Impact of the central hydroxyl groups on the activity of symmetrical HIV-1 protease inhibitors derived from L-mannaric acid

Article abstract of DOI:10.1016/S0040-4020(00)00220-9

The influence of the central hydroxyl groups on the anti-viral activity of symmetrical HIV-1 protease inhibitors derived from L-mannaric acid has been examined. L-Iditol was synthesized and used as a chiral precursor for the synthesis of the corresponding inhibitor with inverted configuration at C-3 and C-4. Key intermediates were 3,4-O-isopropylidene-L-iditol and the activated L-idaric acid succinimidyI ester. The configurations of the central hydroxyl groups required for optimal inhibition of the HIV-1 protease were determined to be the C-3R and C-4R, i.e. the L-manno-configuration. Three C₂-symmetric inhibitors were converted to their thiocarbonates and reduced to provide the corresponding hydroxyethyl transition-state mimics. Deletion of the C-4 hydroxyl group in these inhibitors gave no further improvement in the anti-viral activity. (C) 2000 Published by Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00220-9

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 3219±3225
Impact of the Central Hydroxyl Groups on the Activity of
Symmetrical HIV-1 Protease Inhibitors Derived From
l-Mannaric Acid
a
Johanna Wachtmeister, Anna Muhlman, Bjorn Classon, Ingemar Kvarnstrom,
a
a,²
b
È
È
È
Anders Hallbergc and Bertil Samuelssona, ,²
*
aDepartment of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
b
È
È
Department of Chemistry, Linkoping University, SE-581 83 Linkoping, Sweden
cDepartment of Organic Pharmaceutical Chemistry, Uppsala University, BMC, SE-751 23 Uppsala, Sweden
Received 29 October 1999; revised 24 February 2000; accepted 9 March 2000
AbstractÐThe in¯uence of the central hydroxyl groups on the anti-viral activity of symmetrical HIV-1 protease inhibitors derived from
l-mannaric acid has been examined. l-Iditol was synthesized and used as a chiral precursor for the synthesis of the corresponding inhibitor
with inverted con®guration at C-3 and C-4. Key intermediates were 3,4-O-isopropylidene-l-iditol and the activated l-idaric acid suc-
cinimidyl ester. The con®gurations of the central hydroxyl groups required for optimal inhibition of the HIV-1 protease were determined
to be the C-3R and C-4R, i.e. the l-manno-con®guration. Three C2-symmetric inhibitors were converted to their thiocarbonates and reduced
to provide the corresponding hydroxyethyl transition-state mimics. Deletion of the C-4 hydroxyl group in these inhibitors gave no further
improvement in the anti-viral activity. q 2000 Published by Elsevier Science Ltd.
Introduction
the isoleucine analog of 1 and with 2, it was evident that
the hydroxyl-groups of the central diol do not bind sym-
metrically to the active site Asp 25/125 residues. One of
the hydroxyl groups forms hydrogen bonds with both
carboxyls while the other hydroxyl group points away
The human immunode®ciency virus (HIV) has been identi-
®ed as the etiologic agent of acquired immunode®ciency
syndrome (AIDS).1±3 The human immunode®ciency virus
type 1 (HIV-1) encodes for an aspartic protease which has
been shown to be essential for the formation of a mature,
infectious virus.4,5 Numerous reports describing potent
protease inhibitors have been disclosed.6±12 The HIV-1
protease inhibitors on the market are all non-symmetrical.
The fact that the HIV-1 protease exists as a C2-symmetric
dimer has stimulated the design and synthesis of C2-
symmetric inhibitors.13
Table 1. Inhibitory activities of the compounds 1±6
We have recently demonstrated that l-mannaric acid is a
useful scaffold for the design and synthesis of potent
C2-symmetric HIV-1 protease inhibitors.14 An attractive
feature of these inhibitors is that they are readily available
in just three chemical steps starting from commercially
available starting materials. Compounds 1 and 2, in
particular, have been shown to be potent HIV-1 protease
inhibitors in vitro (Table 1). From examination of the
X-ray crystal structure of HIV-1 protease complex with
Compound
X,Y
Ki (nM)
ED50 (mM)
1
2
3
4
5
6
(R)±OH, (R)±OH
(R)±OH, (R)±OH
(S)±OH, (S)±OH
(R)±OH, H
(R)±OH, H
(S)±OH, H
0.4
0.2
40
2.1
1.4
530
1.1
0.11
24
1.2
Keywords: peptidomimetics; oxidation; hydrolysis; deoxygenation; HIV-1
protease.
* Corresponding author.
Additional address: Medivir AB, Lunastigen 7, SE-141 44 Huddinge,
Sweden.
1.4
No activity
²
0040±4020/00/$ - see front matter q 2000 Published by Elsevier Science Ltd.
PII: S0040-4020(00)00220-9

3220
J. Wachtmeister et al. / Tetrahedron 56 (2000) 3219±3225
from the active site but still maintains one hydrogen bond to
one of the Asp residues.
better ratio of the desired product.19 However, this protect-
ing group was associated with selectivity problems in the
subsequent hydrolysis step. It was observed that the
1,2:3,4:5,6-triacetonide formed preferentially under kineti-
cally controlled reaction conditions, but without going to
complete conversion. The best result was eventually
obtained with 2,2-dimethoxypropane and camphorsulpho-
nic acid (CSA) in acetone and with a reaction time of
30 min producing the triacetonoid 10 in 67% yield. Subse-
quent partial hydrolysis with 70% HOAc at room tempera-
ture furnished the monoacetonide 11 in 74% yield.
It has been reported that deletion of one of the hydroxyl
groups of symmetric diol based HIV-1 protease inhibitors
in some cases enhances anti-HIV activity in cell based
assays.15 The physicochemical background for this observed
bene®cial effect on anti-HIV activity can be rationalized
from reduction of molecular weight, reduction of hydrogen-
bond donating and accepting groups and an increase in
lipophilicity; factors known to enhance permeability over
biological membranes and increase passive absorption.16,17
Selective protection of the primary hydroxyl groups
employing dimethoxytrityl chloride followed by benzyl-
ation of the 2,5-diol with benzyl bromide and sodium
hydride in DMF provided 2,5-di-O-benzyl-1,6-di-O-di-
methoxytriphenylmethyl-3,4-O-isopropylidene-l-iditol.20
Detritylation, in the presence of the isopropylidene group,
using dichloroacetic acid in CH2Cl2 resulted in the 1,6-diol
12 in 53% yield from 11.21 Initially the primary diol of 11
was protected as t-butyldimethylsilyl ethers, but in the
subsequent benzylation step extensive silyl-migration
occurred, and therefore this route was not pursued.14 The
diol 12 was oxidized to the corresponding dicarboxylic acid
In the present work we report on: (a) the deletion of the
hydroxyl at C-4 in inhibitors 1 and 2 to give 4 and 5, (b)
the inversion of the con®guration of the diol in 1 to give 3
and (c) the inversion of the con®guration at C-3 of 4 to give
6. These compounds were assayed for anti-HIV-1 protease
activity and for in vitro anti-HIV activity (Table 1).
Results and Discussion
Chemistry
with
2,2,6,6-tetramethylpiperidine
1-oxyl
radical
(TEMPO)±sodium hypochlorite in a buffered solution.22,23
The very unstable dicarboxylic acid was immediately
reacted with N,N0-disuccinylimidyl carbonate (DSC) in
pyridine to give, after puri®cation, the crystalline activated
diacid 13 in 69% yield from 12.24
For the synthesis of compound 3, the C-3, C-4 epimer of 1,
the previously described bis-lactone route14 could not be
applied as the corresponding l-idaro-1,4:3,6-dilactone was
not readily accessible. Instead, compound 3 was synthesized
from l-iditol (9), which in turn was prepared from l-sorbose
in a three-step reaction sequence (Scheme 1).18 Reduction of
l-sorbose (7) with sodium borohydride in MeOH±water
gave a 1:1 mixture of l-iditol and d-glucitol, which after
removal of boric acid and without further puri®cation was
acetylated using pyridine and acetic anhydride. The crude
product mixture was then crystallized from EtOH to give
l-iditol hexaacetate (8) as white crystals in 47% yield with
d-glucitol hexaacetate remaining in solution. De-O-acetyl-
ation of 8 was accomplished with sodium methoxide in
MeOH and pure l-iditol (9) was afforded in 96% yield.
Coupling of 13 with l-valine methylamide in CH2Cl2±THF
(2:1) gave the desired product in 79% yield. Attempted
selective cleavage of the 3,4-O-isopropylidene with a
variety of acids was unsuccessful and gave complex product
mixtures, whereas 2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone (DDQ) in CH3CN±water (5:1) eventually delivered
the 3,4-diol 3 in 69% yield.25
The deoxygenated compound 6 was prepared by converting
the diol 3 to its corresponding thiocarbonate using N,N0-
thiocarbonyl diimidazole in THF (97% yield), followed by
a reduction with 2,20-azobisisobutyronitrile (AIBN) and
tributyltin hydride to give the desired product 6 in 33%
yield (Scheme 2). Compound 4 was prepared from
Reacting 9 with 2,2-dimethoxypropane, under acidic
anhydrous conditions, produced the desired 1,2:3,4:5,6-
triacetonide 10 together with the 1,3:2,4:5,6-triacetonide
in a 4:1 ratio. Using 3,3-dimethoxypentane gave somewhat
Scheme 1. (a) NaBH4, MeOH, H2O. (b) Ac2O, pyridine. (c) NaOMe, MeOH. (d) 2,2-dimethoxypropane, CSA, acetone. (e) 70% HOAc. (f) DMTrCl, pyridine.
(g) NaH, BnBr, DMF, 08C. (h) dichloroacetic acid, CH2Cl2. (i) TEMPO, NaOCl, KBr, Bu4NBr, NaHCO3, NaCl, CH2Cl2, H2O, 08C. (j) N,N0-disuccinimidyl
carbonate, CH3CN, pyridine. (k) l-valine methylamide, CH2Cl2, THF. (l) DDQ, CH3CN, H2O, 758C.

J. Wachtmeister et al. / Tetrahedron 56 (2000) 3219±3225
3221
Scheme 2. (a) N,N0-Thiocarbonyl diimidazole, THF, re¯ux. (b) Bu3SnH, AIBN, toluene, re¯ux.
Scheme 3. (a) TBDMSOTf, lutidine, CH2Cl2, 08C. (b) Thiocarbonyl diimidazole, THF, re¯ux. (c) Bu3SnH, AIBN, toluene, re¯ux. (d) H1 Dowex, MeOH.
compound 1, according to the same procedure, to give the
thiocarbonate in 83% yield and the deoxygenated product 4
in 35% yield.
but that this advantage is offset by the lower HIV-1 protease
inhibitory activity.
The moderately active compound 3, with the C-3, C-4
hydroxyl groups inverted with respect to inhibitor 1, was
readily obtained from l-sorbose via l-iditol (Scheme 1).
Deoxygenation of one of the hydroxyl groups in 3
proceeded in moderate yield via the cyclic thiocarbonate
and gave the inactive compound 6.
For the deletion of the C-4 hydroxyl in compound 2 the
indanol hydroxyls were silylated using t-butyldimethylsilyl
tri¯ate and lutidine in CH2Cl2 to deliver 57% of the disilyl-
ated product, which subsequently was converted to the
thiocarbonate 15 in 92% yield (Scheme 3). Reduction
gave N1,N6-di(2R-t-butyldimethylsilyloxy-1S-indanyl)-2R,5R-
dibenzyloxy-3R-hydroxy hexanediamide in 20% yield.
Desilylation using H1-Dowex in MeOH gave 5 in 34%
yield. The major by-products from the deoxygenation reac-
tions resulted from desulfurization and from rearrangement
of the thiocarbonates.26
Deletion of one of the central hydroxyl groups in inhibitor 2
(Kiˆ0.2 nM), via the cyclic thiocarbonate, resulted in the
less potent HIV-1 protease inhibitor 5 (Kiˆ1.4 nM).
Notably, a dramatic decrease in anti-viral activity was
observed, going from ED50ˆ0.11 mM for 2 to ED50ˆ
1.4 mM for 5, re¯ecting decreased potency (HIV-1 protease
inhibition) but notably also signi®cantly reduced ef®cacy
for cell membrane permeability.
HIV-1 protease inhibition. (Table 1; column 3) HIV-1
protease was cloned and heterologously expressed in
Escherichia coli27 and Ki-values were determined using a
¯uorometric assay.28
It appears that, for this series of inhibitors, both hydroxyls
contribute to the ef®cacy in the binding of the inhibitor to
the enzyme. Although increased cell membrane perme-
ability is indicative for inhibitor 4 this effect is offset by
lower enzyme inhibition potency. Further studies are
under way to explore the potential for increased in vitro
anti-viral activity for these new types of HIV-1 protease
inhibitors.
In vitro anti HIV activity. (Table 1; column 4) The anti HIV
activity was measured in a HIV cytopathic assay in MT-4
cells where the effect was quanti®ed using vital dye XTT.29
The 50% inhibitory concentrations (ED50) were calculated
from the percent cytoprotection for individual compounds.
Conclusion
Deletion of one of the hydroxyl groups in 1, which was
accomplished smoothly by reduction of the corresponding
cyclic thiocarbonate gave the less potent HIV-1 protease
inhibitor 4 with Kiˆ2.1 nM as compared to Kiˆ0.4 nM for
1. Notably however, both compounds exhibit similar anti-
Experimental
General procedures
All solvents were distilled prior to use. Thin layer chromato-
graphy was performed using silica gel 60 f-254 (Merck)
plates with detection by UV, charring with 8% sulfuric acid,
ninhydrin or ammonium-molybdat±cerium(IV)sulfate±10%
viral activity, ED50ˆ1.2 mM for
4
compared to
ED50ˆ1.1 mM for 1. This result suggests that the inhibitor
4 has superior cell membrane permeability compared to 1,

3222
J. Wachtmeister et al. / Tetrahedron 56 (2000) 3219±3225
sulfuric acid (100 g: 2 g: 2 L). Column chromatography was
performed on silica gel (Matrix Silica Si 60A, 35±70 mm,
Amicon). Organic phases were dried over anhydrous
sodium sulfate. Concentrations were performed under
reduced pressure. Optical rotations were recorded on a
Perkin Elmer 241 polarimeter. NMR spectra were recorded
on a JEOL GSX-270 instrument, shifts are given in ppm
down®eld from tetramethylsilane in CDCl3, acetone-D6
and CD3OD, and from acetone (dC: 31.04) in D2O. Accurate
mass measurement was recorded on a Finnigan MAT 900S
instrument, using electrospray.
33.4 mmol, 67%) as a light yellow syrup. NMR (CDCl3):
dH: 1.87 (6H, s), 1.94 (12H, s), 3.88 (2H, t Jˆ8.1 Hz), 4.01±
4.07 (4H, m), 4.08±4.16 (2H, m); dC: 25.5, 26.2, 27.1, 65.7,
74.9, 76.8, 109.7 and 110.0 [a]Dˆ10.062 (c 1.04, CHCl3).
Anal. Calcd for C15H26O6: C, 59.58; H, 8.67. Found: C,
58.98; H, 8.61.
3,4-O-Isopropylidene-l-iditol (11).
A
solution of
compound 10 (10.1 g, 33.4 mmol) in 70% acetic acid
(200 mL) was stirred at ambient temperature for 5 h. The
solution was concentrated and the remaining acetic acid
removed by co-evaporation with added toluene. The residue
was puri®ed by column chromatography (CHCl3±MeOH
3:1) to give the monoacetonide 11 (5.51 g, 24.7 mmol,
74%) as a pale pink solid. NMR (acetone-d6): dH: 1.40
(6H, s), 3.67 (6H, s), 4.20 (2H, s), 4.82 (4H, s); dC: 27.2,
64.8, 71.4, 78.0, 110.2. [a]Dˆ135.9 (c 0.91, MeOH). Anal.
Calcd for C9H18O6: C, 48.64; H, 8.16. Found: C, 48.45; H,
8.15. Remaining diacetonide was recovered in 17% yield
(1.50 g, 5.72 mmol).
l-Iditol hexaacetate (8). To a stirred solution of l-sorbose
(7) (15.1 g, 83.3 mmol) in MeOH (200 mL) and water
(10 mL) at ambient temperature was added sodium boro-
hydride (6.3 g, 166.6 mmol) in portions during 30 min.
After 1.5 h acetic acid (10 mL) was added. The mixture
was concentrated to give a semi-crystalline syrup, which
was dissolved in MeOH (400 mL) and acetic acid (40 mL)
and concentrated again to give a white solid (hexitol and
NaOAc). To a stirred suspension of this compound in
pyridine (230 mL) was added acetic anhydride (240 mL)
dropwise during 1 h. The mixture was left at 508C over-
night. After addition of water (15 mL), the mixture was
concentrated followed by co-evaporation with added
toluene. The residue was dissolved in CHCl3, washed with
water (4£), saturated aqueous NaHCO3 (1£), brine (1£),
aqueous 10% CuSO4 (3£) and water (3£). The organic
layer was dried and concentrated to give a light brown
solid. The crude product was recrystallized twice from
EtOH (500 mL) to give white crystals of the l-iditol hexa-
acetate 8 (17.1 g, 39.4 mmol, 47%) and the d-glucitol
hexaacetate remaining in solution. NMR (CDCl3): dH:
2.06 (6H, s), 2.10 (6H, s), 2.11 (6H, s), 4.04 (2H, dd,
Jˆ5.9 and 12.1 Hz), 4.31 (2H, dd, Jˆ4.4 and 12.1 Hz),
5.23±5.32 (2H, m), 5.37 (2H, dd, Jˆ1.2 and 3.3 Hz);
dC: 20.4, 20.5, 61.5, 68.5, 69.0, 169.5, 169.7, 170.1,
mp 119±1208C, [a]Dˆ222.7 (c 1.27, CHCl3). Anal.
Calcd for C18H26O12: C, 49.77; H, 6.03. Found: C, 49.67;
H, 5.94.
2,5-Di-O-benzyl-3,4-O-isopropylidene-l-iditol (12). To a
stirred solution of compound 16 (4.3 g, 19.3 mmol) in dry
pyridine (100 mL) under argon atmosphere was added
dimethoxytrityl chloride (15.6 g, 46.0 mmol). After 1 h at
ambient temperature TLC indicated complete reaction and
MeOH (10 mL) was added. The solution was concentrated
and co-evaporated with added toluene. The residue was
dissolved in CHCl3, washed with saturated aqueous
NaHCO3 (2£), dried, concentrated and roughly puri®ed by
quick ¯ash chromatography (toluene±EtOAc 5:1) to give
1,6-di-O-dimethoxytriphenylmethyl-3,4-O-isopropylidene-
l-iditol (15.8 g, 19.1 mmol) as a yellow syrup, which was
used directly in the next step. NMR (CDCl3): dH: 1.35 (6H,
s), 3.22 (4H, d, Jˆ6.7 Hz), 3.60 (2H, br), 3.63 (12H, s), 3.71
(2H, s), 4.14 (2H, s), 6.76 (8H, d, Jˆ9.1 Hz), 7.06±7.50
(18H, m); dC: 27.1, 55.1, 65.4, 69.0, 77.2, 86.3, 109.4,
113.1, 126.8, 127.8, 128.2, 130.1, 136.0, 138.6, 144.9,
158.5. [a]Dˆ115.4 (c 1.38, CHCl3). To a cold (238C)
and stirred suspension of NaH (1.90 g, 79.2 mmol) in dry
DMF (35 mL) under argon atmosphere, were added simul-
taneously during 1 h the tritylated product from above
(15.8 g) in DMF (70 mL) and benzyl bromide (5.50 mL,
46.2 mmol) in DMF (70 mL). The reaction was allowed to
reach room temperature and then stirred overnight before
the addition of MeOH (20 mL). Toluene was added and the
mixture was washed with brine (1£), saturated aqueous
NaHCO3 (1£) and water (1£). The organic layer was
dried, concentrated and puri®ed roughly by ¯ash chromato-
grahy (toluene±EtOAc 15:1) to give 2,5-di-O-benzyl-1,6-
di-O-dimethyoxytriphenylmethyl-3,4-O-isopropylidene-l-
iditol (15.6 g, 15.5 mmol) as a light yellow syrup. NMR
(CDCl3): dH: 1.31 (6H, s), 3.32 (4H, d, Jˆ6.8 Hz), 3.67
(12H, s), 3.75 (2H, s), 4.20 (2H, s), 4.63 (4H, dd, Jˆ11.7
and 51.7 Hz), 6.72 (8H, d, Jˆ9.1 Hz), 7.05±7.48 (18H, m);
dC: 27.0, 55.1, 64.0, 73.1, 76.9, 77.4, 86.4, 109.0, 113.1,
126.7, 127.4, 127.7, 128.2, 130.2, 136.2, 138.6, 144.9,
158.4. [a]Dˆ121.7 (c 1.25, CHCl3). To a stirred solution
of the benzylated product (15.6 g) in CH2Cl2 (170 mL) was
added dichloroacetic acid (7 mL), turning the solution
bright red. After 2 h at ambient temperature the mixture
was washed with saturated aqueous NaHCO3 (3£), dried,
concentrated and puri®ed by column chormatography
l-Iditol (9). To a stirred solution of compound 8 (17.1 g,
39.4 mmol) in MeOH (300 mL) was added NaOMe (1 M,
15 mL). After 7 h at ambient temperature TLC indicated
complete reaction and the mixture was neutralized with
H1 Dowex, ®ltered, concentrated and dried to give l-iditol
(9) (6.9 g, 37.9 mmol, 96%) as a colorless syrup which
solidi®ed after three weeks. NMR (D2O): dH: 3.6±3.77
(6H, m), 3.82±3.88 (2H, m); dC: 63.5, 71.9, 72.5. mp 74±
768C, [a]Dˆ24.3 (c 1.02, H2O). Anal. Calcd for C6H14O6:
C, 39.56; H, 7.75. Found: C, 39.32; H, 7.69. Literature
values:18 mp 74.5±758C, [a]Dˆ23.44 (c 10.0, H2O).
1,2-3,4-5,6-Tri-O-isopropylidene-l-iditol (10). To a stir-
red solution of l-iditol (9) (9.09 g, 49.9 mmol) in dry
acetone (300 mL) were added 2,2-dimethoxypropane
(50 mL, 407 mmol) and camphorsulfonic acid (CSA)
(30 g, 129 mmol). After 30 min at ambient temperature
the mixture was neutralized with NaHCO3, stirred for an
additional 10 min, ®ltered and concentrated. The residue
was dissolved in EtOAc, washed with water (2£), dried,
concentrated and puri®ed by column chromatography
(toluene±EtOAc 12:1) to give the triacetonid 10 (10.1 g,

J. Wachtmeister et al. / Tetrahedron 56 (2000) 3219±3225
3223
(toluene±EtOAc 1:1) to give the diol 12 (4.06 g,
10.2 mmol) as a colorless syrup in 53% yield from 11.
NMR (CDCl3): dH: 3.02 (2H, br), 3.43 (2H, br), 3.70 (4H,
ddd, Jˆ4.7, 11.8 and 25.4 Hz), 4.22 (2H, s), 4.61 (4H, dd,
Jˆ11.8 and 35.2 Hz), 7.15±7.35 (10H, m); dC: 26.9, 61.9,
72.5, 77.0 77.6, 109.5, 127.9, 128.0, 128.5, 138.0.
[a]Dˆ119.0 (c 1.07, CHCl3). Anal. Calcd for C23H30O6:
C, 68.64; H, 7.51. Found: C, 68.43; H, 7.45.
1.29 mmol, 79%) as a white solid. NMR (CDCl3): dH:
0.81 (6H, d, Jˆ7.0 Hz), 0.95 (6H, d, Jˆ7.0 Hz), 1.44 (6H,
s), 2.48±2.58 (2H, m), 2.75 (6H, d, Jˆ4.8 Hz), 3.70 (2H, s),
4.39 (2H, dd, Jˆ4.1 and 9.5 Hz), 4.54 (2H, s), 4.59 (4H, dd,
Jˆ11.5 and 52.2 Hz), 6.81 (2H, d, Jˆ4.8 Hz), 6.92 (2H, d,
Jˆ9.5 Hz), 7.29±7.41 (10H, m); dC: 16.7, 19.7, 26.2 27.2,
28.9 57.8, 73.7, 77.1, 77.7, 110.1, 128.2, 128.4, 128.7,
129.0, 135.7, 169.8, 170.9. To a stirred solution of coupled
compound (775 mg, 1.18 mmol) in a 5:1 mixture of
CH3CN±H2O (30 mL) was added, 2,3-dichloro-5,6-
dicyano-1,4-benzoquinone (DDQ) (30 mg, 0.13 mmol).
After two and four days at 758C additional portions of
DDQ (2£60 mg) were added and after six days the reaction
was concentrated. The residue was dissolved in EtOAc,
washed with water (2£), ®ltered through a pad of char-
coal±celite±Na2SO4 and puri®ed by column chromato-
graphy (CHCl3±MeOH 20:1) to give the diol 3 (501 mg,
0.81 mmol, 69%) as a white solid. NMR (CDCl3): dH:
0.83 (6H, d, Jˆ7.0 Hz), 0.94 (6H, d, Jˆ7.0 Hz), 2.50±
2.68 (2H, m), 2.70 (6H, d, Jˆ4.8 Hz), 3.72 (2H, br), 4.05
(2H, d, Jˆ4.5 Hz), 4.25 (2H, d, Hˆ4.6 Hz), 4.31 (2H, dd,
Jˆ4.1 and 9.5 Hz), 4.65 (4H, d, Jˆ3.5 Hz), 7.05 (2H, d,
Jˆ9.5 Hz), 7.24 (2H, d, Jˆ4.8 Hz), 7.29±7.48 (10H, m);
dC: 16.7, 19.7 26.2, 28.6, 57.7, 69.6, 73.7, 76.6, 128.2,
128.9, 129.0, 135.9, 170.8, 172.3. [a]Dˆ222.9 (c, 1.4,
CHCl3). Anal. Calcd for C32H46N4O8: C, 62.52; H, 7.54;
N, 9.11. Found: C, 62.41; H, 7.39; N, 8.98.
N1,N6-Di-succinimidyl-2R,5R-dibenzyloxy-3S,4S-di-
hydroxy-3,4-O-isopropylidenehexanediester (13). To a
stirred solution of 12 (1.84 g, 4.57 mmol) in CH2Cl2
(90 mL) were added 2,2,6,6-tetramethylpiperidine 1-oxyl
radical (TEMPO) (36 mg, 0.23 mmol), potassium bromide
(104 mg, 0.87 mmol), tetrabutylammonium bromide
(163 mg, 0.51 mmol) and saturated aqueous NaHCO3
(20 mL). The mixture was cooled to 08C and a solution of
NaOCl (42 mL, 1.2 M, 50.4 mmol), saturated aqueous
NaHCO3 (10 mL) and brine (20 mL) was added over a
period of 1.5 h. After 30 min at 08C, the organic layer was
separated and extracted with saturated aqueous NaHCO3
(3£) and water (3£). To the combined water phase was
added EtOH (50 mL) and solution was stirred for 30 min.
Then EtOAc (100 mL) was added and the mixture was
brought from pH 9 to 2 by adding H1-Dowex. The
Dowex was ®ltered, the phases separated, and the water
phase was extracted with EtOAc (4£). The combined
organic layer was dried and concentrated under reduced
pressure without warming to give 2,5-di-O-benzyl-3,4-O-
isopropylidene-l-idaric acid (1.40 g, 3.25 mmol) as a light
yellow syrup, which had to be used without further puri®ca-
tion due to instability. NMR (CD3OD±acetone-d6 2:1): dH:
1.32 (6H, s), 3.98 (2H, s), 4.59 (2H, s), 4.63 (4H, dd, Jˆ12.6
and 103.9 Hz), 7.22±7.44 (10H, m); dC: 27.1, 73.7, 77.4,
78.0, 111.0, 128.8, 129.1, 129.3, 138.6, 172.7. To a stirred
solution of the crude diacid (1.40 g) in dry CH3CN (20 mL)
under argon were added pyridine (1.58 mL, 19.5 mmol) and
N,N0-disuccinylimidyl carbonate (DSC) (3.30 g, 12.9
mmol). After 15 h at ambient temperature EtOAc was
added and the mixture was washed with water (3£) and
brine (1£), dried, concentrated and puri®ed by column chro-
matography (CHCl3±MeOH 20:1). The activated diacid 13
was isolated (1.88 g, 3.17 mmol) as a colorless syrup in 69%
yield from the diol 12. NMR (CDCl3): dH: 1.42 (6H, s), 2.85
(8H, s), 4.46 (2H, d, Jˆ1.5 Hz), 4.65 (2H, dd, Jˆ1.5 and
2.4 Hz), 4.68 (4H, dd, Jˆ11.5 and 99.6 Hz), 7.26±7.34
(10H, m); dC: 25.6, 26.6, 73.1, 75.5, 75.9, 111.7, 128.3,
128.4, 128.6, 136.1, 165.7, 168.5. [a]Dˆ1100.2 (c 0.88,
CHCl3). Anal. Calcd for C31H32N2O10: C, 62.83; H, 5.44;
N, 4.73. Found: C, 62.74; H, 5.35; N, 4.51.
N1,N6-Di[2-methyl-1S-(methylcarbamoyl)propyl]-2R,5R-
dibenzyloxy-3S-hydroxyhexanediamide (6). To a stirred
solution of 3 (58 mg, 94 mmol) in dry THF (5 mL) under an
argon atmosphere at 458C was added N,N0-thiocarbonyl
diimidazole (40 mg, 0.22 mmol). The mixture was re¯uxed
for 30 h, concentrated and puri®ed on column chromato-
graphy (CHCl3±MeOH 20:1) to give N1,N6-di[2-methyl-
1S-(methylcarbamoyl) propyl]-2R,5R-dibenzyloxy-3S,4S-
dihydroxy-3,4-O-thiocarbonylhexanediamide (60 mg, 91
mmol, 97%) as a white solid. NMR (CDCl3): dH: 0.80
(6H, d, Jˆ7.0 Hz), 088 (6H, d, Jˆ7.0 Hz) 2.25±2.46 (2H,
m), 2.86 (6H, d, Jˆ4.8 Hz), 4.07 (2H, s), 4.28 (2H, dd,
Jˆ4.3 and 8.9 Hz), 4.65 (4H, d, Jˆ10.1 Hz), 5.13 (2H, s),
6.49 (2H, d, Jˆ4.8 Hz), 7.06 (2H, d, Jˆ8.9 Hz), 7.28±7.47
(10H, m); dC: 17.2, 19.5, 26.4, 29.7, 58.3, 75.6, 78.0, 83.4,
128.3 128.9, 129.1, 135.2, 167.7, 170.6, 189.6. A suspension
of the thiocharbonate (60 mg, 91 mmol), tributyltin hydride
(50 mL, 0.19 mmol) and 2,20-azobisisobutyronitrile (AIBN)
(15 mg, 91 mmol) in dry toluene (4 mL) was added drop-
wise to re¯uxing toluene (2 mL)over a period of 20 min.
The mixture was re¯uxed for 45 min, allowed to cool and
concentrated. The residue was dissolved in CH3CN and
washed with hexane (2£). The CH3CN layer was concen-
trated and puri®ed by column chromatography (toluene±
acetone 1:1) to give 6 (18 mg, 30 mmol, 33%) as a white
solid. NMR (CDCl3): dH: 0.82 (3H, d, Jˆ7.0 Hz), 0.87 (3H,
d, Jˆ7.0 Hz), 0.95 (6H, d, Jˆ7.0 Hz) 1.86±1.98 (2H, m)
2.30±2.48 (2H, m) 2.73 (3H, d, Jˆ4.9 Hz), 2.76 (3H, d,
Jˆ4.9 Hz), 3.86 (1H, d, Jˆ3.1 Hz), 4.10 (1H, dd, Jˆ3.1
and 8.7 Hz), 4.21±4.32 (3H, m), 4.62 (4H, dd, Jˆ13.4 and
33.7 Hz), 6.53 (1H, d, Jˆ4.8 Hz), 6.68 (1H, d, Jˆ4.8 Hz),
7.07 (2H, d, Jˆ9.1 Hz), 7.25±7.47 (10H, m); dC: 17.3, 17.4,
19.6, 26.3, 29.5, 34.5, 58.0, 58.1, 68.5, 72.7, 73.7, 76.8,
81.1, 127.9, 128.3, 128.5, 128.6, 128.8, 136.2, 136.5,
171.1, 171.4, 171.6, 172.5. [aD]ˆ16.1 (c 0.7, CHCl3).
N1,N6-Di[2-methyl-1S-(methylcarbamoyl)propyl]-2R,5R-
dibenzyloxy-3S,4S-dihydroxy hexanediamide (3). To a
stirred solution of the activated diacid 13 (974 mg,
1.64 mmol) in a 2:1 mixture of CH2Cl2±THF (7 mL)
under argon was added l-valine methylamide (560 g,
4.30 mmol). After 18 h at ambient temperature CH2Cl2
was added and the mixture was washed with saturated
aqueous NH4Cl (1£) and water (1£). The organic layer
was dried, concentrated and puri®ed by column chromato-
graphy (CHCl3±MeOH 20:1) to give N1,N6-di[2-methyl-
1S-(methylcarbamoyl)propyl]-2R,5R-dibenzyloxy-3S,4S-
dihydroxy-3,4-O-iso-propylidenehexanediamide (844 mg,

3224
J. Wachtmeister et al. / Tetrahedron 56 (2000) 3219±3225
Anal. Calcd for C32H46N4O7: C, 64.19; H, 7.74; N, 9.36.
Found: C, 63.95; H, 7.48; N, 9.20.
(922 mg, 1.05 mmol) in dry dichloroethane (21 mL) was
added N,N0-thiocarbonyl diimidazole (598 mg, 3.36
mmol). The mixture was re¯uxed for 22 h, concentrated
and puri®ed on column chromatography (toluene±EtOAc
30:1) to give 14 (887 mg, 0.961 mmol, 92%) as a white
solid. NMR (CDCl3): dH: 0.10 (6H, s), 0.13 (6H, s), 0.75
(18H, s), 2.82 (2H, d, Jˆ15.4 Hz), 3.07 (2H, dd, Jˆ4.6 and
15.4 Hz), 4.43 (2H, s), 4.72 (2H, dd, Jˆ10.8 and 45.3 Hz),
4.73±4.80 (2H, m) 5.17 (2H, dd, Jˆ4.6 and 8.3 Hz), 5.40
(2H, s), 7.05±7.30 (18H, m), 7.60 (2H, d, Jˆ8.3 Hz); dC:
24.8, 24.9, 17.8, 25.6, 40.5, 56.9, 74.3, 75.2, 78.2, 82.7,
124.6, 124.8, 126.6, 128.6, 128.8, 129.0, 135.6, 140.0,
141.5, 165.7, 192.0. Anal. Calcd for C51H66N2O8SSi2: C,
66.34; H, 7.20; N, 3.03. Found: C, 66.35; H, 7.28; N, 3.01.
N1,N6-Di[2-methyl-1S(methylcarbamoyl)propyl]-2R,5R-
dibenzyloxy-3R-hydroxyhexanediamide (4). To a stirred
solution of 1 (144 mg, 0.23 mmol) in dry THF (8 mL) under
argon atmosphere at 458C was added N,N0-thiocarbonyl
diimidazole (104 mg, 0.58 mmol). The mixture was
re¯uxed for 17 h, concentrated and puri®ed on column
chromatography (CHCl3±MeOH 20:1) to give N1,N6-di[2-
methyl-1S-(methylcarbamoyl) propyl]-2R,5R-dibenzyloxy-
3R,4R-dihydroxy-3,4-O-thiocarbonylhexanediamide (125
mg, 0.19 mmol, 83%) as a white solid. NMR (CDCl3): dH:
0.72 (6H, d, Jˆ7.5 Hz), 0.88 (6H, d, Jˆ8.0 Hz) 2.15±2.30
(2H, m), 2.76 (6H, d, Jˆ4.8 Hz), 4.04 (2H, dd, Jˆ8.8 and
9.9 Hz), 4.40 (2H, s), 4.75 (4H, dd, Jˆ11.7 and 77.4 Hz),
5.33 (2H, s), 6.87 (2H, d, Jˆ4.8 Hz), 7.16 (2H, d,
Jˆ8.8 Hz), 7.32±7.41 (10H, m); dC: 17.4, 19.4, 26.3,
30.2, 58.4, 75.8, 77.7, 82.4, 128.9, 129.1, 135.3, 167.0,
170.6, 190.7. To a re¯uxing solution of the thiocarbonate
(125 mg, 0.19 mmol) in dry toluene (4 mL) under argon
atmosphere was added over a period of 10 min a solution
of tributyltin hydride (153 mL, 0.57 mmol) and AIBN
(47 mg, 0.28 mmol) in dry toluene (3 mL). The mixture
was re¯uxed for 20 h, allowed to cool and concentrated.
The residue was dissolved in CH3CN and washed with
hexane (2£). The CH3CN layer was concentrated and puri-
®ed by column chromatography (CHCl3±MeOH 20:1) to
give 4 (40 mg, 67 mmol, 35%) as a white solid. NMR
(CDCl3): dH: 0.83±0.94 (12H, m), 1.90±2.36 (4H, m),
2.67 (3H, d, Jˆ4.8 Hz), 2.74 (3H, d, Jˆ4.8 Hz), 3.89 (1H,
d, Jˆ3.5 Hz), 4.11 (1H, dd, Jˆ5.0 and 7.0 Hz), 4.19±4.29
(3H, m) 4.58 (2H, s), 4.62 (2H, d, Jˆ2.8 Hz), 6.50 (1H, d,
Jˆ4.8 Hz), 6.75 (1H, d, Jˆ4.8 Hz), 6.96 (1H, d, Jˆ9.0 Hz),
7.20 (1H, d, Jˆ9.0 Hz), 7.25±7.37 (10H, m); dC: 17.5, 18.0,
19.4, 19.6, 26.1, 26.3, 29.5, 30.6, 35.5, 58.2, 58.3, 70.2,
73.0, 73.3, 77.2, 83.0, 127.9, 128.0, 128.4, 128.6, 128.7,
136.7, 170.5, 171.3, 171.4, 173.1. [aD]ˆ11.8 (c 0.8,
CHCl3). Anal. Calcd for C32H46N4O7: C, 64.19; H, 7.74;
N, 9.36. Found: C, 64.00; H, 7.50; N, 9.15.
N1,N6-Di[2R-hydroxy-1S-indanyl)-2R,5R-dibenzyloxy-
3R-hydroxyhexanediamide (5). To a re¯uxing solution of
14 (794 mg, 0.86 mmol) in dry toluene (84 mL) under argon
atmosphere were added over a period of 20 min a solution of
tributyltin hydride (0.70 mL, 2.60 mmol) and AIBN
(284 ng, 1.73 mmol) in dry toluene. The mixture was
re¯uxed for 20 h and additional tributyltin hydride
(0.23 mL) and AIBN (71 mg) was added. After 4 h further
re¯ux the mixture was concentrated, dissolved in toluene
and washed with 2.5 M NaOH (1£) and water (3£), dried
and concentrated. The residue was puri®ed by column chro-
matography (toluene±EtOAc 3:1) to give N1,N6-di(2R-t-
butyldimethylsilyloxy-1S-indanyl)-2R,5R-dibenzyloxy-3R-
hydroxyhexanediamide (150 mg, 0.17 mmol, 20%) as a
light yellow syrup. NMR (CDCl3): dH: 0.05 (6H, s), 0.08
(6H, s), 0.76 (18H, s), 1.98±2.25 (1H, m), 2.87 (2H, d,
Jˆ15.5 Hz), 3.10 (2H, dd, Jˆ3.9 and 15.5 Hz), 4.02 (1H,
d, Jˆ5.8 Hz), 4.20±4.35 (2H, m), 4.55±4.76 (6H, m), 5.37
(2H, dd, Jˆ7.8 and 13.6 Hz), 7.15±7.38 (18H, m), 7.52 (2H,
d, Jˆ7.8 Hz); dC: 24.7, 24.8, 18.0, 25.7, 36.4, 40.5, 40.6,
56.3, 56.4, 69.8, 73.3, 74.0, 74.5, 82.0, 124.5, 124.7, 124.8,
126.9, 127.0, 127.1, 127.7, 127.9, 128.0, 128.2, 128.3,
128.4, 128.5, 136.7, 139.7, 141.2, 141.3, 171.3, 173.4. To
a stirred solution of the deoxygenated compound (150 mg,
0.17 mmol), in MeOH (6 mL) was added H1-Dowex. After
three days at ambient temperature the mixture was ®ltered,
concentrated puri®ed by column chromatography (CHCl3±
MeOH 20:1), followed by recrystallization from MeOH to
give 5 (38 mg, 60 mmol, 34%) as white crystals. NMR
(CDCl3±MeOD): dH: 2.01±2.10 (1H, m), 2.86 (2H, d,
Jˆ16.5 Hz), 3.10 (2H, dd, Jˆ4.5 and 16.5 Hz), 4.05 (1H,
d, Jˆ3.5 Hz), 4.17±4.25 (2H, m), 4.54±4.63 (6H, m), 5.20±
5.32 (2H, m), 7.08±7.28 (20H, m); dC: 35.9, 39.8, 39.9,
57.2, 57.3, 69.2, 72.5, 72.7, 73.4, 74.0, 77.6, 84.0, 124.1,
124.2, 125.5, 127.2, 128.3, 128.4, 128.5, 128.8, 137.1,
140.2, 140.4, 140.6, 140.7, 171.4, 174.4. mp 110±1138C,
[a]Dˆ118.2 (c 0.38, CHCl3±MeOH, 1:1). Due to
instability of this compound elemental analysis did not
give satisfying results. HRMS Calcd for C38H40N2O7:
636.2836. Found 636.2844.
N1,N6-Di[2R-t-butyldimethylsilyloxy-1S-indanyl)-2R,5R-
dibenzyloxy-3R,4R-dihydroxy-3R, 4R-dihydroxy-3,4-O-
thiocarbonylhexanediamide (14). To a stirred solution of
2 (400 mg, 620 mmol) in CH2Cl2 (3 mL) at 08C under argon
atmosphere were added lutidine (142 mL, 1.22 mmol) and
t-butyldimethylsilyl tri¯ate (296 mL, 1.29 mmol). After 4 h
1 M NaOH (0.5 mL) was added and the mixture was washed
with 1 M HCl (1£) and brine (1£). The organic layer was
dried, concentrated and puri®ed by column chromatography
(CHCl3±MeOH 80:1) to give N1,N6-di(2R-t-butyldimethyl-
silyloxy-1S-indanyl)-2R,5R-dibenzyloxy-3R,4R-dihydroxy-
hexanediamide (313 mg, 355 mmol, 57%) as a light yellow
syrup. NMR (CDCl3): dH: 20.04 (12H, s), 0.64 (18H, s),
2.95 (4H, dd, Jˆ15.4 and 68.6 Hz), 3.88 (2H, br), 4.02 (2H,
d, Jˆ7.7 Hz) 4.28 (2H, d, Jˆ7.7 Hz), 4.48±4.62 (2H, m),
4.68 (4H, dd, Jˆ12.8 and 27.4 Hz), 5.31 (2H, dd, Jˆ5.1 and
8.6 Hz), 6.80±7.36 (18H, m), 7.52 (2H, d, Jˆ8.6 Hz); dC:
24.8, 17.9, 25.7, 40.6, 56.3, 71.1, 74.0, 77.2, 124.5, 124.8,
126.9, 127.9, 128.2, 128.5, 136.7, 139.8, 140.9, 176.2. The
monosilylated compound was isolated in 24% yield
(116 mg) and starting material was isolated in 7% yield
(28 mg). To a stirred solution of the disilylated compound
Acknowledgements
We thank the Swedish National Board for Industrial and
Technical Development and Medivir AB for ®nancial
support, Helena Danielson at the Department of Bio-
chemistry, Uppsala University, BMC, Sweden and Medivir

J. Wachtmeister et al. / Tetrahedron 56 (2000) 3219±3225
3225
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AstraZeneca AB, for HRMS on compound 5.
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