Recent research developments
in phytochemistry; Pandalai, S. G., Ed.; Research Signpost: Trivan-
drum, India, 1997; pp 255-292.
(9) For a review on the synthesis of medium-sized lactone rings,
see: Rousseau, G. Tetrahedron 1995, 51, 2777-2849. For a list of
papers dealing with the synthesis of 10-membered lactones, see, in
particular, pp 2830-2832. For more recent papers on the synthesis of
natural substances containing 10-membered lactone rings, see: (a)
Fu¨rstner, A.; Mu¨ller, T. Synlett 1997, 1010-1012. (b) J ones, G. B.;
Huber, R. S.; Chapman, B. J . Tetrahedron: Asymmetry 1997, 8, 1797-
1809. (c) Andrus, M. B.; Shih, T.-L. J . Org. Chem. 1996, 61, 8780-
8785. (d) Moricz, A.; Gassmann, E.; Bienz, S.; Hesse, M. Helv. Chim.
Acta 1995, 78, 663-669.
(7) Vurro, M.; Ellis, B. E. Plant Sci. 1997, 126, 29-38.
(8) Preliminary results were presented at the 9th International
Congress of Pesticide Chemistry, London, 2-7 Aug, 1998; De Napoli,
L.; Evidente, A.; Lasalvia, M.; Piccialli, G.; Piccialli, V.

3434 J . Org. Chem., Vol. 65, No. 11, 2000
de Napoli et al.
Sch em e 2
Sch em e 3
(3) The absolute configuration at the C-7, C-8, and C-9
stereogenic centers in a compound (7a ′) stereochemically
related to the selected synthetic material was determined
(see Schemes 5 and 6), and the stereoselective synthesis
of the C6-C18 portion of pinolidoxin accomplished starting
from commercially available D-erythronolactone (see
Scheme 7).
Syn th esis of th e F ou r Ster eoisom er ic F u lly Ben -
zoyla ted 2,3-er yth r o-1,2,3,4-Hep ta n etetr ols Cor r e-
sp on d in g to th e C6-C18 F r a gm en t of P in olid oxin .
The synthesis of the desired four stereoisomeric tetra-
benzoates (two racemic mixtures) corresponding to the
C6-C18 fragment of pinolidoxin (Scheme 2; for the race-
mic materials one enantiomer is shown) began with the
conversion of commercially available meso-tartaric acid
into 2,3-O-isopropylideneerythritol 3 through simple
chemical transformations (see the Supporting Informa-
tion for experimental details).
Reaction of diol 3 with TBSCl in pyridine for 8 h
provided the racemic monosilylated alcohol 4 in 53% yield
along with a 23% amount of the disilylderivative 5 that
was converted to the synthetically useful compound 4 by
hydrolysis to diol 3 (Et3N‚3HF, THF, 16 h, 94%)10
(10) Pirrung, M. C.; Steven, W. S.; Lever, D. C.; Fallon, L. Bioorg.
Med. Chem. Lett. 1994, 4, 1345-1346.

Studies toward the Synthesis of Pinolidoxin
J . Org. Chem., Vol. 65, No. 11, 2000 3435
Sch em e 4
Sch em e 5
Sch em e 6
pyridine in CH2Cl2,12 afforded the aldehyde 6 (81% yield)
that was immediately treated with n-PrMgCl in THF at
25 °C to give a mixture of the diastereoisomeric alcohols
7a and 7b, in 88% combined yield. HPLC separation of
this material (silica, hexanes-EtOAc, 92:8) afforded the
two racemic alcohols 7a and 7b in 37% and 51% yields,
respectively.13 It is to be noted at this stage that the
stereochemistry of compounds 7a and 7b is specified for
sake of clarity and is, anyway, the correct (“natural”) one
as determined through the work carried out afterward
and detailed below. As a next step, we had to select the
racemic alcohol (7a or 7b) correlating with pinolidoxin
from which the enantiomer having the “natural” stereo-
chemistry could be isolated and used for the stereochem-
istry determination at its C-7, C-8, and C-9 chiral centers.
This was accomplished by transforming 7a and 7b into
the corresponding tetrabenzoates, 10a and 10b, respec-
tively, as shown in Scheme 2. In particular, deprotection
of the primary alcoholic functions both in 7a and 7b by
treatment with Et3N‚3HF in THF provided diols 8a and
8b in 95% and 91% yields, respectively. Removal of the
isopropylidene protecting group with CH3COOH-H2O (7:
3) at room temperature for 16 h and subjection of the
resulting tetrols (9a and 9b) to benzoylation with benzoyl
followed by treatment with TBSCl in pyridine as above.
After this recycling step, compound 4 was obtained in
64% overall yield from 3. Silylation with the alternative
procedure using TBSCl (1.5 equiv)/imidazole (2.5 equiv)
in DMF,11 resulted less convenient for our porposes
affording a higher amount of the undesired bis-silyl-
derivative in the resulting mixture (ratio of mono- and
bis-silylderivative, 1:2). Oxidation of alcohol 4 with the
CrO3‚2py complex, generated in situ from CrO3 and
(12) Ratcliffe, R.; Rodehorst, R. J . Org. Chem. 1970, 35, 4000-4002.
(13) For the synthesis of related 1,2-protected 1,2,3,4-heptanetetrols,
see: (a) Cha, J . K.; Christ, W. J .; Kishi, Y. Tetrahedron Lett 1983, 24,
3943-3946. (b) Cha, J . K.; Christ, W. J .; Kishi, Y. Tetrahedron 1984,
40, 2247-2255.
(11) Corey, E. J .; Venkateswarlu, A. J . Am. Chem. Soc. 1972, 94,
6190-6191.

3436 J . Org. Chem., Vol. 65, No. 11, 2000
de Napoli et al.
Sch em e 7
h) that gave diol 13 in 65% yield after HPLC purification.
Scission of the diol system in 13 with Pb(OAc)414 in CH3-
COOH gave a dialdehyde product that was treated,
without purification, with NaBH4 in EtOH to yield the
tribenzoate dihydroxyester 14. The 1H NMR spectrum
of a small amount of this material revealed it to be ca.
80% pure. Treatment of crude 14 with NH4OH in CH3-
OH at 50 °C for 6 h produced the scission of the ester
functions in 14 providing tetrol 15 (40% from 13). Finally,
treatment of crude 15 with BzCl-pyridine at 0 °C for 4
h afforded, after HPLC purification (hexane-EtOAc, 8:2),
the tetrabenzoylated fragment 16 (95%) suitable for
comparison with the synthetic diastereoisomeric tetra-
benzoates 10a and 10b, obtained as above (Scheme 2).
In particular, synthetic 10a displayed NMR spectra and
chromatographic properties (HPLC co-injections of 16
with both 10a and 10b) identical to those exhibited by
the degradation product of pinolidoxin 16. This result
demonstrated that our initial assumption on the syn
relationship of the C-7/C-8 OH groups was correct.
As a consequence, the selection of the enantiomer
possessing the “natural” stereochemistry, to be used for
stereochemistry determination as planned, should be
carried out on one of the racemic materials belonging to
the “a ” series, that is among compounds 7a -10a . Of
these, 7a , being protected at its C-6, C-7, and C-8
hydroxyl groups, was a good candidate for the ac-
complishment of the next steps because its C-9 OH group
could serve as an anchorage of a suitable chiral append-
age likely necessary in its resolution. In addition, we
reasoned that the free OH group at C-9 could also serve
for the formation of the C-9 Mosher’s esters of the
“natural” enantiomer, to be used for the determination
of the configuration at this stereocenter, once this had
been isolated.
Scheme 4 depicts the route leading to the isolation of
the enantiomer possessing the “natural” stereochemistry
belonging to the racemic mixture 7a . First, the resolution
of 7a was attempted by HPLC using a chiral column and
various eluent mixtures. Unfortunately, all the separa-
tions obtained in this way were unsatisfactory. Therefore,
the pair of enantiomers composing 7a was transformed
into the diastereoisomeric compounds 17 by reacting 7a
with (S)-R-methoxy-R-(trifluoromethyl)phenylacetyl chlo-
ride ((S)-MTPACl) in pyridine in 52% overall yield.
Frustratingly, also this mixture did not give a reasonable
HPLC separation in various HPLC conditions. Neverthe-
less, after removal of the silyl protecting group at C-6 a
successful HPLC separation (silica, hexane-EtOAc, 8:2)
of the two diastereoisomers, 18a and 18b, composing the
resulting mixture, could be easily achieved. Each of these
substances was then subjected to the removal of the ester
(NH4OH/CH3OH, 24 h), and acetonide [CH3COOH/H2O
(7:3), rt, 24 h] protecting groups and perbenzoylated with
BzCl-pyridine at 0 °C for 4 h, to give the two tetraben-
zoylated fragments 10a ′ and 10a ′′ (81% and 69% from
18a and 18b, respectively) that could be compared with
their “natural” tetrabenzoate homologue 16 derived from
degradation of pinolidoxin as above-described (Scheme
3). Optical rotation data and circular dicroism spectra
(see Supporting Information) obtained for 16, 10a ′ and
10a ′′ unequivocally indicated 10a ′ to be identical to the
“natural” fragment 16.
chloride in pyridine at 0 °C for 2 h afforded the tetra-
benzoylated derivatives 10a and 10b (71% and 67%
yields from 8a and 8b, respectively) that could be
compared with their “natural” homologue 16, derived
from pinolidoxin through the degradative route shown
in Scheme 3.
Degr adation of P in olidoxin an d Cor r elative Wor k.
Degradation of pinolidoxin was carried out as shown in
Scheme 3, through simple classical chemical transforma-
tions. In particular, treatment of 1 with NH4OH in CH3-
OH at 50 °C for 6 h produced the cleavage of the sole
sorbic acid side chain while leaving intact the 10-
membered lactone ring, suggesting that the carbonyl
function of the 10-membered lactone was inaccessible due
to steric congestion. Benzoylation of the crude material
obtained from the previous reaction with BzCl-pyridine
at 0 °C for 24 h afforded a mixture of the 2,7,8-tribenzoyl
lactone 11 and the 2,8-dibenzoyl lactone 12, the C7-OH
group being unaffected in the latter compound. The
different propensity to benzoylation of the C-7 and C-8
hydroxyl groups of the C-2 deacylated pinolidoxin has
been fruitfully used in a late stage of the present work
when the absolute configuration at C-8 in 1 was ac-
complished by the application of the Mosher’s method
(see Scheme 6). Separation of the above di- and triben-
zoylated derivatives of pinolidoxin by HPLC (silica,
hexane-EtOAc, 8:2) afforded pure 11 and 12 in 71% and
28% yields, respectively. Resubjection of the unwanted
partially benzoylated derivative 12 to benzoylation as
above gave, after purification, another amount of 11
(yield for the conversion of 12 to 11, 95%) bringing its
overall yield to 97%. The degradation sequence continued
with the scission of the C5-C6 double bond in 11 by
reaction of this compound with excess OsO4 in pyridine
for 4h, followed by treatment with aqueous NaHSO3 (0.5
Deter m in a tion of th e Con figu r a tion a t th e C-7,
C-8, a n d C-9 Ster eogen ic Cen ter s of P in olid oxin . We
had now to determine the absolute configuration of the

Studies toward the Synthesis of Pinolidoxin
J . Org. Chem., Vol. 65, No. 11, 2000 3437
three chiral centers C-7, C-8, and C-9 in one of the
compounds of the “a ′” series, namely compounds 8a ′-
10a ′, or in the MTPA(S) derivative 18a , all shown in
Scheme 4. This proved to be more time-consuming than
we could initially suppose. In fact, X-ray crystallographic
analysis on one of these substances could not be ac-
complished due to the difficulties encountered in obtain-
ing well-grown crystals of these substances. Thus, we
turned our attention to the application of the Mosher’s
method15 on a derivative of 8a ′. In particular, the
determination of the chirality at C-9 was accomplished
by transforming diol 8a ′ into the mono-Mosher deriva-
tives 19 and 20 (Scheme 5) by selective silylation of the
primary hydroxyl group with TBSCl (1.9 equiv) in DMF
in the presence of imidazole (2.5 equiv) for 16 h, to give
alcohol 7a ′ in 96% yield, followed by its treatment with
either (S)- or (R)-R-methoxy-R-(trifluoromethyl)phenyl-
acetyl chlorides [(S)- and (R)-MTPACl] and analyzing the
resulting diastereoisomeric alcohols, 19 and 20, respec-
stereoselective synthesis of a protected form of the C6-
C18 portion of pinolidoxin by selecting a suitable chiral
precursor. The synthesis was straightforwardly accom-
plished through a six-step sequence starting from com-
mercially available D-erythronolactone16 (23) as depicted
in Scheme 7. This substance possesses four of the seven
carbons of the target fragment with the required stereo-
chemistry at its C-2 and C-3 carbons, corresponding to
the C-8 and C-7 carbons of pinolidoxin, respectively, and
a functionalization at C-1 that allows the easy attach-
ment of a three-carbon chain needed to complete the
carbon backbone of the C6-C18 segment. Thus, protection
of D-erythronolactone as its acetonide derivative 24 was
accomplished in 95% yield by reaction with excess 2,2-
dimethoxypropane in DMF in the presence of a catalytic
amount (3%) of p-toluensulfonic acid at reflux for 4 h. A
diastereoselective reduction of the ester function of 24
with diisobutylaluminum hydride (Dibal-H)17 in CH2Cl2
at -78 °C for 30 min gave 2,3-O-isopropylidene-â-D-
erythrofuranose18 in 78% yield. The singlet shape of the
signal for the anomeric proton, resonating at δ 5.42 in
the proton spectrum of this compound, pointed to a trans
relationship between H-1 and H-2.18 Gratifyingly, the
reaction of this material with n-PrMgCl19 in THF at 0
°C proceeded with a good diastereoselectivity level af-
fording diol 8a ′, possessing the desired R configuration
at C-9, in 77% yield. Finally, temporary protection of the
primary alcohol in 8a ′ to obtain the TBS-derivative 7a ′
(TBSCl-imidazole, DMF, 90%), followed by protection of
the C-9 alcohol function with the more robust TBDPS
group to give the bis-silylderivative 26 (TBDPSCl-imi-
dazole, DMF, 74%), and selective removal of the C-6
alcohol function by treatment with Et3N‚3HF in THF,
delivered the desired synthetic alcohol 27 (70% yield)
protected as silyl ether at the sole C-9 position. Com-
pound 27 was now ready to be oxidized at C-6 and
coupled to a suitably protected form of the right-hand,
C1-C5, portion of pinolidoxin.
1
tively, by H NMR in the usual way. The observed ∆δ
(δS - δR ) δ19 - δ20) values for the two substances, shown
on the structure, clearly indicated the configuration of
the C-9 chiral center in 7a ′ to be R (for a tridimensional
view of 19 and 20, see the Supporting Information). Note
that in 7a ′ and 8a ′ also the configuration at C-7 and C-8
is the correct (“natural”) one as established later (see
Scheme 6).
At this stage, however, we discarded the possibility of
determining the configuration at the C-7 and C-8 ste-
reocenters through the application of Mosher’s method
on one of the synthetic compounds 7a ′-10a ′ or 18a ,
because this would have required a rather long manipu-
lative work aimed at obtaining the (S)- and (R)-MTPA
ester derivatives at the sole C-7 or C-8 position in these
substances. Instead, the determination of the chirality
at these centers was carried out on pinolidoxin itself. This
was possible because, as established through the degra-
dative work carried out on pinolidoxin (Scheme 3), the
C-7 hydroxyl group could be benzoylated at a slower rate
than the C-8 OH group. We reasoned that this could also
be the case using the Mosher’s chlorides. Indeed, when
pinolidoxin was treated with (S)- or (R)-MTPACl (Scheme
6), the (S)- and (R)-MTPA derivatives of the natural
molecule at C-8, 21 and 22, respectively, were obtained
as the major reaction products. The usual 1H NMR
analysis of these compounds (diagnostic ∆δ values are
shown on the formula) established the R configuration
at C-8. Note that the structurally corresponding C-8
carbon in the fragment 10a ′ ) 16 (Scheme 4) has the
opposite S configuration simply due to a different sub-
stitution pattern. The above result also fixed the R
configuration at the C-7 carbon, standing the syn rela-
tionship between the C(7)-OH and C(8)-OH groups in
the natural substance (the Supporting Information in-
cludes a tridimensional view of the (S)- and (R)-MTPA
derivatives).
Con clu sion
In conclusion, in the present work we have carried out
the determination of the absolute configuration at the
stereogenic centers C-7, C-8, and C-9 of pinolidoxin
through a combination of chemical and spectral methods
as well as the stereoselective synthesis of its C6-C18
portion in a protected form suitable for its total synthesis.
Also worth of mentioning is that the degradative work
performed on pinolidoxin has disclosed interesting infor-
mation on its reactivity which could be fruitfully used to
prepare suitable C-2, C-7, or C-8 derivatives of the
natural substance. Completion of the synthesis of pino-
lidoxin requires the determination of the configuration
(16) For previous works dealing with the use of D-erythronolactone
as a chiral precursor in organic synthesis, see, for example: (a) Musich,
J . A.; Rapoport, H. J . Am. Chem. Soc. 1978, 100, 4865-4872. (b)
Ireland, R. E.; Wilcox, C. S.; Thaisrivongs, S. J . Org. Chem. 1978, 43,
786-787.
(17) (a) Paquette L. A. Encyclopedia of Reagents for Organic
Synthesis; J ohn Wiley & Sons: New York, 1995; Vol. 3, pp 1908-1912.
(b) Vidari, G.; Ferrin˜o, S.; Grieco, P. A. J . Am. Chem. Soc. 1984, 106,
3539-3548
(18) (a) De Bernardo, S.; Weigele, M. J . Org. Chem. 1976, 41, 287-
290. (b) Maehr, H.; Williams, T. H.; Leach, M.; Stempel, A. Helv. Chim.
Acta 1974, 57, 212-213. (c) Stevens, J . D.; Hewitt, G. F., J r. J . Org.
Chem. 1968, 33, 1799-1805.
(19) (a) Stork, G.; Raucher, S. J . Am. Chem. Soc. 1976, 98, 1583-
1584. (b) Hanessian, S. Total Synthesis of Natural Products: the Chiron
Approach; Baldwin, J . E., FRS Ed.; Pergamon Press: New York, 1993.
Ster eoselective Syn th esis of th e C6-C18 F r a gm en t
of P in olid oxin . With the above stereochemical informa-
tion at hand, we were now in a position to carry out the
(14) (a) Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis,
Wiley: New York, 1967; Vol. 1, pp 537-563. (b) Criegee, R. In
Oxidation in Organic Chemistry; Wiberg, K. B., Ed.; Academic Press:
New York, 1965; Part A.
(15) (a) Dale, J . A.; Dull, D. L.; Mosher, H. S. J . Org. Chem. 1969,
34, 2543-2549. (b) Dale, J . A.; Mosher, H S. J . Am. Chem. Soc. 1973,
95, 512-519. (c) Ohtani, I.; Kusumi, T.; Kashman, Y.; Kakisawa, H.
J . Am. Chem. Soc. 1991, 113, 4092-4096.

3438 J . Org. Chem., Vol. 65, No. 11, 2000
de Napoli et al.
relative intensity) 375 (M+ - CH3, 15), 333 (M+ - C(CH3)3,
20), 275 (M+ - SiC(CH3)3(CH3)2, 37); HRMS calcd for C18H39O4-
Si2 (M+ - CH3) 375.2387, found 375.2388; TLC Rf ) 0.9
(CHCl3/CH3OH, 99:1).
at C-2, the enantioselective synthesis of a suitably
protected form of the C1-C5 portion and its coupling with
the C6-C18 fragment (trans-stereoselective formation of
the C5-C6 double bond through, for example, a J ulia-
Lythgoe olefination sequence,20 followed by lactonization),
and attachment of the sorbic acid side chain. The results
of this work will be reported in due course.
Ald eh yd e 6. To a stirred solution of pyridine (950 µL, 12
mmol) in CH2Cl2 (5 mL) was added CrO3 (600 mg, 6 mmol)
under nitrogen at room temperature, and the resulting mixture
was stirred for 15 min. Then, a solution of the alcohol 4 (276
mg, 1 mmol) dissolved in CH2Cl2 (600 µL) was added in one
portion, causing the immediate formation of a black precipi-
tate. After 2 h, the mixture was filtered and the residue was
washed several times with Et2O. The ethereal phase was
washed with a 5% NaOH solution and brine and dried (Na2-
SO4). Evaporation of the solvent gave 222 mg (81%) of aldehyde
6 as a clear oil. The unpurified product (ca. 90% pure by 1H
NMR) was subjected without hesitation to the next step.
Data for 6: 1H NMR (CDCl3, 250 MHz) δ 9.69 (s, 1H), 4.46
(m, 2H), 3.73 (AB system further coupled, A part, J ) 10.7,
3.4 Hz, B part J ) 10.7, 2.4 Hz, 2H), 1,57, 1.38 (s’s, 3H each),
0.88 (s, 9H), 0.05, 0.04 (s’s, 3H each); TLC Rf ) 0.6 (CHCl3-
CH3OH, 99:1).
Alcoh ols 7a a n d 7b. Aldehyde 6 (200 mg, 0.73 mmol)
obtained as above was azeotropically dried with two 5 mL
portions of anhydrous toluene and dissolved in anhydrous THF
(6 mL). To the stirred solution was added n-PrMgCl (2M in
Et2O, 730 µL, 1.46 mmol) via syringe over 5 min, at room
temperature. After 1 h, another 300 µL of the Grignard reagent
was added, and the mixture was stirred for a further 30 min,
after which time the reaction was quenched with saturated
NH4Cl solution (5 mL). The aqueous layer was separated and
extracted with ether. The combined organic layers were dried
(Na2SO4), filtered, and concentrated. Purification of the result-
ing oil by HPLC (column: LiChrosorb Si-60 250 × 10 mm, 7
µm; eluent: hexane-EtOAc, 92:8; flow: 2.5 mL/min) gave the
two diastereoisomeric alcohols 7a (86 mg, 37%; tR ) 7.4 min)
and 7b (116 mg, 51%; tR ) 8.8 min).
Exp er im en ta l Section
Gen er a l Meth od s. Melting points are uncorrected. When
necessary, solvents and reagents were dried in the traditional
fashion prior to use. Routine monitoring of reactions was
performed using precoated silica gel TLC plates (Merck 60 F254
0.25 mm thick). Spots were visualized by UV light and/or
spraying an aqueous solution of sulfuric acid and heating the
plate in an oven, or with I2. Column chromatography was
carried out on Merck silica gel 40 (70-230 mesh). J values
are in hertz. Fourier transform IR (FTIR) spectra were taken
as films on a NaCl plate. Circular dicroism spectra are
expressed in ∆ꢀ vs λ. Mass spectra were run by direct sample
introduction: R ) 104, Tsource ) 120 °C, emission current 500
µA, electron energy 70 eV. Probe accurate mass measurement
using PFK as reference standard. High-performance liquid
chromatographies (HPLC) were performed using dual cell
refractometer or UV detectors, generally using Si-60 (250 ×
10 mm, 7 µm, and 250 × 4 mm, 5 µm) columns; attempts to
separate the diastereoisomers composing the mixture 17 were
carried out on the columns specified in the pertinent section.
A sample of pinolidoxin was obtained as white needles from
the filtrates of Ascochyta pinodes according to a reported
procedure.3
Mon o-TBS Eth er Alcoh ol 4. To a stirred solution of diol
3 (780 mg, 4.81 mmol) in pyridine (8 mL) was added 725 µL
(1 equiv) of a stock solution prepared by dissolving 1.0 g of
TBSCl in pyridine (1 mL). After 8 h at room temperature, TLC
monitoring indicated the complete transformation of the
starting product to two less polar products (Rf ) 0.7 and 0.9;
CHCl3-CH3OH 99:1). The solution was diluted with 5 mL of
a 5% aqueous NaHCO3 solution and extracted with CHCl3. The
combined organic extracts were washed with water, dried (Na2-
SO4), filtered, and concentrated. Column chromatography
(eluent CHCl3) afforded 700 mg (53%) of the monosilyl ether
4 and 430 mg (23%) of the bis-silyl ether 5 as clear oils. The
unwanted disilylated material 5 (430 mg) was desilylated by
treatment with Et3N‚3HF (1.6 mL, 10 equiv) in dry THF (3.5
mL). After being stirred at room temperature for 16 h, the
reaction mixture was diluted with Et3N (3 mL), evaporated,
and chromatographed (eluent: CHCl3-CH3OH 9:1) to give 195
mg (94%) of diol 3. This material was resubjected to silylation
as above to afford further 170 mg (51%) of silyl ether 4 after
chromatography. The overall yield of 4 after this recycle step
was of 64%.
Data for 7a : IR (film) 3477 (br, OH) cm-1; 1H NMR (CDCl3,
400 MHz) δ 4.22 (ddd, J ) 10.4, 5.5, 3.7 Hz, 1H), 4.02 (dd, J
) 9.2, 5.5 Hz, 1H), 3.87 (bd, J ) 3.0 Hz, 1H), 3.79 (dd, J )
10.4, 10.4 Hz, 1H), 3.79 (m, superimposed to another signal,
1H), 3.57 (dd, J ) 10.4, 3.7 Hz, 1H), 1.78-1.37 (overlapped
multiplets, 2H), 1.37, 1.33 (s’s, 3H each), 0.94 (t, J ) 7.3 Hz,
3H); 0.91 (s, 9H), 0.13, 0.12 (s’s, 3H each); 13C NMR (CDCl3,
62.8 MHz) δ 108.3, 80.8, 77.2, 68.7, 62.0, 36.1, 28.1, 25.3, 25.7,
18.3, 18.1, 14.1, -5.5, -5.6; MS m/z (assignment, relative
intensity) 303 (M+ - CH3, 10); HRMS calcd for C15H31O4Si (M+
- CH3) 303.3199, found 303.3187; TLC Rf ) 0.8 (hexane/
EtOAc, 8:2). Anal. Calcd for C16H34O4Si: C, 60.34; H, 10.76;
Si, 8.82. Found: C, 60.54; H, 10.65; Si, 8.64.
Data for 7b: IR (film) 3494 (br, OH) cm-1; 1H NMR (CDCl3,
400 MHz) δ 4.15 (ddd, J ) 6.8, 4.4, 4.4 Hz, 1H), 4.02 (dd, J )
6.3, 4.4 Hz, 1H), 3.91 (dd, J ) 10.7, 6.8 Hz, 1H), 3.78 (m, 1H),
3.72 (dd, J ) 10.7, 4.4 Hz, 1H), 2.70 (d, J ) 5.4 Hz, 1H), 1.47,
1.36 (s’s, 3H each), 1.30-1.60 (overlapped multiplets, 4H), 0.95
(t, J ) 6.8 Hz, 3H), 0.90 (s, 9H), 0.09 (s, 6H); 13C NMR (CDCl3,
62.8 MHz) δ 107.8, 79.7, 77.4, 68.6, 61.8, 36.6, 27.3, 25.0, 25.8,
19.0, 18.1, 13.9, -5.5, -5.7; MS m/z (assignment, relative
intensity) 303 (M+ - CH3, 15); HRMS calcd for C15H31O4Si (M+
- CH3) 303.3199, found 303.3207; TLC Rf ) 0.7 (hexane/
EtOAc, 8:2). Anal. Calcd for C16H34O4Si: C, 60.34; H, 10.76;
Si, 8.82. Found: C, 60.48; H, 10.73; Si, 8.70.
Diols 8a a n d 8b. Alcohol 7a (12 mg, 0.038 mmol) was
dissolved in dry THF (1 mL), and excess Et3N‚3HF (50 µL,
0.38 mmol) was added at room temperature under stirring.
After 16 h, Et3N (3 mL) was added and the mixture taken to
dryness and chromatographed (eluent: CHCl3-CH3OH, 9:1)
to give 7.3 mg (95%) of diol 8a as a white solid. An analogous
procedure applied to the alcohol 7b (12 mg) afforded 7.0 mg
(91%) of diol 8b as a white solid.
Data for mono-TBS 4: IR (film) 3483 (br, OH), cm-1 1H
;
NMR (CDCl3, 200 MHz) δ 4.35 (ddd, J ) 5.9, 5.9, 5.9 Hz, 1H),
4.23 (ddd, J ) 8.8, 5.9, 4.4 Hz, 1H), 3.78 (overlapped multiplets,
3H), 3.67 (dd, J ) 10.6, 4.4 Hz, 1H), 3.00 (dd, J ) 6.9, 6.9 Hz,
1H), 1.41, 1.35 (s’s, 3H each), 0.90 (s, 9H), 0.10 (s, 6H); 13C
NMR (CDCl3, 50.3 MHz) δ 108.2, 77.2, 76.7, 61.4, 60.7, 27.7,
25.1, 25.6, 18.1, -5.5; MS m/z (assignment, relative intensity)
261 (M+ - CH3, 65), 219 (M+ - C(CH3)3, 40); HRMS calcd for
C
12H25O4Si (M+ - CH3) 261.1522, found 261.1531; TLC Rf )
0.7 (CHCl3-CH3OH, 99:1).
Data for bis-TBS 5: 1H NMR (CDCl3, 200 MHz) δ 4.17 (m,
2H), 3.73 (AB system further coupled, A part J ) 10.8, 5.6
Hz, B part J ) 10.8, 5.6 Hz, 4H), 1.43, 1.34 (s’s, 3H each),
0.89 (s, 9H), 0.06 (s, 6-H); 13C NMR (CDCl3, 50.3 MHz) δ 108.3,
77.7, 62.0, 27.8, 25.2, 25.8, 18.3, -5.4; MS m/z (assignment,
Data for 8a : IR (film) 3388 (br, OH) cm-1; 1H NMR (CDCl3,
200 MHz) δ 4.28 (ddd, J ) 7.2, 5.4, 5.4 Hz, 1H), 3.97 (dd, J )
8.6, 5.4 Hz, 1H), 3.83 (m, H-9, 2H), 3.70 (dd, J ) 11.4, 5.4 Hz,
1H), 2.88 (bs, 2H), 1.80-1.30 (overlapped multiplets, 4H), 1.40,
1.35 (s’s, 3H each), 0.95 (t, J ) 7.3 Hz, 3H); 13C NMR (CDCl3,
50.3 MHz) δ: 108.2, 80.0, 77.2, 69.3, 60.8, 36.3, 27.8, 25.3, 18.3,
(20) (a) J ulia, M.; Paris, J .-M. Tetrahedron Lett. 1973, 14, 4833-
4836. (b) Kocienski, P. J .; Lythgoe, B.; Ruston, S. J . Chem. Soc., Perkin
Trans. 1 1978, 829-834. (c) Kocienski, P. J .; Lythgoe, B.; Waterhouse,
I. J . Chem. Soc., Perkin Trans. 1 1980, 1045-1050. For a review, see:
Kocienski, P. Phosphorus Sulfur 1985, 24, 97-127.

Studies toward the Synthesis of Pinolidoxin
J . Org. Chem., Vol. 65, No. 11, 2000 3439
14.0; MS m/z (assignment, relative intensity) 189 (M+ - CH3,
75); HRMS calcd for C9H17O4 (M+ - CH3) 189.1127, found
189.1134; TLC Rf ) 0.6 (CHCl3/CH3OH 9:1).
relative intensity) 580 (M+, 0.3), 336 (M+ - 2PhCOOH, 15),
105 (100), 77 (75); HRMS calcd for C35H32O8 (M+) 580.2096,
found 580.2010; TLC Rf ) 0.54 (benzene/EtOAc 95:5); Rf )
0.5 (hexane-EtOAc 8:2).
Data for 8b: mp 68.5-69.5 (from EtOAc by evaporation);
IR (film) 3414 (br, OH) cm-1 1H NMR (CDCl3, 200 MHz) δ
;
2,7,8-Tr iben zoylla cton e 11 a n d 2,8-Diben zoylla cton e
12. To a solution of pinolidoxin (1, 5.0 mg, 0.015 mmol) in CH3-
OH (0.5 mL) was added a 32% aqueous NH3 solution (0.5 mL),
and the mixture was stirred at 50 °C for 6 h. After evaporation
of the solvent, the crude 2-deacylated pinolidoxin (Rf ) 0.3,
CHCl3-2-propanol, 95:5) was azeotropically dried with three
1 mL portions of anhydrous toluene and dissolved in anhy-
drous pyridine (200 µL). Then, benzoyl chloride (50 µL, 0.4
mmol) was added, and the mixture was stirred at 0 °C. After
24 h, saturated aqueous NaHCO3 (1 mL) was added and the
solution was stirred at room temperature for a further 30 min
and extracted with CHCl3. The combined organic extracts were
washed with water, dried (Na2SO4), filtered, and concentrated
to give a white solid. HPLC separation (LiChrospher Si-60 250
× 4 column, 5 µm; eluent: hexane-EtOAc 8:2; flow: 1 mL/
min) afforded 6.0 mg (71%) of 2,7,8-tribenzoylpinolidoxin 11
(tR ) 9.2 min) and 2.0 mg (28%) of 2,8-dibenzoylpinolidoxin
12 (tR ) 14.3 min). The partially benzoylated product 12 was
converted into the synthetically useful fully benzoylated
derivative 11 in the above conditions to give, after HPLC
purification, additional 2.2 mg (95%) of this material, bringing
the total yield of 11 to 8.2 mg (97%).
Data for 11: [R]D +64.0 (c ) 0.10, CHCl3); IR (film) 1728
(CdO’s), 1266, cm-1; 1H NMR (CDCl3, 200 MHz) δ 8.19, 8.14,
7.86 (dd’s, J ) 7.7, 1.7 Hz, 2H each), 7.73-7.30 (overlapped
multiplets, 9H), 6.07 (bs, W1/2)6.7 Hz, 1H), 5.88 (bd, J ) 15.9
Hz, 1H), 5.78 (ddd, J ) 10.5, 10.5, 3.9 Hz, 1H), 5.62 (bd, J )
15.9 Hz, 1H), 5.53 (bd, J ) 3.9 Hz, 1H), 5.19 (dd, J ) 8.7, 2.0
Hz, 1H), 2.54 (m, 1H), 2.45-2.12, 1.73-1.18 (m’s, 6H), 0.81
(t, J ) 7.1 Hz, 3H); MS m/z (assignment, relative intensity)
556 (M+, 2), 451 (M+ - PhCO, 2), 434 (M+ - PhCOOH, 4),
312 (M+ - 2PhCOOH, 8), 190 (M+ - 3PhCOOH, 14), 105 (100),
77 (92); TLC Rf ) 0.6 (hexane/EtOAc, 7:3).
4.19 (ddd, J ) 6.5, 5.4, 5.4 Hz, 1H), 4.02 (dd, J ) 6.5, 3.0 Hz,
1H), 3.75 (m, 2H), 3.71 (m, 1H), 2.92 (bs, 2H), 1.65-1.30
(overlapped multiplets, 4H), 1.50, 1.37 (s’s, 3H each), 0.93 (t,
J ) 7.3 Hz, 3H); 13C NMR (CDCl3, 50.3 MHz) δ 108.2, 79.2,
77.4, 68.7, 61.0, 37.0, 27.2, 25.0, 19.0, 13.9; MS m/z (assign-
ment, relative intensity) 189 (M+ - CH3, 50); HRMS calcd for
C9H17O4 (M+ - CH3) 189.1127, found 189.1136; TLC Rf ) 0.6
(CHCl3/CH3OH 9:1).
Tetr ols 9a a n d 9b. To 10.0 mg of diol 8a was added 2 mL
of a CH3COOH/H2O (7:3) solution. After 16 h, the mixture was
concentrated by rotary evaporation, and acetic acid was
azeotropically removed by addition and evaporation of four 2
mL portions of n-heptane. Purification by preparative TLC
afforded 8.0 mg (98%) of tetrol 9a as a white solid. An
analogous procedure applied to diol 8b (10.0 mg) gave 7.6 mg
(93%) of tetrol 9b as a white solid.
Data for 9a : IR (film) 3280 (br, OH’s) cm-1 1H NMR
;
(C5D5N, 250 MHz) δ: 4.51, 4.38, 4.26 (partly overlapped m’s,
2H, 2H, 1H, respectively), 2.12, 1.90, 1.65 (partly overlapped
m’s, 1H, 2H, 1H, respectively), 0.95 (t, J ) 7.4 Hz, 3H); 13C
NMR (C5D5N, 62.8 MHz) δ 76.2, 75.0, 73.8, 65.1, 35.9, 19.5,
14.6; MS m/z (assignment, relative intensity) 273 (M+ - CH3-
COO, 10); HRMS for the tetraacetate calcd for C13H21O6 (M+
- CH3COO) 273.1338, found 273.1343; TLC Rf ) 0.2 (CHCl3/
CH3OH 9:1).
Data for 9b: IR (film) 3348 (br, OH) cm-1; 1H NMR (C5D5N,
200 MHz) δ 4.51, 4.34, 4.11 (the first two signals appear as
partly overlapped multiplets; the third signal appears as a
clean dd, J ) 7.3, 1.9 Hz, 3H, 1H, 1H, respectively), 2.14-
1.44 (overlapped m’s, 4H), 0.90 (t, J ) 7.4 Hz, 3H); 13C NMR
(C5D5N, 50.3 MHz) δ 75.0, 73.6, 70.8, 65.4, 37.0, 19.9, 14.5;
MS data for the tetraacetate m/z (assignment, relative inten-
sity) 273 (M+ - CH3COO, 15), calcd for C13H21O6 (M+ - CH3-
COO) 273.1338, found 273.1340; TLC Rf ) 0.2 (CHCl3/CH3OH
9:1).
Tetr a ben zoa tes 10a a n d 10b. To a cooled (0 °C) and
stirred solution of 9a (8.0 mg, 0.048 mmol) in pyridine (1 mL)
was added benzoyl chloride (45 µL, 0.48 mmol). After 2 h, a
saturated NaHCO3 solution (2 mL) was added, and the solution
was stirred at 0 °C for 30 min and then diluted with CHCl3,
poured into a separatory funnel, and extracted with CHCl3.
The combined organic extracts were washed with water, dried
(Na2SO4), filtered, and concentrated. The resulting yellow oil
was purified by HPLC (column: LiChrosorb Si-60 250 × 4 mm,
5 µm; eluent: hexane-EtOAc, 8:2; flow: 1.0 mL/min; tR ) 19.2
min) to afford 19.8 mg (71%) of 10a as a clear oil. Perbenzoy-
lation of tetrol 9b (11.8 mg, 0.072 mmol) as above-reported
Data for 12: IR (film) 3448 (br, OH), 1728 (CdO’s), 1262
1
cm-1; H NMR (CDCl3, 200 MHz) δ 8.13, 8.04 (dd’s, J ) 7.4,
1.8 Hz, 2H each), 7.70-7.41 (overlapped multiplets, 6H), 5.83
(bd, J ) 15.6 Hz, 1H), 5.75 (bd, J ) 15.6 Hz, 1H) 5.59 (ddd, J
) 9.6, 9.6, 4.0 Hz, 1H), 5.49 (bd, J ) 4.0, 1.5 Hz, 1H), 5.02
(dd, J ) 9.7, 2.0 Hz, 1H), 4.60 (bs, W1/2)4.6 Hz, 1H), 2.55 (m,
2H), 2.45-2.00, 1.70-1.20 (m’s, 6H), 0.80 (t, J ) 7.4 Hz, 3H).
MS m/z (assignment, relative intensity) 347 (M+ - 105, 1),
105 (100), 77 (92); TLC Rf ) 0.4 (hexane/EtOAc, 7:3).
Dioltr iben zoa te 13. To a stirred solution of 6.0 mg (0.011
mmol) of tribenzoate 11 in pyridine (1 mL) was added over a
5 min period 5.5 mg (0.022 mmol) of OsO4. After 4 h, 1 mL of
a solution prepared dissolving 200 mg of NaHSO3 in 3 mL of
H2O and 2.5 mL of pyridine was added. After being stirred
for 30 min, the orange solution was extracted with CHCl3 and
the organic phase was washed with water, dried (Na2SO4),
filtered, and concentrated. Purification by HPLC (LiChrospher
Si-60 250 × 4 column, 5 µm; eluent: CHCl3; flow: 1 mL/min)
gave 4.0 mg (65%) of diol 13 (tR ) 2.5 min) as an oil.
for 9a , followed by HPLC purification (above conditions, tR
)
20.2 min) gave 18.7 mg (67%) of 10b as a clear oil.
Data for 10a : IR (film) 1724 (CdO’s), 1265 cm-1; H NMR
(CDCl3, 200 MHz) δ 8.10-7.91 (overlapped multiplets, 8H),
7.64-7.19 (overlapped multiplets, 12H), 5.95 (m, 2H), 5.67
(ddd, J ) 8.4, 3.7, 3.7 Hz, 1H), 4.94 (dd, J ) 11.9, 2.3 Hz, 1H),
4.59 (dd, J ) 11.9, 5.7 Hz, 1H), 1.92, 1.47 (m’s, 2H each), 0.92
(t, J ) 7.2 Hz, 3H); 13C NMR (CDCl3, 50.3 MHz) δ 166.1, 165.8,
165.5, 165.2, 133.4, 132.2, 133.0, 132.9, 129.8, 129.7, 129.3,
128.5, 128.5, 128.3, 72.6, 72.6, 70.4, 63.1, 32.2, 18.6, 13.7; MS
1
Data for 13: 1H NMR (CDCl3, 200 MHz) δ 8.08, 8.01, 7.96
(dd’s, J ) 7.7, 1.8 Hz for all, 2H each), 7.67-7.41 (overlapped
multiplets, 9H), 5.72 (bs, 1H), 5.63 (dd, J ) 6.1, 2.4 Hz, 1H),
5.46 (m, 1H), 5.33 (dd, J ) 6.7, 2.5 Hz, 1H), 4.18 (bs, 1H), 4.02
(bs, 1H), 0.82 (t, J ) 7.1 Hz, 3H); TLC Rf ) 0.8 (CHCl3-CH3-
OH, 9:1).
m/z (assignment, relative intensity) 580 (M+, 0.5), 336 (M+
-
2PhCOOH, 20), 105 (100), 77 (87); HRMS calcd for C35H32O8
(M+) 580.2096, found 580.2091; TLC Rf ) 0.58 (benzene/EtOAc
95:5); Rf ) 0.5 (hexane/EtOAc 8:2).
Tetr ol 15. To a solution of dioltribenzoate 13 (4.0 mg, 0.008
mmol) in CH3COOH (2 mL) was added crystalline Pb(OAc)4
(4.0 mg, 0.01 mmol)14 over a 5 min period under stirring. The
stirring was continued for further 5 min, then the reaction
mixture was quenched by addition of two drops of ethylene
glicole, diluted with ice-water, and extracted with CHCl3. The
organic phase was washed with a saturated aqueous NaHCO3
solution and water, dried (Na2SO4), filtered, and evaporated
to give 4.0 mg of a crude dialdehyde product: 1H NMR (CDCl3,
200 MHz) (selected data from the crude reaction mixture) δ
9.85, 9.83 (two apparent s’s, 2H), 8.19, 7.86 (overlapped
multiplets, 6H), 7.62-7.30 (overlapped multiplets, 9H), 5.86,
1
Data for 10b: IR (film) 1724 (CdO’s), 1265 cm-1; H NMR
(CDCl3, 200 MHz) δ 8.12-7.90 (overlapped multiplets, 8H),
7.64-7.32 (overlapped multiplets, 12H), 5.92 (dd, J ) 6.7, 4.2
Hz, 1H), 5.78 (ddd, J ) 6.7, 6.7, 3.4 Hz, 1H), 5.67 (ddd, J )
6.7, 6.7, 4.2 Hz, 1H), 4.85 (dd, J ) 12.7, 3.4 Hz, 1H), 4.55 (dd,
J ) 12.7, 6.7 Hz, 1H), 1.80, 1.43 (m’s, 2H), 0.91 (t, J ) 6.8 Hz,
3H); 13C NMR (CDCl3, 50.3 MHz) δ 166.0, 165.7, 165.4, 165.4,
133.5, 133.2, 133.0, 133.0, 129.8, 129.7, 129.4, 128.5, 128.3,
72.1, 71.6, 69.9, 62.7, 33.2, 18.5, 13.8; MS m/z (assignment,

3440 J . Org. Chem., Vol. 65, No. 11, 2000
de Napoli et al.
5.74 (m’s, 1H each), 5.62 (m, 1H), 5.35 (m, 1H), 0.90 (t, J )
7.0 Hz, 3H).
Hz, 1H), 3.55 (s, 3H), 3.44 (t, J ) 5.8 Hz, 2H), 1.85-1.62 (m,
4H), 1.38, 1.33 (s’s, 3H each), 0.93 (t, J ) 7.0 Hz, 3H); 13C NMR
(CDCl3, 62.5 MHz) δ 165.7, 131.9, 129.7, 128.4, 127.3, 121.0,
108.6, 77.4, 76.2, 73.8, 61.1, 55.4, 33.7, 27.7, 25.4, 17.7, 13.9;
MS m/z (assignment, relative intensity) 405 (M+-CH3, 40), 389
(M+-OCH3, 20); HRMS calcd for C19H24O6F3 (M+ - CH3)
405.1525, found 405.1505; TLC Rf ) 0.2 (hexane/EtOAc, 8:2).
Data for 18b: 1H NMR (CDCl3, 200 MHz) δ 7.55 (m, 2H),
7.41 (m, 3H), 5.30 (ddd, J ) 7.0, 7.0, 5.0 Hz, 1H), 4.22 (dd, J
) 7.0, 5.8 Hz, 1H), 4.16 (ddd, J ) 5.8, 5.8, 5.8 Hz, 1H), 3.53 (a
3H singlet overlapped to a 2H multiplet), 1.46, 1.36 (s’s, 3H
each), 0.90 (t, J ) 7.0 Hz, 3H); MS m/z (assignment, relative
intensity) 405 (M+ - CH3, 30), 389 (M+ - OCH3, 25); HRMS
calcd for C19H24O6F3 (M+ - CH3) 405.1525, found 405.1519;
TLC Rf ) 0.2 (hexane/EtOAc, 8:2).
Diols 8a ′ a n d 8a ′′. To a solution of 18a (5.0 mg, 0.01 mmol)
in CH3OH (1 mL) was added 32% aqueous NH3 (1.5 mL), and
the mixture was stirred at room temperature for 24 h.
Evaporation of the solvent and chromatography (eluent:
CHCl3-CH3OH, 9:1) afforded 2.0 mg (98%) of diol 8a ′ as a
white solid. An analogous procedure applied to 18b (5.0 mg,
0.01 mmol) followed by chromatography in the same conditions
used for the purification of 8a ′ gave 1.9 mg (93%) of diol 8a ′′
as a white solid.
The unpurified dialdehyde obtained as above (4.0 mg, 0.008
mmol) was dissolved in EtOH (2 mL), and NaBH4 (12.0 mg,
0.32 mmol) was added. After the mixture was stirred for 4 h
at room temperature, CH3COOH (two drops) was added and
the reaction mixture was extracted with CHCl3. The organic
phase was washed with water, dried (Na2SO4), filtered, and
evaporated to give 4.0 mg of a product whose chromatographyc
mobility (Rf ) 0.8; CHCl3/CH3OH 9:1) was in agreement with
that of the expected 5,6-dihydroxy-2,7,8-tribenzoyl-5,6-seco-
pinolidoxin 14. The unpurified substance was subjected to the
next step of the sequence.
To a solution of the crude dioltribenzoate 14, obtained as
above, in CH3OH (1 mL) was added aqueous 32% NH3 (1.5
mL), and the solution was stirred at 50 °C for 6h. Then the
mixture was extracted with CHCl3, the organic phase was
dried (Na2SO4), filtered, and evaporated. Preparative TLC
afforded 1.0 mg (40% from 13) of tetrol 15 as a withe solid:
[R]D -14.5 (c 0.1, CH3OH). Spectral data (1H NMR, 13C NMR,
IR, MS), and chromatographic properties (TLC Rf ) 0.2;
CHCl3/CH3OH 9:1) of this material were identical to those
exhibited by the synthetic racemic tetrol 13a , obtained as
above, and the enantiomerically pure tetrol 9a ′ (see later and
Scheme 5). In addition, the [R]D value of 15 well matched that
exhibited by 9a ′.
Tetr a ben zoa te 16. Perbenzoylation of tetrol 15 (1.0 mg,
0.006 mmol) in the same conditions used to perbenzoylate
racemic tetrol 9a (BzCl, py, 0 °C, 4 h) gave, after purification
as described for 9a , 3.5 mg (95%) of tetrabenzoate 16: [R]D
+30.8 (c 0.3, CHCl3). Spectral data (1H NMR, 13C NMR, IR,
MS), and chromatographic properties (co-injection of 16 with
both 10a and 10b on a LiChrosorb Si-60 250 × 4 column, 5
µm; eluent hexane-EtOAc, 8:2; flow: 1.0 mL/min) were
identical to those exhibited by the synthetic racemic tetraben-
zoate 10a obtained as above-described. The [R]D value for 16
is in good agreement with that exhibited by enantiomerically
pure 10a ′ obtained as described later (Scheme 4).
Data for 8a ′: [R]D -33.3 (c ) 0.30, CHCl3); spectral data
(1H NMR, 13C NMR, IR, MS), and chromatographic properties
(TLC Rf ) 0.6; CHCl3/CH3OH 9:1) of this material were
identical to those exhibited by the synthetic racemic diol 8a
obtained as above-described.
Data for 8a ′′: [R]D +32.4 (c) 0.25, CHCl3).
Tetr ols 9a ′ a n d 9a ′′. To 5.0 mg (0.026 mmol) of diol 8a ′
was added 1.5 mL of a CH3COOH/H2O (7:3) solution. After 24
h, the mixture was evaporated and the residual acetic acid
was azeotropically removed by addition of n-heptane (4 × 2
mL). Purification by preparative TLC (CHCl3-CH3OH, 8:2)
afforded 4.0 mg (98%) of tetrol 9a ′ as a white solid. An
analogous procedure applied to diol 8a ′′ (2.0 mg, 0.010 mmol)
gave 1.5 mg (91%) of tetrol 9a ′′ as a white solid.
Mosh er ’s Ester Der iva tives 17. To a solution of the
racemic alcohol 7a (10.0 mg, 0.031 mmol) in pyridine (500 µL)
was added (S)-MTPA chloride (30 µL, 0.19 mmol). After the
mixture was stirred for 2 h at room temperature, a saturated
NaHCO3 solution (1 mL) was added and the solution was
stirred for further 30 min then transferred into a separatory
funnel and extracted with CHCl3. The combined organic
extracts were washed with water, dried (Na2SO4), filtered, and
concentrated. HPLC purification (Hibar LiChrosorb Si-60 250
× 10 column; eluent: hexane-EtOAc, 8:2; flow: 2.5 mL/min)
afforded 10 mg (52%) of a mixture of the two diastereoisomeric
(S)-MTPA derivatives 17 (one peak at tR ) 12.0 min) as an
oil. TLC Rf ) 0.65 (hexane/EtOAc, 8:2).
Data for 9a ′: [R]D -13.1 (c 0.35, CH3OH); mp 115-117 °C
(microneedles from pyridine/CHCl3, 1:1). Spectral data (1H
NMR, 13C NMR, IR, MS) and chromatographic properties (TLC
Rf ) 0.2; CHCl3-CH3OH, 9:1) were identical to those exhibited
by tetrol 15 derived from degradation of pinolidoxin, and
synthetic racemic tetrol 9a obtained as described above.
Data for 9a ′′: [R]D) +14.0 (c 0.15, CH3OH).
Tetr a ben zoa tes 10a ′ a n d 10a ′′. Tetrols 9a ′ and 9a ′′ were
perbenzoylated as described above for 9a and 9b and purified
by HPLC in the same conditions. From 4.0 mg (0.024 mmol)
of tetrol 9a ′ were obtained 11.9 mg (85%) of tetrabenzoate 10a ′,
while 1.5 mg (0.009 mmol) of tetrol 9a ′′ gave 4.3 mg (82%) of
tetrabenzoate 10a ′′, both as oils.
The following attempts to separate the two diastereoisomers
composing the mixture 17 were unsuccessful: (1) column:
LiChrospher Si-60 (250 × 4 mm), 5 µm; eluent: hexane-
EtOAc 98:2; flow: 0.7 mL/min; tR ) 22.5 min; (2) column:
Supelcosil LC-®-DNB-PG (250 × 4.6 mm), 5 µm; eluent:
hexane-EtOAc, 98:2; 0.7 mL/min; tR ) 19.5 min; (3) column:
Whatman Partisphere C-18 (15 × 4 mm); eluent: CH3OH;
flow: 0.7 mL/min; tR ) 7.9 min; (4) column: Hibar Supersphere
RP-18 (250 × 4 mm), 5 µm; eluent: CH3OH or CH3OH-H2O
(95:5); flow: 0.7 mL/min; tR ) 4 or 9 min, respectively.
Alcoh ols 18a a n d 18b. To a stirred solution of 17 (10 mg,
0.016 mmol) in dry THF (750 µL) was added 100 µL (0.51
mmol) of Et3N‚3HF at room temperature. After 16 h, the
mixture was diluted with Et3N (2 mL), evaporated, and filtered
through a short pad of silica gel (eluent CHCl3-CH3OH, 9:1)
to give a mixture of the alcohols 18 as an oil. HPLC separation
(LiChrospher Si-60 250 × 4 mm column, 5 µm; eluent:
hexane-EtOAc, 8:2; flow: 1 mL/min) of this material afforded
3.7 mg (58%) of 18a (tR ) 11.5 min) and 2.3 mg (32%) of 18b
(tR ) 13.0 min).
Data for 10a ′: [R]D +32.2 (c 1.1, CHCl3); spectral data (1H
NMR, 13C NMR, IR, MS) and chromatographic properties (TLC
Rf ) 0.5; hexane/EtOAc, 8:2) were identical to those exhibited
by tetrabenzoate 16, derived from degradation of pinolidoxin,
and synthetic racemic tetrol 10a obtained as described above.
Anal. Calcd for C35H32O8: C, 72.40; H, 5.56. Found: C, 72.29;
H, 5.63.
Data for 10a ′′: [R]D -31.1 (c 0.34, CHCl3). Anal. Calcd for
35H32O8: C, 72.40; H, 5.56. Found: C, 72.48; H, 5.59.
C
Mosh er ’s Ester Der iva tives 19 a n d 20. A mixture of diol
8a ′ (5.0 mg, 0.024 mmol), imidazole (4.1 mg, 0.060 mmol), and
tert-butyldimethylsilyl chloride (6.0 mg, 0.046 mmol) in DMF
(1 mL) was stirred overnight at room temperature, quenched
with water (3 mL), and extracted with CHCl3. The organic
solution was dried (Na2SO4) and concentrated. Purification of
the residue by HPLC (column: LiChrosorb Si-60 250 × 10 mm,
7 µm; eluent: hexane-EtOAc, 92:8; flow: 2.5 mL/min) deliv-
ered 7.3 mg (96%) of alcohol 7a ′ as an oil.
Data for 7a ′: [R]D -13.2 (c 0.71, CHCl3); spectral data (1H
NMR, 13C NMR, IR, MS) and chromatographic properties (TLC
Rf ) 0.8; hexane/EtOAc, 8:2) were identical to those exhibited
by synthetic racemic alcohol 7a obtained as described above.
To a solution of the alcohol 7a ′ obtained as above (3.0 mg,
0.009 mmol) in pyridine (400 µL) was added (S)-MTPA chloride
Data for 18a : [R]D +28.7 (c 0.86, CHCl3); IR (film) 3489 (br,
1
OH), 1747 (CdO), 1250 cm-1; H NMR (CDCl3, 250 MHz) δ:
7.55 (m, 2H), 7.41 (m, 3H), 5.26 (ddd, J ) 7.0, 7.0, 5.0 Hz,
1H), 4.18 (dd, J ) 7.0, 5.8 Hz, 1H), 4.07 (ddd, J ) 5.8, 5.8, 5.8

Studies toward the Synthesis of Pinolidoxin
J . Org. Chem., Vol. 65, No. 11, 2000 3441
(30 µL, 0.054 mmol). After the solution was stirred for 2 h at
room temperature, a saturated NaHCO3 solution (1 mL) was
added, and the mixture was stirred for 30 min and then
transferred into a separatory funnel and extracted with CHCl3.
The combined organic extracts were washed with water, dried
(Na2SO4), filtered, and concentrated. HPLC purification on a
Hibar LiChrosorb Si-60 (250 × 4) column (eluent: hexane-
EtOAc, 8:2) afforded 4.7 mg (98%) of the (S)-MTPA derivative
19 as a clear oil. Using the (R)-MTPA chloride and the above
procedure, alcohol 7a ′ (2.5 mg, 0.008 mmol) gave 4.0 mg (96%)
of the (R)-MTPA derivative 20 as a clear oil after HPLC
purification in the above conditions.
Data for 24: [R]D -104.4 (c 1.67, CHCl3);21 IR (film) 1780
(CdO), cm-1; 1H NMR (CDCl3, 200 MHz) δ 4.85 (ddd, J ) 5.7,
3.8, 1.2 Hz, 1H), 4.73 (d, J ) 5.7 Hz, 1H), 4.41 (AB system
further coupled, A part J ) 14.3 Hz, B part J ) 14.3, 3.8 Hz,
2H), 1.44, 1.35 (s’s, 3H each); 13C NMR (CDCl3, 50.3 MHz) δ
174.2, 113.8, 75.4, 74.5, 70.1, 26.6, 25.4; EIMS (assignment,
relative intensity) m/z 158 (M+, 10), 120 (M+ - CO2, 92); TLC
Rf ) 0.5 (hexane-EtOAc, 1:1).
La ctol 25. A cold (-78 °C) solution of lactone 24 (65 mg,
0.41 mmol) in CH2Cl2 (2 mL) was treated with diisobutylalu-
minum hydride (284 µL of a 1 M solution in CH2Cl2) during 5
min, stirred for 30 min at this temperature, and quenched with
saturated NH4Cl (2 mL). The reaction mixture was stirred at
room temperature for further 30 min and diluted with CH2-
Cl2 (2 mL). The separated aqueous phase was extracted with
CH2Cl2, and the combined organic solutions were dried (Na2-
SO4), filtered, and concentrated. Preparative TLC (CHCl3-
CH3OH, 9:1) afforded 51 mg (78%) of lactol 25 as a clear oil.
Data for 25: [R]D -58.5 (c 1.53, CHCl3); IR (film) 3418 (br,
Data for 19: [R]D +23.0 (c 0.15, CHCl3); IR (film) 1748 (Cd
1
O), 1254 cm-1; H NMR (CDCl3, 200 MHz) δ 7.55, 7.39 (m’s,
2H and 3H, respectively), 5.42 (ddd, J ) 5.0, 6.4, 6.4 Hz, 1H),
4.16 (dd, J ) 6.4, 6.4 Hz, 1H), 4.04 (ddd, J ) 6.4, 5.7, 4.6 Hz,
1H), 3.59 (AB system further coupled, A part J ) 11.5, 4.6
Hz, B part J ) 11.5, 5.7 Hz, 2H), 3.55 (bs, 3H), 1.73 (m, 2H),
1.37, 1.29 (s’s, 3H each), 1.50-1.20 (m, 2H), 0.91 (t, J ) 7.1
Hz, 3H), 0.90 (s, 9H), 0.06, 0.05 (s’s, 3H each); TLC Rf ) 0.7
(hexane-EtOAc, 85:15).
1
OH) cm-1; H NMR (CDCl3, 200 MHz) δ: 5.47 (bs, 1H), 4.84
(dd, J ) 5.8, 3.3 Hz, 1H), 4.57 (d, J ) 5.8 Hz, 1H), 4.04 (AB
system further coupled, A part J ) 10.3, 3.3 Hz, B part J )
10.3 Hz, 2H), 2.88 (bs, 1H), 1.47, 1.32 (s’s, 3H each); 13C NMR
(CDCl3, 50.3 MHz) δ 112.3, 101.8, 85.1, 79.9, 71.9, 26.2, 24.7;
EIMS (assignment, relative intensity) m/z 160 (M+, 10), 143
(M+ - OH, 68); TLC Rf ) 0.5 (CHCl3-CH3OH, 9:1).
Diol 8a ′. To a stirred and cold (0 °C) solution of lactol 25
(248 mg, 1.55 mmol) in THF (2 mL) was added n-PrMgCl (2
M in Et2O, 2.3 mL, 4.65 mmol) via syringe over a 5 min period.
TLC monitoring (hexane-EtOAc, 7:3, double migration) showed
the reaction to be complete after some 5 h. To the mixture,
diluted with Et2O (10 mL), was added a saturated NH4Cl
solution (10 mL), and the whole was transferred into a
separatory funnel. The aqueous layer was separated and
extracted with Et2O. The combined organic layers were dried
(Na2SO4), filtered, concentrated, and chromatographed (eluent
CHCl3-CH3OH, 9:1) to give 240 mg (77%) of diol 8a ′ as a white
solid.
Data for 20: [R]D -20.0 (c 0.10, CHCl3); IR (film) 1748 (Cd
1
O), 1259 cm-1; H NMR (CDCl3, 200 MHz) δ 7.56, 7.39 (m’s,
2H and 3H, respectively), 5.42 (ddd, J ) 7.4, 5.2, 5.2 Hz, 1H),
4.25 (dd, J ) 5.2, 5.2 Hz, 1H), 4.14 (ddd, J ) 5.6, 5.2, 5.2 Hz,
1H), 3.64 (AB system further coupled, A part J ) 11.5, 5.2
Hz, B part J ) 11.5, 5.7 Hz, 2H), 3.54 (bs, 3H), 1.67 (m, 2H),
1.45, 1.33 (s’s, 3H each), 1.40-1.15 (m, 2H), 0.88 (s, 9H), 0.85
(t, J ) 7.2 Hz, 3H), 0.04, 0.03 (s’s, 3H each); TLC Rf ) 0.7
(hexane-EtOAc, 85:15).
C-8 Mosh er ’s Ester Der iva tives of P in olid oxin (21 a n d
22). To a stirred solution of pinolidoxin 1 (2.0 mg, 0.006 mmol)
in pyridine (100 µL) was added (S)-MTPA chloride (90 µL,
0.009 mmol). After 5 h, a saturated NaHCO3 solution (300 µL)
was added, and the mixture was stirred for 30 min and then
extracted with CHCl3. The combined organic extracts were
washed with water, dried (Na2SO4), filtered, and concentrated.
HPLC purification on a Hibar LiChrosorb Si-60 (250 × 4)
column (eluent: cyclohexane-EtOAc, 8:2) afforded 3.0 mg
(90%) of the C-8 (S)-MTPA derivative of pinolidoxin 21 as an
oil. Using the (R)-MTPA chloride (200 µL, 0.02 mmol) and the
above procedure, pinolidoxin (2.0 mg, 0.006 mmol) gave 2.6
mg (80%) of the C-8 (R)-MTPA derivative of pinolidoxin 22 as
an oil, after HPLC purification as described for 21. In this case,
the reaction required 24 h to go to completion.
Data for 21: IR (film) 3415 (br, OH), 1734 (3 × CdO), 1260
cm-1; 1H NMR (CDCl3, 250 MHz) δ 7.60-750, 7.43-4.38 (m’s,
5H), 7.32 (dd, J ) 15.4, 9.8 Hz, 1H), 6.25 (m, 2H), 5.88 (d, J )
15.4 Hz, 1H), 5.69 (bd, J ) 14.8 Hz, 1H), 5.61 (bdd, 14.8, 14.8
Hz, 1H), 5.36 (ddd, J ) 9.4, 9.4, 2.8 Hz, 1H), 5.27 (dd, J ) 5.6,
1.7 Hz, 1H), 4.95 (dd, J ) 9.4, 2.5 Hz, 1H), 4.60 (bs, 1H), 3.61
(s, 3H), 2.46 (m, 1H), 2.30-1.93 (overlapped multiplets, 4H),
1.91 (bd, J ) 5.5 Hz, 3H), 1.0-1.3 (overlapped multiplets, 3H),
0.69 (t, J ) 7.3 Hz, 3H); TLC Rf ) 0.4 (cyclohexane/EtOAc
8:2).
Data for 22: IR (film) 3426 (br, OH), 1730 (3 × CdO), 1262
cm-1; 1H NMR (CDCl3, 200 MHz) δ 7.60-750, 7.45-4.35 (m’s,
5H), 7.32 (dd, J ) 15.4, 9.7 Hz, 1H), 6.25 (m, 2H), 5.88 (d, J )
15.4 Hz, 1H), 5.63 (bd, J ) 14.8 Hz, 1H), 5.62 (bdd, 14.8, 14.8
Hz, 1H), 5.41 (ddd, J ) 9.5, 9.5, 2.6 Hz, 1H), 5.27 (dd, J ) 5.6,
1.7 Hz, 1H), 4.96 (dd, J ) 9.5, 2.5 Hz, 1H), 4.49 (bs, 1H), 3.61
(s, 3H), 2.46 (m, 1H), 2.30-1.93 (overlapped multiplets, 4H),
1.91 (bd, J ) 5.5 Hz, 3H), 1.0-1.3 (overlapped multiplets, 3H),
0.80 (t, J ) 7.3 Hz, 3H); TLC Rf ) 0.5 (cyclohexane/EtOAc
8:2).
Aceton id e La cton e 24. A mixture of D-erythronolactone
23 (947 mg, 8.02 mmol), p-tolenesulfonic acid monohydrate (40
mg), and 2,2-dimethoxypropane (8 mL) in DMF (10 mL) was
refluxed for 4 h. Then saturated NaHCO3 solution (1 mL) was
added, and excess 2,2-dimethoxypropane was evaporated in
vacuo. Extraction with CHCl3, filtration, anhydrification (Na2-
SO4), and evaporation delivered 1.206 g (95%) of acetonide
lactone 24 as an oil. An analytical sample of 24 was obtained
by preparative TLC (hexane-EtOAc, 7:3).
Data for 8a ′: [R]D -32.7 (c 0.33, CHCl3). Spectral data (1H
NMR, 13C NMR, IR, MS) and chromatographic properties (TLC
Rf) 0.6; CHCl3-CH3OH, 9:1) were identical to those exhibited
by synthetic 8a ′ obtained as described above (Scheme 4).
Silyl Eth er 7a ′. A mixture of diol 8a ′ (231 mg, 1.13 mmol),
imidazole (115 mg, 1.69 mmol), and tert-butyldimethylsilyl
chloride (205 mg, 1.36 mmol) in DMF (500 µL) was stirred for
16 h at room temperature, quenched with water (3 mL), and
extracted with CHCl3. The organic solution was dried (Na2-
SO4), filtered, and concentrated. Purification by HPLC as
described above for this compound afforded 270 mg (91%) of
7a ′ as an oil.
Data for 7a ′: [R]D -13.3 (c 0.25, CHCl3). Spectral data (1H
NMR, 13C NMR, IR, MS) and chromatographic properties (TLC
Rf) 0.8; hexane-EtOAc, 8:2) were identical to those exhibited
by synthetic 7a ′ obtained as described above (Scheme 5).
Disilyl Eth er 26. A mixture of alcohol 7a ′ (268 mg, 0.84
mmol), imidazole (200 mg, 2.94 mmol), and tert-butyldiphen-
ylsilyl chloride (647 µL, 2.53 mmol) in DMF (1 mL) was stirred
for 22 h at room temperature, quenched by addition of water
(3 mL), and extracted with CHCl3. The organic phase was dried
(Na2SO4), filtered, concentrated, and chromatographed (elu-
ent: petroleum ether-EtOAc, 95:5) to give 345 mg (74%) of
26 as an oil.
1
Data for 26: [R]D +15.5 (c 2.97, CHCl3); H NMR (CDCl3,
200 MHz) δ: 7.78-7.64, 7.44-7.30 (m’s, 10H), 4.13 (overlapped
multiplets, 2H), 3.95 (ddd, J ) 4.9, 4.9, 4.9 Hz, 1H), 3.73 (A
part of an AB system further coupled, J ) 13.5, 3.3 Hz, 1H),
3.55 (B part of an AB system further coupled, J ) 13.5, 7.5
Hz, 1H), 1.57-1.11 (overlapped signals, 2H), 1.46, 1.31 (s’s,
(21) The [R]D value for the enantiomer of compound 24 is reported
to fall in the range +105 to +116.3°. (a) Hudlicky, T.; Luna, H.; Price,
J . D.; Rulin, F. J . Org. Chem. 1990, 15, 4683-4687. (b) Vanhessche,
K.; Van der Eyken, E.; Vanderwalle, M.; Ro¨eper, H. Tetrahedron Lett.
1990, 16, 2337-2340. (c) Munier, P.; Giudicelli, M.-B.; Picq, D.; Anker,
D. J . Carboydr. Chem. 1996, 6, 739-762.

3442 J . Org. Chem., Vol. 65, No. 11, 2000
de Napoli et al.
3H each), 1.05 (s, 9H), 0.85 (s, 9H), 0.66 (t, J ) 7.0 Hz, 3H),
-0.01, -0.02 (s’s, 3H each); 13C NMR (CDCl3, 50.3 MHz) δ:
136.0, 135.8, 134.2, 133.7, 129.6, 127.4, 107.7, 79.1, 78.4, 71.4,
63.3, 36.4, 27.8, 25.4, 26.9, 25.9, 19.4, 18.3, 18.2, 13.9, -5.3;
MS m/z (assignment, relative intensity) 541 (M+ - CH3, 10),
499 (M+ - C4H9, 20), 441 (M+ - SiC(CH3)3(CH3)2, 55); HRMS
calcd for C31H49O4Si2 (M+ - CH3) 541.3169, found 541.3182;
TLC Rf ) 0.6 (hexane-EtOAc, 9:1).
Alcoh ol 27. To a solution of disilyl ether 26 (35 mg, 0.063
mmol) in THF (1 mL) was added excess Et3N‚3HF (102 µL,
0.63 mmol) under stirring at room temperature. After 5 h, the
mixture was diluted with Et3N (2 mL) and evaporated.
Preparative TLC (hexane-EtOAc. 7:3) afforded 18 mg (70%)
of alcohol 27 as an oil.
Ack n ow led gm en t. This work was supported by
grants from the “Ministero dell’ Universita` e della
Ricerca Scientifica e Tecnologica (Italy), PRIN 1997” and
the “Consiglio Nazionale delle Ricerche”. Throuhout the
NMR work the facilities of the “Centro di Metodologie
Chimico-Fisiche dell’Universita` degli Studi di Napoli”
were used. Mass spectral data were provided by the
“European Mass Spectrometry Facility Centre”, CNR-
Napoli (Italy); the assistance of Dr. Gabriella Pocsfalvi
is gratefully acknowledged. We are also grateful to Dr.
Anna Andolfi for the isolation and HPLC purification
of a sample of pinolidoxin.
Data for 27: [R]D +2.6 (c 0.83, CHCl3); IR (film) 3479 (br,
OH) cm-1 1H NMR (CDCl3, 200 MHz) δ: 7.76-7.64, 7.46-
;
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails for the transformation of meso-tartaric acid into 2,3-O-
isopropylideneerythritol 3, stereochemical view of Mosher’s
ester derivatives 19-22, 1H NMR spectra for compounds 4-6,
7a -10a , 7b-10b, 11-13, 18a ,b (mixture), 18a , 18b, 19-22,
24, 26, and 27, and HPLC chromatograms and CD spectra for
compounds 16, 10a ′, and 10a ′′. This material is available free
of charge via the Internet at http://pubs.acs.org.
7.33 (m’s, 10H), 4.19 (m, 1H), 4.12 (dd, J ) 5.4, 5.4 Hz, 1H),
3.99 (ddd, J ) 4.8, 4.8, 4.8 Hz, 1H), 3.60 (m, 2H), 2.42 (bs,
1H), 1.49, 1.35 (s’s, 3H each), 1.07 (s, 9H), 0.91 (t, J ) 7.7 Hz,
3H); 13C NMR (CDCl3, 50.3 MHz) δ: 136.1, 135.9, 133.8, 133.0,
129.8, 127.5, 107.9, 78.5, 71.3, 62.0, 36.9, 28.0, 25.6, 27.0, 19.3,
18.1, 13.8; MS m/z (assignment, relative intensity) 427 (M+
-
CH3, 15), 385 (M+ - C4H9, 12); HRMS calcd for C25H35O4Si
(M+ - CH3) 427.2305, found 427.2321; TLC Rf ) 0.5 (hexane-
EtOAc, 7:3). Anal. Calcd for C26H38O4Si: C, 70.57; H, 8.66; Si,
6.35. Found: C, 70.69; H, 8.51; Si, 6.20.
J O991722F