On the reactivity of ascomycin at the binding domain. Part 1: Liberation of the tricarbonyl portion of ascomycin

Article abstract of DOI:10.1016/j.tet.2003.10.045

Within the binding domain, ascomycin features the unusual pattern of a masked tricarbonyl moiety, which potentially allows for high structural diversity via simple isomerisation events. Herein, methodologies, allowing the liberation of the tricarbonyl unit by blocking the 14-hydroxy group are reported.

Full text of DOI:10.1016/j.tet.2003.10.045

Tetrahedron 59 (2003) 10075–10087
On the reactivity of ascomycin at the binding domain. Part 1:
Liberation of the tricarbonyl portion of ascomycin
*
Karl Baumann, Markus Bacher, Annelaure Damont, Klemens Hogenauer and Andrea Steck
¨
Department of Medicinal Chemistry, Novartis Research Institute Vienna, Brunnerstrasse 59, A-1235 Vienna, Austria
Received 18 June 2003; revised 8 September 2003; accepted 6 October 2003
Abstract—Within the binding domain, ascomycin features the unusual pattern of a masked tricarbonyl moiety, which potentially allows for
high structural diversity via simple isomerisation events. Herein, methodologies, allowing the liberation of the tricarbonyl unit by blocking
the 14-hydroxy group are reported.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
enolisation of the tricarbonyl portion (T, E), hemiketal
formation at C9 or C10 could potentially lead to the
formation of eight diastereomeric six- or seven-membered
hemiketal forms (A, B).5 Furthermore, anticipating an 1,4-
addition of the 14-hydroxy group to the enolised
tricarbonyl form (E) would allow the generation of a set
of isomeric ‘furano-ascomycins’ (F).6 As observed for
ascomycin itself, each potential equilibria product may
exhibit a mixture of rotamers with respect to the geometry
of the amide bond. The structural flexibility of ascomycin
in the binding domain translates into a tremendous
reactivity within this portion. In this context, oxidative,
reductive and nucleophilic induced cleavage reactions,5c,7
unexpected base induced rearrangement reactions,8
Ascomycin (1, Fig. 1) and the related compound FK 506 (2),
represent highly functionalized 23-membered macrocycles,
containing a pipecolate residue linked by an amide (C8) and
an allylic ester moiety (C26–29) to a polyketide backbone.1
Elidelw, a topical formulation of ASM 981 (3), the 33-epi-
chloro derivative of ascomycin, heralds major advances in
the treatment of inflammatory skin diseases as compared to
traditional treatment schedules.2 As confirmed by X-ray
crystal structure analysis and NMR-studies, the left hand
part of the macrolactams mediate binding to their common
immunophilin (macrophilin, FK 506-binding protein,
FKBP) and has therefore been termed the ‘binding domain’.
The right hand part of the macrocycles, together with
elements of the immunophilin, interact with the protein
phosphatase calcineurin, which plays a key role in the Ca2þ
dependent activation of lymphocytes, and thus represents
the ‘effector domain’.3
unusual deoxygenation and amination reactions,9
a
surprisingly high reactivity towards diazomethane10 as
well as a pronounced photosensitivity11 have been
reported. For some of these reactions, it is not yet clear
whether they proceed via the six- or seven-membered
hemiketal form or whether the liberated tricarbonyl
portion is essential. In order to study the reactivity of
ascomycin in the binding domain in more detail, we
planned the synthesis of derivatives bearing the unmasked
tricarbonyl portion. Herein, several protocols leading to
such derivatives are reported.
Most notably, the macrolactams feature the unusual
pattern of three adjacent carbonyl groups within the
binding domain (C8–C10, tricarbonyl portion, a,b-
diketoamide moiety), whereby one carbonyl group (C10)
is involved in hemiketal formation with the secondary
hydroxyl group at C14 to form the tetrahydropyrane unit
(C10–14). Although the structure at the binding domain
of ascomycin shown by formula A (Fig. 2) is the main
isomeric form adopted in organic solution,4 the close
proximity of the tricarbonyl portion to the hydroxyl group
at C-14 could potentially lead to the formation of
numerous alternative isomers. Thus, via liberation and
2. Results and discussion
2.1. Liberation of the tricarbonyl portion via silylation
As published earlier, reaction of ascomycin (1) with an
excess of t-butyldimethylsilyl chloride (TBDMSCl) and
imidazole in DMF furnishes 24,33-bis-OTBDMS-ascomy-
cin 4 in high yield.12 No further silylation was observed,
Keywords: ascomycin; binding domain; tricarbonyl portion.
*
Corresponding author. Tel.: þ43-186-634-326; fax: þ43-186-634-354;
e-mail: karl.baumann@pharma.novartis.com
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.10.045

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K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
Figure 1.
even when a vast excess of reagents was used. However,
screening different silylation reagents, bases and solvent
systems led to the development of a suitable method for the
liberation of the tricarbonyl portion via selective protection
of the 14-hydroxy group (Fig. 3). Thus, addition of
t-butyldimethylsilyl triflate (TBDMSOTf, 10 equiv.) to a
solution of ascomycin and 2,6-lutidine (33 equiv.) in
dichloromethane furnished the yellow colored 14,24,33-
tris-OTBDMS-ascomycin 5 as the main product in 72%
yield. The major byproduct 9 (12.5%) also contains the free
tricarbonyl portion, but in addition a silyl enol ether
formation at the C22-carbonyl has taken place. The
formation of the minor tris-silylated byproducts (ketal 6,
the 10,11-silyl enol ether 7 and the seven-membered ketal 8)
can be explained by trapping some of the previously
discussed potential equilibria products of ascomycin. The
same holds true for the tetra-silylated 22,23-silyl enol ether
derivatives 10 and 11. Quenching the reaction after a short
time (15 min) allowed the isolation of 24,33-bis-OTBDMS-
ascomycin 4 in excellent yield (93%), thus indicating that
silylation occurs primarily at the 33-and 24-hydroxyl
followed by the slow liberation and silylation of the 14-
hydroxy group.
2.2. Liberation of the tricarbonyl portion with
trichloromethyl chloroformate (diphosgene)
Next, we attempted to block the 14-hydroxy group via
carbamate formation (Fig. 4). For this purpose, a solution of
24,33-bis-OTBDMS-ascomycin 4 in acetonitrile was
reacted with diphosgene (1.5 equiv.) in the presence of an
excess 4-dimethylaminopyridine (DMAP, Steglich-base).
Surprisingly, quenching the crude reaction mixture with an
aqueous solution of ammonia, methylamine or imidazole
did not result in the formation of the corresponding O-14-
carbamates. Instead, the 24-OTBDMS-14,33-bis-carba-
mates 14, 15 and 16 were generated in substantial yields.
Obviously, action of diphosgene blocked not only the 14-
hydroxy group, but also led to a desilylation and subsequent
acylation of OH-33. Probably due to steric hindrance, the
24-OTBDMS-group remained unchanged, even after pro-
longed reaction times. Attempts to avoid concomitant
desilylation of the 33-OTBDMS group failed. For example,
applying a larger excess of DMAP only led to a significantly
decreased reaction rate and did not result in suppression of
the desilylation. This problem could be avoided by
replacing the comparatively labile 33-OTBDMS-group
Figure 2.

K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
10077
Figure 3.
with a 33-O-formyl group via regioselective desilylation
(4!12), followed by formylation with the mixed anhydride
of acetic acid and formic acid13 to give 33-O-formyl-24-
OTBDMS derivative 13. Thus, treatment of 13 with
diphosgene/DMAP provided compound 17 in excellent
yield after an aqueous work-up in presence of ammonia. An
alternative work-up using an excess a-amino ethyl acetate
resulted in the formation of the 14-(OCONHCH2COOEt)-
derivative 18.
R33 (4, 12 or 13, R33¼OTBDMS, OH or OCHO; R24¼
OTBDMS), (chloromethylene)dimethyliminium chloride
in acetonitrile at ambient temperature furnished the 24-
OTBDMS-14,33-bis-O-formyl ascomycin derivative 20 in
good yield after a basic, aqueous work up. Once again,
starting from the 33-OTBDMS-protected ascomycin
derivative 4, capture of OH-14 is accompanied by a
simultaneous silyl/acyl exchange at OH-33. Monitoring the
course of the reaction by TLC revealed that silyl/acyl
exchange occurs prior to the acylation of OH-14. Applying
the same reaction conditions to the readily available 24,33-
bis-OCHO-ascomycin 19 (prepared from ascomycin by
acylation with the mixed anhydride of formic acid and
acetic acid) allowed the preparation of 14,24,33-tris-
OCHO-ascomycin 21 in excellent yield. The same product
is also obtained starting from unprotected ascomycin 1,
albeit in low yield (Fig. 5).
2.3. Liberation of the tricarbonyl portion with iminium
chlorides
(Chloromethylene)dimethyliminium chloride (generated in
situ from DMF and diphosgene)14 gave similar reactions on
protected ascomycin derivatives as described above for
diphosgene. Thus, independent of the protecting group at

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K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
Figure 4.
Attempts to introduce an acetyl group in an analogous
manner gave an unexpected result. Thus, attempting the
preparation of (1-chloroethylidene)dimethylammonium
chloride15 from N,N-dimethyl acetamide, we added a
solution of phosgene in toluene to a solution of excess
N,N-dimethyl acetamide in diethyl ether and reacted the
resulting solution with 24,33-bis-O-formyl-ascomycin 19.
Surprisingly, after several hours at room temperature the
unexpected ascomycin derivatives 22 and 23 instead of the
desired 14-O-acetyl compound could be isolated (Fig. 6).
Inspection of these structures clearly suggests that the
initially formed 1-(chloroethylidene)dimethylammonium
chloride P reacted further with phosgene to give the
phosgeneimmonium complex Q,16 which in turn reacts
with the 10-hydroxyl of the six-membered hemiketal
form or the liberated 14-hydroxyl of the tricarbonyl form
of 19 to finally give the isolated structures 22 and 23,
respectively.
Figure 5.

K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
10079
Figure 6.
3. Analytical evidence and structural features
be determined. The 10,11-silyl-enol ether motif in com-
pound 7 (Fig. 3) could be confirmed by the absence of H11,
the simplification of the 11-methyl signal to a singlet at
1.93 ppm and the presence of two additional quaternary
olefinic carbon resonances (143.22 and 137.79 ppm) which
All compounds described herein represent single isomers.
The presence of an unmasked tricarbonyl unit can easily be
recognized due to its characteristic yellow color, caused by
the conjugation of three adjacent carbonyls. Further
evidence could be obtained from one- and two-dimensional
NMR-techniques: (a) the 10-hemiketal resonance is
replaced by an additional carbonyl resonance (C10; 199–
202 ppm), (b) the C9 resonance (184–187 ppm) is shifted
upfield by approximately 10 ppm, with respect to asco-
mycin, due to the additional conjugation with the C10
carbonyl, (c) the H11 resonance is shifted downfield due to
the adjacent C10 carbonyl and (d) 3JCH and 2JCH long range
cross peaks from H11 to the C9 and C10 carbonyl signals
and from 11-methyl to C11 and C10 are observed.
Analogously, the presence of a fixed seven-membered
ketal form (compounds 8, 10 in Figure 3) could also be
supported by NMR. Thus, as H11 is a- to a carbonyl (C-10),
the signal is significantly shifted downfield and the C10
carbonyl, now lacking conjugation to an adjacent carbonyl
appears at 206–207 ppm as expected for isolated carbonyls.
3
2
show JCH and JCH cross peaks to H12a, H12b and the
11-methyl group. The geometry at the 10,11-double bound
(E or Z) could not be deduced due to the absence of
diagnostically relevant NOEs. In contrast, cross-peaks
between H21/H23 in the T-Roesy spectra of the tetra-silyl
derivatives 9, 10 and 11 confirmed the Z-geometry of the
22,23-silyl enol ether motif in these compounds. For the
rigid compound 23, the absence of the C9 carbonyl
resonance, a downfield shift of C10 and the appearance of
a double bond with two quaternary substituted carbon atoms
together with two additional carbonyl resonances
(CONMe2, and –C(O)O– of the furanone system) are
characteristic. In contrast to the parent compound ascomy-
cin, which adopts preferentially the cis-geometry at the
amide bond (cis–trans¼2:1 in CDCl3 solution),4 liberation
of the tricarbonyl unit forces the macrocycles to adopt
preferentially the trans-conformation (cis–trans,2:10).
Interestingly, the 22-silyl enol ether derivatives 9–11 as
well as the 10,11-silylenolether 7 adopt exclusively the trans
geometry, whereas the rigid derivative 23 exists completely
in the cis-configuration in CDCl3 solution. Assignment of
the amide configuration could easily be done by inspection
of the C2/C6 and the H-2/H-6ax/H-6eq resonances. Thus, as
we have reported earlier,17 the 13C-resonances of C2 and C6
do not spread over several ppm units but clearly form two
distinct groups: transition from cis to trans causes the C6
resonances to shift to lower field (from 39–39.5 to 43–
45 ppm), whereas the C2 resonances are shifted to higher
3
Furthermore, all relevant JCH long range cross peaks,
especially from H14 to C9 (which appears at 99–102 ppm,
in accordance with the proposed ketal structure) substantiate
the assigned seven-membered cyclic structure in the binding
domain. With the exception of obvious differences caused
by different substitution patterns at the 24- and 33-hydroxyl,
the H and 13C NMR-spectra of the trapped six-membered
1
ketal forms (6, 11 in Figure 3) are comparable to the spectra
of the parent compound ascomycin. The absolute configur-
ation at C9 or C10 of the silylated, isomerically pure six-
and seven-membered compounds 6, 8, 10 and 11 could not

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K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
field (from 56–56.5 to 50.5–52 ppm). An analogous
trend is found for the protons: the transition from cis to
trans shifts H2 and H6ax to lower field and H-6eq to
higher field.
a slight stream of inert gas (argon). The gas outlet was
bubbled through a solution of 20 w/w% aq. potassium
hydroxide solution. Commercially available reagents were
applied without further purification. Formic acetic anhy-
dride was prepared following a procedure described in the
literature.13
4. Conclusion
5.1.1. Preparation and isolation of the compounds 5–11.
To a cooled (ice-bath), magnetically stirred solution of 30 g
(0.38 mol) ascomycin (1) and 145 ml (33 equiv.,
1.252 mmol) 2,6-lutidine in 600 ml dichloromethane
88 ml (10 equiv., 0.38 mol) tert-butyldimethylsilyl tri-
fluoromethanesulfonate (TBDMSOTf) were added in such
a manner that the temperature was kept below 108C. After
complete addition (15 min), the cooling bath was removed
and the reaction mixture was stirred for 11 h at room
temperature. The mixture was concentrated under reduced
pressure to approximately one half of its volume and
partitioned between ethyl acetate and saturated aq.
NaHCO3. The organic layer was separated and sequentially
washed with 3£300 ml 1N HCl and 2£200 ml brine, dried
over anhydrous sodium sulfate, filtered and concentrated
under reduced pressure at max. 408C. The residual yellow
oil was subjected to flash column chromatography (silica
gel, n-heptane–ethyl acetate¼7:1) to give 10 g of a mixture
of the compounds 6, 7, 9, 10 and 11 and the separated
compounds 8 and 5. The first fraction was further separated
(silica gel, n-heptane–ethyl acetate¼10:1) to give a mixture
of 7, 10 and 11 and the separated compounds 6 and 9. The
mixture of 7, 10 and 11 was separated by a third flash
chromatography (silica gel, toluene–acetonitrile¼70:1). In
order to get rid of low molecular weight impurities, all
fractions ,1 g were subjected to size exclusion chroma-
tography (Sephadexw LH20, ethyl acetate), evaporated to
dryness and lyophilized from dioxane. The following
products were obtained:
In summary, suitable methods allowing the chemoselective
liberation of the tricarbonyl unit in the binding domain of
ascomycin have been discovered. In addition, an unex-
pected rigid ascomycin derivative (23) in which the flexible
binding domain is blocked via furanone formation, has been
identified. Having accomplished the synthesis of ascomycin
derivatives bearing the unmasked tricarbonyl moiety, more
detailed investigations addressing the reactivity of this
peculiar unit, can now be performed. The results of these
future studies will be reported in due course.
5. Experimental
5.1. General
All NMR spectra were recorded on a BRUKER AVANCE
500 MHz spectrometer (resonance frequencies 500.13 MHz
1
for H, 125.76 MHz for 13C), equipped with a broadband
inverse probe head with z-gradients, in 0.6 ml CDCl3
(Merck Uvasolw, 99.8% D) at 301 K. Chemical shifts are
given in values of ppm, referenced to residual CHCl3 signals
1
(7.26 for H, 77.0 for 13C). Proton and carbon-13 signal
1
assignments were deduced from H, 13C, gradient-selected
1H,1H-COSY (correlated spectroscopy), gradient-selected
1
inverse H,13C-HSQC (heteronuclear single-quantum cor-
relation), and gradient-selected inverse 1H,13C-HMBC
(heteronuclear multiple-bond correlation) experiments.18
Stereochemical information was extracted from two-dimen-
sional T-ROESY (transverse rotating-frame Overhauser
effect spectroscopy)19 or selective one-dimensional
ROESY20 experiments. Mass spectroscopy (ESI, electro-
spray ionization) was performed on a Finnigan Navigator
AQA mass spectrometer with HP 1100 LC system, using
methanol (Merck LiChrosolvw, gradient grade) as solvent.
Solutions of approx. 50–100 mg/ml of the test compound in
acetonitrile (Merck LiChrosolvw) were used for injection.
Two scans in each experiments were applied, with 25 and
50 V cone voltages, respectively. The probe temperature
was 523 K. All reactions were monitored by HPTLC
(Merck HPTLC-plates, silica gel 60, F254). Visualisation
of the reaction components was obtained by spraying with a
solution of molybdatophosphoric acid (20% in EtOH/H2O,
3:1). Flash column chromatography was performed on silica
gel (Merck, silica gel 60, 0.04–0.063 mm, 230–400 mesh
ASTM) at approximately 3–5 bar. The solvents used for
chromatography (reagent grade) were used as purchased.
Isolated minor by-products were subjected to molecular size
exclusion chromatography (Sephadexw LH20, ethyl acet-
ate) in order to remove low molecular weight impurities
(originating from the solvent used for chromatography)
which might have been enriched during chromatographic
isolation. Caution. Phosgene and diphosgene are health and
environmental hazards. All reactions with phosgene or
diphosgene were carried out in a well-ventilated hood under
Compound 5. 30.95 g, 72%. Yellow powder; MS: 1156
(MNaþ), 1197 (MNaþ·CH3CN); CHN (C61H111NO12Si3)
calcd: 64.56/9.86/1.23, found: 64.60/10.12/1.05; 13C NMR
(CDCl3, E–Z¼1:4), d (E/Z-isomer, ppm): 168.66/168.83
(C1); 56.15/51.87 (C2); 25.9 (br)/25.9 (br) (C3); 20.72/
21.15 (C4); 25.36/25.36 (C5); 39.44/43.89 (C6); 165.01/
165.54 (C8); 187.19/185.37 (C9); 203.6 (br)/199.4 (C10);
38.55/36.17 (C11); 31.7 (br)/34.66 (C12); 81.92/81.11
(C13); 75.53/75.45 (C14); 79.11/78.0 (br) (C15); 41.27/
41.22 (C16); 27.33/27.46 (C17); 46.85/46.59 (C18); 139.62/
139.14 (C19); 123.78/123.39 (C20); 55.62/55.39 (C21);
209.43/209.24 (C22); 48.00/47.6 (br) (C23); 67.97/68.16
(C24); 38.74/38.86 (C25); 83.69/82.8 (br) (C26); 130.98/
131.34 (C27); 11.24/11.33 (C28); 136.73/135.75 (C29);
35.13/35.02 (C30); 36.17/36.17 (C31); 84.11/84.11 (C32);
75.13/75.13 (C33); 33.96/33.96 (C34); 30.64/30.73 (C35);
23.69/23.69 (C36); 11.63/11.63 (C37); 57.03/57.48 (13-
OMe); 60.17/59.07 (15-OMe); 57.85/57.76 (32-OMe);
15.58/15.69 (11-CH3); 19.52/19.52 (17-CH3); 16.52/16.52
(19-CH3); 8.83/9.65 (25-CH3); 26.06, 26.02, 25.87, 25.63,
18.41, 18.37, 18.17, 18.04 (Si–t-Bu); 23.98, 24.17, 24.43,
24.49, 24.76 (SiMe2). 1H NMR (CDCl3, E–Z¼1:4,
selected data), d (E-isomer, ppm): 4.26 (d, J¼5.1 Hz,
H-2); 4.41 (br d, J¼13 Hz, H-6a); 3.06 (H-6b); 3.20 (H-11);
3.02 (H-13); 3.69 (dd, J¼7.3þ1.7 Hz, H-14); 3.11 (H-15);
4.70 (d, J¼10.4 Hz, H-20); 3.22 (H-21); 2.85 (H-23a); 2.23

K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
10081
(H-23b); 4.09 (dd, J¼10.0þ4.5 Hz, H-24); 5.08 (d,
J¼10.2 Hz, H-26); 5.34 (d, J¼8.8 Hz, H-29); 2.92 (ddd,
J¼11.3þ8.4þ4.4 Hz, H-32); 3.39 (H-33); 1.24 (d, 3H,
J¼7.1 Hz, 11-Me); 1.75 (s, 3H, 19-Me); 1.54 (d, 3H,
J¼1.1 Hz, 27-Me); 0.02, 0.04, 0.06, 0.07, 0.09 (s, each 3H,
Si–Me); d (Z-isomer, ppm): 5.18 (d, J¼5.0 Hz, H-2); 3.44
(H-6a); 3.20 (H-6b); 3.42 (H-11); 3.22 (H-13); 3.73 (dd,
J¼5.7þ3.7 Hz, H-14); 3.19 (H-15); 4.83 (d, J¼10.3 Hz,
H-20); 3.22 (H-21); 2.82 (dd, J¼16.8þ10.0 Hz, H-23a);
2.28 (H-23b); 4.16 (dd, J¼9.2þ4.5 Hz, H-24); 5.15 (d,
J¼9.2 Hz, H-26); 5.30 (d, J¼9.0 Hz, H-29); 2.92 (ddd,
J¼11.3þ8.4þ4.4 Hz, H-32); 3.39 (H-33); 1.16 (d, 3H,
J¼7.0 Hz, 11-Me); 1.74 (s, 3H, 19-Me); 1.51 (d, 3H,
J¼1.0 Hz, 27-Me); 0.02, 0.05, 0.06, 0.07, 0.08, 0.10 (s, each
3H, Si–Me); 0.09 (s, 6H, Si–Me); 0.88 (s, 18H, (CH3)3);
0.91, 0.90 (s, each 9H, (CH3)3).
(d, J¼9.2 Hz, H-14); 3.22 (H-15); 4.66 (d, J¼10.6 Hz,
H-20); 3.17 (H-21); 2.90 (dd, J¼15.7þ11.2 Hz, H-23a);
2.12 (dd, J¼15.7þ3.8 Hz, H-23b); 4.16 (dd,
J¼11.2þ3.8 Hz, H-24); 4.86 (d, J¼11.2 Hz, H-26); 5.37
(d, J¼8.8 Hz, H-29); 2.92 (H-32); 3.40 (H-33); 1.93 (s, 3H,
11-Me); 1.81 (s, 3H, 19-Me); 1.48 (s, 3H, 27-Me); 0.02,
0.07, 0.12, 0.20 (s, each 3H, Si–Me); 0.06, 0.13 (s, each 6H,
Si–Me); 0.87, 0.89, 0.96, 0.96 (s, each 9H, (CH3)3).
Compound 8. 860 mg, 2%. White powder; MS: 1156
(MNaþ), 1197 (MNaþ·CH3CN); CHN (C61H111NO12Si3)
calcd: 64.56/9.86/1.23, found: 64.14/9.65/1.12; 13C NMR
(CDCl3, E–Z¼2:1), d (E/Z-isomer, ppm): 168.55/170.24
(C1); 55.84/52.74 (C2); 31.39/26.51 (C3); 21.30/20.97
(C4); 25.58/24.78 (C5); 39.72/43.60 (C6); 166.38/167.75
(C8); 102.73/102.10 (C9); 207.10/207.86 (C10); 38.43/
38.01 (C11); 39.77/39.03 (C12); 78.44/77.42 (C13); 75.94/
nd (C14); 82.02/nd (C15); 36.70/36.36 (C16); 25.27/28.75
(C17); 47.37/47.90 (C18); 139.70/137.77 (C19); 124.33/
123.70 (C20); 57.03/54.48 (C21); 208.90/210.50 (C22);
49.92/47.44 (C23); 68.71/68.56 (C24); 40.94/39.75 (C25);
85.33/nd (C26); 129.98/nd (C27); 10.90/12.90 (C28);
138.09/nd (C29); 35.17/35.05 (C30); 35.91/35.91 (C31);
84.08/84.20 (C32); 75.03/75.15 (C33); 33.91/33.91 (C34);
30.57/30.72 (C35); 23.09/24.69 (C36); 11.46/11.91 (C37);
56.68/56.25 (13-OMe); 59.26/58.22 (15-OMe); 57.64/57.91
(32-OMe); 17.20/17.20 (11-CH3); 20.72/20.95 (17-CH3);
15.83/16.80 (19-CH3); 9.97/10.90 (25-CH3); 26.50, 25.96,
19.22, 18.99, 18.16, 18.06, 18.00 (Si–t-Bu); 22.38, 22.47,
23.59, 23.94, 24.05, 24.13, 24.32, 24.50, 24.75
(SiMe2). 1H NMR (CDCl3, E–Z¼2:1, selected data), d
(E-isomer, ppm): 5.51 (br d, J¼4.0 Hz, H-2); 4.28 (br d,
J¼13.5 Hz, H-6a); 3.28 (H-6b); 2.80 (H-11); 3.38 (H-13);
3.59 (dd, J¼9.6þ2.5 Hz, H-14); 3.45 (H-15); 4.59 (d,
J¼10.8 Hz, H-20); 3.39 (H-21); 2.86 (H-23a); 2.19 (H-23b);
4.03 (dd, J¼11.0þ3.4 Hz, H-24); 4.88 (d, J¼10.3 Hz,
H-26); 5.40 (d, J¼8.9 Hz, H-29); 2.92 (H-32); 3.39
(H-33); 1.18 (d, 3H, J¼6.4 Hz, 11-Me); 1.79 (s, 3H,
19-Me); 1.42 (s, 3H, 27-Me); 0.02, 0.03, 0.06, 0.07, 0.12,
0.25 (s, each 3H, Si–Me); 0.83, 0.87, 0.91 (s, each 9H,
(CH3)3); d (Z-isomer, ppm): 5.08 (br d, J¼4.0 Hz, H-2);
4.70 (br d, J¼13.7 Hz, H-6a); 3.17 (H-6b); 2.97 (H-11);
3.36 (H-13); 4.91 (d, J¼9.9 Hz, H-20); 3.19 (H-21); 2.88
(H-23a); 2.29 (H-23b); 4.22 (H-24); 5.35 (br s, H-26); 5.24
(br d, J¼8.5 Hz, H-29); 2.92 (H-32); 3.39 (H-33); 1.18 (d,
3H, J¼6.4 Hz, 11-Me); 1.65 (s, 3H, 19-Me); 1.58 (s, 3H,
27-Me); 0.05, 0.06, 0.07, 0.08, 0.16, 0.22 (s, each 3H, Si–
Me); 0.85, 0.88, 0.90 (s, each 9H, (CH3)3).
Compound 6. 175 mg, 0.4%. White powder; MS: 1156
(MNaþ), 1197 (MNaþ·CH3CN); CHN (C61H111NO12Si3)
calcd: 64.56/9.86/1.23, found: 64.46/9.95/1.58; 13C NMR
(CDCl3, E–Z,1:10), d (Z-isomer, ppm): 169.25 (C1);
50.54 (C2); 26.39 (C3); 20.88 (C4); 24.90 (C5); 43.21 (C6);
165.19 (C8); 198.10 (C9); 99.21 (C10); 39.94 (C11); 33.64
(C12); 73.94 (C13); 76.10 (C14); 76.8 (br) (C15); 35.13
(C16); 26.16 (C17); 47.89 (C18); 141.25 (C19); 121.54
(C20); 56.53 (C21); 211.25 (C22); 43.21 (C23); 73.0 (br)
(C24); 41.8 (br) (C25); 76.5 (br) (C26); 133.47 (C27); 13.32
(C28); 125.02 (C29); 34.93 (C30); 36.47 (C31); 84.15
(C32); 75.15 (C33); 33.93 (C34); 30.74 (C35); 22.74 (C36);
11.25 (C37); 56.43 (13-OMe); 57.10 (15-OMe); 57.87 (32-
OMe); 15.58 (11-CH3); 18.90 (17-CH3); 15.51 (19-CH3);
10.49 (25-CH3); 25.91, 25.87, 18.16, 17.86 (Si–t-Bu);
1
22.61, 22.91, 23.96, 24.49, 24.75, 25.07 (SiMe2). H
NMR (CDCl3, E–Z,1:10, selected data), d (Z-isomer,
ppm): 5.16 (d, J¼5.3 Hz, H-2); 3.40 (m, 2H, H-6a,b); 1.81
(H-11); 3.47 (H-13); 3.50 (H-14); 3.41 (H-15); 4.62 (d,
J¼10.1 Hz, H-20); 3.21 (H-21); 2.40 (dd, J¼14þ9.3 Hz,
H-23a); 2.18 (H-23b); 4.05 (ddd, J¼9.3þ3.3þ3.3 Hz,
H-24); 5.38 (br s, H-26); 5.20 (d, J¼9.0 Hz, H-29); 2.93
(H-32); 3.38 (H-33); 1.05 (d, 3H, J¼6.8 Hz, 11-Me); 1.56
(s, 3H, 19-Me); 1.60 (s, 3H, 27-Me); 20.06, 20.01, 0.06,
0.07, 0.18, 0.20 (s, each 3H, Si–Me); 0.86 (s, 9H, (CH3)3),
0.88 (s, 18H, (CH3)3).
Compound 7. 240 mg, 0.5%. White powder; MS: 1270
(MNaþ), 1311 (MNaþ·CH3CN); CHN (C67H125NO12Si4)
calcd: 64.43/10.09/1.12, found: 64.44/9.83/0.87; 13C NMR
(CDCl3, E–Z¼0:1), d (ppm): 169.12 (C1); 51.11 (C2);
25.07 (C3); 20.95 (C4); 24.88 (C5); 44.59 (C6); 165.84
(C8); 189.94 (C9); 137.79 (C10); 143.22 (C11); 32.93
(C12); 85.20 (C13); 76.78 (C14); 79.12 (C15); 41.06 (C16);
26.17 (C17); 45.64 (C18); 140.40 (C19); 123.60 (C20);
55.76 (C21); 208.37 (C22); 46.94 (C23); 67.34 (C24); 37.83
(C25); 83.77 (C26); 130.77 (C27); 10.81 (C28); 137.11
(C29); 35.09 (C30); 36.21 (C31); 84.32 (C32); 75.18 (C33);
34.05 (C34); 30.75 (C35); 22.42 (C36); 11.65 (C37); 57.35
(13-OMe); 61.27 (15-OMe); 57.72 (32-OMe); 22.93
(11-CH3); 20.43 (17-CH3); 16.23 (19-CH3); 8.42 (25-
CH3); 25.98, 25.89, 25.88, 18.49, 18.19, 18.17, 18.08 (Si–t-
Bu); 23.57, 23.75, 24.15, 24.31, 24.56 (SiMe2). 1H
NMR (CDCl3, E–Z¼0:1, selected data), d (ppm): 5.20 (d,
J¼4.2 Hz, H-2); 3.28 (H-6a); 2.83 (H-6b); 2.61 (dd,
J¼12.6þ3.1 Hz, H-12a); 2.48 (H-12b); 3.34 (H-13); 3.72
Compound 9. 5.95 g, 12.5%. Yellow powder; MS: 1270
(MNaþ), 1311 (MNaþ·CH3CN); CHN (C67H125NO12Si4)
calcd: 64.43/10.09/1.12, found: 64.35/10.10/0.78; 13C NMR
(CDCl3, E–Z¼0:1), d (ppm): 167.86 (C1); 52.14 (C2);
26.73 (C3); 21.56 (C4); 25.19 (C5); 43.66 (C6); 165.87
(C8); 185.66 (C9); 204.0 (br) (C10); 36.90 (C11); 32.92
(C12); 80.89 (C13); 75.89 (C14); 79.79 (C15); 40.92 (C16);
26.17 (C17); 45.54 (C18); 136.11 (C19); 127.24 (C20);
45.40 (C21); 153.36 (C22); 108.14 (C23); 69.53 (C24);
42.09 (C25); 75.59 (C26); 133.37 (C27); 14.81 (C28);
128.04 (C29); 34.96 (C30); 36.78 (C31); 84.21 (C32);
75.21 (C33); 33.91 (C34); 31.08 (C35); 28.55 (C36); 11.84
(C37); 57.01 (13-OMe); 60.33 (15-OMe); 57.95 (32-OMe);
17.01 (11-CH3); 20.01 (17-CH3); 15.98 (19-CH3); 9.04

10082
K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
(25-CH3); 26.07, 25.92, 25.90, 25.86, 25.19, 18.38, 18.15,
18.04 (Si–t-Bu); 22.72, 23.55, 23.82, 24.42, 24.51,
24.65, 24.73 (SiMe2). 1H NMR (CDCl3, E–Z¼0:1,
selected data), d (ppm): 5.18 (d, J¼5 Hz, H-2); 3.52 (br d,
J¼13 Hz, H-6a); 3.43 (H-6b); 3.38 (H-11); 3.03 (dd,
J¼6.6þ6.6 Hz, H-13); 3.68 (d, J¼8.2 Hz, H-14); 3.08
(ddd, J¼9.5þ8.2þ2.7 Hz, H-15); 5.13 (d, J¼8.8 Hz, H-20);
2.65 (ddd, J¼9.2þ9.2þ2.7 Hz, H-21); 4.32 (d, J¼9.2 Hz,
H-23); 4.69 (dd, J¼9.2þ5.3 Hz, H-24); 5.53 (br s, H-26);
4.98 (d, J¼9.0 Hz, H-29); 2.94 (ddd, J¼11.3þ8.6þ4.6 Hz,
H-32); 3.37 (H-33); 1.22 (d, 3H, J¼7.0 Hz, 11-Me); 1.52 (s,
3H, 19-Me); 1.62 (s, 3H, 27-Me); 20.04, 20.01, 0.06, 0.07,
0.07, 0.08, 0.18, 0.23 (s, each 3H, Si–Me); 0.85, 0.88, 0.91,
0.96 (s, each 9H, (CH3)3).
4.28 (d, J¼9.0 Hz, H-23); 4.63 (dd, J¼9.0þ5.0 Hz, H-24);
5.48 (s, H-26); 4.95 (d, J¼9.0 Hz, H-29); 2.94 (ddd,
J¼11.2þ8.2þ4.4 Hz, H-32); 3.37 (H-33); 1.07 (d, 3H,
J¼7.0 Hz, 11-Me); 1.58 (s, 3H, 19-Me); 1.61 (s, 3H, 27-
Me); 20.07, 20.04, 0.06, 0.07, 0.13, 0.18, 0.20, 0.22 (s,
each 3H, Si–Me); 0.83, 0.95 (s, each 9H, (CH3)3), 0.88 (s,
18H, (CH3)3).
5.1.2. 24-O-TBDMS-ascomycin 12. To a magnetically
stirred solution of 5 g (4.9 mmol) 24,33-bis-O-TBDMS-
ascomycin (4) in 130 ml acetonitrile were added 5 ml of an
aq. hydrogen fluoride solution (40 w/w%) in one portion.
After 15 min, the mixture was partitioned between saturated
aqueous sodium hydrogen carbonate solution (200 ml) and
ethyl acetate. The organic layer was washed three times
with brine, dried over anhydrous sodium sulfate, filtered end
concentrated. The residual crude product was purified by
flash chromatography (silica gel, ethyl acetate–n-
heptane¼2:1). The product fraction was concentrated
under reduced pressure and dried for 15 h under high
vacuum.
Compound 10. 95 mg, 0.2%. White powder; MS: 1270
(MNaþ), 1311 (MNaþ·CH3CN); CHN (C67H125NO12Si4)
calcd: 64.43/10.09/1.12, found: 64.17/9.99/0.95; 13C NMR
(CDCl3, E–Z¼0:1), d (ppm): 168.52 (C1); 53.30 (C2);
27.32 (C3); 21.28 (C4); 25.63 (C5); 43.98 (C6); 170.50
(C8); 99.33 (C9); 206.16 (C10); 35.03 (C11); 37.50 (C12);
78.47 (C13 or C15); 79.36 (C14); 78.41 (C15 or C13); 36.74
(C16); 30.38 (C17); 49.12 (C18); 135.27 (C19); 126.17
(C20); 45.38 (C21); 152.78 (C22); 109.00 (C23); 69.50
(C24); 41.41 (C25); 74.50 (C26); 133.17 (C27); 14.88
(C28); 126.94 (C29); 34.95 (C30); 36.91 (C31); 84.31
(C32); 75.34 (C33); 34.01 (C34); 31.07 (C35); 29.09 (C36);
11.25 (C37); 56.98 (13-OMe); 56.77 (15-OMe); 57.91 (32-
OMe); 16.82 (11-CH3); 19.27 (17-CH3); 19.72 (19-CH3);
9.00 (25-CH3); 26.19, 26.04, 25.87, 25.63, 18.33, 18.16,
18.04, 18.01 (Si–t-Bu); 22.13, 22.86, 23.72, 23.89,
24.50, 24.58 (SiMe2). 1H NMR (CDCl3, E–Z¼0:1,
selected data), d (ppm): 5.15 (d, J¼5.0 Hz, H-2); 4.02 (br
d, J¼13 Hz, H-6a); 3.32 (H-6b); 3.14 (H-11); 3.58 (H-13);
3.97 (dd, J¼9.0þ1.8 Hz, H-14); 3.60 (H-15); 5.48 (d,
J¼9.8 Hz, H-20); 2.70 (ddd, J¼9.8þ9.0þ3.3 Hz, H-21);
4.50 (d, J¼8.8 Hz, H-23); 4.74 (dd, J¼8.8þ5.9 Hz, H-24);
5.58 (br s, H-26); 4.88 (d, J¼9.0 Hz, H-29); 2.94 (ddd,
J¼11.2þ8.4þ4.4 Hz, H-32); 3.37 (H-33); 1.15 (d, 3H,
J¼6.8 Hz, 11-Me); 1.67 (s, 3H, 19-Me); 1.57 (s, 3H, 27-
Me); 20.11, 20.04, 0.06, 0.07, 0.15, 0.17, 0.22, 0.31 (s,
each 3H, Si–Me); 0.79, 0.88, 0.89, 0.96 (s, each 9H,
(CH3)3).
4.45 g (95%). Colorless foam; MS: 906 (MHþ), 928
(MNaþ); CHN (C49H83NO12Si) calcd: 64.94/9.23/1.55,
found: 64.52/9.27/1.43; 13C NMR (CDCl3, E–Z¼2:1), d
(E/Z-isomer, ppm): 169.00/168.25 (C1); 56.36/52.70 (C2);
27.62/26.49 (C3); 20.57/20.83 (C4); 24.22/24.64 (C5);
39.00/43.64 (C6); 164.62/165.74 (C8); 196.48/191.30
(C9); 97.53/98.69 (C10); 34.72/33.33 (C11); 32.57/32.75
(C12); 73.54/73.66 (C13); 72.78/71.70 (C14); 75.35/76.36
(C15); 34.85/35.98 (C16); 25.44/26.18 (C17); 49.33/48.31
(C18); 138.07/139.32 (C19); 123.78/122.73 (C20);
55.53/55.62 (C21); 210.24/210.80 (C22); 48.31/44.63
(C23); 69.73/70.80 (C24); 40.51/41.18 (C25); 81.3
(br)/77.1 (br) (C26); 131.74/132.79 (C27); 12.14/14.14
(C28); 134.4 (br)/129.69 (C29); 35.00/34.89 (C30);
34.55/34.55 (C31); 84.08/84.16 (C32); 73.44/73.44 (C33);
31.24/31.19 (C34); 30.37/30.62 (C35); 24.38/23.15 (C36);
11.58/11.60 (C37); 57.12/57.43 (15-OMe); 16.02/16.09
(11-CH3); 19.49/18.85 (17-CH3); 15.33/16.37 (19-CH3);
10.32/10.36 (25-CH3); 56.51/56.29/56.24/56.23 (both con-
formers, 32-OMe and 15-OMe); 25.83, 25.79, 17.97, 17.89
(Si–t-Bu); 24.20, 24.35, 24.49, 24.90 (SiMe2). 1H NMR
(CDCl3, E–Z¼2:1, selected data), d (E-isomer, ppm): 4.83
(H-2); 4.40 (br d, J¼13.5 Hz, H-6a); 3.10 (H-6b); 2.26
(H-11); 3.46 (H-13); 3.79 (dd, J¼9.6þ1.6 Hz, H-14); 3.60
(ddd, J¼11.2þ4.1þ1.8 Hz, H-15); 4.80 (d, J¼10.3 Hz,
H-20); 3.29 (H-21); 2.78 (dd, J¼14.2þ7.6 Hz, H-23a);
2.22 (dd, J¼14.2þ5.3 Hz, H-23b); 4.04 (ddd,
J¼7.3þ5.7þ1.8 Hz, H-24); 5.19 (d, J¼7.3 Hz, H-26);
5.26 (d, J¼9.2 Hz, H-29); 3.00 (H-32); 3.38 (H-33); 0.95
(d, 3H, J¼6.6 Hz, 11-Me); 1.63 (s, 3H, 19-Me); 1.48 (s, 3H,
27-Me); 0.02, 0.03 (s, each 3H, Si–Me); 0.86 (s, 9H,
(CH3)3); 4.20 (s, 10-OH); d (Z-isomer, ppm): 4.99 (br dd,
J¼5.5þ2.0 Hz, H-2); 3.88 (br d, J¼13.5 Hz, H-6a); 3.28
(H-6b); 2.19 (H-11); 3.46 (H-13); 3.93 (dd, J¼9.4þ2.5 Hz,
H-14); 3.57 (ddd, J¼11.0þ4.6þ2.8 Hz, H-15); 5.07 (d,
J¼10.1 Hz, H-20); 3.08 (H-21); 2.46 (dd, J¼16.5þ6.9 Hz,
H-23a); 2.41 (dd, J¼16.5þ4.1 Hz, H-23b); 4.23 (H-24);
5.25 (d, J¼2.8 Hz, H-26); 5.04 (d, J¼8.9 Hz, H-29); 3.00
(H-32); 3.38 (H-33); 1.00 (d, 3H, J¼6.6 Hz, 11-Me); 1.69
(s, 3H, 19-Me); 1.63 (s, 3H, 27-Me); 20.04, 0.03 (s, each
3H, Si–Me); 0.85 (s, 9H, (CH3)3); 5.42 (br s, 10-OH).
Compound 11. 191 mg, 0.4%. White powder; MS: 1270
(MNaþ), 1311 (MNaþ·CH3CN); 13C NMR (CDCl3, E–
Z¼0:1), d (ppm): 169.29 (C1); 50.98 (C2); 26.35 (C3);
20.62 (C4); 24.48 (C5); 43.06 (C6); 165.70 (C8); 197.43
(C9); 99.33 (C10); 39.68 (C11); 33.11 (C12); 74.23 (C13);
77.21 (C14); 77.84 (C15); 34.43 (C16); 29.40 (C17); 47.79
(C18); 133.02 (C19); 128.52 (C20); 46.37 (C21); 155.14
(C22); 106.96 (C23); 69.81 (C24); 42.58 (C25); 74.14
(C26); 134.21 (C27); 14.68 (C28); 127.11 (C29); 34.86
(C30); 36.81 (C31); 84.25 (C32); 75.24 (C33); 33.91 (C34);
31.05 (C35); 28.80 (C36); 12.74 (C37); 56.14 (13-OMe);
57.43 (15-OMe); 57.92 (32-OMe); 15.50 (11-CH3); 20.20
(17-CH3); 19.59 (19-CH3); 9.32 (25-CH3); 26.01, 25.92,
25.88, 18.42, 18.17, 18.05, 17.93 (Si–t-Bu); 22.81, 22.99,
1
23.34, 23.86, 24.62, 24.74 (SiMe2). H NMR (CDCl3,
E–Z¼0:1, selected data), d (ppm): 5.03 (d, J¼5.7 Hz, H-2);
3.53 (ddd, J¼12.8þ12.8þ3.3 Hz, H-6a); 3.34 (H-6b); 1.77
(H-11); 3.43 (H-13); 3.31 (H-14); 3.38 (H-15); 5.58 (d,
J¼9.5 Hz, H-20); 2.61 (ddd, J¼9.5þ9.5þ3.5 Hz, H-21);

K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
10083
5.1.3. 33-O-formyl-24-O-TBDMS-ascomycin 13. To a
stirred solution of 4 g (4.41 mmol) 24-O-TBDMS-ascomy-
cin (11) and 5.4 g DMAP (10 equiv., 44.1 mmol) in 130 ml
acetonitrile were added at room temperature 1.94 g
(5 equiv., 22 mmol) of the mixed anhydride of acetic acid
and formic acid (H(CO)O(CO)CH3).21 After TLC analysis
confirmed completion of the reaction, the mixture was
partitioned between ethyl acetate and saturated aqueous
sodium hydrogen carbonate. The organic layer was washed
twice with 1N hydrochloric acid (to remove DMAP) and
brine, dried over anhydrous sodium sulfate, filtered and
concentrated under reduced pressure. The residual crude
product was purified by flash chromatography (silica gel,
ethyl acetate–n-heptane¼3:2). The product fraction was
concentrated under reduced pressure and dried for 15 h
under high vacuum.
was dropped via syringe into a solution of 1.0 g
(0.98 mmol) 24,33-bis-OTBDMS-ascomycin (4) and
0.96 g (8 equiv., 7.84 mmol) 4-(N,N-dimethylamino)-pyr-
idine (DMAP) in 70 ml acetonitrile. The reaction was
allowed to stir at room temperature until TLC indicated the
complete consumption of starting material (6 h). The
reaction mixture was poured into a rapidly stirred mixture
of 100 ml aq. ammonia (15 w/w%) and 200 ml ethyl acetate.
After 10 min the organic phase was separated, washed twice
with 1N hydrochloric acid and brine, dried over anhydrous
sodium sulfate, filtered and evaporated at reduced pressure.
The residual crude product was purified by flash chroma-
tography (silica gel, ethyl acetate–n-heptane¼7:1), fol-
lowed by filtration through Sephadexw LH20 (ethyl
acetate). The product containing fraction was evaporated
at reduced pressure and dried via lyophilization from
dioxane at high vacuum.
3.63 g (88%). Colorless foam; MS: 934 (MHþ), 956
(MNaþ), 997 (MNaþ·CH3CN); CHN (C50H83NO13Si)
calcd: 64.28/8.95/1.50 found: 63.93/8.82/1.50; 13C NMR
(CDCl3, E–Z¼2:1), d (E/Z-isomer, ppm): 168.98/168.23
(C1); 56.23/52.71 (C2); 27.57/26.21 (C3); 20.84/20.64
(C4); 24.62/24.24 (C5); 39.03/43.65 (C6); 164.62/165.80
(C8); 196.43/191.22 (C9); 97.55/98.72 (C10); 34.62/33.36
(C11); 32.78/32.59 (C12); 73.57/73.67 (C13); 72.83/71.71
(C14); 75.37/76.35 (C15); 34.6 (br)/36.02 (C16);
25.52/25.83 (C17); 49.29/48.34 (C18); 138.11/139.29
(C19); 123.73/122.76 (C20); 55.60/55.50 (C21);
210.72/210.25 (C22); 48.34/44.71 (C23); 69.74/70.67
(C24); 40.54/41.05 (C25); 80.8 (br)/76.9 (br) (C26); 132.3
(br)/133.21 (C27); 12.34/14.22 (C28); 133.5 (br)/128.95
(C29); 34.72/34.50 (C30); 35.82/36.13 (C31); 80.43/80.48
(C32); 75.81/75.88 (C33); 29.72/29.66 (C34); 30.22/30.43
(C35); 24.40/23.22 (C36); 11.58/11.61 (C37); 56.33/56.23
(13-OMe); 57.10/57.41 (15-OMe); 56.97/57.15 (32-OMe);
16.01/16.09 (11-CH3); 19.57/18.85 (17-CH3); 15.37/16.38
(19-CH3); 10.26/10.26 (25-CH3); 160.96/160.96 (33-
OCHO); 25.80/25.83 and 17.97/17.89 (Si–t-Bu); 24.20,
24.33, 24.50, 24.89 (SiMe2). 1H NMR (CDCl3, E–Z¼2:1,
selected data), d (E-isomer, ppm): 4.42 (br s, H-2); 4.41 (br
d, J¼13 Hz, H-6a); 3.09 (H-6b); 2.28 (H-11); 3.46 (H-13);
3.79 (dd, J¼9.5þ1.5 Hz, H-14); 3.60 (ddd,
J¼11.4þ4.0þ1.5 Hz, H-15); 4.80 (d, J¼10.1 Hz, H-20);
3.29 (H-21); 2.77 (dd, J¼14.5þ7.6 Hz, H-23a); 2.22 (dd,
J¼14.5þ5.5 Hz, H-23b); 4.05 (br dd, J¼6þ6 Hz, H-24);
5.19 (d, J¼7.1 Hz, H-26); 5.25 (d, J¼10.0 Hz, H-29); 3.24
(H-32); 4.71 (H-33); 0.96 (d, 3H, J¼6.6 Hz, 11-Me); 1.63
(s, 3H, 19-Me); 1.49 (s, 3H, 27-Me); 0.02, 0.03 (s, each 3H,
Si–Me); 0.86 (s, 9H, (CH3)3); 4.20 (s, 10-OH); 8.12 (s, 33-
CHO). d (Z-isomer, ppm): 4.99 (br d, J¼5.5 Hz, H-2); 4.90
(br d, J¼13.5 Hz, H-6a); 3.28 (H-6b); 2.20 (H-11); 3.46 (H-
13); 3.93 (dd, J¼9.6þ2.6 Hz, H-14); 3.58 (ddd,
J¼11.3þ4.5þ2.6 Hz, H-15); 5.09 (d, J¼10.1 Hz, H-20);
3.07 (H-21); 2.46 (dd, J¼16.5þ7.1 Hz, H-23a); 2.41 (dd,
J¼16.5þ3.6 Hz, H-23b); 4.24 (H-24); 5.23 (s, H-26); 5.02
(d, J¼8.8 Hz, H-29); 3.24 (H-32); 4.71 (H-33); 1.01 (d, 3H,
J¼6.6 Hz, 11-Me); 1.69 (s, 3H, 19-Me); 1.63 (s, 3H, 27-
Me); 20.04, 0.03 (s, each 3H, Si–Me); 0.85 (s, 9H, (CH3)3);
5.49 (s, 10-OH); 8.11 (s, 33-CHO).
670 mg (69%). Yellow powder; MS: 1014 (MNaþ), 1055
(MNaþ·CH3CN); CHN (C51H85N3O14Si) calcd:
61.73/8.63/4.23, found: 61.51/8.41/4.04; 13C NMR
(CDCl3, E–Z,1:10), d (Z-isomer, ppm): 169.08 (C1);
52.01 (C2); 25.66 (C3); 21.26 (C4); 25.42 (C5); 43.83 (C6);
165.82 (C8); 184.46 (C9); 200.17 (C10); 32.06 (C11); 35.07
(C12); 78.07 (C13); 73.02 (C14); 76.49 (C15); 38.31 (C16);
27.68 (C17); 46.87 (C18); 138.72 (C19); 123.11 (C20);
54.80 (C21); 208.63 (C22); 48.67 (C23); 66.93 (C24); 38.29
(C25); 84.31 (C26); 131.61 (C27); 10.97 (C28); 135.95
(C29); 34.78 (C30); 35.82 (C31); 80.78 (C32); 76.64 (C33);
30.21 (C34); 30.32 (C35); 23.63 (C36); 11.81 (C37); 56.93
(13-OMe); 58.03 (15-OMe); 56.63 (32-OMe); 16.98 (11-
CH3); 18.91 (17-CH3); 17.71 (19-CH3); 9.91 (25-CH3);
156.65 (33-OCONH2); 156.02 (14-OCONH2); 25.87, 18.07
1
(Si–t-Bu); 23.77, 24.15 (SiMe2). H NMR (CDCl3, E–
Z,1:10, selected data), d (Z-isomer, ppm): 5.19 (br d,
J¼5.4 Hz, H-2); 3.47 (H-6a); 3.17 (H-6b); 3.84 (H-11); 3.45
(H-13); 5.31 (d, J¼9.0 Hz, H-14); 3.48 (H-15); 5.00 (d,
J¼10.2 Hz, H-20); 3.17 (H-21); 2.98 (dd, J¼17.2þ10.2 Hz,
H-23a); 2.29 (dd, J¼17.2þ3.4 Hz, H-23b); 4.20 (dd,
J¼10.2þ3.4 Hz, H-24); 5.11 (d, J¼10.7 Hz, H-26); 5.32
(d, J¼8.9 Hz, H-29); 3.15 (H-32); 4.56 (ddd,
J¼11.3þ9.4þ4.9 Hz, H-33); 1.09 (d, 3H, J¼6.7 Hz, 11-
Me); 1.74 (s, 3H, 19-Me); 1.52 (s, 3H, 27-Me); 0.01, 0.04 (s,
each 3H, Si–Me); 0.88 (s, 9H, (CH3)3); 4.69, 4.85 (s, each
1H, CONH2).
5.1.5. 14,33-Bis-O-(N-methylaminocarbonyl)-24-O-
TBDMS-ascomycin 15. Starting from 0.5 g (0.49 mmol)
24,33-bis-OTBDMS-ascomycin (4), compound 15 was
prepared as described above for compound 14, with the
exception that a mixture of an aq. solution of methylamine
(15 w/w%) and ethyl acetate was used for quenching the
reaction. Purification of the crude reaction mixture was
performed by flash chromatography (silica gel, ethyl
acetate–n-heptane¼5:1).
720 mg (72%). Yellow powder; MS: 1020 (MHþ), 1042
(MNaþ), 1083 (MNaþ·CH3CN); CHN (C53H89N3O14Si)
calcd: 62.39/8.79/4.12, found: 62.37/8.85/3.95; 13C NMR
(CDCl3, E–Z,1:10), d (Z-isomer, ppm): 169.08 (C1);
51.96 (C2); 25.69 (C3); 21.26 (C4); 25.44 (C5); 43.79 (C6);
165.83 (C8); 184.47 (C9); 200.13 (C10); 32.1 (br) (C11);
35.09 (C12); 78.28 (C13); 72.92 (C14); 76.74 (C15); 38.55
5.1.4. 14,33-Bis-O-(aminocarbonyl)-24-O-TBDMS-asco-
mycin 14 (representative run). 0.355 ml (0.58 g, 3 equiv.,
2.94 mmol) trichloromethyl-chloroformate (diphosgene)

10084
K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
(C16); 27.47 (C17); 46.92 (C18); 138.74 (C19); 123.24
(C20); 54.86 (C21); 208.51 (C22); 48.65 (C23); 67.00
(C24); 38.41 (C25); 84.19 (C26); 131.55 (C27); 10.90
(C28); 136.00 (C29); 34.82 (C30); 35.83 (C31); 80.80
(C32); 76.22 (C33); 30.42 (C34); 30.34 (C35); 23.63 (C36);
11.81 (C37); 56.9 (br) (13-OMe); 58.07 (15-OMe); 56.64
(32-OMe); 16.95 (11-CH3); 18.93 (17-CH3); 17.53 (19-
CH3); 9.90 (25-CH3); 156.89, 27.72 (33-OCONHCH3);
156.45, 27.84 (14-OCONHCH3); 25.87, 18.07 (Si–t-Bu);
23.82, 24.15 (SiMe2). 1H NMR (CDCl3, E–Z,1:10,
selected data), d (Z-isomer, ppm): 5.19 (br d, J¼5.5 Hz, H-
2); 3.47 (H-6a); 3.18 (H-6b); 3.86 (H-11); 3.42 (H-13); 5.32
(d, J¼9.0 Hz, H-14); 3.47 (H-15); 5.01 (d, J¼10.4 Hz, H-
20); 3.17 (H-21); 2.97 (dd, J¼17.0þ10.0 Hz, H-23a); 2.27
(dd, J¼17.0þ3.3 Hz, H-23b); 4.20 (dd, J¼10.0þ3.3 Hz, H-
24); 5.12 (d, J¼10.5 Hz, H-26); 5.32 (d, J¼8.8 Hz, H-29);
3.15 (H-32); 4.57 (H-33); 1.08 (d, 3H, J¼6.8 Hz, 11-Me);
1.74 (s, 3H, 19-Me); 1.50 (d, 3H, J¼1.0 Hz, 27-Me); 0.01,
0.05 (s, each 3H, Si–Me); 0.88 (s, 9H, (CH3)3); 4.76 (br q,
J¼5.0 Hz, 14-CONHCH3); 2.82 (d, J¼5.0 Hz, 14-
CONHCH3); 4.59 (br s, 33-CONHCH3); 2.79 (d,
J¼5.0 Hz, 33-CONHCH3).
was prepared as described above for compound 14 (8 equiv.
DMAP, 3 equiv. diphosgene, reaction time 5 h). Purification
of the crude product was performed by flash chromato-
graphy (silica gel, ethyl acetate–n-heptane¼1:1).
720 mg (86%). Yellow powder; MS: 977 (MHþ), 999
(MNaþ), 1040 (MNaþ·CH3CN); CHN (C51H84N2O14Si)
calcd: 62.68/8.66/2.87, found: 62.35/8.51/2.78; 13C NMR
(CDCl3, E–Z¼1:10), d (Z-isomer, ppm): 169.14 (C1); 52.01
(C2); 25.67 (C3); 21.27 (C4); 25.42 (C5); 43.82 (C6);
165.83 (C8); 184.47 (C9); 200.16 (C10); 32.06 (C11); 35.09
(C12); 78.07 (C13); 73.08 (C14); 76.48 (C15); 38.32 (C16);
27.67 (C17); 46.89 (C18); 138.74 (C19); 123.12 (C20);
54.82 (C21); 208.57 (C22); 48.69 (C23); 66.93 (C24); 38.32
(C25); 84.25 (C26); 131.89 (C27); 11.01 (C28); 135.66
(C29); 34.62 (C30); 35.61 (C31); 80.48 (C32); 76.08 (C33);
29.83 (C34); 30.27 (C35); 23.62 (C36); 11.82 (C37); 56.64
(13-OMe); 58.06 (15-OMe); 56.94 (32-OMe); 16.99 (11-
CH3); 18.93 (17-CH3); 17.69 (19-CH3); 9.91 (25-CH3);
161.15 (33-OCHO); 155.89 (14-OCONH2); 25.87, 18.08
1
(Si–t-Bu); 23.74, 24.14 (SiMe2). H NMR (CDCl3, E–
Z¼1:10, selected data), d (Z-isomer, ppm): 5.20 (d,
J¼5.5 Hz, H-2); 3.48 (H-6a); 3.18 (H-6b); 3.85 (H-11);
3.45 (H-13); 5.32 (d, J¼9.0 Hz, H-14); 3.49 (H-15); 5.00 (d,
J¼10.0 Hz, H-20); 3.18 (H-21); 2.99 (dd, J¼17.2þ10.4 Hz,
H-23a); 2.28 (H-23b); 4.21 (dd, J¼10.2þ3.4 Hz, H-24);
5.12 (d, J¼10.5 Hz, H-26); 5.33 (d, J¼9.1 Hz, H-29); 3.22
(H-32); 4.70 (H-33); 1.10 (d, 3H, J¼6.7 Hz, 11-Me); 1.75
(s, 3H, 19-Me); 1.53 (d, 3H, J¼1.1 Hz, 27-Me); 0.02, 0.05
(s, each 3H, Si–Me); 0.89 (s, 9H, (CH3)3); 8.13 (s, 33-
CHO); 4.6–4.9 (br s, 2H, 14-CONH2).
5.1.6. 14,33-Bis-O-(1-imidazolyl-carbonyl)-24-O-
TBDMS-ascomycin 16. Starting from 1.0 g (0.98 mmol)
24,33-bis-OTBDMS-ascomycin (4), compound 16 was
prepared as described above for compound 14, with the
exception that a mixture of an aq. solution of imidazole (25
w/w%) and ethyl acetate was used for quenching the
reaction. Purification of the crude reaction mixture was
performed by flash chromatography (silica gel, ethyl
acetate–acetonitrile¼20:1).
5.1.8. 14-O-(Ethoxycarbonylmethyl)-33-O-formyl-24-O-
TBDMS-ascomycin 18. 0.39 ml (0.64 g, 3 equiv.,
3.21 mmol) trichloromethyl-chloroformate (diphosgene)
was dropped via syringe into a solution of 1.0 g
(1.07 mmol) 33-O-formyl-24-O-TBDMS-ascomycin (13)
and 1.05 g (8 equiv., 8.56 mmol) 4-(N,N-dimethylamino)-
pyridine (DMAP) in 60 ml acetonitrile. The reaction was
stirred at room temperature until TLC indicated a complete
consumption of the starting material (5 h). The reaction
mixture was poured into a rapidly stirred mixture of 100 ml
water/10 g glycine ethyl ester hydrochloride/10 ml satu-
rated aq. potassium carbonate and 250 ml ethyl acetate.
After 20 min, the organic phase was separated, washed
twice with 1N hydrochloric acid and brine, dried over
anhydrous sodium sulfate, filtered and concentrated under
reduced pressure. The residual crude product was purified
by flash chromatography (silica gel, ethyl acetate–n-
heptane¼1:1) followed by filtration through Sephadexw
LH20 (ethyl acetate). The purified product was lyophilized
from benzene under high vacuum.
1.07 g (72%). Yellow powder; MS: 1094 (MHþ), 1042
(MNaþ); CHN (C57H87N5O14Si) calcd: 62.56/8.01/6.40
found: 62.32/7.85/6.26; 13C NMR (CDCl3, E–Z¼1:10), d
(Z-isomer, ppm): 168.87 (C1); 52.00 (C2); 25.70 (C3);
21.18 (C4); 25.39 (C5); 43.97 (C6); 165.53 (C8); 184.83
(C9); 199.9 (br) (C10); 33.9 (br) (C11); 34.62 (C12); 77.68
(C13); 77.79 (C14); 76.20 (C15); 39.34 (C16); 27.51 (C17);
46.65 (C18); 138.64 (C19); 123.54 (C20); 55.07 (C21);
208.78 (C22); 47.0 (br) (C23); 67.40 (C24); 38.61 (C25);
83.59 (br) (C26); 132.17 (C27); 11.28 (C28); 135.00 (C29);
34.57 (C30); 35.73 (C31); 80.53 (C32); 80.27 (C33); 29.69
(C34); 30.18 (C35); 23.60 (C36); 11.72 (C37); 57.35 (13-
OMe); 58.50 (15-OMe); 57.18 (32-OMe); 16.62 (11-CH3);
19.14 (17-CH3); 17.22 (19-CH3); 9.78 (25-CH3); 148.47,
148.36 (14,33-bis-OCvO), 137.0 (br), 130.87, 130.47,
117.25, 117.19 (2£1-imidazolyl); 25.86, 18.06 (Si–t-Bu);
23.82, 24.13 (SiMe2). 1H NMR (CDCl3, E–Z¼1:10), d (Z-
isomer, ppm): 5.20 (d, J¼5.6 Hz, H-2); 3.45 (H-6a); 3.20
(H-6b); 3.70 (H-11); 3.59 (H-13); 5.49 (dd, J¼7.0þ3.5 Hz,
H-14); 3.56 (H-15); 4.94 (d, J¼10.0 Hz, H-20); 3.21 (H-21);
2.92 (H-23a); 2.31 (H-23b); 4.20 (dd, J¼9.8þ4.0 Hz, H-
24); 5.13 (d, J¼10.0 Hz, H-26); 5.34 (d, J¼8.9 Hz, H-29);
3.33 (H-32); 4.88 (H-33); 1.14 (d, 3H, J¼7.0 Hz, 11-Me);
1.75 (s, 3H, 19-Me); 1.55 (s, 3H, 27-Me); 0.03, 0.06 (s, each
3H, Si–Me); 0.90 (s, 9H, (CH3)3); 8.16, 8.15, 7.45, 7.44,
7.07, 7.10 (s, each 1H, imidazole-H).
730 mg (67%) yellow powder; MS: 1085 (MNaþ); CHN
(C55H90N2O16Si)
calcd:
62.12/8.53/2.63
found:
61.95/8.65/2.59; 13C NMR (CDCl3, E–Z¼1:10), d (Z-
isomer, ppm): 169.15 (C1); 51.98 (C2); 25.65 (C3); 21.27
(C4); 25.42 (C5); 43.80 (C6); 165.88 (C8); 184.54 (C9);
200.12 (C10); 32.0 (br) (C11); 34.95 (C12); 78.08 (C13);
73.30 (C14); 76.44 (C15); 38.28 (C16); 27.72 (C17); 46.90
(C18); 138.81 (C19); 123.10 (C20); 54.78 (C21); 208.45
(C22); 48.71 (C23); 66.89 (C24); 38.39 (C25); 84.24 (C26);
131.92 (C27); 10.96 (C28); 135.65 (C29); 34.61 (C30);
5.1.7. 14-O-Formyl-33-O-(aminocarbonyl)-24-O-
TBDMS-ascomycin 17. Starting from 0.8 g (0.86 mmol)
33-O-formyl-24-O-TBDMS-ascomycin (13), compound 17

K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
10085
35.61 (C31); 80.48 (C32); 76.10 (C33); 29.83 (C34); 30.27
4.21 (s, 10-OH);
d
(Z-isomer, ppm): 4.98 (dd,
(C35); 23.59 (C36); 11.81 (C37); 56.63 (13-OMe); 58.02
(15-OMe); 56.93 (32-OMe); 16.85 (11-CH3); 18.83
(17-CH3); 17.68 (19-CH3); 9.92 (25-CH3); 161.12 (33-
OCHO); 155.98, 42.98, 169.78, 61.45, 14.13 (14-
OCONHCH2COOCH2CH3); 25.86, 18.07 (Si–t-Bu);
23.77, 24.15 (SiMe2). 1H NMR (CDCl3, E–Z¼1:10,
selected data), d (Z-isomer, ppm): 5.20 (d, J¼5.5 Hz, H-2);
3.48 (H-6a); 3.18 (H-6b); 3.83 (H-11); 3.47 (H-13); 5.36 (d,
J¼8.9 Hz, H-14); 3.48 (H-15); 5.01 (d, J¼10.0 Hz, H-20);
3.17 (H-21); 2.99 (dd, J¼17.2þ10.3 Hz, H-23a); 2.28 (dd,
J¼17.2þ3.4 Hz, H-23b); 4.22 (H-24); 5.12 (d, J¼10.6 Hz,
H-26); 5.32 (H-29); 3.21 (H-32); 4.70 (H-33); 1.08 (d, 3H,
J¼6.9 Hz, 11-Me); 1.74 (s, 3H, 19-Me); 1.52 (d, 3H,
J¼1.1 Hz, 27-Me); 0.02, 0.05 (s, each 3H, Si–Me); 0.89 (s,
9H, (CH3)3); 5.30 (br s, 14-CONH); 4.01 (dd,
J¼6.2þ2.2 Hz, H-2); 3.77 (br d, J¼13.2 Hz, H-6a); 3.32
(H-6b); 2.27 (H-11); 3.45 (H-13); 3.87 (dd, J¼9.7þ2.8 Hz,
H-14); 3.55 (H-15); 5.05 (d, J¼9.0 Hz, H-20); 3.15 (H-21);
2.76 (dd, J¼17.6þ5.0 Hz, H-23a); 2.63 (dd,
J¼17.6þ6.9 Hz, H-23b); 5.35 (H-24); 5.10 (d, J¼5.5 Hz,
H-26); 5.05 (d, J¼9.1 Hz, H-29); 3.25 (H-32); 4.71 (ddd,
J¼11.3þ9.5þ4.8 Hz, H-33); 0.99 (d, 3H, J¼6.5 Hz,
11-Me); 1.68 (d, 3H, J¼1.2 Hz, 19-Me); 1.63 (d, 3H,
J¼1.2 Hz, 27-Me); 8.00 (s, 14-CHO); 8.12 (s, 33-CHO);
5.04 (s, 10-OH).
5.1.10. 14,33-Bis-O-formyl-24-O-TBDMS-ascomycin 20.
Starting from 4. To a cooled (ice-bath), magnetically stirred
solution of 4 ml (30 equiv., 44.1 mmol) N,N-dimethyl
formamide in 100 ml acetonitrile were added drop wise
via a syringe 1.77 ml (10 equiv., 14.7 mmol, 2.91 g)
trichloromethyl-chloroformate (diphosgene) in such a rate,
that the temperature was kept below 58C. After an additional
30 min at 0–58C, 1.5 g (1.47 mmol) 24,33-bis-O-TBDMS-
ascomycin (4) were added in one portion and the cooling
bath was removed. The course of the reaction was
monitored by TLC. After 20 min, the complete consumption
of the starting material and the formation of 33-O-formyl-
24-OTBDMS-ascomycin (13) together with minor amounts
of the target compound 20 could be detected. After 6 h, the
complete conversion of the intermediate 13 into 20 was
observed. The reaction mixture was partitioned between a
saturated aqueous sodium hydrogen carbonate solution
(200 ml) and ethyl acetate (400 ml). The organic layer
was washed twice with brine, dried over anhydrous sodium
sulfate, filtered and concentrated under reduced pressure.
The crude product was purified using flash column
chromatography (silica gel, toluene–acetonitrile¼5:1) to
give 0.98 g (69%) of the title compound 20.
J¼18.1þ6.2 Hz,
14-CONHCH2-a);
3.90
(dd,
J¼18.1þ5.4 Hz, 14-CONHCH2-b); 4.20 (q, J¼7.1 Hz,
COOCH2CH3); 1.28 (t, J¼7.1 Hz, COOCH2CH3); 8.12 (s,
33-CHO).
5.1.9. 24,33-Bis-O-formyl-ascomycin 19. To a stirred
solution of 5 g (6.31 mmol) ascomycin (1) and 15.46 g
DMAP (20 equiv., 0.126 mol) in 150 ml acetonitrile, 5.55 g
(10 equiv., 63.1 mmol) of the mixed anhydride of acetic
acid and formic acid (H(CO)O(CO)CH3 were added at room
temperature.21 After TLC showed completion of the
reaction (70 min) the mixture was worked up as described
above for the preparation of compound 12. Purification of
the crude product was accomplished using flash column
chromatography (silica gel; ethyl acetate–toluene¼1:2).
4.71 g (88%). Colorless foam; 848 (MHþ), 870 (MNaþ),
1081 (MNaþ·CH3CN); 13C NMR (CDCl3, E–Z¼2:1), d
(E/Z-isomer, ppm): 169.08/168.79 (C1); 56.35/52.74 (C2);
27.53/26.25 (C3); 20.84/20.66 (C4); 24.49/24.29 (C5);
39.16/43.92 (C6); 164.75/166.08 (C8); 196.42/192.42
(C9); 97.35/98.53 (C10); 34.63/33.61 (C11); 32.62/32.62
(C12); 73.66/73.86 (C13); 73.02/72.49 (C14); 75.32/76.98
(C15); 33.99/35.54 (C16); 26.01/26.59 (C17); 48.98/48.17
(C18); 138.40/139.28 (C19); 123.57/123.20 (C20);
55.23/54.60 (C21); 208.34/208.05 (C22); 43.05/41.87
(C23); 71.44/71.56 (C24); 37.86/37.04 (C25); 79.31/78.51
(C26); 131.39/131.58 (C27); 12.77/13.52 (C28);
132.36/130.72 (C29); 34.54/34.51 (C30); 35.84/35.93
(C31); 80.45/80.45 (C32); 75.82/75.82 (C33); 29.66/29.66
(C34); 30.11/30.24 (C35); 24.38/23.87 (C36); 11.66/11.60
(C37); 57.10/57.15 (13-OMe); 57.15/57.42 (15-OMe);
56.23/56.067 (32-OMe); 16.08/15.99 (11-CH3);
19.90/19.68 (17-CH3); 15.67/16.27 (19-CH3); 10.28/10.10
(25-CH3); 160.9 (33-OCHO); 159.68/169.88 (24-OCHO).
1H NMR (CDCl3, E–Z¼2:1, selected data), d (E-isomer,
ppm): 4.54 (br dd, J¼4þ3 Hz, H-2); 4.43 (br d, J¼13.5 Hz,
H-6a); 3.06 (ddd, J¼13.5þ13.3þ2.8 Hz, H-6b); 2.27
(H-11); 3.45 (H-13); 3.74 (dd, J¼9.7þ1.5 Hz, H-14); 3.60
Starting from 12. Using 0.5 g (0.552 mmol) 24-O-TBDMS-
ascomycin (12), 1.53 ml (30 equiv., 16.55 mmol) DMF and
0.67 ml (10 equiv., 5.52 mmol) diphosgene, the reaction
was performed as described above to give 385 mg (72%) 20.
Starting from 13. Using 0.5 g (0.53 mmol) 33-O-formyl-24-
O-TBDMS-ascomycin (13), 1.47 ml (30 equiv., 15.9 mmol)
DMF and O.64 ml (10 equiv., 5.3 mmol) diphosgene, the
reaction was performed as described above to give 440 mg
(86%) 20.
980/385/440 mg (69/72/86% from 4/12/13) yellow foam;
962 (MHþ), 984 (MNaþ), 1025 (MNaþ·CH3CN); CHN
(C51H83NO14Si) calcd: 63.66/8.69/1.46, found: 63.75/8.48/
1.43; 13C NMR (CDCl3, E–Z¼1:10), d (Z-isomer, ppm):
168.97 (C1); 52.00/56.24 (C2); 25.62 (C3); 21.23 (C4);
25.38 (C5); 43.90 (C6); 165.69 (C8); 184.61 (C9); 199.95
(C10); 32.6 (br) (C11); 34.61 (C12); 77.67 (C13); 72.41
(C14); 75.92 (C15); 38.57 (C16); 27.50 (C17); 46.86 (C18);
138.63 (C19); 123.26 (C20); 54.83 (C21); 208.59 (C22);
48.41 (C23); 67.06 (C24); 38.23 (C25); 84.05 (C26); 131.89
(C27); 11.09 (C28); 135.57 (C29); 34.64 (C30); 35.65
(C31); 80.48 (C32); 76.06 (C33); 29.82 (C34); 30.17 (C35);
23.60 (C36); 11.76 (C37); 56.81 (13-OMe); 58.09
(15-OMe); 56.95 (32-OMe); 16.80 (11-CH3); 18.91
(17-CH3); 17.60 (19-CH3); 9.88 (25-CH3); 161.09
(33-OCHO); 160.11 (14-OCHO); 25.86, 18.07 (Si–t-Bu);
(ddd,
J¼10.9þ3.6þ1.5 Hz,
H-15);
4.89
(dq,
J¼10.1þ1.2 Hz, H-20); 3.27 (H-21); 2.85 (dd,
J¼15.2þ6.3 Hz, H-23a); 2.42 (dd, J¼15.2þ6.6 Hz, H-23b);
5.22 (ddd, J¼6.6þ6.3þ2.8 Hz, H-24); 5.10 (d, J¼5.5 Hz,
H-26); 5.13 (d, J¼9.1 Hz, H-29); 3.25 (H-32); 4.71 (ddd,
J¼11.3þ9.5þ4.8 Hz, H-33); 0.98 (d, 3H, J¼6.5 Hz,
11-Me); 1.64 (d, 3H, J¼1.2 Hz, 19-Me); 1.54 (d, 3H,
J¼1.2 Hz, 27-Me); 8.00 (s, 14-CHO); 8.12 (s, 33-CHO);

10086
K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
23.79, 24.15 (SiMe2). 1H NMR (CDCl3, E–Z¼1:10), d (Z-
isomer, ppm): 5.19 (d, J¼5.0 Hz, H-2); 3.44 (br d, J¼13 Hz,
H-6a); 3.17 (H-6b); 3.73 (H-11); 3.49 (H-13); 5.56 (dd,
J¼8.2þ1.7 Hz, H-14); 3.50 (H-15); 4.98 (d, J¼10.3 Hz,
H-20); 3.18 (H-21); 2.97 (dd, J¼17.1þ10.2 Hz, H-23a);
2.29 (dd, J¼17.1þ3.8 Hz, H-23b); 4.21 (dd,
J¼10.2þ3.8 Hz, H-24); 5.11 (d, J¼10.4 Hz, H-26); 5.33
(dq, J¼8.9þ1.2 Hz, H-29); 3.21 (H-32); 4.70 (ddd,
J¼11.5þ9.5þ5.0 Hz, H-33); 1.10 (d, 3H, J¼6.7 Hz,
11-Me); 1.75 (s, 3H, 19-Me); 1.54 (d, 3H, J¼1.2 Hz,
27-Me); 0.02, 0.05 (s, each 3H, Si–Me); 0.89 (s, 9H,
(CH3)3); 8.19 (s, 14-CHO); 8.12 (s, 33-CHO).
mixture was partitioned between a saturated solution of
aqueous sodium hydrogen carbonate (100 ml) and ethyl
acetate (200 ml). The organic layer was washed twice with
brine, dried over anhydrous sodium sulfate, filtered and
concentrated under reduced pressure. The crude mixture
was separated by using flash column chromatography
(silica gel, ethyl acetate–n-heptane¼2:1!5:1). The
two fractions isolated were further purified by size
exclusion chromatography (Sephadexw LH20, ethyl
acetate) and dried via lyophilization from dioxane under
high vacuum.
Compound 22. 42 mg, 7.4%. Yellow powder; 983 (MNaþ),
1024 (MNaþ·CH3CN); 13C NMR (CDCl3, E–Z,1:10), d
(Z-isomer, ppm): 168.95 (C1); 51.78 (C2); 25.09 (C3);
21.19 (C4); 25.28 (C5); 44.06 (C6); 166.01 (C8); 184.57
(C9); 200.21 (C10); 32.3 (br) (C11); 35.1 (br) (C12); 77.78
(C13); 72.44 (C14); 76.03 (C15); 37.56 (C16); (C17); 46.66
(C18); 139.04 (C19); 123.02 (C20); 54.33 (C21); 206.73
(C22); 43.86 (C23); 69.51 (C24); 37.70 (C25); 84.18 (C26);
130.75 (C27); 10.80 (C28); 135.85 (C29); 34.48 (C30);
35.47 (C31); 80.57 (C32); 76.03 (C33); 29.72 (C34); 29.92
(C35); 23.51 (C36); 11.77 (C37); 56.64 (13-OMe); 57.73
(15-OMe); 56.90 (32-OMe); 16.76 (11-CH3); 18.64
(17-CH3); 18.64 (19-CH3); 10.50 (25-CH3); 161.07
(33-OCHO); 159.94 (24-OCHO); 166.81, 41.17, 165.64,
5.1.11. 14,24,33-Tris-O-formyl-ascomycin 21. Starting
from 19. Using 1.2 g (1.42 mmol) 24,33-bis-O-formyl-
ascomycin (19), 4 ml (30 equiv., 15.9 mmol) DMF and
1.72 ml (10 equiv., 5.3 mmol) diphosgene, the reaction was
performed as described above for the preparation of
compound 20. Flash chromatography (silica gel, ethyl
acetate–n-heptane¼2:1) provided 1.11 g (89%) 21.
Starting from 1. Using 1.0 g (1.26 mmol) ascomycin (1),
4.7 ml (40 equiv., 50.4 mmol) DMF and 2.28 ml (15 equiv.,
18.9 mmol) diphosgene, the reaction was performed as
described above to give 0.61 g (55%) 21.
1
1.11/0.61 g (89/55% from 19/1) yellow foam; 876 (MHþ),
898 (MNaþ), 939 (MNaþ·CH3CN); CHN (C46H69NO15)
calcd: 63.07/7.94/1.60 found: 62.98/7.79/1.65; 13C NMR
(CDCl3, E–Z¼1:10), d (Z-isomer, ppm): 168.88 (C1); 51.82
(C2); 25.24 (C3); 21.18 (C4); 25.03 (C5); 44.09 (C6);
165.85 (C8); 184.34 (C9); 199.84 (C10); 31.9 (br) (C11);
34.52 (C12); 77.31 (C13); 71.03 (C14); 75.66 (C15); 37.22
(C16); 27.65 (C17); 46.60 (C18); 138.81 (C19); 122.93
(C20); 54.23 (C21); 206.97 (C22); 43.80 (C23); 69.46
(C24); 35.42 (C25); 84.27 (C26); 130.68 (C27); 10.81
(C28); 135.87 (C29); 34.45 (C30); 35.44 (C31); 80.53
(C32); 75.96 (C33); 29.69 (C34); 29.91 (C35); 23.58 (C36);
11.77 (C37); 56.72 (13-OMe); 57.65 (15-OMe); 56.92
(32-OMe); 16.93 (11-CH3); 18.86 (17-CH3); 18.53
(19-CH3); 10.55 (25-CH3); 161.11 (33-OCHO); 159.96
(14 and 24-OCHO). 1H NMR (CDCl3, E–Z¼1:10), d
(Z-isomer, ppm): 5.22 (d, J¼5.5 Hz, H-2); 3.43 (br d,
J¼13 Hz, H-6a); 3.06 (H-6b); 3.74 (H-11); 3.54 (H-13);
5.57 (d, J¼9.2 Hz, H-14); 3.49 (H-15); 5.01 (d, J¼10.1 Hz,
H-20); 3.22 (H-21); 3.00 (dd, J¼17.9þ10.8 Hz, H-23a);
2.64 (dd, J¼17.9þ3.2 Hz, H-23b); 5.27 (dd,
J¼10.8þ3.2 Hz, H-24); 4.93 (d, J¼10.3 Hz, H-26); 5.18
(dd, J¼9.0 Hz, H-29); 3.20 (H-32); 4.67 (H-33); 1.10 (d,
3H, J¼6.9 Hz, 11-Me); 1.77 (s, 3H, 19-Me); 1.62 (s, 3H,
27-Me); 8.19 (s, 14-CHO); 8.10 (s, 33-CHO); 7.95 (s,
24-CHO).
35.55, 35.52 (14-OCOCH2CON(CH3)2). H NMR (CDCl3,
E–Z,1:10, selected data), d (Z-isomer, ppm): 5.22 (d,
J¼5.4 Hz, H-2); 3.44 (H-6a); 3.06 (H-6b); 3.75 (H-11); 3.51
(H-13); 5.51 (dd, J¼9.0þ1.8 Hz, H-14); 3.47 (H-15); 5.01
(d, J¼10.2 Hz, H-20); 3.20 (H-21); 2.99 (H-23a); 2.62 (dd,
J¼17.9þ3.2 Hz, H-23b); 5.27 (br d, J¼10.8 Hz, H-24);
4.93 (d, J¼10.3 Hz, H-26); 5.17 (d, J¼9.1 Hz, H-29); 3.20
(H-32); 4.66 (H-33); 1.11 (d, 3H, J¼6.6 Hz, 11-Me); 1.76
(s, 3H, 19-Me); 1.60 (s, 3H, 27-Me); 8.10 (s, 33-CHO); 7.95
(s, 24-CHO); 3.49, 3.52 (each d, 1H, J¼15.2 Hz,
14-OCOCH2); 2.99, 2.94 (s, each 3H, NCH3).
Compound 23. 362 mg, 65%. Colorless powder; 943
(MHþ), 965 (MNaþ), 1006 (MNaþ·CH3CN); CHN
(C50H74N2O15) calcd: 63.68/7.91/2.97 found: 63.51/7.82/
2.86; 13C NMR (CDCl3, E–Z.10:1), d (E-isomer, ppm):
168.82 (C1); 58.27 (C2); 26.81 (C3); 21.75 (C4); 24.65
(C5); 39.56 (C6); 161.25 (C8); 150.82 (C9); 108.53 (C10);
34.17 (C11); 32.85 (C12); 73.01 (C13); 76.61 (C14); 75.18
(C15); 32.56 (C16); 26.20 (C17); 48.00 (C18); 138.26
(C19); 123.49 (C20); 53.53 (C21); 210.09 (C22); 41.76
(C23); 72.08 (C24); 38.26 (C25); 77.34 (C26); 132.51
(C27); 14.77 (C28); 129.01 (C29); 34.45 (C30); 36.07
(C31); 80.40 (C32); 75.79 (C33); 29.62 (C34); 30.40 (C35);
24.17 (C36); 11.50 (C37); 56.44 (13-OMe); 56.70
(15-OMe); 57.19 (32-OMe); 15.30 (11 or 19-CH3); 20.40
(17-CH3); 15.27 (19 or 11-CH3); 10.41 (25-CH3); 166.50
(C9a); 126.09 (C9); 160.09 (C9c); 160.93 (33-OCHO);
160.31 (24-OCHO): 37.81, 34.51 (CON(CH3)2). 13C NMR
(CDCl3, E–Z.10:1), d (E-isomer, ppm): 4.42 (H-2); 4.44
(H-6a); 2.77 (ddd, (J¼13þ13þ3 Hz, H-6b); 2.30 (H-11);
3.48 (H-13); 3.69 (d, J¼9.5 Hz, H-14); 3.55 (d, J¼11.5 Hz,
H-15); 4.94 (d, J¼9.3 Hz, H-20); 3.33 (H-21); 3.02 (dd,
J¼17.4þ9.1 Hz, H-23a); 2.73 (dd, J¼17.4þ3.0 Hz,
H-23b); 5.41 (H-24); 5.05 (H-26); 5.06 (H-29); 3.23
(H-32); 4.71 (H-33); 1.03 (d, 3H, J¼6.6 Hz, 11-Me); 1.61
(s, 3H, 19-Me); 1.63 (d, 3H, J¼1.0 Hz, 27-Me); 8.11 (s,
5.1.12. 24,33-Bis-O-formyl-14-O-(N,N-dimethylcarba-
moylacetyl)-ascomycin 22 and compound 23. To a cooled
and magnetically stirred solution of 1.6 ml (30 equiv.,
17.3 mmol) N,N-dimethyl acetamide in 50 ml diethyl ether
were added 10 ml (30 equiv., 17.7 mmol) of a solution of
phosgene (20 w/w% in toluene) in such a rate (10 min), that
the temperature was kept below 58C. After additional 2 h at
0–58C, 0.5 g (5.89 mmol) 24,33-bis-O-formyl-ascomycin
(19) was added in one portion, the cooling bath was
removed and the mixture was stirred for 20 h. The reaction

K. Baumann et al. / Tetrahedron 59 (2003) 10075–10087
10087
Danishefsky, S. J. Heterocycles 1989, 28(1), 157–161. (c)
Goulet, M. T.; Mills, S. G.; Parsons, W. H.; Rupprecht, K. M.;
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Microb. Prod. 1993, 141–212. (d) Luengo, J. I.; Rozamus,
L. W.; Holt, D. A. Tetrahedron Lett. 1993, 34(29),
4599–4602.
33-CHO); 8.02 (s, 24-CHO); 2.93, 2.94 (s, each 3H,
N–CH3).
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