Stereoselective synthesis of 3-amino-4,5-dihydroxyaldehydes - A novel preparation of N-acetyl-L-daunosamine

Article abstract of DOI:10.1016/S0957-4166(00)00056-2

A general route for the stereoselective synthesis of 3-amino-4,5-dihydroxyaldehydes, with almost any desired configuration at the three stereogenic centers, is described by applying a combination of enzymatic and chemical steps. L-Daunosamine 1, for example, the glycosidic fragment of many important anthracycline antibiotics has been prepared by this route starting from O-allyl-L-lactaldehyde (S)-6a. (R)-Hydroxynitrile lyase (HNL) catalyzed addition of HCN to (S)-6a yields the 2,3-dihydroxynitrile (2S,3S)-7a with high stereoselectivity (91% de) in 75% yield. The addition of allyl Grignard to the O-protected 2,3-dihydroxynitrile (2S,3S)-9a and subsequent hydrogenation of the imino intermediate leads to 4-amino-2,3-dihydroxy-1-heptene (4S,5S,6S)-12a, which after ozonization and deprotection gives N-acetylated L-daunosamine 14a in a total yield of 15% referring to (S)-6a. The general applicability of this chemoenzymatic multistep procedure is demonstrated in the stereoselective synthesis of the unnatural aminodeoxy sugar (2S,3S,4S)-14b, starting from isovaleraldehyde 3. Copyright (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0957-4166(00)00056-2

Tetrahedron: Asymmetry 11 (2000) 1085±1095
Stereoselective synthesis of 3-amino-4,5-dihydroxyaldehydesÐ
a novel preparation of N-acetyl-l-daunosamine1
Franz E€enberger* and Jurgen Roosy
Institut fur Organische Chemie der Universitat Stuttgart, Pfa€enwaldring 55, D-70569 Stuttgart, Germany
È
È
Received 12 November 1999; accepted 7 February 2000
Abstract
A general route for the stereoselective synthesis of 3-amino-4,5-dihydroxyaldehydes, with almost any
desired con®guration at the three stereogenic centers, is described by applying a combination of enzymatic
and chemical steps. l-Daunosamine 1, for example, the glycosidic fragment of many important anthracycline
antibiotics has been prepared by this route starting from O-allyl-l-lactaldehyde (S)-6a. (R)-Hydroxynitrile
lyase (HNL) catalyzed addition of HCN to (S)-6a yields the 2,3-dihydroxynitrile (2S,3S)-7a with high
stereoselectivity (91% de) in 75% yield. The addition of allyl Grignard to the O-protected 2,3-dihydroxy-
nitrile (2S,3S)-9a and subsequent hydrogenation of the imino intermediate leads to 4-amino-2,3-dihydroxy-
1-heptene (4S,5S,6S)-12a, which after ozonization and deprotection gives N-acetylated l-daunosamine 14a
in a total yield of 15% referring to (S)-6a. The general applicability of this chemoenzymatic multistep
procedure is demonstrated in the stereoselective synthesis of the unnatural aminodeoxy sugar (2S,3S,4S)-
14b, starting from isovaleraldehyde 3. # 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
l-Daunosamine (1, 3-amino-2,3,6-trideoxy-l-lyxo-hexose) is the glycosidic fragment of a
number of important anthracycline antibiotics such as daunomycin 2a2 and adriamycin 2b3 (Fig. 1)
which exhibit impressive activity against a wide range of experimental and human tumors.2,4
Daunosamine was found to be essential for the activity of anthracycline antibiotics and more-
over, it reduces signi®cantly their toxicity.5 Therefore, there has been considerable interest in the
synthesis of this class of sugars in recent years.6 Most of the syntheses of l-daunosamine have
been started from carbohydrate precursors. l-Rhamnose was the most widely used starting
material6,7 because it has the requisite l-con®guration and is a 6-deoxy hexose. Whereas hexoses
with l-con®guration are uncommon in nature, certain l-pentoses occur and can readily be
homologated to 2-deoxy-l-hexoses. These possibilities have been used in total syntheses of
daunosamine starting from l-arabinose.4c,8 Among the d-hexoses frequently used as precursors,
* Corresponding author. E-mail: franz.e€enberger@po.uni-stuttgart.de
y
Part of a dissertation, Universitat Stuttgart, 1999.
0957-4166/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(00)00056-2

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F. E€enberger, J. Roos / Tetrahedron: Asymmetry 11 (2000) 1085±1095
Figure 1.
which are easily available but require inversion of con®guration at C-5, are methyl a-d-manno-
side4a,9 and d-glucose.10
Non-carbohydrate precursors such as l-tartaric acid5c,d,11 as well as l-lactic acid and its
derivatives5b,12 have been applied as starting materials for the synthesis of daunosamine.
Syntheses starting from achiral precursors, where chiral auxiliaries13 or enzymes4d,14 were used
for introduction of the chiral centers, are also known.
In a recent publication1 we have reported the hydroxynitrile lyase (HNL) catalyzed addition of
HCN to O-protected a-hydroxyaldehydes A, allowing the stereoselective preparation of 2,3-
dihydroxynitriles B. The diastereoselective conversion of (R)- and (S)-2-hydroxynitriles, via
addition of a Grignard reagent to the cyano group and subsequent hydrogenation of the imino
intermediate with sodium borohydride, to the corresponding erythro-1,2-amino alcohols is well
known.15 We now describe a preparation of l-daunosamine and other l-amino sugars starting
from suitable aldehydes, combining the enzyme catalyzed enantioselective cyanohydrin formation
and the stereoselective chemical follow-up reactions (Scheme 1).
Scheme 1.
This method o€ers the advantage that almost any 3-amino-2,3,6-trideoxyhexose could be pre-
pared stereoselectively referring to all stereogenic centers not only from `chiral pool' derived
precursors, but from simple aldehydes. The proposed procedure would also represent a general
approach to unnatural higher homologues of 3-amino-2,3,6-trideoxyhexoses.
2. Results and discussion
Since the stereoselective synthesis of 2,3-dihydroxynitriles should be investigated not only
starting from the readily accessible l-lactaldehyde,16 we have developed two general approaches
to prepare allyl-protected (S)-2-hydroxyaldehydes starting from aldehydes. Scheme 2 shows the
two pathways exemplary for the stereoselective preparation of (S)-2-allyloxy-4-methylpentanal
(S)-6b starting from isovaleraldehyde 3.

F. E€enberger, J. Roos / Tetrahedron: Asymmetry 11 (2000) 1085±1095
1087
Scheme 2.
The ®rst method involves the (S)-MeHNL catalyzed addition of HCN to isovaleraldehyde 3 as
the key reaction.17 The resultant (S)-cyanohydrin (S)-4 (92% ee) was converted to the ethyl ester
(S)-5 via a Pinner reaction.18 (S)-2-Allyloxy-4-methylpentanal (S)-6b was obtained in 85% yield
and 92% ee from (S)-5 by O-protection with allyl bromide and subsequent hydrogenation with
diisobutylaluminium hydride (DIBALH). Since as an enzyme source for (R)-PaHNL simple
almond meal can be applied, we have developed a second procedure to obtain the (S)-2-hydroxy
ester (S)-5 without using the less easily available (S)-MeHNL. For the (R)-PaHNL catalyzed
enantioselective addition of HCN to aldehyde 3 defatted almond meal was used, and HCN was
generated from potassium cyanide with acid.19 Analogous to a literature procedure20 the obtained
(R)-cyanohydrin (R)-4 (93% ee) was ®rst O-tosylated, then reacted with potassium acetate to give
the corresponding (S)-cyanohydrin acetate which a€orded the hydroxy ester (S)-5 (92% ee) via a
Pinner reaction (Scheme 2).
The total syntheses of N-acetyl-l-daunosamine 14a and the unnatural N-acetylated l-3-amino-
deoxy sugar 14b starting from the lactaldehyde derivative (S)-6a and aldehyde (S)-6b, respectively,
are summarized in Scheme 3.
(R)-PaHNL catalyzes the HCN addition to (S)-6a with high stereoselectivity, giving the 2,3-
dihydroxynitrile (2S,3S)-7a in 75% yield with 91% de.1 It is also possible to start from racemic
(RS)-6a, since the diastereoisomers of 7a resulting from (R)-PaHNL catalyzed addition of
HCN to (RS)-6a can be separated by chromatography on silica gel after removal of the allyl
protecting group and subsequent isopropylidene protection. In this way, the isopropylidene-protected
dihydroxynitrile (4S,5S)-8 was isolated in 43% yield with >99% de.
Preliminary investigations of the reaction of silylated cyanohydrins with the Grignard reagent
from 2-bromomethyl-1,3-dioxolane21 or Z-2-(tert-butyldimethylsilyloxy)vinyl lithium22 have
shown that an addition of these organometallic compounds to a cyano group is not possible.
Therefore allyl Grignard has been chosen for introducing the `CH2CHO' moiety. In order to
perform the Grignard addition (2S,3S)-7a was ®rst reacted with trimethylchlorosilane,15a giving
the O-silylated (2S,3S)-9a in 66% yield without racemization. Although the Grignard reagent from
allyl bromide is very reactive,23 activation by soni®cation was necessary to react (2S,3S)-9a with
allyl Grignard in diethyl ether as solvent. After in situ hydrogenation of the addition product with
NaBH4, the intermediate amino diol was acetylated to give (4S,5S,6S)-11a in 67% yield with high
diastereoselectivity (diastereomeric ratio (dr)=95:4:1). Due to the high activation by soni®cation,
a second mole of Grignard reacts with the imino intermediate,24 yielding the carbinamine derivative
(10S,20S)-10a as a by-product in 10% yield, which can be separated by chromatography.

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F. E€enberger, J. Roos / Tetrahedron: Asymmetry 11 (2000) 1085±1095
Scheme 3.
The isopropylidene-protected (4S,5S)-8 reacts less diastereoselectively. Both diastereomers,
(4S,5S,6S)- and (4R,5S,6S)-12a, are obtained in nearly equal amounts (Scheme 3) (dr=51:49).
Also in this case, the corresponding carbinamine derivative (10S,20S)-10c results as by-product in
11% yield.
The signi®cant di€erences in diastereoselectivity of the hydrogenation of the imino inter-
mediates derived from (2S,3S)-9a,b and (4S,5S)-8, respectively, can be explained by molecular
modeling calculations25,26 of the intermediate magnesium chelate complexes. In the case of the
isopropylidene-protected intermediate, the diol is ®xed in a syn-periplanar conformation by the
dioxolane ring, allowing attack of a hydride from both sides with comparable probability.
In contrast, in the silylated compounds 9, in which an anti-periplanar conformation is preferred,
the substituent R protects the front side. Hydride attack therefore occurs preferentially from the
back, resulting in high diastereoselectivity. Thus the synthesis via the trimethylsilyloxy derivatives
9a,b is preferable.
For ozonolysis, compound (4S,5S,6S)-11a had to be transformed into the isopropylidene
derivative 12a. For this purpose the allyl protecting group was removed by Pd/C in acidic
medium followed by removal of the acetyl group according to Zemplen.27 The isopropylidene
protecting group was then introduced, yielding (4S,5S,6S)-12a (dr=95:4:1) in 65% yield.
Ozonolysis of (4S,5S,6S)-12a a€orded the aldehyde (3S,4S,5S)-13a in 85% yield. Finally 13a was
deprotected and cyclized to N-acetyl-l-daunosamine (2S,3S,4S)-14a using an acidic ion-exchange
material DOWEX in water/THF. Compound 14a was obtained in 95% yield with an anomeric

F. E€enberger, J. Roos / Tetrahedron: Asymmetry 11 (2000) 1085±1095
1089
ratio a:b=1:1.6. The corresponding furanose derivative could be detected by 1H NMR spectros-
copy as a by-product.
The unnatural aminodeoxy sugar (2S,3S,4S)-4-acetamido-2-isobutyl-3,6-dihydroxytetra-
hydropyran 14b has been synthesized analogously (Scheme 3). (S)-2-Allyloxy-4-methylvaler-
aldehyde (S)-6b, however, is a poorer substrate for (R)-PaHNL than (S)-6a. In this case a sixfold
amount of enzyme was necessary compared to the reaction of 6a. Under these conditions the
cyanohydrin (2S,3S)-7b was obtained in 88% yield with 95% ee (referred to the new stereogenic
center at C-2). The conversion of 7b with trimethylchlorosilane to give (2S,3S)-9b in 64% yield
proceeded without epimerization. The allyl Grignard addition to 9b, subsequent hydrogenation
and acetylation a€orded (4S,5S,6S)-11b in 60% yield (dr=92:4:2:2). The removal of the acetyl
group in the following reaction sequence causes the low total yield of 19% for (4S,5S,6S)-12b.
The con®guration of (4S,5S,6S)-12b could be proved by X-ray crystallographic analysis.26 After
ozonolysis, the resulting aldehyde (3S,4S,5S)-13b was deprotected and cyclized as described for
13a to give the aminodeoxy sugar (2S,3S,4S)-14b in 89% yield in an anomeric ratio a:b=1:1.2.
3. Experimental
3.1. Materials and methods
Melting points were determined on a Buchi SMP-20 and are uncorrected. Unless otherwise
1
stated, H NMR spectra were recorded on a Bruker AC 250 F (250 MHz) and ARX 500 (500
MHz) in CDCl3 with TMS as internal standard. Chromatography was performed using silica gel
S (Riedel-de Haen), grain size 0.032±0.063 mm. Optical rotations were measured in a thermo-
stated polarimeter with l=10 cm. Diastereomeric excesses: GC separations were conducted with a
OV 1701 column (30 mÂ0.32 mm), carrier gas hydrogen (0.45 bar). Enantiomeric excesses: GC
separations were conducted with a Chiraldex B-TA (ICT) column (30 mÂ0.32 mm), carrier gas
hydrogen (0.9 bar), or with a Bondex-unb-5.5-Et-105 column (20 m), carrier gas hydrogen (0.4
bar). All solvents were dried and distilled. Reactions with organometallic compounds and tri-
methylchlorosilane were performed in ¯ame-dried glassware under an argon atmosphere.
3.2. (S)-MeHNL catalyzed preparation of (S)-2-hydroxy-4-methylpentanenitrile (S)-4
The enzyme catalyzed addition of HCN to isovaleraldehyde 3 was performed as described
20
ꢀ
1
previously1,17 to give 83% of (S)-4; bp 99 C/13 torr; ‰aŠD = 24.9 (c 1.5, CHCl3), 92% ee. H
NMR (250 MHz): ꢀ 0.98 (d, J=6.4 Hz, 6H), 1.65±2.00 (m, 3H), 2.50 (br s, 1H), 4.52 (t, J=7.2
Hz, 1H). For comparison see published data.28
3.3. Ethyl (S)-2-hydroxy-4-methylpentanoate (S)-5
A solution of (S)-4 (9.4 g, 83.1 mmol) in 8 M ethanolic HCl (60 mL) in a sealed tube was
heated to 90ꢀC for 8 h, then 20 vol% water were added to hydrolyze the iminium hydrochloride
formed. The reaction mixture was extracted with diethyl ether (3Â50 mL). The combined extracts
were washed with sat. NaHCO3 solution to neutralize, dried (MgSO4), and concentrated. The
residue was distilled under vacuum to give 10.25 g (77%) of (S)-5; bp 79ꢀC/11 torr; ‰aŠD20= 7.2 (c
0.75, CHCl3), 92% ee. 1H NMR (250 MHz): ꢀ 0.95, 0.96 (2 d, J=6.7 Hz, 3H), 1.30 (t, J=7.2 Hz,

1090
F. E€enberger, J. Roos / Tetrahedron: Asymmetry 11 (2000) 1085±1095
3H), 1.49±1.64 (m, 2H), 1.90 (sept, 1H), 2.70 (br s, 1H), 4.16±4.28 (m, 3H). Anal. calcd for
C8H16O3 (160.3): C, 59.98; H, 10.07. Found: C, 59.98; H, 10.19.
3.4. (S)-Allyloxy-4-methylpentanal (S)-6b
(i) The allyl protecting group was introduced according to Aurich et al.16 From (S)-5 (14.8 g,
92.4 mmol), allyl bromide (24.7 mL, 292 mmol), Ag2O (65.5 g, 283 mmol), MgSO4 (2.2 g, 18.3
mmol), and diethyl ether (370 mL) in 10 h was obtained 16.8 g (91%) of ethyl (S)-2-allyloxy-4-
methylpentanoate; bp 93ꢀC/11 torr; ‰aŠD20= 63.6 (c 1.0, CHCl3), 92% ee. 1H NMR (500 MHz): ꢀ
0.92 (d, J=6.9 Hz, 3H), 0.94 (d, J=6.7 Hz, 3H), 1.29 (t, J=7.1 Hz, 3H), 1.47±1.52 (m, 1H), 1.63±
1.72 (m, 1H), 1.79±1.88 (m, 1H), 3.87±4.26 (m, 5H), 5.19±5.31 (m, 2H), 5.88±5.95 (m, 1H). Anal.
calcd for C11H20O3 (200.3): C, 65.97; H, 10.07. Found: C, 65.71; H, 9.81.
(ii) The reduction was performed as described previously.1 From ethyl 2-allyloxy-4-methyl-
pentanoate (16.8 g, 83.9 mmol) in diethyl ether (200 mL), 1 M DIBALH solution in dichloro-
methane (100 mL, 100 mmol), water (15 mL) in 4 h was obtained 11.14 g (85%) of (S)-6b; bp
67ꢀC/11 torr; ‰aŠD20= 67.8 (c 1.8, CHCl3), 92% ee. 1H NMR (250 MHz): ꢀ 0.93, 0.95 (2 d, J=6.6
Hz, 6H), 1.36±1.93 (m, 3H), 3.77 (ddd, J1=4.7, J2=8.9 Hz, 1H), 3.95±4.20 (m, 2H), 5.20±5.35
(m, 2H), 5.84±5.99 (m, 1H), 9.65 (d, J=2.2 Hz, 1H). Anal. calcd for C9H16O2 (156.2): C, 69.19;
H, 10.32. Found: C, 69.35; H, 10.46.
3.5. Dihydroxynitriles (2S,3S)-7a,b by (R)-PaHNL catalyzed HCN addition to aldehydes (S)-6a,b
The enzyme catalyzed HCN addition was performed as described previously.1
3.5.1. 3-Allyloxy-2-hydroxybutanenitrile (2S,3S)-7a
20
1
Yield: 75%; ‰aŠD =+17.8 (c 1.5, CHCl3), 91% de. H NMR (300 MHz): ꢀ 1.31 (d, J=6.3 Hz,
3H), 3.16 (br s, 1H), 3.77 (dq, J=4.5 Hz, 1H), 4.07±4.21 (m, 2H), 4.33 (d, 1H), 5.22±5.36 (m, 2H),
5.85±5.98 (m, 1H).
3.5.2. 3-Allyloxy-2-hydroxy-5-methylhexanenitrile (2S,3S)-7b
Yield: 88%; bp 79ꢀC/0.001 torr; ‰aŠD20= 15.8 (c 1.2, CHCl3), 95% ee (referred to the stereo-
genic center at C-2), 87% de. 1H NMR (500 MHz): ꢀ 0.95 (d, J=6.6 Hz, 6H), 1.39±1.45 (m, 1H),
1.56±1.62 (m, 1H), 1.74 (sept, 1H), 3.04 (br s, 1H), 3.67±3.70 (m, 1H), 4.18±4.28 (m, 2H), 4.35 (d,
J=2.6 Hz, 1H), 5.24±5.35 (m, 2H), 5.89±5.97 (m, 1H).
3.6. 2,2,5-Trimethyl-1,3-dioxolane-4-carbonitrile (4S,5S)-8
(i) According to a known procedure29 a solution of (2S,3S)-7a (0.2 g, 1.42 mmol), 85 mg of Pd/
.
C, 0.8 mL of water and p-toluenesulfonic acid (TsOH H2O) (43 mg, 0.23 mmol) in 7 mL of
methanol was heated to 60ꢀC for 19 h. The reaction mixture was ®ltered, and the ®ltrate was
concentrated. The residue was taken up in 150 mL of diethyl ether, dried (Na2SO4), concentrated,
and reacted without further puri®cation.
(ii) The crude diol obtained was taken up in 10 mL of 2,2-dimethoxypropane, and TsOH (33
mg, 0.2 mmol) was added. After being stirred for 24 h at room temperature, pyridine (2 equiv.
referred to TsOH) was added. The precipitate was ®ltered o€, and the ®ltrate was concentrated. The
residue was taken up in toluene (2Â50 mL) which was immediately removed. Chromatography

F. E€enberger, J. Roos / Tetrahedron: Asymmetry 11 (2000) 1085±1095
1091
on silica gel with petroleum ether:ethyl acetate (7:1) a€orded 142 mg (71%) of (4S,5S)-8; bp
20
ꢀ
1
62 C/10 torr; ‰aŠD =+15.8 (c 1.0, CHCl3), 91% de. H NMR (500 MHz): ꢀ 1.43 (d, J=5.9 Hz,
3H), 1.47, 1.49 (2 s, 6H), 4.18 (d, J=7.0 Hz, 1H), 4.48 (dq, 1H). CIMS (m/z,%): 142.1 (MH+,
20), 126.1 (M±CH3, 100), 115.1 (M±CN, 50), 43 (22). HRMS calcd for C7H12NO2 (MH+):
142.0868. Found: 142.0863.
3.7. Silylation of (2S,3S)-7a,b to (2S,3S)-9a,b: general procedure
According to E€enberger et al.15a trimethylchlorosilane was added dropwise over 10 min to a
solution of 7 and pyridine in dry diethyl ether at 0ꢀC, and the reaction mixture was stirred at
room temperature for 10 h. The precipitate was ®ltered o€, and the ®ltrate was concentrated.
The residue was taken up in diethyl ether (50 mL), and again the precipitate was ®ltered o€. The
®ltrate was concentrated, and the residue distilled under vacuum.
3.7.1. 3-Allyloxy-2-trimethylsilyloxybutanenitrile (2S,3S)-9a
Yield: 66%; bp 53ꢀC/0.02 torr; ‰aŠ2D0=+15.2 (c 1.35, CHCl3), 91% de. 1H NMR (500 MHz): ꢀ
0.22 (s, 9H), 1.31 (d, J=6.3 Hz, 3H), 3.57±3.62 (m, 1H), 4.04±4.15 (m, 2H), 4.43 (d, J=5.3 Hz,
1H), 5.27±5.33 (m, 2H), 5.86±5.94 (m, 1H). Anal. calcd for C10H19NO2Si (213.3): C, 56.30; H,
8.98; N, 6.57. Found: C, 56.10; H, 9.13; N, 6.64.
3.7.2. 3-Allyloxy-5-methyl-2-trimethylsilyloxyhexanenitrile (2S,3S)-9b
20
ꢀ
1
Yield: 64%; bp 58 C/0.002 torr; ‰aŠD = 12.0 (c 1.0, CHCl3), 87% de. H NMR (500 MHz): ꢀ
0.23 (s, 9H), 0.93, 0.97 (2 d, J=6.6 Hz, 6H), 1.23±1.36 (m, 2H), 1.56±1.65 (m, 1H), 3.24±3.28 (m,
1H), 3.84±3.99 (m, 2H), 4.21 (d, J=5.6 Hz, 1H), 4.97±5.08 (m, 2H), 5.64±5.72 (m, 1H). Anal.
calcd for C13H25NO2Si (255.4): C, 61.13; H, 9.87; N, 5.48. Found: C, 61.10; H, 9.83; N, 5.43.
3.8. Preparation of (4S,5S,6S)-11a,b, and 12a: general procedure
(i) To a soni®ed solution of allyl Grignard reagent in diethyl ether [prepared by slow addition of
allyl bromide (3.2 mmol for 9a, 23.6 mmol for 9b, 10.8 mmol for 8) to equimolar amounts of Mg
in diethyl ether] a solution of 9a (1.6 mmol), 9b (5.9 mmol) or 8 (6.7 mmol) in diethyl ether (30 mL
for 9a, 8, 200 mL for 9b) was added dropwise over 25 min. After soni®cation for 1±5 h (TLC control),
the reaction mixture was cooled to 78ꢀC. Methanol (5±40 mL) was added followed by NaBH4
(ca. 2 equiv. referred to 8 and 9) in three portions. The reaction mixture was allowed to warm to
room temperature (12 h), and hydrolyzed with water (50 mL). Workup for allyl protected amino diols:
the aqueous phase was adjusted to pH 2 with 1 M HCl and separated. The organic phase was
extracted with dilute HCl (pH 2, 2Â20 mL). The combined aqueous phases were adjusted to pH 10
with NaOH, and extracted with ethyl acetate (3Â150 mL). The combined extracts were dried
(Na2SO4), concentrated, and acetylated without further puri®cation. Workup for isopropylidene
protected amino diol: the organic phase was separated, and the aqueous phase extracted with
diethyl ether (3Â150 mL). The combined organic phases were dried (Na2SO4), concentrated, and
acetylated.
(ii) To a solution of the respective amino diol (1.3±3.8 mmol) and dimethylaminopyridine
(DMAP, 0.15 equiv. referred to amino diol) in pyridine (4.5 or 10 mL) at 0ꢀC acetic anhydride
(ca. 3.4±5 equiv. referred to amino diol) was added over 0.5 h. After being stirred for 14 h at
room temperature, dichloromethane (50 mL) and ice (50 g) was added, and the organic phase was

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F. E€enberger, J. Roos / Tetrahedron: Asymmetry 11 (2000) 1085±1095
washed to neutralize with dilute HCl (pH 2). Concentration and chromatography on silica gel
with petroleum ether:ethyl acetate (3:1) (11a), (2:1) (12a) or dichloromethane:methanol (30:1) and
bulb-to-bulb distillation (11b) gave the products.
3.8.1. 4-Acetamido-4-(1-acetoxy-2-allyloxypropyl)-1,6-heptadiene 10a
1
Characterized as diastereomeric mixture: bp 125/0.007 torr. H NMR (500 MHz): ꢀ 1.09, 1.14
(2 d, J=6.3 Hz, 3H), 1.89, 1.92 (2 s, 3H), 2.10 (s, 3H), 2.39±3.02 (m, 4H), 3.84±4.17 (m, 3H),
4.97±5.35 (m, 7H), 5.75±5.98 (m, 3H), 6.51, 6.94 (2 br s, 1H). Anal. calcd for C17H27NO4 (309.4):
C, 65.99; H, 8.80; N, 4.53. Found: C, 66.04; H, 8.92; N, 4.56.
3.8.2. 4-Acetamido-(2,2,5-trimethyl-1,3-dioxolan-4-yl)-1,6-heptadiene 10c
‰aŠ2D0= 5.6 (c 0.5, CHCl3). 1H NMR (500 MHz): ꢀ 1.33 (d, J=6.0 Hz, 3H), 1.38, 1.40 (2 s, 6H),
1.95 (s, 3H), 2.44±2.51 (m, 4H), 3.98 (d, J=7.8 Hz, 1H), 4.18 (dq, 1H), 5.12±5.16 (m, 4H), 5.44 (s,
1H), 5.80±5.91 (m, 2H). Anal. calcd for C15H25NO3 (267.4): C, 67.38; H, 9.43; N, 5.24. Found: C,
66.98; H, 9.39; N, 4.85.
3.8.3. 4-Acetamido-5-acetoxy-6-allyloxy-1-heptene (4S,5S,6S)-11a
Yield: 67%; ‰aŠ2D0=+6.38 (c 0.8, CHCl3), dr=95:4:1 (4th diastereomer could not be detected;
1
assignment only of main diastereomer). H NMR (500 MHz): ꢀ 1.16 (d, J=6.3 Hz, 3H), 1.95 (s,
3H), 2.11 (s, 3H), 2.10±2.30 (m, 2H), 3.84±4.19 (m, 3H), 4.35±4.41 (m, 1H), 4.85±4.90 (m, 1H),
5.06±5.34 (m, 4H), 5.74±5.99 (m, 2H), 6.43 (d, J=7.9 Hz, 1H). Anal. calcd for C14H23NO4
(269.3): C, 62.43; H, 8.61; N, 5.20. Found: C, 62.61; H, 8.89; N, 5.01.
3.8.4. 4-Acetamido-5-acetoxy-6-allyloxy-8-methyl-1-nonene (4S,5S,6S)-11b
Yield: 60%; bp 140ꢀC/0.01 torr; ‰aŠD20= 4.4 (c 1.1, CHCl3), dr=92:4:2:2 (assignment only of
1
main diastereomer). H NMR (500 MHz): ꢀ 0.89 (d, J=6.7 Hz, 3H), 0.89 (d, J=6.4 Hz, 3H),
1.33±1.49 (m, 2H), 1.55±1.62 (m, 1H), 1.95 (s, 3H), 2.10 (s, 3H), 2.23±2.36 (m, 2H), 3.73 (dt,
J1=3.0, J2=7.3 Hz, 1H), 3.98±4.19 (m, 2H), 4.35±4.40 (m, 1H), 4.92 (dd, J=5.5 Hz, 1H), 5.07±
5.35 (m, 4H), 5.75±6.00 (m, 2H), 6.47 (d, J=8.5 Hz, 1H). Anal. calcd for C17H29NO4 (311.4): C,
65.57; H, 9.39; N, 4.50. Found: C, 65.37; H, 9.47; N, 4.43.
3.8.5. 4-Acetamido-5,6-isopropylidenedioxy-1-heptene 12a
20
ꢀ
1
(4S,5S,6S)-12a: yield: 34%; mp 94±96 C; ‰aŠD = 10.0 (c 0.6, CHCl3). H NMR (500 MHz): ꢀ
1.28 (d, J=6.1 Hz, 3H), 1.39, 1.40 (2 s, 6H), 1.98 (s, 3H), 2.25±2.53 (m, 2H), 3.52 (dd, J1=5.8,
J2=8.1 Hz, 1H), 4.00±4.04 (m, 1H), 4.13±4.18 (m, 1H), 5.09±5.13 (m, 2H), 5.54 (d, J=7.3 Hz,
1H), 5.76±5.84 (m, 1H). Anal. calcd for C12H21NO3 (227.3): C, 63.41; H, 9.31; N, 6.16. Found: C,
63.06; H, 9.39; N, 6.12.
(4R,5S,6S)-12a: yield: 29%; mp 89±91ꢀC; ‰aŠD20=+13.4 (c 0.5, CHCl3). 1H NMR (500 MHz): ꢀ 1.27
(d, J=5.9 Hz, 3H), 1.38, 1.40 (2 s, 6H), 2.00 (s, 3H), 2.34 (dd, J=7.2 Hz, 2H), 3.59 (dd, 1H), 3.76
(dq, J=8.4 Hz, 1H), 4.07±4.12 (m, 1H), 5.07±5.13 (m, 2H), 5.70 (d, J=9.2 Hz, 1H), 5.70±5.82 (m, 1H).
Anal. calcd for C12H21NO3 (227.3): C, 63.41; H, 9.31; N, 6.16. Found: C, 63.23; H, 9.38; N, 6.06.
3.9. Preparation of (4S,5S,6S)-12a,b from (4S,5S,6S)-11a,b: general procedure
(i) The allyl protecting group was removed from 11a (0.74 mmol) or 11b (0.64 mmol) according
to a known procedure29 as described above for 8.

F. E€enberger, J. Roos / Tetrahedron: Asymmetry 11 (2000) 1085±1095
1093
(ii) The obtained crude product was taken up in 7 mL of methanol, and a 0.5 M solution of
sodium methanolate (0.3 mL for 12a, 1 mL for 12b) was added. After being stirred for 14±16 h,
the reaction mixture was neutralized with acidic ion exchanger DOWEX-H+ (pH control). The
ion exchanger was ®ltered o€, and the ®ltrate was concentrated and reacted without further
puri®cation.
(iii) As described above for (4S,5S)-8, the crude product was taken up in 10 mL of 2,2-di-
methoxypropane, and TsOH (ca. 0.18 equiv. referred to 11) was added. After being stirred for 10
min (12a) or 1 h (12b), pyridine was added. The precipitate was ®ltered o€, and the ®ltrate was
concentrated. The residue was taken up in toluene (2Â50 mL), which was immediately removed.
Chromatography on silica gel with petroleum ether:ethyl acetate (1:1 for 12a, 1:2 for 12b) a€or-
ded products 12.
3.9.1. 4-Acetamido-5,6-isopropylidenedioxy-1-heptene (4S,5S,6S)-12a
Total yield: 65%; ‰aŠ2D0= 9.0 (c 1.84, CHCl3), dr=95:4:1 (4th diastereomer could not be detected).
1H NMR see above.
3.9.2. 4-Acetamido-5,6-isopropylidenedioxy-8-methyl-1-nonene (4S,5S,6S)-12b
Total yield: 19%; mp 111ꢀC (pentane); ‰aŠD20= 42.6 (c 1.2, CHCl3), dr=95:5 (assignment only
of main diastereomer). 1H NMR (500 MHz, acetone): ꢀ 0.88, 0.91 (2 d, J=6.8 Hz, 6H), 1.32, 1.34
(2 s, 6H), 1.36±1.48 (m, 2H), 1.74±1.80 (m, 1H), 1.87 (s, 3H), 2.14±2.53 (m, 2H), 3.46 (dd, J=7.7
Hz, 1H), 4.00±4.11 (m, 2H), 4.99±5.09 (m, 2H), 5.76±5.84 (m, 1H), 6.96 (d, J=8.3 Hz, 1H). Anal.
calcd for C15H27NO3 (269.4): C, 66.88; H, 10.10; N, 5.20. Found: C, 66.78; H, 10.11; N, 5.11.
3.10. Ozonolysis of (4S,5S,6S)-12a,b to (3S,4S,5S)-13a,b: general procedure
Ozone (40 L/h) was passed through a solution of 12a (0.44 mmol) or 12b (0.41 mmol) in methanol
(8 mL) at 78ꢀC over 10 min, and subsequently O2 was passed through for 5 min to remove
excess O3. Then dimethylsul®de (6.8 mmol for 13a, 4.1 mmol for 13b) was added, and the
reaction mixture was allowed to warm to room temperature (12 h). The reaction mixture was
concentrated, and the residue was chromatographed on silica gel with petroleum ether:ethyl
acetate (1:2 to 1:20).
3.10.1. 3-Acetamido-4,5-isopropylidenedioxyhexanal (3S,4S,5S)-13a
Yield: 85%; mp 84ꢀC; ‰aŠD20=+8.4 (c 0.8, CHCl3), dr could not be determined by GC and
NMR spectroscopy. 1H NMR (500 MHz): ꢀ 1.30 (d, J=5.9 Hz, 3H), 1.34, 1.38 (2 s, 6H), 1.99 (s,
3H), 2.70±2.89 (m, 2H), 3.64 (dd, J1=6.8, J2=7.9 Hz, 1H), 3.93 (dq, J1=5.9, J2=7.9 Hz, 1H),
4.42±4.48 (m, 1H), 6.19 (d, J=8.8 Hz, 1H), 9.78 (d, J=1.9 Hz, 1H). CIMS (m/z,%): 230.1
(MH+, 100). HRMS calcd for C11H20NO4 (MH+): 230.1392. Found: 230.1398.
3.10.2. 3-Acetamido-4,5-isopropylidenedioxy-7-methyloctanal (3S,4S,5S)-13b
Yield: 79%; mp 105ꢀC; ‰aŠD20= 24.8 (c 1.1, CHCl3), dr could not be determined by GC and
1
NMR spectroscopy; H NMR (500 MHz): ꢀ 0.84 (d, J=6.6 Hz, 3H), 0.87 (d, J=6.7 Hz, 3H),
1.18±1.49 (m, 2H), 1.30 (s, 6H), 1.72±1.74 (m, 1H), 1.91 (s, 3H), 2.61±2.81 (m, 2H), 3.62 (dd,
J=6.5 Hz, 1H), 3.78±3.82 (m, 1H), 4.37±4.41 (m, 1H), 6.05 (d, J=9.0 Hz, 1H), 9.71 (d, J=1.9
Hz, 1H). FAB-MS (m/z,%): 272.2 (MH+, 100). HRMS-FAB calcd for C14H26NO4 (MH+):
272.1862. Found: 272.1860.

1094
F. E€enberger, J. Roos / Tetrahedron: Asymmetry 11 (2000) 1085±1095
3.11. Cyclization of (3S,4S,5S)-13a,b to aminodeoxy sugars (2S,3S,4S)-14a,b: general procedure
To a solution of 13a (0.33 mmol) or 13b (0.28 mmol) in THF/water (10 mL/3 mL) DOWEX-
H+ (250 mg) was added. After being stirred for 5.5 h (14a) or 10 h (14b) (TLC control), the ion
exchanger was ®ltered o€, and the ®ltrate was concentrated to give products 14.
3.11.1. N-Acetyl-l-daunosamine (2S,3S,4S)-14a
Yield: 95%; a:b=1:1.6; dr could not be determined. a-anomer: H NMR (500 MHz, D2O): ꢀ
1.18 (d, J=6.6 Hz, 3H), 1.70 (dd, J1=4.7, J2=13.5 Hz, 1H), 1.86±1.91 (m, 2H), 2.00 (s, 6H), 3.67
1
(d, J=6.9 Hz, 1H), 4.20 (q, 1H), 4.22±4.24 (m, 1H), 5.33 (d, 1H).
b-anomer: 1H NMR (500 MHz, D2O): ꢀ 1.23 (d, J=6.4 Hz, 3H), 1.56±1.63 (m, 1H), 1.86±1.91
(m, 2H), 2.00 (s, 6H), 3.56 (d, 1H), 3.75 (dq, J=0.8 Hz, 1H), 3.99 (dt, J1=3.7, J2=12.3 Hz, 1H),
4.89 (dd, J1=2.1, J2=9.9 Hz, 1H). For comparison see published data.8 Anal. calcd for
C8H15NO4 (189.2): C, 50.78; H, 7.99; N, 7.40. Found: C, 50.82; H, 8.03; N, 7.41.
3.11.2. 4-Acetamido-2-isobutyl-3,6-dihydroxytetrahydropyran (2S,3S,4S)-14b
Yield: 89%; mp 56ꢀC (decomp.); a:b=1:1.2. a-anomer: 1H NMR (500 MHz, D2O): ꢀ 0.90 (d, 12H),
1.31 (ddd, J1=5.0, J2=8.0, J3=13.4 Hz, 1H), 1.47±1.73 (m, 6H), 1.86±1.91 (m, 2H), 2.00 (s, 6H),
3.69 (d, 1H), 4.08±4.12 (m, 1H), 4.20 (ddd, J1=2.8, J2=4.9, J3=13.2 Hz, 1H), 5.32 (d, J=3.3 Hz, 1H).
1
b-anomer: H NMR (500 MHz, D2O): ꢀ 0.90 (d, 12H), 1.39 (ddd, J1=5.8, J2=7.7, J3=13.5
Hz, 1H), 1.47±1.73 (m, 6H), 1.86±1.91 (m, 2H), 2.00 (s, 6H), 3.61 (d, 1H), 3.64±3.67 (m, 1H), 3.99
(ddd, J1=2.9, J2=4.7, J3=12.9 Hz, 1H), 4.86 (dd, J1=2.0, J2=9.8 Hz, 1H). Anal. calcd for
C11H21NO4 (231.3): C, 57.12; H, 9.15; N, 6.06. Found: C, 57.27; H, 9.30; N, 6.23.
3.12. Determination of enantiomeric and diastereomeric excesses
(i) A solution of compounds 4 or 7 (10 mg), acetic anhydride (50 mL) and pyridine (10 mL) in
dichloromethane (300 mL) was heated to 60ꢀC in a sealed tube for 5 h. The reaction mixture was then
®ltered through a silica gel column (3Â0.5 cm) with dichloromethane as eluent. The enantiomeric
and diastereomeric excess was determined directly from the ®ltrate by gas chromatography.
(ii) The ee- and de-values of compounds 5, 9, 11, and 12 could be determined by gas chroma-
tography directly without derivatization.
Acknowledgements
We would like to thank the Bundesministerium fur Bildung und Forschung (Zentrales
Schwerpunktprogramm Bioverfahrenstechnik, Stuttgart) and the Degussa-Huls AG for ®nancial
support.
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