The isolation and synthesis of novel nematocidal dithiocyanates from an Australian marine sponge, Oceanapia sp.

Article abstract of DOI:10.1021/jo0106750

Bioassay-directed fractionation of the EtOH extract of an Oceanapia sp. collected off the northern Rottnest Shelf, Australia, has yielded three novel dithiocyanates, thiocyanatins A (1), B (2a), and C (2b). The structures were determined by detailed spectroscopic analysis and confirmed by total synthesis. In addition to featuring an unprecedented dithiocyanate functionality, thiocyanatins possess an unusual 1,16-difunctionalized n-hexadecane carbon skeleton and are revealed as a hitherto unknown class of nematocidal agent.

Full text of DOI:10.1021/jo0106750

J . Org. Chem. 2001, 66, 7765-7769
7765
Th e Isola tion a n d Syn th esis of Novel Nem a tocid a l Dith iocya n a tes
fr om a n Au str a lia n Ma r in e Sp on ge, Ocea n a pia sp .
Robert J . Capon,*,† Colin Skene,† Edward Hsiang-Te Liu,† Ernest Lacey,1 J ennifer H. Gill,‡
Kirstin Heiland,§ and Thomas Friedel§
School of Chemistry, University of Melbourne, Parkville, Victoria 3010, Australia
r.capon@unimelb.edu.au
Received J uly 5, 2001
Bioassay-directed fractionation of the EtOH extract of an Oceanapia sp. collected off the northern
Rottnest Shelf, Australia, has yielded three novel dithiocyanates, thiocyanatins A (1), B (2a ), and
C (2b). The structures were determined by detailed spectroscopic analysis and confirmed by total
synthesis. In addition to featuring an unprecedented dithiocyanate functionality, thiocyanatins
possess an unusual 1,16-difunctionalized n-hexadecane carbon skeleton and are revealed as a
hitherto unknown class of nematocidal agent.
In tr od u ction
thiocyanate psammaplin B,12 from the sponge Psamma-
plysilla purpurea, and the alkaloid thiocyanate cylindri-
cines F-H,13,14 from the ascidian Clavelina cylindrica.
Marine thiocyanates have been attributed a range of
biological properties, including cytotoxicity,6 antifouling,7
antimalarial,9 and antifungal11 activity. In this paper, we
describe the isolation, structural elucidation, and syn-
thesis of three new dithiocyanates, designated thiocy-
anatin A (1), B (2a ), and C (2b), from a marine sponge of
the genus Oceanapia, collected off the northern Rottnest
Shelf, Australia. In addition to featuring an unprec-
edented dithiocyanate functionality, thiocyanatins pos-
sess an unusual 1,16-difunctionalized n-hexadecane car-
bon skeleton and are revealed as a hitherto unknown
class of nematocidal agent. Preliminary structure-activ-
ity relationship (SAR) studies have identified key aspects
of the nematocidal pharmacophore and as such indicate
worthwhile directions for future SAR investigations.
During our ongoing investigations into Australian
marine metabolites as antiparasitic agents with potential
application in animal health, we have encountered
numerous structurally novel nematocides. These have
included an extensive array of epoxylipids from the brown
alga Notheia anomala,1 as well as the alkaloids geodin
A Mg salt,2 the amphilactams,3 and onnamide F4 from
various southern Australian sponges. These prior suc-
cesses have encouraged a belief that marine metabolites
hold considerable promise as a source for bioprospecting
new-generation antiparasitics. In this paper, we extend
the class of marine natural products that display promis-
ing nematocidal properties to include lipid thiocyanates.
While marine metabolites incorporating a thiocyanate
moiety are known, reports on such compounds do not
feature prominently in the marine natural products
literature. Such accounts as do exist tend to be dominated
by monothiocyanate substituted terpenes from sponges.5-11
Departures from this trend include the bromotyrosine
* To whom correspondence should be addressed. Phone: +61 3 8344
6468. Fax: +61 3 9347 5180.
† School of Chemistry, University of Melbourne, Parkville, Victoria
3010, Australia.
‡ Microbial Screening Technologies, Kemps Creek, New South Wales
2171, Australia.
§ Novartis Animal Health Australia Pty. Ltd., Kemps Creek, New
South Wales 2171, Australia.
(1) Capon, R. J .; Barrow, R. A.; Rochfort, S.; J obling, M.; Skene, C.;
Lacey, E.; Gill, J .; Friedel, T.; Wadsworth, D. Tetrahedron 1998, 54,
2227-2242.
(2) Capon, R. J .; Skene, C.; Lacey, E.; Gill, J . H.; Wadsworth, D.;
Friedel, T. J . Nat. Prod. 1999, 62, 1256-1259.
(3) Ovenden, S. P. B.; Capon, R. J .; Lacey, E.; Gill, J . H.; Friedel,
T.; Wadsworth, D. J . Org. Chem. 1999, 64, 1140-1144.
(4) Vuong, D.; Capon, R. J .; Lacey, E.; Gill, J . H.; Heiland, K.;
Friedel, T. J . Nat. Prod. 2001, 64, 640-642.
Resu lts a n d Discu ssion
The crude aqueous ethanol extract of an Oceanapia sp.
collected during scientific trawling operations off the
northern Rottnest Shelf, Australia, displayed potent
nematocidal activity against the commercial livestock
(5) He, H.; Faulkner, D. J .; Shumsky, J . S.; Hong, K.; Clardy, J . J .
Org. Chem. 1989, 54, 2511-2514.
(6) Pham, A. T.; Ichiba, T.; Yoshida, W. Y.; Scheuer, P. J .; Uchida,
T.; Tanaka, J .; Higa, T. Tetrahedron Lett. 1991, 32, 4843-4846.
(7) Okino, T.; Yoshimura, E.; Hirota, H.; Fusetani, N. Tetrahedron
1996, 52, 9447-9454.
(8) He, H.; Salva´, J .; Catalos, R. F.; Faulkner, D. J . J . Org. Chem.
1992, 57, 3191-3194.
(9) Simpson, J . S.; Garson, M. J .; Hooper, J . N. A.; Cline, E. I.;
Angerhofer, C. K. Aust. J . Chem. 1997, 50, 1123-1127.
(10) Simpson, J . S.; Garson, M. J . Tetrahedron Lett. 1998, 39, 5819-
5822.
(11) Fusetani, N.; Wolstenholme, H. J .; Shinoda, K.; Asai, N.;
Matsunaga, S.; Onuki, H.; Hirota, H. Tetrahedron Lett. 1992, 33, 6823-
6826.
(12) J ime´nez, C.; Crews, P. Tetrahedron 1991, 47, 2097-2102.
(13) Li, C.; Blackman, A. J . Aust. J . Chem. 1994, 47, 1355-1361.
(14) Li, C.; Blackman, A. J . Aust. J . Chem. 1995, 48, 955-965.
10.1021/jo0106750 CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/02/2001

7766 J . Org. Chem., Vol. 66, No. 23, 2001
Capon et al.
parastite Haemonchus contortus (LD99 ) 135 µg/mL).
Bioassay-directed fractionation proceeded via concentrat-
ing the decanted aqueous EtOH extract in vacuo, tritu-
rating with CH2Cl2, and submitting the soluble fraction
to silica SPE, followed by normal-phase HPLC. This
processing afforded as the sole bioactive principle thio-
cyanatin A (1) (LD99 ) 1.3 µg/mL), together with an
inseparable mixture of inactive analogues, thiocyanatins
B (2a ) and C (2b).
component mixture was not immediately evident from
the data described above, but was unambiguously ap-
parent on examination of the 13C NMR spectrum. The
13C NMR spectrum of 2a /2b exhibited two sets of
resonances in a ratio of 2:1.
A
13C NMR DEPT experiment revealed the more
intense set of resonances in the 13C NMR data for 2a /2b
to consist of one olefinic methine (130.2 ppm), one
quaternary (112.4 ppm) and seven methylene (27.9-34.0
ppm) carbons. This implied a high degree of symmetry,
and thus, thiocyanatin B (2a ) was determined to be the
symmetrical 1,16-dithiocyanato-8-hexadecene as shown.
The E stereochemistry about ∆8,9 was assigned on the
basis of the 13C NMR chemical shift for the allylic
methylene (E 32.6 ppm, Z 29.9 ppm, 2a 32.4 ppm).16
The 13C NMR data attributed to 2b included distinct
resonances for two olefinic methine (129.9 and 130.6
ppm) and 10 methylene (27.7 to 32.5 ppm) carbons. 13C
NMR resonances for terminal methylenes C1, C2, C15,
and C16 and thiocyanate carbons in 2b overlapped with
those in 2a , suggestive of greater similarity in structure
at the molecular termini. This analysis was consistent
with 2b being the ∆7,8 double-bond regioisomer of 2a .
Supportive of this proposition was the realization that
2a /2b could be biosynthetically related to 1 through
simple dehydration. Such a transformation would be
expected to yield a 1:1 mixture of alkenes, as proposed
for 2a /2b. The E stereochemistry about ∆7,8 in 2b was
assigned on the basis of the 13C NMR chemical shift for
the allylic methylenes (13C: C6/C9: 32.3/32.5 ppm). Thus,
thiocyanatin C (2b) was proposed to be (E)-1,16-dithio-
cyanato-7-hexadecene as shown. Confirmation of the
structures for both 2a and 2b was secured by total
synthesis.
High-resolution ESI(+)MS analysis of 1 revealed a
pseudomolecular ion (M + H, m/z 357.2022) consistent
with a molecular formula (C18H32N2OS2, ∆mmu ) -1.2)
requiring four double-bond equivalents (DBE). The 1H
NMR (400 MHz, CDCl3) spectrum of 1 exhibited reso-
nances consistent with a hydroxymethine (δ 3.60, m) and
two symmetric deshielded methylenes (δ 2.95, t). The 13
C
NMR (100 MHz, CDCl3) data for 1 revealed 15 methylene
carbons (25.4-37.4 ppm), along with a hydroxymethine
(71.8 ppm) and a quaternary (112.4 ppm) resonance. The
data described above required that 1 consist of an
unbranched acyclic C16 lipid incorporating a secondary-
OH and identical deshielding terminal functional groups.
Each terminal functional group must incorporate the
elements of SCN and account for two DBE and a
deshielded quaternary carbon (112.4 ppm). The only two
functional groups that satisfy these requirements are
thiocyanate (-SCN) and isothiocyanate (-NCS). The IR
data for 1 was supportive of this conclusion, revealing
absorbances at 3500 (br) and 2155 (sh) cm-1 consistent
with the presence of hydroxy and SCN or NCS substit-
1
uents, respectively. H and 13C NMR chemical shifts for
the terminal C1 and C16 methylenes unambiguously
identified the terminal functional groups as thiocyanates.
Connection to the more electronegative nitrogen in an
isothiocyanate (-NCS) as opposed to the sulfur in a
thiocyanate (-SCN) results in greater deshielding of the
methylene (1H δ 3.5; 13C 45 ppm)15 compared to that
observed in 1 (1H δ 2.95; 13C 34.0 ppm).
The position of the hydroxy moiety along the C16 chain
in 1 was determined by EIMS, which revealed intense
ions at m/z 186 [HOdCH(CH2)7SCN]•+ and m/z 200 [HOd
CH(CH2)8SCN]•+ consistent with cleavage either side of
a C8 hydroxy. Thus, the structure of thiocyanatin A (1)
was determined to be 1,16-dithiocyanato-8-hydroxyhexa-
decane. Given the almost symmetric nature of 1, it was
not surprising that no optical rotation was observed. At
this stage, the stereochemical character of 1 remains
unknown. This structure assignment was confirmed by
the total synthesis of thiocyanatin A (1) in seven steps
from 8-bromooctanoic acid (3), as described later in this
paper.
Thiocyanatin A (1) was synthesized in seven steps from
8-bromooctanoic acid (3) as outlined in Scheme 1. Thus,
commercially available 8-bromooctanoic acid (3) was
esterified to its methyl ester 4, followed by conversion to
the known Wittig salt 5 17 in a two-step yield of 71%. The
one-pot oxidation-Wittig coupling procedure of Noiret et
al.18 was modified by bubbling oxygen into the reaction
mixture, affording the olefin-diester 6 in 72% yield with
an Z/E ratio19 of 14:1. Treatment of 6 with m-CPBA gave
the corresponding epoxide, which was fully reduced with
LiAlH4 to the triol 7 in a two-step yield of 61%. The triol
7 is itself a terrestrial natural product, having been
isolated from the stem cutin of Psilotum nudum.20 To the
best of our knowledge, this current synthesis of 7
represents the first total synthesis and complete char-
acterization of this natural product. The triol 7 was
treated with 2 equiv of TsCl to give the ditosylate 8,
which was resolved from mono- and tritosylate byprod-
ucts by preparative silica gel chromatography. Displace-
ment of the tosylate groups by thiocyanate afforded
racemic thiocyanatin A ((()-1) in 38% yield from the triol
7. Synthetic (()-1 and natural 1 were spectroscopically
identical and exhibited the same nematocidal properties.
High-resolution ESI(+)MS analysis of the mixture2a /
2b revealed a pseudomolecular ion (M + H, m/z 339.1919)
consistent with
a molecular formula (C18H30N2S2,
∆mmu ) -1.0) that suggested 2a /2b were dehydration
products of 1. Supportive of this conclusion, the 1H NMR
spectrum of 2a /2b differed from 1 in that the H8
hydroxymethine multiplet was replaced by a two proton
olefinic resonances (δ 5.4) and four proton allylic meth-
ylene resonances (δ 2.0). Likewise, the IR spectrum of
2a /2b did not display the hydroxy absorbance so promi-
nent in 1, but rather was limited to the thiocyanate
absorbance at 2155 cm-1. That 2a /2b was a two-
(16) Sadtler Standard Carbon-13 Indexes; Sadtler Research Labo-
ratories: Philadelphia, 1980.
(17) Dawson, M. I.; Vasser, M. J . Org. Chem. 1977, 42, 2783-2785.
(18) Poulain, S.; Noiret, N.; Patin, H. Tetrahedron Lett. 1996, 37,
7703-7706.
(19) Determined by 13C NMR peak height measurement of the
olefinic carbon and comparison to literature chemical shift data (see
ref 22).
(15) The Aldrich Library of 13C and 1H FT NMR Spectra Edition 1;
The Aldrich Chemical Co.: Milwaukee, 1993; Vol. 1.
(20) Caldicott, A. B.; Simoneit, B. R. T.; Eglinton, G. Phytochemistry
1975, 14, 2223-2228.

Synthesis of Novel Nematocidal Dithiocyanates
J . Org. Chem., Vol. 66, No. 23, 2001 7767
Sch em e 1a
ment of the secondary-OH with other functional groups.
A more detailed account of SAR investigations will be
reported at a future date.
Exp er im en ta l Section
Gen er a l Exp er im en ta l P r oced u r es. Melting points were
determined using a hot-stage apparatus and are uncorrected.
Rapid silica filtrations were carried out by stepwise elution,
under low vacuum, using Merck 9385 silica gel loaded into a
sintered glass funnel. Solid-phase extraction was carried out
by using either Alltech Maxi-clean silica 900 mg cartridges or
Alltech Maxi-clean C18 900 mg cartridges attached to luer-lock
syringes. Thin-layer chromatography was carried out using
Merck silica gel 60 F254 sheets and visualized using both short
(254 nm) and long wavelength (365 nm) ultraviolet light, as
well as by dipping with 1.25% vanillin in 1:50 concentrated
sulfuric acid/acetic acid solution followed by moderate heating.
Chiroptical measurements ([R]D) were obtained on a digital
polarimeter in a 100 by 2 mm cell. Ultraviolet (UV) absorption
spectra were obtained using a double-beam spectrophotometer,
while infrared (IR) spectra were acquired using a FT-IR
spectrometer under PC control running Bio-rad Win-IR soft-
ware. 1H and 13C NMR spectra as well as two-dimensional
NMR experiments were performed at 400 and 100 MHz,
respectively, in the solvents indicated and referenced to
residual 1H signals in the deuterated solvents. EI mass spectra
were acquired at 70 eV, and high-resolution ESI mass mea-
surements were made at a cone voltage of 100 kV. The term
standard workup refers to extraction of the quenched reaction
mixture with the indicated organic solvent, washing of the
organic extract with water, then brine, drying of the organic
extract over anhydrous MgSO4 or Na2SO4, and removal of the
organic solvent under reduced pressure.
a
Reagents: (a) H2SO4, MeOH, reflux 16 h; (b) PPh3, MeCN,
reflux 16 h; (c) NaHMDS, THF/DMPU, O2, 60 °C, 16 h; (d)
m-CPBA, CH2Cl2, rt, 16 h; (e) LiAlH4, reflux 20 h; (f) MsCl, CH2Cl2,
-10 °C, 1 h; (h) p-TsCl, CH2Cl2, DMAP/NEt3, rt, 32 h; (g) KSCN,
THF, reflux 16 h; (i) p-TsOH, toluene, reflux 16 h.
An im a l Ma ter ia l. The Oceanapia specimen (35.3 g dry
weight) collected off the northern Rottnest Shelf by epibenthic
sled in J anuary 1996 was assigned the Museum of Victoria
Registry No. F80009. A description is as follows: growth form,
excavating base with hollow fistules (10-20 mm); color in life
pink-beige, color in EtOH beige; texture compressible but
harsh; oscules large, apical on fistules; surface opaque, opti-
cally smooth but minutely hispid; spicules megascleres oxeas
hastate-strongylote 130-140 × 10 µm); micorscleres none;
ectosome tangential spicules on the exterior surface of the
fistule and a thin collagenous layer on the interior of the fistule
wall; choanosome not seen, section through fistule shows a
circular mesh formed by multispicular bundles of oxeas.
Isola tion . The specimen was diced, steeped in EtOH, and
stored at -20 °C until required. The EtOH extract was then
concentrated under reduced pressure, the residue triturated
with CH2Cl2 and the CH2Cl2 soluble material subjected to silica
SPE. Fractions eluted by 25-50% EtOAc/hexane were sub-
jected to normal-phase HPLC (2.0 mL/min isocratic 40%
EtOAc/hexane through a Phenomenex spherex 5µ 250 × 10
mm silica column) to give thiocyanatin A (1) as a colorless oil
(18.2 mg, 0.10% specimen dry weight). The silica SPE fraction
eluted with 5% EtOAc/hexane was also subjected to normal
phase HPLC as described above using 15% EtOAc/hexane as
eluent to give the inseparable mixture of thiocyanatin B (2a )
and C (2b) as a colorless oil (20.3 mg, 0.12% specimen dry
weight).
Treatment of the ditosylate 8 with TsOH in refluxing
toluene effected nonregiospecific dehydration to a mixture
of the sterically more favored (E)-hexadecene ditosylates
9. Subsequent displacement of the tosylate groups with
thiocyanate yielded a mixture of thiocyanatin B and C
(2a /2b) in an overall yield of 46% from 8. Synthetic 2a /
2b was spectroscopically identical to the natural mixture
and, as with the natural 2a /2b, displayed no nematocidal
properties.
To provide further evidence for assignment of E ster-
eochemistry in 2a /2b, the symmetric (Z)-dithiocyanate
12 was prepared by reducing the (Z)-alkene diester 6 with
LiAlH4 to give the diol 10 in 86% yield. Conversion to
the dimesylate 11 and subsequent displacement of the
mesylate groups by thiocyanate afforded (Z)-1,16-dithio-
cyanato-8-hexadecene (12), the stereoisomer of thiocy-
anatin B (2a ), in 57% yield from 10. Noteworthy in the
characterization of the (Z)-alkene 12 was the 13C NMR
chemical shifts of the allylic methylenes (27.0 ppm),
which were significantly shielded by comparison to the
natural and synthetic 2a /2b (E)-alkenes (32.3-32.5 ppm),
confirming prior assignment of double bond stereochem-
istry.
The in vitro nematocidal activities21 against Haemon-
chus contortus for natural and synthetic 1 were found to
be equipotent, while no in vitro nematocidal activity was
found for either natural or synthetic 2a /2b or for the
geometric isomer 12. From this analysis, it can be seen
that the secondary-OH substituent appears necessary for
nematocidal activity. Future investigations into the
pharmacophore for this structure class might explore
chain length, secondary-OH regioisomers, and replace-
Th iocya n a tin A (1): stable colorless oil; [R]D 0° (c 1.0 in
CHCl3); IR νmax (film) 3500, 2155 cm-1 1H NMR (400 MHz,
;
CDCl3) δ 1.2-1.5 (m, methylene envelope), 1.85 (quin, J ) 7.4
Hz, H22, H215), 2.95 (t, J ) 7.4 Hz, H21, H216), 3.6 (m, H8);
13C NMR (100 MHz, CDCl3) δ 25.4, 25.5 (t, C6, C10), 28.7, 28.8
(t, C4, C13), 29.2, 29.3, 29.4 (t, C5, C11, C12), 29.8 (t, C2, C15),
33.9, 34.0 (t, C1, C16), 37.3, 37.4 (t, C7, C9), 71.8 (d, C8), 112.4
(s, SCN); ESI(+)MS m/z 379 (M + Na, 65), 374 (M + NH4,
100), 357 (M + H, 85); EIMS m/z 200 (80), 186 (78); HRESI-
(+)MS m/z 357.2022 (M + H) (calcd for C18H33S2N2O 357.2034).
Th iocya n a tin B a n d C (2a /2b): stable colorless oil; UV
(EtOH) λmax 203 nm (ꢀ 900); IR υmax (film) 2155 cm-1; 1H NMR
(400 MHz, CDCl3) δ 1.25-1.40 (m, methylene envelope), 1.43
(21) Gill, J . H.; Redwin, J . M.; Van Wyk, J . A.; Lacey, E. Int. J .
Parasitol. 1995, 25, 463-470.

7768 J . Org. Chem., Vol. 66, No. 23, 2001
Capon et al.
(br quin, J ) ∼7.0 Hz, H23, H214), 1.82 (quin, J ) 7.4 Hz, H22,
to room temperature and the THF removed under reduced
pressure. Water (50 mL) was added, and then standard
workup with Et2O followed by silica column chromatography
(30% EtOAc/hexane) yielded racemic thiocyanatin A ((()-1)
(45 mg, 77%) as a colorless oil that was spectroscopically
identical to the natural thiocyanatin A (1).
H215), 1.97 (m, H26 [2b], H27 [2a], H29 [2b], H210 [2a]), 2.95
(t, J ) 7.4 Hz, H21, H216), 5.38 (m, H7 [2b], H8, H9 [2a]); 13
C
NMR (100 MHz, CDCl3) 2a δ 27.9 (t, C3, C14), 28.7, 28.76,
29.36 (t, C4 and C13, C5 and C12, C6 and C11), 29.8 (t, C2,
C15), 32.4 (t, C7, C10), 34.0 (t, C1, C16), 112.4 (s, SCN), 130.2
(d, C8, C9); 2b δ 27.7, 27.9 (t, C3, C14), 28.3, 28.8, 28.9, 29.1,
29.2, 29.4 (t, C4, C5, C10, C11, C12, C13), 29.8 (t, C2, C15),
32.3, 32.5 (t, C6, C9), 34.0 (t, C1, C16), 112.4 (s, SCN), 129.9,
130.6 (d, C7, C8); ESI(+)MS m/z 361 (M + Na, 55), 356 (M +
NH4, 100), 339 (M + H, 40); HRESI(+)MS m/z 339.1919 (M +
H) (calcd for C18H31S2N2 339.1929).
Syn th etic Th iocya n a tin B a n d C (2a /2b). A mixture of
the ditosylate 8 (100 mg, 0.17 mmol) and TsOH (10 mg, 0.053
mmol) in toluene (10 mL) was heated at reflux for 16 h. The
toluene was removed under reduced pressure and the residue
purified by silica column chromatography (10-20% EtOAc/
hexane) to give the crude ditosyl alkene mixture 9 as an oily
solid (45 mg, 46%), which was used in the next step without
further purification. A mixture of ditosyl alkenes 9 (45 mg,
0.080 mmol) and KSCN (23.3 mg, 0.24 mmol) in dry THF (10
mL) was heated at reflux for 18 h. The reaction was cooled to
room temperature and the solvent removed under reduced
pressure. Water (50 mL) was added, and then standard
workup with Et2O afforded a mixture of dithiocyanate alkene
regioisomers 2a /2b as a clear oil (27.0 mg, 100%), which was
spectroscopically identical to the natural thiocyanatin B and
C mixture.
(Z)-8-Hexa d ecen ed ioc Acid Dim et h yl E st er (6). To a
solution of 5 (6.00 g, 12 mmol) in dry THF (48 mL) and dry
DMPU (16 mL) stirrred under N2 at room temperature was
added dropwise NaHMDS (12 mL, 12 mmol, 1 M solution in
THF). The subsequent red solution was stirred at room
temperature for 30 min, and then O2 was bubbled into the
reaction mixture. Stirring was continued at 60 °C for 16 h,
after which time the red color of the reaction mixture had
dissipated to a pale yellow. The reaction was quenched with
saturated NH4Cl(aq) (15 mL) and the mixture poured into
water (150 mL). Standard workup with EtOAc, followed by
column chromatography (silica gel, 10% EtOAc/hexane), af-
forded the diester 6 as a colorless oil (1.35 g, 72%):22,23 IR υmax
(Z)-1,16-Dih yd r oxy-8-h exa d ecen e (10). To a mixture of
LiAlH4 (0.1 g, 2.6 mmol) in dry Et2O (5 mL) under N2 was
added dropwise a solution of the diester alkene 6 (0.26 g, 0.84
mmol) in dry Et2O (5 mL) at such a rate as to maintain a gentle
reflux. Once the addition was complete, reflux was continued
for 1 h. The reaction mixture was cooled, quenched with
EtOAc, and 1 M HCl (10 mL) added followed by water (10 mL).
The aqueous phase was extracted with Et2O (3 × 20 mL), and
the combined organic extract was washed with 1 M HCl (3 ×
50 mL), water (3 × 50 mL), and brine (50 mL) and then dried
(anhyd MgSO4). The Et2O was removed under reduced pres-
sure to give the diol 10 as a colorless semisolid (0.18 g, 86%),
which was recrystallized from hexane, EtOAc: mp 40-41 °C;
1
(film) 1743 cm-1; H NMR (300 MHz, CDCl3,) δ 1.2-1.3 (m,
methylene envelope), 1.5-1.6 (m, H23, H214), 1.9-2.0 (m, H27,
H210), 2.25 (t, J ) 7.5 Hz, H22, H215), 3.60 (s, 2 × OMe), 5.3
(m, H8, H9); 13C NMR (75 MHz, CDCl3) 24.8, 27.0, 28.8, 28.9,
29.4, 33.9, 51.3, 129.7, 174.1; ESI(+)MS m/z 335 (M + Na, 100).
1,8,16-Tr ih yd r oxyh exa d eca n e (7). To a solution of 6 (1.24
g, 3.96 mmol) in dry CH2Cl2 (120 mL) under N2 at room
temperature was added m-CPBA (1.30 g, 7.53 mmol). Stirring
was continued for 16 h, then the reaction mixture was washed
with saturated NaHCO3(aq) (3 × 100 mL) and water (3 × 100
mL) and dried (anhyd Na2SO4) and the solvent removed under
reduced pressure. Purification of the residue by column
chromatography (silica gel, 35% EtOAc/hexane) gave the
epoxide as a pale yellow oil (0.99 g, 76%), which was used in
the next step without further purification. To a stirred
suspension of LiAlH4 (0.25 g, 6.6 mmol) in dry Et2O (10 mL)
under N2 at room temperature was added dropwise a solution
of the epoxide (0.43 g, 1.32 mmol) in dry Et2O (10 mL) so as to
maintain a gentle reflux. Refluxing was continued by heating
for 20 h, and then the reaction was quenched with EtOAc
followed by addition of 1 M HCl (20 mL) and water (20 mL).
The aqueous phase was extracted with Et2O (3 × 40 mL) and
the combined organic extract washed with 1 M HCl (3 × 100
mL), water (3 × 100 mL), and brine (100 mL) and dried (anhyd
MgSO4). Removal of the solvent under reduced pressure gave
the triol 7 (0.29 g, 80%) as a white solid that was recrystallized
from hexane/EtOAc: mp 72-73 °C (lit.20 mp 78-79.5 °C);. IR
1
IR υmax 3400 cm-1; H NMR (300 MHz, CDCl3) δ 1.2-1.6 (m,
methylene envelope), 1.9-2.1 (m, H27, H210), 3.64 (t, J ) 6.6
Hz, H21, H216), 5.3-5.4 (m, H8, H9); ESI(+)MS m/z 279 (M +
Na, 100); HRESI(+)MS m/z 295.2031 (M + K) (calcd for
C
16H32O2K 295.2041).
(Z)-1,16-Dith iocya n a to-8-h exa d ecen e (12). A mixture of
diol 10 (0.18 g, 0.71 mmol) and Et3N (0.25 mL, 1.78 mmol) in
dry CH2Cl2 (8 mL) was stirred at -10 °C under N2. MsCl (0.12
mL, 1.49 mmol) was added dropwise and stirring continued
at -10 °C for 1 h, and then the mixture was poured onto ice
and the organic phase separated. The aqueous phase was
extracted with CH2Cl2 (2 × 10 mL) and the combined organic
extract washed with ice-cold water (2 × 20 mL), 4% oxalic acid
solution (20 mL), 5% NaHCO3(aq) (20 mL), and brine (20 mL),
and then dried (anhyd Na2SO4). The CH2Cl2 was removed
under reduced pressure to give the dimesylate 11 as a colorless
oil (0.28 g, 95%) that was used without further purification in
the next step. A mixture of the dimesylate 11 (0.32 g, 0.78
mmol) and KSCN (0.19 g, 1.95 mmol) in EtOH (10 mL) was
refluxed under N2 for 16 h. The EtOH was removed under
reduced pressure and water (20 mL) added to the residue.
Standard workup (Et2O) followed by silica column chroma-
tography (5% EtOAc/hexane) afforded the dithiocyanate 12 as
a colorless oil (0.16 g, 60%): IR υmax (film) 2152 cm-1; 1H NMR
(400 MHz, CDCl3) δ 1.3-1.45 (m, methylene envelope), 1.80
(quin, J ) 7.4 Hz, H22, H215), 1.9-2.1 (m, H27, H210), 2.92 (t,
J ) 7.4 Hz, H21, H216), 5.3-5.4 (m, H8, H9); 13C NMR (100
MHz, CDCl3) δ 27.0 (C7, C10), 27.8 (C3, C14), 28.6, 28.8, 29.4
(C4 and C13, C5 and C12, C6 and C11), 29.7 (C2, C15), 33.9
(C1, C16), 112.3 (SCN), 129.7 (C8, C9); ESI(+)MS m/z 361
(M + Na, 100); HRESI(+)MS m/z 361.1744 (M + Na) (calcd
for C18H30S2N2Na 361.1751).
1
υmax (KBr) 3308 cm-1; H NMR (300 MHz, CDCl3,) δ 1.3-1.6
(m, methylene envelope), 3.59 (m, H8), 3.64 (t, J ) 6.6 Hz,
H21, H216); ESI(+)MS m/z 297 (M + Na, 100); HRESI(+)MS
m/z 297.2403 (M + Na) (calcd for C16H34O3Na 297.2407).
Syn th etic Th iocya n a tin A ((()-1). To a stirred suspension
of the triol 7 (0.20 g, 0.74 mmol), DMAP (6.5 mg, 0.053 mmol),
and TsCl (0.28 g, 1.47 mmol) in dry CH2Cl2 (5.5 mL) was added
Et3N (0.21 mL, 1.48 mmol) at 0 °C. After the mixture was
stirred at room temperature for 16 h, additional TsCl (0.28
g, 1.47 mmol) and Et3N (0.21 mL, 1.48 mmol) were added and
stirring continued at room temperature for a further 16 h. The
reaction mixture was concentrated under reduced pressure and
the residue triturated with EtOAc. The EtOAc extract was
concentrated under reduced pressure and subjected to silica
column chromatography (20-40% EtOAc/hexane) to give the
ditosylate 8 as a colorless oil (0.21 g, 49%), which was used in
the next step without further purification. A mixture of 8 (95
mg, 0.16 mmol) and KSCN (40 mg, 0.41 mmol) in dry THF (5
mL) was refluxed under N2 for 20 h. The reaction was cooled
Ack n ow led gm en t. We acknowledge the CSIRO
Division of Oceanography and the crew and scientific
personnel aboard the O. R. V. Franklin for collection of
the Oceanapia specimen. We also acknowledge technical
support by A. Loveless, taxonomic classification by L.
Goudie, and high-resolution mass measurements by S.
(22) Baker, R.; Crimmin, M. J . Tetrahedron Lett. 1977, 441-442.
(23) Gensler, W. J .; Prasad, R. S.; Chaudhuri, A. P.; Alam, I. J . Org.
Chem. 1979, 44, 3643-3650.

Synthesis of Novel Nematocidal Dithiocyanates
J . Org. Chem., Vol. 66, No. 23, 2001 7769
the synthetic compound 12, as well as IR, DEPT NMR, and
MS data for natural 1 and 2a /2b. COSY NMR data for natural
2a /2b, H NMR data for 6, 7, and 10, and synthetic samples
Duck of Monash University. This research was sup-
ported by the Australian Research Council and Novartis
Animal Health Australasia Pty Ltd.
1
of thiocyanatins (1 and 2a /2b). This material is available free
of charge via the Internet at http://pubs.acs.org.
Su p p or t in g In for m a t ion Ava ila b le: 1H NMR and 13C
NMR data for the natural thiocyanatins (1 and 2a /2b) and
J O0106750