Enantiospecific synthesis of the phospholipase A2 inhibitor (-)-cinatrin B

Article abstract of DOI:10.1021/jo016221k

The first enantiospecific synthesis of phospholipase A₂ (PLA₂) inhibitor (-)-cinatrin B (2) from the D-arabinose derivative 9 is described. The spirolactone system was formed by an Ireland-Claisen rearrangement of the allyl ester 8 followed by hydrolysis and stereoselective iodolactonization. The stereoselectivity of the rearrangement was controlled by the asymmetry in the allylic alcohol fragment. Ester (S)-8 gave the desired rearrangement product 7 and the epimer 13 in high yield as a 73:27 ratio, respectively. The final stereocenter at C2 was introduced via a chelation-controlled addition of the Grignard reagent derived from trimethylsilylacetylene to α-hydroxy ketone 6. Transformation of the terminal alkyne into the methyl ester 21 followed by acetal hydrolysis and selective lactol oxidation afforded cinatrin B methyl ester (22). Base hydrolysis and acid-induced relactonization then gave (-)-cinatrin B (2).

Full text of DOI:10.1021/jo016221k

4392
J . Org. Chem. 2002, 67, 4392-4398
En a n tiosp ecific Syn th esis of th e P h osp h olip a se A2 In h ibitor
(-)-Cin a tr in B
Anthony N. Cuzzupe, Romina Di Florio,† and Mark A. Rizzacasa*
School of Chemistry, The University of Melbourne, Melbourne, Victoria 3010, Australia
masr@unimelb.edu.au
Received October 22, 2001
The first enantiospecific synthesis of phospholipase A2 (PLA2) inhibitor (-)-cinatrin B (2) from the
D-arabinose derivative 9 is described. The spirolactone system was formed by an Ireland-Claisen
rearrangement of the allyl ester 8 followed by hydrolysis and stereoselective iodolactonization. The
stereoselectivity of the rearrangement was controlled by the asymmetry in the allylic alcohol
fragment. Ester (S)-8 gave the desired rearrangement product 7 and the epimer 13 in high yield
as a 73:27 ratio, respectively. The final stereocenter at C2 was introduced via a chelation-controlled
addition of the Grignard reagent derived from trimethylsilylacetylene to R-hydroxy ketone 6.
Transformation of the terminal alkyne into the methyl ester 21 followed by acetal hydrolysis and
selective lactol oxidation afforded cinatrin B methyl ester (22). Base hydrolysis and acid-induced
relactonization then gave (-)-cinatrin B (2).
In tr od u ction
The rate-limiting step in the biosynthesis of eicosanoids
is the hydrolytic cleavage of arachidonic acid from the
ester linkage to the phospholipid backbone.1 This is
achieved via the action of the lipolytic enzyme, phospho-
lipase A2 (PLA2), which specifically hydrolyses the 2-acyl
position of a glycerophospholipid.2 PLA2 also mediates
the formation of the precursor of platelet-activating factor
(PAF). PAF is released from many inflammatory cells
when activated and is responsible for producing most
phenomena of inflammation.3
While screening for microbial products that possess
pharmacological activity, Itazaki and co-workers isolated
a family of PLA2 inhibitors, cinatrins A (1), B (2), C1 (3),
C2 (4), and C3 (5), from the fermentation broth of the
microorganism Circinotrichum falcatisporum RF-641.4
The cinatrins are potent inhibitors of rat platelet PLA2
with maximal inhibition shown by cinatrin C3 (5) (IC50
70 µM) and B (2) (IC50 120 µM).5 As several eicosanoids
are potent mediators of disease, inhibition of the enzy-
matic activity of PLA2 would be therapeutically benefi-
cial; therefore, the cinatrins are potential antiinflamma-
tory agents.
The structures of all the members of the cinatrin family
were determined by elemental analysis, SI-mass spec-
trometry, various NMR techniques, and analysis of the
respective methyl esters, which also serve to confirm the
number of carboxylic acid residues present.4 A single-
crystal X-ray structure of cinatrin C3 (5) was determined,
and this revealed the relative configuration while CD
spectroscopy was used to assign the absolute stereochem-
istry. In 1997, Evans and co-workers reported the first
total synthesis of (-)-cinatrin C1 (3) and (+)-cinatrin C3
(5)6 using a tartrate aldol methodology.7 This work
established the structures of the cinatrins were in fact
enantiomeric to that originally proposed.4 The revised
stereochemical assignment of cinatrin C3 (5) and cinatrin
C1 (3) reveals that these compounds are stereochemically
related to the zaragozic acids.8 The novel structure and
biological activity of the cinatrins makes them interesting
targets, and we have embarked on a synthetic program
toward these compounds. We now report the first total
synthesis of spirolactone (-)-cinatrin B (2), which is in
agreement with the absolute stereochemical assignment
for this family of compounds as reported by Evans.6
Retr osyn th etic An a lysis
A retrosynthetic analysis of (-)-cinatrin B (2) is shown
† Current address: Starpharma Pty Ltd, c/o CSIRO, Bayview Ave,
Clayton, Victoria 3168, Australia.
in Scheme 1. A chelation-controlled9 carbanion addition
(1) van den Bosch, H. Biochem. Biophys. Acta 1980, 604, 191.
(2) Rang, H. P.; Dale, M. M. Pharmacology, 2nd ed.; Churchhill
Livingstone: Edinburgh, 1991.
(3) Vadas, P.; Pruzanski, W. Lab. Invest. 1986, 55, 391.
(4) Itazaki, H.; Nagashima, K.; Kawamura, Y.; Matsumoto, K.;
Nakai, H.; Terui, Y. J . Antibiot. 1992, 45, 38.
(6) Evans, D. A.; Trotter, B. W.; Barrow, J . C. Tetrahedron 1997,
53, 8779.
(7) Naef, R.; Seebach, D. Angew. Chem., Int. Ed. Engl. 1981, 20,
1030.
(8) Nadin, A.; Nicolaou, K. C. Angew. Chem., Int. Ed. Engl. 1996,
35, 1622.
(5) Tanaka, K.; Itazaki, H.; Yoshida, T. J . Antibiot. 1992, 45, 50.
10.1021/jo016221k CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/23/2002

Synthesis of the Phospholipase A2 Inhibitor (-)-Cinatrin B
J . Org. Chem., Vol. 67, No. 13, 2002 4393
Sch em e 1
F igu r e 1.
Sch em e 2
to R-hydroxy ketone 6 should provide a method for the
introduction of C2 acid functionality. In this step, the free
hydroxyl group delivers an appropriate nucleophile to the
ketone from the â-face. Stereoselective iodolactonization
of the acid derived from ester 7 and reduction would form
the spirolactone system. Intermediate 7 is available via
an Ireland-Claisen rearrangement10 of the allylic ester
8 derived from acid 9, which in turn could be obtained
from the chiral pool starting material D-arabinose.
We have utilized the Ireland-Claisen rearrangement
in the presence of a â-leaving group11 for the synthesis
of 2,2-disubstituted furanoid natural products such as
sphydrofuran12 and the core of the zaragozic acids.13,14
This approach involves enolization and silylation of an
allylic ester I, derived from a furansiduronic acid, and
subsequent stereoselective [3,3]-rearrangement of the
resulting silyl ketene acetal to give tetrahydrofuran II
(Figure 1). Critical to the success of this approach is the
mode of addition in which a solution of the ester is added
to a solution of the base/silylating mixture (TMSCl/NEt3)
in THF at -100 °C in the presence of HMPA as
cosolvent.12,13b,15 Under such conditions, â-elimination
does not occur and rearrangement can proceed via the
less hindered face opposite to the â-OP group in high
yield as shown in Figure 1.
and esterification with racemic alcohol 1217 afforded the
rearrangement substrate 8.
Addition of ester 8 to a solution of LDA and the
11,12,18
centrifugate from a 1:1 v/v mixture of TMSCl/NEt3
in THF/HMPA at -100 °C followed by warming to room
temperature afforded, after hydrolysis and esterification,
esters 13 and 7 in excellent yield but as a 43:57 mixture.
The stereochemistry of major ester 7 was assigned on
the basis of a strong NOE observed between the allylic
protons and H2 in the NOESY spectrum of 7. We
attributed the low stereoselectivity to the fact that facial
selectivity of the rearrangement is mainly governed by
the allyl ester stereocenter marked (Scheme 3), which
overrides the influence of the â-stereocenter on the THF
ring observed previously.12-14 Enolization and silylation
should provide a (Z)-O-silyl ketene acetal 14 as the major
isomer,19 and this intermediate then rearranges via the
two chairlike transition states20 in which the alkyl chain
is in a pseudoequatorial orientation in each.21 Therefore,
the R-epimer would then provide ester 13 while the
desired ester 7 would form from the S-epimer as shown.
Resu lts a n d Discu ssion
The route to cinatrin B (2) began with the synthesis
of the enantiopure acid 9 (Scheme 2). Treatment of
D-arabinose with HCl in dry methanol followed by trityl-
ation of the crude product gave diol 1016 (50%) and the
corresponding â-anomer (16%), which were easily sepa-
rated by flash chromatography. The major product
R-anomer 10 was utilized for the rest of the synthesis.
Thus, compound 10 was perbenzylated and subsequent
removal of the trityl protecting group gave alcohol 11.
Two-step oxidation12 provided acid 9 in excellent yield,
To test this proposal, diasteroisomerically pure (S)-8,
synthesized from acid 9 and optically pure (S)-12,22 was
subjected to the rearrangement conditions (Scheme 3).
A higher selectivity was observed, favoring the desired
(16) (a) Glaudemans, C. P. J .; Fletcher, H. G., J r. J . Am. Chem. Soc.
1965, 87, 4637. (b) Mikhailopulo, I. A.; Sivets, G. G. Helv. Chim. Acta
1999, 82, 2052.
(17) Prepared by the addition of vinylmagnesium bromide to deca-
nal.
(18) Paterson, I.; Hulme, A. N. J . Org. Chem. 1995, 60, 3288. Burke,
S. D.; Ng, R. A.; Morrison, J . A.; Alberti, M. J . J . Org. Chem. 1998, 63,
3160.
(19) Ireland, R. E.; Wipf, P.; Armstrong, J . D., III. J . Org. Chem.
1991, 56, 650.
(20) Ireland, R. E.; Willard, A. K. Tetrahedron Lett. 1975, 16, 3975.
(21) Paterson, I.; Hulme, A. N.; Wallace, D. J . Tetrahedron Lett.
1991, 32, 7601. Wipf, P. In Comprehensive Organic Synthesis; Paquette,
L. A., Ed.; Pergamon Press: Oxford, 1991; Vol. 5, p 827.
(9) Mengel, A.; Reiser, O. Chem. Rev. 1999, 99, 1191.
(10) Ireland, R. E.; Mueller, R. H. J . Am. Chem. Soc. 1972, 94, 5897.
Review: Pereira, S.; Srebnik, M. Aldrichim. Acta 1993, 26, 17.
(11) Ireland, R. E.; Norbeck, D. W. J . Am. Chem. Soc. 1985, 107,
3279.
(12) Di Florio, R.; Rizzacasa, M. A. J . Org. Chem. 1998, 63, 8595.
(13) (a) McVinish, L. M.; Rizzacasa, M. A. Tetrahedron Lett. 1994,
35, 923. (b) Gable, R. W.; McVinish, L. M.; Rizzacasa, M. A. Aust. J .
Chem. 1994, 47, 1537.
(14) Mann, R. K.; Parsons, J . G.; Rizzacasa, M. A. J . Chem. Soc.,
Perkin Trans 1 1998, 1283.
(15) Werschkun, B.; Thiem, J . Synthesis 1999, 121.

4394 J . Org. Chem., Vol. 67, No. 13, 2002
Cuzzupe et al.
Sch em e 3
F igu r e 2.
The stereochemistry of resultant diol 17 was assigned
on the basis of the NMR data shown in Figure 2. In
particular, the strong NOE observed between H2 and H5
indicated that the desired stereochemistry had been
installed at C5. A similar NOE enhancement was de-
tected between the 2-OH group and H5 in cinatrin B (2)
itself.4
Protection of the less hindered alcohol by treatment
with TBSCl and imidazole provided monoether 18, and
Dess-Martin oxidation25 followed by careful HF-induced
desilylation gave labile R-hydroxy ketone 6, which was
utilized in the addition reaction immediately. Prolonged
reaction times (>4 h) for the desilylation resulted in a
large amount of decomposition. After some experimenta-
tion, the chelation-controlled addition26 to the R-hydroxy
ketone27 6 was achieved using 3 equiv of the Grignard
reagent derived from TMS acetylene28 in THF at -78 °C
(Scheme 4). This gave the desired C2 isomer 19 and the
corresponding epimer as a 3.3:1 mixture, respectively, in
acceptable yield for three steps from alcohol 18. Multiple
addition products and starting ketone accounted for the
remaining material. Attempts to drive the reaction to
completion led only to the production of multiple addition
products. Removal of the TMS group enabled separation
of the C2 epimers to give pure alkyne 20 and partial
reduction followed by ozonolysis, oxidation, and esteri-
fication yielded methyl ester 21. One-step oxidation to
form the lactone29 failed, so a two-step sequence was
employed that involved acid hydrolysis of the methyl
ketal followed by selective lactol oxidation30 to provide
(-)-cinatrin B methyl ester (22). The data obtained for
synthetic 22 compared well to that reported for naturally
derived material.4 Base hydrolysis of 22 followed by
relactonization and purification by reversed-phase HPLC
afforded (-)-cinatrin B (2) [synthetic: [R]D -10.4 (c 0.17,
MeOH); natural sample: [R]D -14.5 (c 0.17, MeOH)],
which was identical with the natural product4,31 in all
respects.
isomer 7; however, some of the undesired ester 13 was
also obtained. In this case, it appears that the ratio of
13/7 (27:73) corresponds to the original E/Z ratio obtained
since the (E)-O-ketene acetal would give 13 upon rear-
rangement via the transition state shown in Scheme 3.
This is in close agreement with the observation that
enolization of ethyl 2-tetrahydrofuroate with LDA in
THF/23% HMPA followed by silylation gives a 63:37 ratio
of (Z)- and (E)-O-ketene acetals, respectively.19 As ex-
pected, exposure of the corresponding diastereoisomer
(R)-8 to the rearrangement conditions gave ester 13 as
the major product but with lower selectivity (Scheme 3).
This suggests that the â-stereocenter in the THF ring
may have some effect on the stereochemical outcome as
was observed when the mixture of esters 8 was rear-
ranged.
In conclusion, we have completed the first total syn-
thesis of (-)-cinatrin B (2), which utilized a high-yielding
With ester 7 in hand, we proceeded to investigate the
formation of the spirolactone (Scheme 4). Hydrolysis of
7 provided the corresponding acid, which upon treatment
with I2 in ether23 gave the predicted iodolactone 15 in
high yield as the major isomer (88% ds by 1H NMR).
Radical deiodination24 was effected by Bu3SnH/AIBN in
toluene at 60 °C to give spirolactone 16, which was
debenzylated by exposure to 60 psi H2 gas and Pd(OH)2.
(25) Dess, D. B.; Martin, J . C. J . Am. Chem. Soc. 1991, 113, 7277.
Ireland, R. E.; Liu, L. J . Org. Chem. 1993, 58, 2899.
(26) Still, W. C.; McDonald, J . H., III. Tetrahedron Lett. 1980, 21,
1031. Still, W. C.; Schneider, J . A. Tetrahedron Lett. 1980, 21, 1035.
(27) For an acyclic example see Evans, D. A.; Kaldor, S. W.; J ones,
T. K.; Clardy, J .; Stout, T. J . J . Am. Chem. Soc. 1990, 112, 7001.
(28) For
a recent use of this reagent in a chelation-controlled
addition, see: Carreira, E. M.; Du Bois, J . J . Am. Chem. Soc. 1995,
117, 8106.
(29) Grieco, P. A.; Oguri, T.; Yokoyama, Y. Tetrahedron Lett. 1978,
20, 419.
(22) Tanikaga, R.; Hosoya, K.; Kaji, A. Chem. Lett. 1987, 829. (S)-
12 was obtained by kinetic resolution of racemic 12: Gao, Y.; Hanson,
R. M.; Klunder, J . M.; Ko, S. Y.; Masamune, H.; Sharpless, K. B. J .
Am. Chem. Soc. 1987, 109, 5765. See the Experimental Section for
details.
(23) Bartlett, P. A.; Richardson, D. P.; Myerson, J . Tetrahedron 1984,
40, 2317.
(30) Corey, E. J .; Kang, M.; Desai, M. C.; Ghosh, A. K.; Houpis, I.
N. J . Am. Chem. Soc. 1988, 110, 649.
(31) The specific rotation reported4 for 2 was -24.4 (c 0.308, MeOH).
A natural sample provided by Dr. Toshiyuki Kamigauchi originally
had a specific rotation of -23.0 (c 0.16, MeOH); however, when this
sample was treated with acid, a value of -14.5 (c 0.17, MeOH) was
obtained. We believe the authentic sample was originally ionized and
this was also evident by slight changes observed in the 1H NMR
spectrum of the natural sample upon acidification.
(24) Kuivila, H. G. Synthesis 1970, 499. Miller, J . A.; Pugh, A. W.;
Ullah, G. M. Tetrahedron Lett. 2000, 41, 3265.

Synthesis of the Phospholipase A2 Inhibitor (-)-Cinatrin B
J . Org. Chem., Vol. 67, No. 13, 2002 4395
Sch em e 4
IR (thin film) 3400, 2923, 1487, 1445, 1045, 1001, 765, 701,
Ireland-Claisen rearrangement in the presence of a
â-leaving group. Other highlights of the synthesis in-
cluded a stereoselective iodolactonization to form the C5
stereocenter and a chelation-controlled addition to an
R-hydroxy ketone to introduce the C2 substituent. The
synthesis of other members of this family of compounds
will be reported in due course.
1
632 cm-1; H NMR (300 MHz) δ 2.37 (br s, 1H), 2.50 (d, J )
9.3 Hz, 1H), 3.26 (d, J ) 4.8 Hz, 2H), 3.40 (s, 3H), 3.95 (m,
1H), 4.07 (m, 2H), 4.83 (d, J ) 4.0 Hz, 1H), 7.32 (m, 15H); 13
C
NMR (75.5 MHz) δ 55.4, 64.8, 78.0, 80.8, 86.5, 101.8, 127.0,
127.8, 128.7, 143.9; HRMS (ESI) calcd for C25H26O5Na [M +
Na]+ 429.1678, found 429.1677.
Alcoh ol 11. To a mixture of NaH (3.05 g) (60% w/w
dispersion in mineral oil, washed with dry pentane) and benzyl
bromide (9.16 mL, 76.41 mmol) in dry DMF (71 mL) was added
a solution of the diol 10 (11.53 g, 28.37 mmol) in dry DMF (85
mL) via cannula. The reaction mixture was allowed to stir at
rt for 3 h and then quenched by the slow addition of water,
and the aqueous phase was extracted with ether. The com-
bined extracts were washed with water and brine and dried
(MgSO4), and the solvent was removed under reduced pres-
sure. To the crude product was added 80% aqueous acetic acid
(145 mL), and the mixture was heated at 70 °C for 1.5 h. Water
was added, and the aqueous phase was extracted with ether.
The combined extracts were washed with water, saturated
aqueous NaHCO3, and brine and dried (MgSO4). The solvent
was removed under reduced pressure, and the residue was
purified by silica gel chromatography with 30% EtOAc/petrol
as the eluent to give the alcohol 11 (7.70 g, 79%) as a yellow
Exp er im en ta l Section
1
Gen er a l Meth od s. Unless otherwise stated, H NMR and
proton-decoupled 13C NMR spectra were recorded for deuterio-
chloroform solutions with residual chloroform as internal
standard. Optical rotations were recorded in a 10 cm microcell.
HRMS [electrospray ionization (ESI) or electron impact (EI)]
mass spectra were run at Monash University, Clayton, Vic-
toria. Microanalyses were carried out at the University of
Otago, Dunedin, New Zealand. Flash chromatography was
carried out on Merck silica gel 60. Anhydrous THF was
distilled from sodium metal/benzophenone under a nitrogen
atmosphere. All other anhydrous solvents were purified ac-
cording to standard methods. Petrol refers to the fraction
boiling between 40 and 60 °C.
Meth yl Keta l 10. This method is a modification of the
literature procedure:16b To a suspension of D-arabinose (10.0
g, 66.5 mmol) in dry methanol (384 mL) was added acetyl
chloride (2.0 mL, 28.1 mmol), and the mixture was allowed to
stir at rt overnight, after which time a clear solution resulted.
The reaction mixture was neutralized with Amberlite resin
IRA-400 (OH) (60.0 g) and then filtered, and the resin was
washed with methanol (3 × 500 mL). The combined methanol
washings and the filtrate were concentrated and pumped
under high vacuum (0.05 mmHg) overnight. The crude product
was dissolved in dry DMF (100 mL) and dry pyridine (13.7
mL, 166.3 mmol), DMAP (794 mg, 6.50 mmol) and triphenyl-
methyl chloride (43.5 g, 156 mmol) were added, and the
reaction was stirred at 65 °C for 4 h. Saturated aqueous
NaHCO3 was added, and the aqueous phase was extracted
with ether. The combined extracts were washed with saturated
aqueous CuSO4, water, and brine and dried (MgSO4). The
solvent was removed under reduced pressure, and the residue
was purified by flash chromatography with 60% EtOAc/petrol
as eluent to give the methyl ketal 10 (13.1 g, 50%) as a yellow
solid: mp 113-114 °C (lit.16a 112-113 °C); [R]24D +85.9 (c 1.06,
oil: [R]24 +83.2 (c 1.14, CHCl3); IR (thin film) 3459, 2914,
D
1493, 1451, 1104, 737, 698 cm-1; H NMR (300 MHz) δ 2.10
1
(br s, 1H), 3.39 (s, 3H), 3.64 (dd, J ) 12.3, 4.2 Hz, 1H), 3.84
(dd, J ) 12.3, 3.0 Hz, 1H), 3.99 (m, 2H), 4.15 (m, 1H), 4.51
(ABq, J ) 11.7 Hz, 2H), 4.56 (ABq, J ) 12.0 Hz, 2H), 4.94 (s,
1H), 7.33 (m, 10H); 13C NMR (75.5 MHz) δ 54.9, 62.2, 71.9,
72.3, 82.3, 82.5, 87.7, 107.4, 127.8, 127.85, 127.89, 127.93,
128.4, 128.5, 137.3, 137.6; HRMS (ESI) calcd for C20H24O5Na
[M + Na]+ 367.1521, found 367.1516.
Acid 9. To a solution of the alcohol 11 (7.35 g, 21.34 mmol)
in CH2Cl2 (70 mL) was added Dess-Martin periodinane (13.67
g, 32.01 mmol), and the mixture was stirred at rt for 3 h. Ether,
saturated aqueous NaHCO3, and 1.5 M aqueous Na2S2O3 were
added, and stirring was continued until two clear layers
formed. The aqueous phase was extracted with ether, and the
combined extracts were washed with water and brine and
dried (MgSO4). The solvent was removed under reduced
pressure, and the residue was dissolved in ethanol (109 mL).
A solution of AgNO3 (8.28 g) in H2O (11.5 mL) was added
followed by the dropwise addition of a solution of KOH (7.58
g) in H2O (106.9 mL), the resultant Ag2O suspension was
stirred for 12 h at rt and then filtered through Celite, and the
filter cake was washed with aqueous 6% KOH. Most of the
ethanol was removed under reduced pressure, and the remain-
ing aqueous solution was washed with ether, acidified with
concentrated HCl at 0 °C, and extracted with ether. The
combined extracts were washed with brine and dried (MgSO4),
and the solvent was removed under reduced pressure to give
CHCl3) [lit.2 [R]20 +62.4 (c 1.56, EtOAc)]; IR (Nujol) 3399,
D
2927, 1487, 1445, 1074, 633 cm-1; H NMR (300 MHz) δ 1.59
1
(s, 1H), 2.79 (d, J ) 11.1 Hz, 1H), 3.25 (dd, J ) 10.5, 2.1 Hz,
1H), 3.41 (s, 3H), 3.66 (dd, J ) 10.5, 3.0 Hz, 1H), 3.84 (d, J )
11.1 Hz, 1H), 3.98 (d, J ) 11.1 Hz, 1H), 4.11 (m, 1H), 5.01 (s,
1H), 7.33 (m, 15H); 13C NMR (75.5 MHz) δ 54.9, 63.5, 78.3,
78.9, 86.4, 88.4, 109.3, 127.4, 128.0, 128.8, 142.8; Anal. Calcd
for C25H26O6: C, 73.87; H, 6.44. Found: C, 73.90; H, 6.37.
Further elution using 60% EtOAc/petrol as eluent gave the
â-anomer (4.45 g, 16%) as a gum: [R]24D -31.7 (c 0.89, CHCl3);
the acid 9 (7.00 g, 92%) as a clear, viscous oil: [R]21 +37.7 (c
D
1.04, CHCl3); IR (thin film) 3475, 2933, 1733, 1451, 1355, 1203,

4396 J . Org. Chem., Vol. 67, No. 13, 2002
Cuzzupe et al.
1
1112, 1065, 1027, 953, 739, 698 cm-1; H NMR (300 MHz) δ
filtrate was washed with 10% aqueous HCl, saturated aqueous
NaHCO3, and brine and dried (MgSO4). The solvent was
removed under reduced pressure, and the residue was purified
by flash chromatography with 10% EtOAc/petrol as eluent to
give diastereoisomerically pure ester (S)-8 (477 mg, 62%) as a
3.44 (s, 3H), 3.98 (s, 1H), 4.20 (d, J ) 4.0 Hz, 1H), 4.43 (s,
2H), 4.65 (ABq, J ) 12.3 Hz, 2H), 4.70 (d, J ) 4.2 Hz, 1H),
5.13 (s, 1H), 7.30 (m, 10H); 13C NMR (75.5 MHz) δ 55.4, 71.6,
72.1, 80.9, 84.6, 85.8, 108.2, 127.6, 127.8, 127.9, 128.3, 136.8,
137.0, 174.1; HRMS (ESI) calcd for C20H22O6Na [M + Na]+
381.1314, found 381.1310.
pale yellow oil: [R]20 +37.5 (c 1.49, CHCl3); IR (thin film)
D
1
2922, 2851, 1750, 1451, 1274, 1197, 1101, 735, 697 cm-1; H
Alcoh ol 12. To a solution of decyl aldehyde (8.30 g, 53.11
mmol) in dry ether (120 mL) was added vinylmagnesium
bromide (106 mL, 106 mmol, 1 M solution in THF), and the
reaction was allowed to stir at 0 °C for 1 h and then at rt
overnight. Saturated aqueous NH4Cl was added slowly and
the aqueous phase extracted with ether. The combined extracts
were washed with water and brine and dried (MgSO4). The
solvent was removed under reduced pressure and the residue
purified by flash chromatography with 5% EtOAc/petrol as
eluent to give the racemic alcohol 12 (9.27 g, 95%) as a colorless
oil: IR (thin film) 3386, 2923, 2854, 1466, 1378, 1063, 988,
918 cm-1; 1H NMR (300 MHz) δ 0.87 (t, J ) 6.9 Hz, 3H), 1.26
(s, 14H), 1.53 (m, 2H), 4.07 (m, 1H), 5.09 (d, J ) 10.5 Hz, 1H),
5.21 (d, J ) 17.1 Hz, 1H), 5.86 (ddd, J ) 17.1, 10.5, 6.3 Hz,
1H); 13C NMR (75.5 MHz) δ 14.1, 14.2, 22.7, 25.3, 29.3, 29.6,
31.9, 37.1, 60.4, 73.3, 114.4, 141.4; HRMS (ESI) calcd for
NMR (300 MHz) δ 0.89 (t, J ) 6.3 Hz, 3H), 1.26 (m, 14H),
1.63 (m, 2H), 3.44 (s, 3H), 3.97 (br s, 1H), 4.15 (dd, J ) 4.8,
1.8 Hz, 1H), 4.46 (ABq, J ) 12.0 Hz, 2H), 4.62 (m, 3H), 5.11
(s, 1H), 5.15-5.35 (m, 3H) 5.72 (ddd, J ) 12.4, 10.5, 6.9 Hz,
1H), 7.34 (m, 10H); 13C NMR (75.5 MHz) δ 14.0, 22.6, 24.9,
29.2, 29.3, 29.4, 29.5, 31.8, 34.0, 55.5, 71.7, 72.1, 76.1, 80.8,
85.0, 86.6, 108.1, 117.4, 127.7, 127.79, 127.83, 127.9, 128.33,
128.35, 135.8, 137.2, 137.3, 169.5. Anal. Calcd for C32H44O6:
C, 73.25; H, 8.45. Found: C, 73.45; H, 8.57.
Ester (R)-8. Prepared from alcohol (R)-12 (490 mg, 2.66
mmol) and acid 9 (1.24 g, 3.46 mmol) using the same method
as described above to give (R)-8 (983 mg, 67%): [R]20 +39.8
D
(c 1.93, CHCl3); IR (thin film) 2921, 2851, 1750, 1451, 1273,
1
1194, 1100, 1065, 1027, 735, 697 cm-1; H NMR (300 MHz) δ
0.87 (t, J ) 6.9 Hz, 3H), 1.22 (m, 14H), 1.58 (m, 2H), 3.43 (s,
3H), 3.96 (br s, 1H), 4.16 (dd, J ) 4.8, 1.8 Hz, 1H), 4.46 (ABq,
J ) 12.0 Hz, 2H), 4.61 (ABq, J ) 12.3 Hz, 2H), 4.62 (d, J )
4.5 Hz, 1H), 5.12 (s, 1H), 5.16 (d, J ) 10.5 Hz, 1H), 5.30 (m,
2H) 5.76 (ddd, J ) 17.1, 10.5, 6.6 Hz, 1H), 7.33 (m, 10H); 13C
NMR (75.5 MHz) δ 14.1, 22.7, 25.0, 29.26, 29.31, 29.39, 29.46,
29.51, 31.9, 34.1, 55.5, 71.8, 72.2, 76.0, 81.0, 85.1, 86.6, 108.1,
117.3, 127.7, 127.8, 127.86, 127.91, 128.4, 135.9, 137.3, 169.4.
Anal. Calcd for C32H44O6: C, 73.25; H, 8.45. Found: C, 73.52;
H, 8.64.
C
12H24ONa [M + Na]+ 207.1725, found 207.1719.
Alcoh ol (S)-12. To a solution of the allylic alcohol 12 (933
mg, 5.06 mmol) and (-)-diisopropyl-D-tartrate (142 mg, 0.607
mmol) in CH2Cl2 (20 mL) at rt under argon was added
powdered activated 4 Å molecular sieves (430 mg). The mixture
was cooled to -20 °C, treated with Ti(OiPr)4 (149 µL, 0.506
mmol), and allowed to stir for 20 min. The reaction was then
treated with a solution of TBHP (644 µL, 3.54 mmol, 5-6 M
in decane dried with freshly activated 4 Å pellets) and stored
at -20 °C for 3 days, after which time it was quenched with
an aqueous solution of FeSO4 and citric acid at -20 °C and
stirred vigorously without cooling until two clear layers
resulted. The phases were separated, and the aqueous phase
was extracted with CH2Cl2. The combined extracts were
concentrated to half the original volume and stirred for 30 min
with a solution of 30% NaOH in brine (5 mL). The phases were
again separated, the aqueous phase was extracted with CH2-
Cl2, and the combined extracts were washed with water and
brine. The solvent was removed under reduced pressure, and
the residue was purified by silica gel chromatography with 5%
EtOAc/petrol as eluent to give the alcohol (S)-12 as a colorless
oil (352 mg, 38%): [R]23 +12.1 (c 1.22, MeOH) [lit.22 [R]21
Ester s 7 a n d 13. A solution of n-BuLi in hexanes (2.3 M,
6.63 mL, 15.25 mmol) was added dropwise to a solution of iPr2-
NH (2.0 mL, 15.25 mmol) in dry THF (35 mL) at 0 °C under
argon. The resultant base solution was stirred at 0 °C for 5
min, cooled to -78 °C, and added dropwise via cannula to a
solution of the ester 8 (4.00 g, 7.62 mmol), HMPA (8.41 mL),
and the supernatant from a centrifuged mixture of freshly
distilled TMSCl (3.39 mL, 26.68 mmol) and NEt3 (3.72 mL,
26.68 mmol) in dry THF (48 mL) at -100 °C (liquid N2/MeOH
bath). The resulting mixture was stirred at -100 °C for 10
min, allowed to warm to rt, and then cooled to 0 °C, and
aqueous 1 M NaOH (52.57 mL) was added followed by ether
and water. The aqueous phase was then acidified with
concentrated HCl at 0 °C and extracted with ether, and the
combined extracts were washed with water and brine and
dried (MgSO4). The solvent was removed under reduced
pressure, and the residue was dissolved in ether (50 mL) and
treated with excess CH2N2 to give a mixture of esters in a 43:
57 ratio which were separated by flash chromatography.
Elution using 5% EtOAc/petrol gave ester 13 (1.74 g, 42%) as
D
D
+11.4 (c 1.0, MeOH)]. Further elution with 15% EtOAc/petrol
gave the epoxide (413 mg, 41%) as an oil: [R]28D -12.3 (c 1.05,
CHCl3); IR (thin film) 3838, 2925, 2855, 2360, 1653, 1559,
1
1507, 1457 cm-1; H NMR (300 MHz) δ 0.87 (t, J ) 6.6 Hz,
3H), 1.26 (m, 14H), 1.53 (m, 2H), 1.81 (br s, 1H), 2.73 (m, 1H),
2.80 (dd, J ) 5.1, 3.0 Hz, 1H), 3.01 (dd, J ) 6.9, 3.0 Hz, 1H),
3.83 (m, 1H); 13C NMR (75.5 MHz) δ 14.1, 22.7, 25.3, 29.3,
29.5, 29.6, 31.9, 33.4, 43.4, 54.5, 68.4. Anal. Calcd for
a pale yellow oil: [R]24 +16.3 (c 0.93, CHCl3); IR (thin film)
D
2921, 2850, 1727, 1451, 1108, 1027, 735, 697 cm-1; H NMR
1
C
25H26O6: C, 71.95; H, 12.08. Found: C, 71.99; H, 12.28.
Alcoh ol (R)-12. Prepared as described above but using (+)-
(300 MHz) δ 0.88 (t, J ) 6.3 Hz, 3H), 1.25 (m, 14H), 1.98 (m,
2H), 2.70 (m, 2H), 3.45 (s, 3H), 3.67 (s, 3H), 3.96 (br s, 1H),
4.21 (d, J ) 2.4 Hz, 1H), 4.42 (s, 2H), 4.65 (ABq, J ) 12.0 Hz,
2H), 5.04 (s, 1H), 5.45 (m, 2H), 7.33 (m, 10H); 13C NMR (75.5
MHz) δ 14.1, 22.6, 29.1, 29.3, 29.5, 29.6, 31.9, 32.7, 37.5, 52.2,
55.9, 71.8, 72.8, 84.7, 86.7, 89.6, 107.9, 123.5, 127.66, 127.77,
127.80, 127.9, 128.3, 134.9, 137.4, 137.7, 172.9. Anal. Calcd
for C33H46O6: C, 73.57; H, 8.61. Found, C, 73.70; H, 8.39.
Further elution with 5% EtOAc/petrol gave a mixed fraction
of esters 13 and 7 (483 mg, 12%). Elution with 10% EtOAc/
diethyl-L-tartrate: [R]28 -11.9 (c 1.14, MeOH).
D
Ester 8. To a solution of the acid 9 (2.97 g, 8.29 mmol) in
dry CH2Cl2 (20 mL) were added the alcohol 12 (1.17 g, 6.35
mmol) and DMAP (100 mg, 0.82 mmol). After being stirred at
rt for 20 min, the reaction was cooled to 0 °C, DCC (1.70 g,
8.24 mmol) was added, stirring was continued for 10 min, and
the resulting white suspension was allowed to stir at rt
overnight. The reaction was diluted with petroleum ether and
filtered through a pad of Celite. The filtrate was washed with
10% aqueous HCl, saturated NaHCO3, and brine and dried
(MgSO4).The solvent was removed under reduced pressure,
and the residue was purified by silica gel chromatography with
5% EtOAc/petrol as eluent to give an inseparable mixture of
esters 8 (3.18 g, 95%) in 1:1 ratio, as a pale yellow oil.
petrol then gave ester 7 (1.78 g, 43%) as a pale yellow oil: [R]24
D
+32.2 (c 1.03, CHCl3); IR (thin film) 2921, 2850, 1732, 1451,
1
1202, 1112, 734, 697 cm-1; H NMR (300 MHz) δ 0.88 (t, J )
6.6 Hz, 3H), 1.25 (m, 14H), 2.00 (m, 2H), 2.54 (dd, J ) 13.5,
5.4 Hz, 1H), 2.66 (dd, J ) 13.5, 6.3 Hz, 1H), 3.53 (s, 3H), 3.75
(s, 3H), 3.94 (m, 1H), 4.00 (m, 1H), 4.40 (ABq, J ) 12.0 Hz,
Ester (S)-8. The alcohol (S)-12 (269 mg, 1.46 mmol) was
added to a solution of the acid 9 (680 mg, 1.90 mmol) and
DMAP (21 mg, 0.173 mmol) in CH2Cl2 (6 mL). The mixture
was cooled to 0 °C, and DCC (392 mg, 1.90 mmol) was added.
The mixture was then allowed to warm to rt, stirred overnight,
diluted with petrol, and filtered through a pad of Celite. The
2H), 4.59 (s, 2H), 5.05 (s, 1H), 5.44 (m, 2H), 7.34 (m, 10H); 13
C
NMR (75.5 MHz) δ 14.0, 22.6, 29.0, 29.2, 29.3, 29.4, 29.5, 31.8,
32.5, 40.9, 51.8, 55.7, 71.8, 72.7, 85.3, 86.3, 90.6, 108.5, 123.4,
127.4, 127.6, 127.66, 127.70, 127.9, 128.2, 128.3, 135.1, 137.4,
171.3. Anal. Calcd for C33H46O6: C, 73.57; H, 8.61. Found: C,
73.68; H, 8.53.

Synthesis of the Phospholipase A2 Inhibitor (-)-Cinatrin B
J . Org. Chem., Vol. 67, No. 13, 2002 4397
Ir ela n d -Cla isen r ea r r a n gem en t of ester (S)-8. The
rearrangement conditions described for ester 8 were applied
to the ester (S)-8 (477 mg, 0.909 mmol). Methylation of the
crude acids with CH2N2 gave a mixture of methyl esters 13
and 7 (400 mg, 82%) in a 27:73 ratio (as determined by
integration of the 1H NMR spectrum of the crude product)
which were separated by silica gel chromatography with 10%
EtOAc/petrol as eluent.
Ir ela n d -Cla isen Rea r r a n gem en t of Ester (R)-8. The
rearrangement conditions described for ester 8 were applied
to the ester (R)-8 (740 mg, 1.41 mmol). Methylation of the
crude acids with CH2N2 gave a mixture of methyl esters 13
and 7 (686 mg, 76%) in a 62:38 ratio (as determined by
integration of the 1H NMR spectrum of the crude product)
which were separated by silica gel chromatography with 10%
EtOAc/petrol as eluent.
concentrated HCl followed by Pd(OH)2 on carbon (20 wt % Pd,
66.4 mg, 0.125 mmol), and the resulting suspension was stirred
vigorously under a H2 atmosphere at 60 psi for 17 h. The
suspension was then filtered through Celite, and the filtrate
was concentrated under reduced pressure. The residue was
purified by flash chromatography with 20-50% EtOAc/petrol
as eluent to give the diol 17 (189 mg, 88%) as a crystalline
solid: mp 54-56 °C; [R]18 +93.8 (c 0.84, CHCl3); IR (KBr)
D
3470, 3411, 2919, 2852, 1771, 1466, 1214, 1044, 1001 cm-1
;
1H NMR (300 MHz) δ 0.87 (t, J ) 6.6 Hz, 3H), 1.18-1.52 (m,
16H), 1.54-1.67 (m, 1H), 1.69-1.82 (m, 1H), 2.10 (dd, J ) 12.9,
10.5 Hz, 1H), 2.57 (dd, J ) 12.9, 5.1 Hz, 1H), 3.36 (br s, 2H),
3.50 (s, 3H), 4.11 (d, J ) 2.4 Hz, 1H), 4.27 (s, 1H), 4.46 (m,-
1H), 4.98 (s, 1H); 13C NMR (75.5 MHz) δ 13.9, 22.5, 24.7, 29.1,
29.2, 29.3, 29.4, 31.7, 35.1, 40.8, 55.5, 77.0, 79.1, 80.5, 88.3,
108.9, 174.6; HRMS (ESI) calcd for C18H32NaO6 [M + Na]+
367.2097, found 367.2080.
Iod ola cton e 15. To a solution of the methyl ester 7 (906
mg, 1.68 mmol) in THF (27.7 mL) and water (8.3 mL) was
added NaOH (404 mg, 10.1 mmol), and the solution was heated
at reflux for 48 h. Most of the THF was removed under reduced
pressure, and ether and water were added. The aqueous phase
was acidified at 0 °C with concentrated HCl and then extracted
with ether, and the combined extracts were washed with water
and brine and dried (MgSO4). The solvent was removed under
reduced pressure, the residue was dissolved in ether (9.5 mL),
and saturated aqueous NaHCO3 (9.5 mL) was added. The
mixture was cooled to 0 °C, a solution of I2 (265 mg, 1.04 mmol)
in ether (9.5 mL) was added dropwise by cannula, and the
mixture was stirred at 0 °C for 15 min. Water was added, and
the mixture was extracted with ether. The combined extracts
were washed with 1.5 M aqueous Na2S2O3, saturated aqueous
NaHCO3, water, and brine and dried (MgSO4). The solvent was
removed under reduced pressure, and the residue was purified
by flash chromatography. Elution with 5% EtOAc/petrol gave
an inseparable mixture of diastereoisomeric iodolactones (130
mg, 12%) as a pale yellow oil followed by the iodolactone 15
Eth er 18. To a solution of the diol 17 (183 mg, 0.53 mmol)
in DMF (5.2 mL) at rt under argon was added imidazole (72.4
mg, 1.06 mmol) followed by tert-butyldimethylsilyl chloride
(96.1 mg, 0.638 mmol), and the solution was stirred at rt for
15 h. Water and ether were added, and the aqueous phase was
extracted with ether. The combined extracts were washed with
water and brine and dried (MgSO4). The solvent was removed
under reduced pressure, and the residue was purified by flash
chromatography with 10% EtOAc/petrol as eluent to give the
TBS ether 18 (214 mg, 88%) as a yellow oil: [R]14 +57.3 (c
D
1.19, CHCl3); IR (thin film) 3526, 2929, 2857, 1783, 1464, 1120,
1
851 cm-1; H NMR (300 MHz) δ 0.11 (s, 6H), 0.87 (t, J ) 6.6
Hz, 3H), 0.88 (s, 9H), 1.20-1.54 (m, 16H), 1.56-1.82 (m, 2H),
2.07 (dd, J ) 12.9, 10.8 Hz, 1H), 2.49 (dd, J ) 12.9, 5.1 Hz,
1H), 3.50 (s, 3H), 3.94 (s, 1H), 4.15 (s, 1H), 4.42 (m, 1H), 4.87
(s,1H); 13C NMR (75.5 MHz) δ -5.0, -4.9, 14.1, 17.9, 22.6, 25.0,
25.6, 29.3, 29.4, 29.47, 29.53, 31.9, 35.2, 41.3, 55.3, 76.8, 80.1,
81.1, 89.2, 109.6, 174.1; HRMS (ESI) calcd for C24H46NaO6Si
[M + Na]+ 481.2961, found 481.2942.
(931 mg, 85%) as a low melting solid: [R]18 +67.2 (c 1.00,
Alk yn e 20. To a solution of the alcohol 18 (109 mg, 0.238
mmol) in CH2Cl2 at 0 °C under argon was added Dess-Martin
reagent (251 mg, 0.593 mmol), and the mixture was allowed
to warm to rt and stirred for 2 h. Ether (5 mL), saturated
aqueous NaHCO3 (5 mL), and 1.5 M aqueous Na2S2O3 (5 mL)
were added, and the mixture was stirred until two clear layers
formed. The aqueous phase was extracted with ether, and the
combined extracts were washed with water and brine and
dried (MgSO4). The solvent was removed under reduced
pressure to give the ketone as a yellow oil (109 mg, 100%).
The ketone (164 mg, 0.359 mmol) was dissolved in 4 mL of a
solution of 48% aqueous HF (2 mL) in MeCN (8 mL), and the
mixture was stirred vigorously at rt for 4 h. Ether was added,
and the reaction was quenched with saturated aqueous
NaHCO3. The aqueous phase was extracted with ether, and
the combined extracts were washed with water and brine and
dried (MgSO4). The solvent was removed under reduced
pressure to give the R-hydroxy ketone 6 as a yellow solid (126
mg) that was utilized immediately in the next step. To a
solution of ethylmagnesium bromide (1.0 M in THF, 3.68 mL,
3.68 mmol) in THF (0.6 mL) at 0 °C under argon was added
TMS acetylene (0.526 mL, 3.72 mmol), and the mixture was
stirred for 0.5 h before being allowed to warm to 30 °C and
stirred for a further 10 min. An aliquot of the Grignard reagent
(1.28 mL, 1.1 mmol) was then added dropwise to a solution of
the crude R-hydroxy ketone 6 (126 mg) in THF (0.72 mL) at
-78 °C under argon, and the mixture was stirred for 2.25 h.
The mixture was then allowed to warm to 0 °C and was
quenched immediately with saturated aqueous NH4Cl. The
aqueous phase was extracted with ether, and the combined
extracts were washed with water and brine and dried (MgSO4).
The solvent was removed under reduced pressure, and the
residue was purified by flash chromatography with 5-30%
EtOAc/petrol as eluent to give an inseparable mixture of bis-
addition products (26 mg) followed by an inseparable 3.3:1
mixture of TMS acetylenes 19 (61 mg, 38%) as yellow oils.To
a solution of the mixture of alkynes 19 (81 mg, 0.186 mmol)
in THF (2.25 mL) at rt was added TBAF‚3H2O (71 mg, 0.225
mmol), and the mixture was stirred for 20 min. Water was
D
CHCl3); IR (thin film) 2955, 2927, 2856, 1794. 1455, 1118, 755
1
cm-1; H NMR (300 MHz) δ 0.90 (t, J ) 6.6 Hz, 3H), 1.20-
1.40 (m, 13H), 1.46-1.60 (m, 1H), 1.62-1.78 (m, 1H), 1.82-
1.96 (m, 1H), 2.20 (dd, J ) 13.5, 8.7 Hz, 1H), 2.52 (dd, J )
13.5, 4.8 Hz, 1H), 3.49 (s, 3H), 3.88-4.05 (m, 2H), 4.08 (d, J )
5.4 Hz, 1H), 4.33 (dd, J ) 5.1, 3.0 Hz, 1H), 4.49 (d, J ) 12.6
Hz, 1H), 4.60 (ABq, J ) 12.0 Hz, 2H), 4.79 (d, J ) 12.6 Hz,
1H), 5.04 (d, J ) 3.0 Hz, 1H), 7.36 (m, 10H); 13C NMR (75.5
MHz) δ 14.1, 22.6, 28.6, 28.8, 29.2, 29.4, 29.5, 31.8, 35.6, 38.4,
42.3, 56.0, 72.2, 72.5, 77.8, 85.8, 86.0, 86.1, 108.6, 127.8, 128.0,
128.06, 128.11, 128.49, 128.53, 137.0, 137.3, 173.3; HRMS
(ESI) calcd for C32H43INaO6 [M + Na]+ 673.2002, found
673.1998.
La cton e 16. To a solution of the iodolactone 15 (380 mg,
0.584 mmol) and AIBN (33.7 mg) in toluene (3.9 mL) at 45 °C
under argon was added a solution of Bu3SnH (0.473 mL, 1.76
mmol) in toluene (10.2 mL) by cannula. The resulting solution
was heated to 60 °C and then stirred for 1 h. After cooling to
rt, saturated aqueous NH4Cl was added and the mixture was
extracted with ether. The combined extracts were washed with
water and brine and dried (MgSO4). The solvent was removed
under reduced pressure, and the residue was purified by flash
chromatography with 10% EtOAc/petrol containing 1% NEt3
as eluent to give the lactone 16 (288 mg, 94%) as a low melting
solid: [R]20 +69.8 (c 1.04, CHCl3); IR (thin film) 2927, 2855,
D
1786, 1456, 1118, 698 cm-1; 1H NMR (300 MHz) δ 0.88 (t, J )
6.6 Hz, 3H), 1.22-1.56 (m, 17H), 1.58-1.72 (m, 1H), 2.07 (dd,
J ) 12.9, 9.9 Hz, 1H), 2.25 (dd, J ) 12.9, 5.7 Hz, 1H), 3.49 (s,
3H), 4.03 (d, J ) 4.8 Hz, 1H), 4.07 (m, 1H), 4.32 (dd, J ) 5.1,
2.7 Hz, 1H), 4.48 (d, J ) 12.9 Hz, 1H), 4.58 (ABq, J ) 11.7
Hz, 2H), 4.78 (d, J ) 12.9 Hz, 1H), 5.04 (d, J ) 3.0 Hz, 1H),
7.34 (m, 10H); 13C NMR (75.5 MHz) δ 14.0, 22.5, 24.8, 29.1,
29.2, 29.3, 29.37, 29.43, 31.8, 35.3, 41.0, 55.8, 72.0, 72.3, 76.0,
85.6, 85.9, 86.1, 108.4, 127.7, 127.8, 127.88, 127.92, 128.3,
128.4, 137.1, 137.3, 173.6; HRMS (ESI) calcd for C32H44NaO6
[M + Na]+ 547.3036, found 547.3028.
Diol 17. To a solution of the dibenzyl ether 16 (329 mg,
0.627 mmol) in MeOH (10 mL) was added one drop of

4398 J . Org. Chem., Vol. 67, No. 13, 2002
Cuzzupe et al.
added, the aqueous phase was extracted with ether, and the
combined extracts were washed with water and brine and
dried (MgSO4). The solvent was removed under reduced
pressure, and the residue was purified by flash chromatogra-
phy with 20-40% EtOAc/petrol as eluent to give the minor
1H), 4.75 (d, J ) 5.1 Hz, 1H), 5.12 (d, J ) 5.4 Hz, 1H); 13C
NMR (75.5 MHz) δ 14.1, 22.7, 24.9, 29.2, 29.3, 29.4, 29.46,
29.54, 31.9, 35.7, 37.9, 53.7, 57.0, 76.9, 80.2, 85.3, 85.8, 108.4,
171.3, 173.8; HRMS (ESI) calcd for C20H34NaO8 [M + Na]+
425.2151, found 425.2157.
C2 epimer (12.1 mg, 18%) as a pale yellow oil: [R]17 +42.9 (c
D
Cin a tr in B Meth yl Ester 22. A solution of the methyl ketal
21 (11.8 mg, 0.029 mmol) in 80% aqueous acetic acid (1.42 mL)
and 10% aqueous HCl (50µL) was heated at 100 °C for 3.5 h
and then cooled to rt. Water was added, the aqueous phase
was extracted with ether, and the combined extracts were
washed with water, saturated aqueous NaHCO3, and brine and
dried (MgSO4). The solvent was removed under reduced
pressure, and the residue was dissolved in MeOH (0.75 mL)
and water (75 µL). CaCO3 (87.5 mg, 0.87 mmol) and I2 (181
mg, 0.71 mmol) were then added, and the resulting brown
suspension was stirred at 70 °C for 18 h and then cooled to rt.
Water was added, and the aqueous phase was extracted with
ether. The combined extracts were washed with 1.5 M aqueous
Na2S2O3 and brine and dried (MgSO4). The solvent was
removed under reduced pressure, and the residue was purified
by flash chromatography with 40% EtOAc/petrol as eluent to
give cinatrin B methyl ester (22) (7.8 mg, 61%) as a white
powder: mp 124-126 °C; [R]14D -13.2 (c 0.39, MeOH); IR (KBr)
3509, 3420, 2957, 2926, 2854, 1820, 1772, 1740, 1444, 1223,
0.82, CHCl3); IR (thin film) 3468, 3267, 2956, 2926, 2855, 1770,
1
1466, 1202, 1124, 1013, 738 cm-1; H NMR (300 MHz) δ 0.88
(t, J ) 6.3 Hz, 3H), 1.16-1.54 (m, 16H), 1.56-1.69 (m, 1H),
1.71-1.85 (m, 1H), 2.00 (dd, J ) 13.8, 8.7 Hz, 1H), 2.59 (s,
1H), 3.03 (dd, J ) 13.8, 6.0 Hz, 1H), 3.51 (s, 3H), 4.55 (m, 1H),
4.76 (d, J ) 5.1 Hz, 1H), 4.96 (d, J ) 5.4 Hz, 1H); 13C NMR
(75.5 MHz) δ 14.1, 22.7, 25.0, 29.3, 29.4, 29.5, 29.6, 31.9, 35.4,
35.8, 57.2, 73.6, 76.0, 77.7, 79.3, 80.0, 90.3, 108.4, 174.5; HRMS
(ESI) calcd for
C
20H32NaO6 [M + Na]+ 391.2097, found
391.2102. Further elution gave the major C2 epimer 20 (41.4
mg, 61%) as a pale yellow oil: [R]17 +52.6 (c 1.02, CHCl3); IR
D
(thin film) 3434, 3287, 2926, 2556, 1776, 1467, 1203, 1029, 739
1
cm-1; H NMR (300 MHz) δ 0.87 (t, J ) 6.6 Hz, 3H), 1.18-
1.52 (m, 16H), 1.54-1.68 (m, 1H), 1.70-1.82 (m, 1H), 2.10 (dd,
J ) 13.8, 9.9 Hz, 1H), 2.80 (s, 1H), 2.92 (dd, J ) 13.8, 5.4 Hz,
1H), 3.53 (s, 3H), 4.22 (s, 1H), 4.62 (m, 1H), 5.03 (s, 1H); 13C
NMR (75.5 MHz) δ 14.1, 22.6, 24.9, 29.3, 29.4, 29.47, 29.54,
31.9, 35.5, 40.7, 56.1, 77.7, 78.2, 78.5, 80.3, 81.2, 89.1, 108.0,
173.6; HRMS (ESI) calcd for C20H32NaO6 [M + Na]+ 391.2097,
found 391.2101.
1
1148 cm-1; H NMR (300 MHz, DMSO-d6) δ 0.86 (t, J ) 6.6
Hz, 3H), 1.18-1.40 (m, 16H), 1.63 (m, 2H), 2.31 (dd, J ) 14.4,
9.6 Hz, 1H), 2.39 (dd, J ) 14.4, 6.0 Hz, 1H), 3.75 (s, 3H), 4.53
(m, 1H), 4.76 (d, J ) 6.6 Hz, 1H), 6.81 (d, J ) 6.6 Hz, 1H),
7.34 (s, 1H); 13C NMR (75.5 MHz, DMSO-d6) δ 13.9, 22.0, 24.3,
28.6, 28.7, 28.8, 28.9, 31.2, 34.3, 36.0, 52.8, 73.0, 77.2, 84.2,
84.3, 168.7, 172.0, 172.1; HRMS (ESI) calcd for C19H30NaO8
[M + Na]+ 409.1838, found 409.1821.
Meth yl Ester 21. To a solution of the alkyne 20 (30 mg,
0.081 mmol) in MeOH (1.5 mL) was added Lindlar catalyst
(8.4 mg, 0.004 mmol), the suspension was stirred under a H2
atmosphere for 2 h and then filtered through Celite, and the
filtrate was concentrated under reduced pressure. The residue
was purified by flash chromatography with 20-40% EtOAc/
petrol as eluent to give the alkene as an oil (25 mg, 83%): [R]17
D
Cin a tr in B (2). A solution of the methyl ester 22 (11.9 mg,
0.031 mmol) in THF (0.5 mL) and 2 M aqueous NaOH (0.5
mL, 1.0 mmol) was stirred at 40 °C for 24 h. Aqueous HCl (2
M, 0.56 mL, 1.12 mmol) was added, and stirring was continued
for a further 1 h. The solution was allowed to cool to rt and
stirred for a further 3.5 h. Water was added, the mixture was
extracted with EtOAc, and the combined extracts were washed
with brine and then dried (Na2SO4). The solvent was removed
under reduced pressure to give a white powder (11.5 mg) that
was purified by preparative reversed-phase HPLC (C-18 5 µm,
250 × 10 mm, 0.1% TFA-80% MeCN/H2O as eluent, flow
rate: 2 mLmin-1; tR 14.13 min; natural sample, tR 14.13 min)
+63.7 (c 1.16, CHCl3); IR (thin film) 3471, 2927, 2856, 1770,
1
1642, 1467, 1201, 1108, 1018, 738 cm-1; H NMR (300 MHz)
δ 0.87 (t, J ) 6.6 Hz, 3H), 1.16-1.48 (m, 16H), 1.51-1.61 (m,
1H), 1.63-1.78 (m, 1H), 1.97 (dd, J ) 13.8, 9.9 Hz, 1H), 2.67
(dd, J ) 13.8, 5.7 Hz, 1H), 3.52 (s, 3H), 4.26 (d, J ) 2.4 Hz,
1H), 4.29 (m, 1H), 4.97 (d, J ) 2.1 Hz, 1H), 5.51 (dd, J ) 10.8,
1.5 Hz, 1H), 5.75 (dd, J ) 17.1, 1.5 Hz, 1H), 6.15 (dd, J ) 17.1,
10.8 Hz, 1H); 13C NMR (75.5 MHz) δ 14.1, 22.7, 24.9, 29.3,
29.4, 29.47, 29.54, 31.9, 35.6, 38.6, 56.2, 77.4, 81.6, 82.0, 89.4,
108.8, 119.4, 132.1, 174.9; HRMS (ESI) calcd for C20H34NaO6
[M + Na]+ 393.2253, found 393.2255.Ozone gas was bubbled
through a solution of the alkene (24 mg, 0.065 mmol) in CH2-
Cl2 (1.45 mL) and MeOH (50 µL) at -78 °C until a pale blue
color persisted. Me2S (23.7 µL, 0.323 mmol) was added, the
solution was allowed to warm to rt, and stirring was continued
for a further 30 min. Water and ether were added, and the
aqueous phase was extracted with ether. The combined
extracts were washed with water and brine and dried (MgSO4),
and the solvent was removed under reduced pressure. The
resulting crude aldehyde was dissolved in tert-butyl alcohol
(0.42 mL), and 2-methyl-2-butene (67.9 µL) was added. A
solution of NaH2PO4‚H2O (17.8 mg, 0.13 mmol) and NaClO2
(23.3 mg, 0.26 mmol) in water (0.23 mL) was then added and
the mixture was stirred at rt for 17 h. Water and EtOAc were
added, the aqueous phase was acidified with 10% aqueous HCl
and then extracted with EtOAc, and the combined extracts
were washed with water and brine and dried (Na2SO4). The
solvent was removed under reduced pressure, and the residue
was treated with excess CH2N2. Purification by flash silica gel
chromatography with 30-50% EtOAc/petrol as eluent gave the
to give cinatrin B (2) (3.4 mg, 30%) as a white powder: [R]18
D
-10.4 (c 0.17, MeOH). Natural sample: [R]16 -14.1 (c 0.17,
D
1
MeOH); H NMR (300 MHz, DMSO-d6) δ 0.84 (t, J ) 6.9 Hz,
3H), 1.14-1.39 (m, 16H), 1.63 (m, 2H), 2.31 (dd, J ) 14.1, 9.6
Hz, 1H), 2.39 (dd, J ) 14.1, 6.0 Hz, 1H), 4.53 (m, 1H), 4.74 (s,
1H); 13C NMR (75.5 MHz, DMSO-d6) δ 13.9, 22.0, 24.4, 28.56,
28.6, 28.8, 28.88, 28.9, 31.2, 34.4, 36.2, 72.7, 77.1, 83.7, 84.1,
169.5, 172.3, 172.4; HRMS (ESI) calcd for C18H27O8 [M - H]-
371.1706, found 371.1700.
Ack n ow led gm en t. We thank Dr. Toshiyuki Kami-
gauchi (Shionogi Research Laboratories, Osaka, J apan)
for an authentic sample of (-)-cinatrin B (2) as well as
copies of the NMR spectra of 2 and cinatrin B methyl
ester (22). We also thank the Australian Research
Council for financial support.
Su p p or tin g In for m a tion Ava ila ble: Copies of the 1H and
13C NMR spectra of all key intermediates and synthetic and
natural cinatrin B (2) as well as HPLC traces of synthetic and
natural 2. This material is available free of charge via the
Internet at http://pubs.acs.org.
methyl ester 21 (19.3 mg, 74%) as a clear oil: [R]17 +31.4 (c
D
0.97, CHCl3); IR (thin film) 3473, 2956, 2927, 2856, 2361, 1780,
1
1742, 1457, 1208, 1125, 1027, 737 cm-1; H NMR (300 MHz)
δ 0.87 (t, J ) 6.6 Hz, 3H), 1.16-1.48 (m, 16H), 1.50-1.62 (m,
1H), 1.64-1.78 (m, 1H), 2.09 (dd, J ) 14.4, 8.7 Hz, 1H), 2.23
(dd, J ) 14.4, 6.0 Hz, 1H), 3.52 (s, 3H), 3.94 (s, 3H), 4.31 (m,
J O016221K