On the reactivity of ascomycin at the binding domain. Part 2: Hydroxide mediated rearrangement reactions

Tetrahedron 60 (2004) 5965–5981

On the reactivity of ascomycin at the binding domain.

Part 2: Hydroxide mediated rearrangement reactions

a

b

Karl Baumann,^aMarkus Bacher, Andrea Steck and Trixie Wagner

,

*

^aDepartment of Medicinal Chemistry; Novartis Research Institute Vienna, Brunnerstrasse 59, A-1235 Vienna, Austria

^bNovartis Pharma AG, Lichtstrasse 35, CH-4002 Basle, Switzerland

Received 29 October 2003; revised 11 May 2004; accepted 13 May 2004

Available online 8 June 2004

Abstract—The natural product ascomycin represents a highly functionalised 23-membered macrocycle with a polyketide backbone. 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, highly stereoselective, hydroxide mediated rearrangement reactions at the binding domain

are reported.

1. Introduction

and whose structure had originally not been elucidated, was

later shown to be a close structural analogue of FK 506

(ethyl in position 21 instead of allyl).^10–13Pimecrolimus

(Elidel^w, SDZ ASM 981, 3), derived from ascomycin and

featuring a more lipophilic cyclohexyl-part, has been shown

to possess a high therapeutic potential for the treatment of

FK 506 1 is a 23-membered macrolactam isolated from the

fermentation broth of Streptomyces tsukubaensis 9993.^7–9

Interestingly, ascomycin 2, a compound which had been

isolated earlier as a consequence of its antifungal activities,

Figure 1.

Keywords: Ascomycin; Ring contraction; Rearrangement; Binding domain; Tricarbonyl.

*

Corresponding author. Tel.: þ43-1-866-34326; fax: þ43-1-866-34354; e-mail address: karl.baumann@pharma.novartis.com

doi:10.1016/j.tet.2004.05.028

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K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

inﬂammatory skin diseases. Pimecrolimus cream 1%, which

combines a skin selective, anti-inﬂammatory activity with a

low risk for systemic side effects, has successfully been

introduced into the market for the treatment of atopic

dermatitis and contact dermatitis.^14–16In the left hand part

(‘binding domain‘, Fig. 1),^17–21ascomycin features the

unusual pattern of three adjacent carbonyl groups (C8–

C10), whereby one carbonyl group (C10) is involved in

hemiketal formation. The inherently labile hemiketal

structure at C10 potentially allows the formation of

numerous alternative isomers via liberation of the tricarbo-

nyl portion, tautomerisation, enolisation and non-speciﬁc

Scheme 1.

Table 1.

Entry^a

Educt

Base

Solvent

Time

5a/5b^b

Products (isol. %)^c

1

2

3

4

5

6

7

8

4

7

4

5 equiv. LiOH

5 equiv. KOH

THF/H₂O¼3:1

THF/H₂O¼7:1

THF/H₂O¼20:1

THF/H₂O¼80:1

DMSO

12 min

10 min

30 min

60 min

3 h

82:18

83:17

86:14

.98:2

,2:98

n.d.

5a (72), 5b (11)

5a (70), 5b (12)

5a (69), 5b (9)

5a (91) or 6a (95%)^d

5a (91)

5 equiv. NaOH

10 equiv. Ca(OH)₂

1.2 equiv. LiOH

1.2 equiv. KOH

5 equiv. NaOD

10 equiv. Ca(OH)₂

5 equiv. NaOD

5a (86)

5a (74)

30 h

20 min

30 min

40 min

30 min

10 min

1.5 min

40 min

12 min

30 min

40 min

15 min

5b (75) or 6b (78)^d

5b (78)

9

DMSO

10

11

12

13

14

15

16

17

18

19

THF/18-crown-6

THF/D₂O¼3:1

5b (82), 7(trace)

5b (75), 7 (6)

5b (52), 7 (24)

7 (74),^d4 (11), 6b (trace)

5b (85) or 6b (78)^d

5a (71),^e5b (9)^f

5a (93)^e

n.d.

0:100

81:19

.98:2

0:100

100:0

0:100

7

6a

6b

5b (71%)^f

5a (91)^e

5b (89)^e

a

All reactions were carried out at room temperature.

b

c

d

e

f

Determined by ¹H NMR of the crude reaction mixture after esteriﬁcation with diazomethane.

Isolated yields (not optimised) after esteriﬁcation with diazomethane.

Acidic work up without esteriﬁcation.

No deuterium incorporations detected.

.95% deuterium incorporation at C2.

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

5967

re-hemiketalsation events (B, C in Fig. 1).^3–6The resulting

structural diversity at the binding domain translates into a

tremendous reactivity towards manifold reaction con-

ditions.^22–27As a consequence, selective reactions directed

to other parts of the macrocycle are not easily achieved

without provoking concomitant transformations within this

peculiar unit. Thus, several attempts to cleave the

endocyclic ester linkage led to a facile ring contraction

via rearrangement of the C9/C10 (A in Fig. 1) region instead

of yielding the desired 1,26-seco-derivative. For this

reaction, a benzilic acid type rearrangement process has

been proposed.^1,2As part of our research program on the

ascomycins, aiming at the generation of more stable and

structurally less ﬂexible binding domain mimics, we

decided to investigate this reaction in more detail, in order

to assess its scope and limitations and to get more insight

into the reaction pathway(s) involved.

water (3:1) solution, afforded after esteriﬁcation almost

exclusively the 10(S)-isomer 5a in high yield (entry 4).

Changing the amount of water in the calcium hydroxide

mediated rearrangement reaction had a strong inﬂuence on

the reaction times required but no effect on stereo selectivity

(entries 5–7). Remarkably, a complete change in stereo

selectivity is observed under aprotic conditions. Thus, the

treatment of 4 with powdered lithium or potassium

hydroxide in dimethylsulfoxide (DMSO) solution or with

potassium hydroxide in anhydrous tetrahydrofuran in the

presence of 18-crown-6, yielded, dependent on the work up

procedure applied, the diastereoisomerically pure 10(R)-

hydroxy acid 6b or the corresponding methyl ester 5b in

reasonable yields (entries 8–10). Careful monitoring of the

latter reaction revealed that the 10(R)-hydroxy acid 6b is

formed via the unexpected novel intermediate 7. Thus, short

treatment of 4 with KOH/18-crown-6 led preferentially to 7

together with minor amounts of 5b, whereas prolonged

reaction times resulted in an increase in 6b at the expense of

7 (entries 10–13). As could be anticipated from these

results, treatment of pure 7 under identical reaction

conditions, gave diastereoisomerically pure 6b or (after

esteriﬁcation) 5b (entry 14). In order to answer the question

whether or not a similar intermediate might also be involved

in the formation of the 10(S)-hydroxy-acid 6a, 24,33-bis-

OTBDMS-ascomycin 4 was treated with calcium deuter-

oxide or sodium deuteroxide in THF–D₂O solution.

Analysis of the NMR spectra of the products 5a,b showed

no deuterium–hydrogen exchange in 5a but a quantitative

deuterium incorporation at C2 of 5b (entries 15 and 16).

Complete deuteration at C2 of 5b could be conﬁrmed by the

absence of the H2-signal, a highﬁeld shift and signal

broadening of H6_eqand H3_eqin the ¹H NMR and a

downﬁeld shift of the C2-resonance by 0.2 ppm. As

expected, analogous treatment of 7 gave 5b deuterated

almost quantitatively at C2 (entry 17). Treatment of isolated

6a and 6b with NaOD in THF–D₂O resulted in no

deuteration at any position, thus giving evidence that the

deuterium incorporation at C2 of 6b when starting from 4,

occurs not after the formation of 6b. Furthermore, as no

2. Results and discussion

2.1. Hydroxide mediated rearrangement reactions

In order to prevent cross-reactivity at the potentially base

sensitive b-hydroxyketone portion of ascomycin (C22–

C24),²⁸24,33-bis-OTBDMS-protected ascomycin 4 was

chosen as the starting material for our investigations

(Scheme 1, Table 1). First, we treated 4 with lithium

hydroxide in THF–water solution (Table 1, entry 1). After

an acidic work up, followed by esteriﬁcation of the crude

reaction mixture with diazomethane, two diastereoisomers,

the ring contracted 10(S)-a-hydroxy acid methyl ester 5a

together with minor amounts of the not yet known 10(R)-

epimer 5b could be isolated (for stereo chemical determi-

nations see Section 2.3). Replacement of lithium hydroxide

by potassium or sodium hydroxide led to similar results

(entries 2 and 3). Notably, replacement of lithium hydroxide

by calcium hydroxide resulted in an almost complete

diastereoselectivity of the rearrangement reaction. Thus,

the reaction of 4 with 10 equiv. calcium hydroxide in THF/

Figure 2.

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K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

hydrogen–deuterium exchange is observed when 4 is

converted to 6a, using calcium hydroxide in THF–D₂O

solution (entry 16), this conﬁrms that the conﬁgurations at

all other potentially base labile positions (i.e., C2, C21 and

C11) of 5a and 6a are not affected and thus are identical

with the corresponding conﬁgurations in the starting

material 4. In summary, these experiments clearly

demonstrate that involvement and deprotonation at C2

occurs in the formation of the 10(R)-hydroxy-acid 6b, but

can be excluded for the 10(S)-hydroxy-acid 6a. The

diastereoisomers 6a and 6b are thus formed via distinct,

highly diastereoselective reaction pathways.

2.2. Discussion of reaction mechanisms

Scheme 2.

2.2.1. Formation of 6a. Taking into consideration the

ketone/hemiketal equilibrium at the binding domain (com-

pare Fig. 1), at least three different pathways for the

formation 6a (Fig. 2) can be formulated. Route A suggests

an acyl migration as the key step of the rearrangement

process, initiated by a nucleophilic attack of a hydroxide ion

at the most reactive central carbonyl of the tricarbonyl form

(B!H!6a, intermolecular nucleophile induced acyl shift).

This benzilic acid type rearrangement reaction has already

been proposed from the results of a study with 9-¹³C-

labelled material: the ¹³C-label was mostly found in the

carboxyl group which is in agreement with an acyl(C8)-

migration.^1,2However, the labelling study ﬁts also to route

B, which supposes essentially the same mechanism, but

with participation of the 14-hydroxy group as internal

nucleophile (C!L!6a, intramolecular nucleophile

induced acyl shift), thus leading to a seven-membered

lactone intermediate which might yield the ﬁnal product on

lactone hydrolysis. Such a lactone intermediate could also

be formed if the hydroxyl ion acts rather as a base than as a

nucleophile (route C; A!L!6a, base induced alkyl shift).

Although a seven-membered lactone derivative (L) was not

found in the rearrangement reactions, it cannot be excluded

as intermediate because its formation may be much slower

than its hydrolysis to the ﬁnal product. In order to shed some

light on this, we attempted to prepare such lactone

derivatives, starting from the corresponding acids 6a and

6b (Scheme 2).

Lactonisation of 6a was performed with N,N⁰-dicyclo-

hexylcarbodiimide (DCC) in the presence of catalytic

amounts of 4-dimethylaminopyridine (DMAP) in dichloro-

methane to provide 9 in excellent yield. Apparently, the

carboxyl function and the 14-hydroxy group in 6a are in a

perfect orientation for lactonisation, since even in methanol

only 9 instead of the expected methyl ester 5a was obtained.

In contrast, all attempts to convert the 10(R)-hydroxy acid

6b to the corresponding lactone failed. Hydrolysis of 9 with

calcium hydroxide (10 equiv.) in THF/water (3:1) resulted

in the acid 6a as expected, but the reaction time was

markedly longer (15 h) than the conversion of 4 to 6a under

comparable reaction conditions (30 min; compare Table 1,

entry 4). This clearly rules out 9 as an intermediate during

the rearrangement process and supports the proposed

intermolecular benzilic acid type rearrangement event

(compare Fig. 2). Additional evidence for this suggestion

was gained starting from the easily available 14,24,33-tris-

OTBDMS-protected ascomycin derivative 10,²⁹in which

the binding domain is ﬁxed in the tricarbonyl form by

blocking the 14-hydroxy group (Scheme 3).

Thus, treatment of the characteristically yellow coloured 10

with calcium hydroxide (10 equiv.) in THF/water (3:1) led

almost instantaneously to the disappearance of the yellow

colour and afforded in a fast reaction (,5 min) and with

Scheme 3.

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

5969

excellent diastereoselectivity after esteriﬁcation with

diazomethane (10(S)/10(R)¼96:4) the 14,24,33-tris-

OTBDMS-protected hydroxy acid methyl esters 11a and

11b. Saponiﬁcation of the separated esters with excess

calcium hydroxide in tetrahydrofuran–water solution

allowed the isolation of the corresponding acids 12a and

12b as well. Desilylation of 11a and 5a, using aqueous

hydrogen ﬂuoride in acetonitrile solution furnished the same

hydroxy acid methyl ester 13a, thus corroborating that 5a,

11a, 12a and 13a differ only with respect to their protection

pattern but exhibit the same stereochemistry at C10. The

same relationship could be shown for the 10(S)-epimers 5b,

11b, 12b and 13b, respectively.

as a starting material and applying the same reaction

conditions led in an overall yield of 62% to the compounds

17 and 5b as well, thus emphasising once again the key role

of 7 as intermediate and further conﬁrming that 17 has the

same conﬁgurations as 7 at all chiral positions. The

compounds 14 and 15 represent trapped versions of the

potential equilibrium products of 4 and thus their formation

is explicable. Inspective is the formation of the O-methyl-

derivative 16 since in this compound a cyclisation between

C2 and C10 together with an intact (not rearranged) carbon

chain (C8–C11) can easily be recognised. Interestingly,

compound 15 is completely stable under the conditions of

its formation. Thus, no further cyclisation to 16 is observed.

Taking this into consideration, a reaction mechanism

involving a cyclisation prior to a rearrangement can be

proposed (Fig. 3). Thus, cyclisation between C2 and C10

may start from the O-deprotonated seven-membered hemi-

ketal form C via a, most probably, intramolecular assisted

deprotonation at C2 (no intramolecular assistance is

possible in the O-methylated derivative 15) followed by

ring closure to give the intermediate D, which has the

possibility to be in a hemiketal/ketone equilibrium with the

unmasked a-ketoamide form F. Taking into consideration

intermediate F, an a-ketol-type rearrangement easily

explains the formation of 7 which in turn, upon a hydroxide

mediated retro-ester condensation event, provides the

hydroxy acid 6b. The rearrangement process F to 7 is not

unlikely, since thereby the destabilising electronic

repulsion of two adjacent carbonyls (C8, C9) is removed.

However, although the suggested reaction pathway is

supported by the quenching experiment, other reaction

2.2.2. Formation of 6b and 7. Inspection of the structure of

7 clearly reveals that a rearrangement process and a

cyclisation event are required for its formation. Therefore,

two general pathways, a cyclisation prior to a rearrangement

or vice versa should be considered. In order to gain some

insight into the reaction pathway involved, we repeated the

reaction leading to 7 and 6b in the presence of excess methyl

iodide as trapping reagent (Scheme 4).

In the event, 24,33-bis-OTBDMS-ascomycin 4 was added

in one portion at room temperature to a well stirred

suspension of powdered potassium hydroxide (1.5 equiv.),

18-crown-6 (0.5 equiv.) and methyl iodide (10 equiv.) in

tetrahydrofuran. After an acidic work up a complex mixture

was obtained which could be separated by column

chromatography on silica gel to afford the O-methylated

derivatives 14-17 and the 10(R)-hydroxy ester 5b. Using 7

Scheme 4.

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K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

Figure 3.

pathways can be proposed as well. Further attempts to

identify decisive experiments which allow the mechanism

to be unambiguously deﬁned are ongoing.

that the rearrangement product 7 and its O-methylated

congener 17 relate to the 10(R) hydroxy acid 6b. However,

since the formation of the 6b evidently involves position C2,

6a and 6b may not only differ at the newly created chiral

center (C10), but also in the conﬁguration at C2. In order to

compare those isomers with respect to their relative

conﬁgurations, it was necessary to remove or modify

the chirality at C10 without affecting the remaining

chiral positions. This could be achieved by an oxidative

decarboxylation of the diastereoisomeric acids 6a and 6b

or by a thermal decarboxylation of the 14,24,33-tri-

s-OTBDMS-protected hydroxy acids 12a and 12b

(Scheme 5).

2.3. Stereochemical assignments

2.3.1. Stereochemical correlations via regioselective

degradation. As already shown above, the ring contracted

hydroxy acid derivatives 5a, 6a, 11a, 12a and 13a differ

only with respect to their substitution pattern and not in their

stereochemical arrangement. The same applies to the series

5b, 6b, 11b, 12b and 13b. From the mechanistic

investigations and the trapping experiments it is also clear

Scheme 5.

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

5971

Thus, reacting 6a or 6b with excess lead tetra acetate in

benzene solution afforded, independent of the starting

material applied, the common degradation product 18,

which upon desilylation provided the nor-9-carbonyl-

ascomycin derivative 19 in high overall yield. It is

interesting to note, that 18 exists in deuterochloroform

solution exclusively in the 9(R)-hemiketal form (NOE from

9-OH to H14) and as a single conformer with E-conﬁgur-

ation at the amide bond. In contrast, the deprotected

congener 19 is in equilibrium with the free 9-keto form

(hemiketal form/keto-form¼5:1) whereby the hemiketal

form adopts most probably exclusively the E-amide and the

keto form the Z-amide orientation.³⁰Alternatively, heating

up 12a or 12b in the absence of solvent to 160 8C for 10 min

accomplished a clean decarboxylation to give mixtures of

the a-hydroxy amides 20a and 20b, which differ only in

their conﬁguration at C10. As expected, oxidative conver-

sion of both, applying the Dess–Martin protocol,³¹gave the

14,24,33-tris-OTBDMS-protected a-keto amide 21, which

could be deprotected to 18 as well, thus once again

corroborating that 6a and 6b (or 12a and 12b) differ only

in their conﬁguration at C10. Together with the deuteration

experiments, listed in Table 1, this also substantiate, that all

other chiral positions of 6a,b and its differently protected

congeners are identical as compared to those in natural

ascomycin.

Figure 5.

only differently protected congeners: i.e., 5a, 6a, 11a and

12a) exhibits the S-conﬁguration at the quaternary carbon

C10 and the natural S-stereochemistry at C2. Consequently,

and as deduced from the selective degradations, the series

5b, 6b, 11b and 12b should exhibit the same stereo-

chemistry at C2 (S) but the opposite conﬁguration (R) at

C10. The latter is in agreement with the X-ray structure of 8

(Fig. 5), which exhibits the 2(R), 10(S)-conﬁguration. With

the aid of the X-ray-structure of 8, the absolute conﬁgur-

ations of congeners 7 and 17 at C2 and C10, together with

the 2-(R)-conﬁguration at C2 of the cyclised but not yet

rearranged compound 16 could be assigned unambiguously

as well.

2.3.2. X-ray analysis of the compounds 8 and 13a. After

having carefully established the relative stereochemical

relationships, crystalline material for X-ray analysis was

required in order to determine absolute conﬁgurations.

Gratifyingly, suitable crystals could be obtained from the

compounds 8 (8·3H₂O from methanol–water) and 13a

(13a·THF from tetrahydrofuran). ORTEP-plots of the

structures (atomic displacement ellipsoids drawn at the

50% probability level, hydrogen atoms drawn as spheres of

arbitrary radius) are depicted in Figures 4 and 5.³²

The rearrangement product 13a (and consequently all of its

3. Summary

Starting from 24,33-bis-OTBDMS-ascomycin 4 carefully

chosen reaction conditions allow either the diastereo-

selective preparation of the 10(S)-a-hydroxy acid 6a or its

10(R)-congener 6b in reasonable yields. Mechanistic

investigations conﬁrmed, that 6a is formed via an benzilic

acid type rearrangement process as proposed earlier,^1,2

whereas, trapping experiments and the isolation of the novel

rearrangement product 7 clearly suggest, that the 10(R)-

isomer 6b, which has been isolated for the ﬁrst time, is

formed through a cascade of reaction steps including

tautomerisation, cyclisation and a acyloin-rearrangement

followed by a retro-ester condensation. The relative and

absolute stereochemistry at newly formed chiral centers of

most of the compounds disclosed herein could be deter-

mined unambiguously via regioselective degradation

reactions and X-ray analysis. The structures of all

compounds are fully supported by one- and two-dimen-

sional NMR data. Since the tricarbonyl portion of

ascomycin is a source of lability, the ﬁndings described

herein may be of use for researchers in the ﬁeld, who are

attempting to replace the tricarbonyl by more stable binding

domain mimics.

Figure 4.

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K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

4. Experimental

and 35 ml water were added 25 ml (25 mmol, 5 equiv.) of

an aq. 1 N-lithium hydroxide solution and the resultant

slightly turbid mixture was magnetically stirred for 12 min

at room temperature. For work up the mixture was

partitioned between ethyl acetate (600 ml) and 1 N

hydrochloric acid (150 ml). The aqueous layer was

separated and washed twice with ethyl acetate (100 ml).

The combined organic layers were washed with brine, dried

over anhydrous sodium sulfate and concentrated at reduced

pressure to a volume of about 100 ml. The resultant solution

was titrated with an approx. 1 M ethereal diazomethane

solution until the yellow colour did not disappear. Excess

diazomethane was removed in a slight stream of nitrogen

and the remaining solution was evaporated to dryness at the

rotary evaporator. Flash column chromatography (silica gel,

toluene/acetonitrile¼5:1) provided 5b as the ﬁrst and 5a as

the second fraction. The product fractions were evaporated

under reduced pressure and dried for 15 h under high

vacuum to give 3.71 g (72%) 5a and 0.57 g (11%) 5b as

amorphous powders.

4.1. 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 Uvasol^w, 99.8% D) at 301 K. Chemical shifts are

given in values of ppm, referenced to residual CHCl₃signals

1

(7.26 for H, 77.0 for ¹³C). Proton and carbon-13 signal

assignments were deduced from H, ¹³C, gradient-selected

1

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.

Stereochemical information was extracted from two-dimen-

sional T-ROESY (transverse rotating-frame Overhauser

effect spectroscopy) or selective one-dimensional ROESY²⁰

experiments. Routine mass spectroscopy (ESI, electrospray

ionisation) was performed on a Finnigan Navigator AQA

mass spectrometer with HP 1100 LC system, using

methanol (Merck LiChrosolv^w, gradient grade) as solvent.

Solutions of approx. 50–100 mg/ml of the test compound in

acetonitrile (Merck LiChrosolv^w) were used for injection.

Two scans in each experiment were applied, with 25 and

50 V cone voltages, respectively. The probe temperature

was 523 K. High-resolution mass spectra (HRMS) were

measured on a Finnigan MAT900 S mass spectrometer or on

a 9.4T Bruker APEX III Fourier Transform mass spec-

trometer in positive-ESI mode. Unit cell determination and

intensity data collection for compound 8 were performed on

an Enraf Nonius CAD4 with graphite monochromatised

Cu(K_a) radiation. Non-hydrogen atoms were reﬁned with

anisotropic displacement parameters, hydrogen atoms were

calculated in idealised positions and reﬁned using a riding

model. Unit cell determination and intensity data collection

for 13b were performed on a Bruker AXS SMART 6000

CCD, with Cu(K_a) radiation from rotating anode generator

with Osmic multilayer mirrors. A semi-empirical absorption

correction was applied, based on the intensities of

symmetry-related reﬂections measured at different angular

settings. The structures were solved by direct methods and

reﬁned by full-matrix least-squares on F ². 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 molybdato-

phosphoric 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 approx.

3–5 bar. Solvents and reagents (reagent grade) were used as

purchased. Samples for micro-elementary analysis were

subjected to size exclusion chromatography (Sephadex^w

LH20, in order to get rid of minor low molecular weight

impurities which might originate from the solvents used for

chromatography) and lyophilised from dioxane or benzene

at high vacuum.

Compounds 5a,b (entries 2 and 3). Starting from 5.1 g

24,33-bis-OTBDMS-ascomycin 4, but using 1 N

aqueous potassium hydroxide (or sodium hydroxide)

solution, the reaction, work up, esteriﬁcation and puriﬁ-

cation was performed as described above to give the title

compounds as colourless foams in yields as indicated in

Table 1.

Compound 5a or 6a (entry 4). To a solution of 10.2 g 24,33-

bis-OTBDMS-ascomycin 4 (10 mmol) in 300 ml tetra-

hydrofuran and 50 ml water were added 7.41 g

(100 mmol, 10 equiv.) calcium hydroxide in one portion

and the resultant suspension was stirred at room temperature

until TLC indicated the complete consumption of the

starting material (30 min). The mixture was partitioned

between ethyl acetate (1200 ml) and 1 N hydrochloric acid

(400 ml). The aqueous layer was separated and extracted

twice with ethyl acetate (200 ml). The combined organic

layers were washed with brine, dried over anhydrous

sodium sulfate and evaporated to dryness at reduced

pressure to give the crude acid 6a.

Isolation as hydroxy acid 6a. Half of the above crude

product was subjected to a short ﬂash column chromato-

graphy (silica gel, dichloromethane/methanol¼10:1). The

product containing fraction was evaporated at the rotary

evaporator, re-dissolved in 200 ml ethyl acetate, washed

with 20 ml 1 N-hydrochloric acid (to remove salt

forming impurities originating from the silica gel) and

brine, dried over anhydrous sodium sulfate and ﬁltered

through a Whatman^w(A) glass microﬁbre ﬁlter. The

ﬁltrate was evaporated at reduced pressure and dried on

high vacuum to give 4.93 g (95%) 6a as an amorphous

powder.

Isolation as hydroxy acid, methyl ester 5a. The remaining

crude acid 6a was dissolved in 100 ml ethyl acetate, titrated

with an approx. 1 M ethereal diazomethane solution until

the yellow colour remained. Excess diazomethane was

removed in a slight stream of nitrogen and the remaining

solution was evaporated to dryness at the rotary evaporator.

Flash column chromatography (silica gel, toluene/ethyl

4.2. Preparation of 5a, 5b, 6a, 6b and 7 and 2-deuterio-5b

according to Table 1

Compounds 5a,b (entry 1). To a solution of 5.1 g 24,33-bis-

OTBDMS-ascomycin 4 (5 mmol) in 300 ml tetrahydrofuran

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

5973

acetate¼2:1) provided 4.79 g (91%) 5b as amorphous

subjected to ﬂash column chromatography (silica gel,

toluene/ethyl acetate¼1:1) to give 0.22 g (11%) of

recovered starting material 4 and 1.48 g (74%) 7 as

amorphous powders.

powder.

Compound 5a (entries 5–7). To solutions of in each case

2.0 g (1.96 mmol) 4 in mixtures of 70 ml tetrahydrofuran/

water¼7:1, 20:1 and 80:1 were added 1.45 g (10 equiv.,

19.6 mmol) calcium hydroxide and the reactions were

stirred at room temperature until TLC indicated complete

consumption of the starting material (1, 3 and 30 h). Work

up, esteriﬁcation and puriﬁcation as described above

provided 1.88 (91%), 1.77 (86%) and 1.53 g (74%) 5a as

colorless foams.

Compound 5b from 7 (entry 14). To a solution of 0.5 g

(0.49 mmol) 7 and 25 mg (0.098 mmol, 20 mol%) 18-

crown-6 in 25 ml tetrahydrofuran were added 33 mg

(1.2 equiv.; 0.59 mmol) powdered potassium hydroxide

and the suspensions were allowed to stir at room

temperature for 40 min. Work up, esteriﬁcation and

puriﬁcation as described above provided 0.44 g (85%) 5b

as amorphous powder.

Compound 5b and 6b (entry 8). To a solution of 3.0 g

(2.94 mmol) 24,33-bis-OTBDMS-ascomycin 4 in 30 ml

dimethyl sulfoxide (DMSO) were added 85 mg (1.2 equiv.;

3.53 mmol) powdered lithium hydroxide, monohydrate in

one portion and the resultant suspension was vigorously

stirred at room temperature (30 min). The reaction

mixture was partitioned between ethyl acetate (200 ml)

and 1 N-hydrochloric acid (50 ml). The organic layer was

ﬁve times washed with water, dried over anhydrous sodium

sulfate and evaporated at reduced pressure. The residual oil

was subjected to size exclusion chromatography

(Sephadex^wLH20, ethyl acetate) in order to remove

DMSO completely and the relevant fraction was evaporated

to dryness. The crude product was divided into two equal

parts and further manipulated as described above (entry 4)

to give 1.19 g (78%) 6b and 1.16 g (75%) 5b as amorphous

powders.

Compound 5a and 2-deuterio-5b (entry 15). To a solution of

0.51 g 24,33-bis-OTBDMS-ascomycin 4 (0.5 mmol) in

30 ml tetrahydrofuran and 3.5 ml deuterium oxide were

added 2.5 ml (2.5 mmol, 5 equiv.) of an aq. 1 N-sodium

deuterium oxide solution in deuterium oxide and the

resultant mixture was stirred for 12 min at room tempera-

ture. Work up, esteriﬁcation and puriﬁcation as described

for entry 1 provided 0.38 g (71%) 5a and 0.047 g (9%)

2-deuterio-5b.

Compound 5a (entry 16). 1.02 g 24,33-bis-OTBDMS-

ascomycin 4 (1 mmol) were added in one portion to a pre-

stirred (10 min) suspension of 0.74 g (10 mmol, 10 equiv.)

calcium hydroxide in 30 ml tetrahydrofuran and 5 ml

deuterium oxide. After 30 min, an acidic work up, followed

by esteriﬁcation and puriﬁcation as described for entry 4

provided 0.98 g (93%) 5a. No deuteration could be seen by

1

Compound 5b (entry 9). Starting from 1.0 g (0.98 mmol)

24,33-bis-OTBDMS-ascomycin 4 in 10 ml DMSO and

66 mg (1.2 equiv.; 1.18 mmol) powdered potassium

hydroxide, the reaction was performed and worked up as

described above (30 min reaction time) to give after

esteriﬁcation and puriﬁcation 0.81 g (78%) 5b as

amorphous powder.

MS and H NMR.

Compound 2-deuterio-5b from 7 (entry 17). To a solution of

0.51 g 7 (0.5 mmol) in 30 ml tetrahydrofuran and 3.5 ml

deuterium oxide were added 2.5 ml (2.5 mmol, 5 equiv.) of

a 1 N-sodium deuteride solution in deuterium oxide and the

resultant mixture was magnetically stirred for 40 min at

room temperature. Work up, esteriﬁcation and puriﬁcation

as described for entry 1 provided 0.37 g (71%) 2-deuterio-

5b as amorphous powder.

Compounds 5b and 7 (entries 11–14). To solutions of in

each case 2.0 g (1.96 mmol) 24,33-bis-OTBDMS-

ascomycin

4 and 100 mg (0.38 mmol, 20 mol%)

18-crown-6 in 100 ml tetrahydrofuran were added 132 mg

(1.2 equiv.; 2.36 mmol) powdered potassium hydroxide and

the suspensions were allowed to stir at room temperature for

1.5/10/30 and 40 min, respectively. For work up, the

mixtures were partitioned between ethyl acetate (300 ml)

and 1 N-hydrochloric acid (60 ml). The organic layers were

washed with brine, dried over anhydrous sodium sulfate and

evaporated at reduced pressure to give the crude products as

slightly brownish foams.

Compound 5a and 5b from 6a and 6b (entries 18 and 19).

To a solution of 0.52 g (0.5 mmol) 6a or 6b in 30 ml

tetrahydrofuran and 3.5 ml deuterium oxide were added

2.5 ml (2.5 mmol, 5 equiv.) of a 1 N-sodium deuteride

solution in deuterium oxide and the resultant mixtures was

stirred for 15 min at room temperature. Work up, esteriﬁca-

tion and puriﬁcation as described for above provided 0.48 g

(91%) 5a and 0.47 g (89%) 5b as amorphous powders.

4.2.1. Compound 5a. CHN (C₅₆H₁₀₁NO₁₃Si₂) calcd: 63.90/

9.67/1.33, found: 63.64/9.51/1.24. HRMS (MþNa;

calcd/found): 1074.6709/1074.6713. ¹³C NMR (CDCl₃,

Z/E¼3:2), d (Z/E-isomer, ppm): 168.38/168.93 (C1);

53.99/56.63 (C2); 26.32/28.20 (C3); 20.95/20.60 (C4);

24.93/25.01 (C5); 43.58/42.00 (C6); 169.47/168.93 (C8);

81.61/81.43 (C9); 172.16/172.16 (C10); 35.08/36.02 (C11);

36.10/36.08 (C12); 79.23/82.19 (C13); 74.39/73.48 (C14);

77.69/77.51 (C15); 41.0br/n.d. (C16); 28.80/26.55 (C17);

47.22/47.43 (C18); 139.17/139.72 (C19); 122.92/123.89

(C20); 55.03/56.25 (C21); 209.29/209.24 (C22); 45.40/

48.40 (C23); 67.70/68.28 (C24); 38.98/39.47 (C25); 83.95/

The crude products of the 40/30 and 10 min runs were re-

dissolved in 40 ml dichloromethane and titrated with an

approx. 1 M ethereal solution of diazomethane until the

characteristic yellow colour remained. The resultant

solutions were evaporated and subjected to ﬂash column

chromatography (silica gel, toluene/ethyl acetate¼2:1 to

1:1) to give the title compounds 5b and 7 as amorphous

powders. 40 min run (entry 10): 1.69 g (82%) 5b; 30 min

run (entry 11): 1.55 g (75%) 5b and 0.12 g (6%) 7; 10 min

run (entry 12): 1.07 g (52%) 5b and 0.48 g (24%) 7. The

crude product of the 1.5 min run (entry 13) was directly

5974

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

81.25 (C26); 131.19/131.57 (C27); 12.25/11.30 (C28);

136.46/135.72 (C29); 35.08/35.11 (C30); 36.37/36.16

(C31); 84.19/84.10 (C32); 75.18/75.11 (C33); 33.93/33.87

(C34); 30.81/30.67 (C35); 23.25/23.53 (C36); 11.63/11.57

(C37); 52.86/52.75 (10-OMe); 56.76/56.63 (13-OMe);

57.42/59.07 (15-OMe); 57.89/57.83 (32-OMe); 14.33/

13.43 (11-Me); 20.05/20.61 (17-Me); 18.50/16.60 (19-

Me); 9.00/9.35 (25-Me); 25.91, 25.86, 25.78, 18.13, 18.04,

24.03, 24.36, 24.52, 24.75 (2£TBDMS). ¹H NMR

(CDCl₃, selected data), d (Z-isomer, ppm): 5.22 (d,

J¼5.5 Hz, H-2); 4.03 (d, J¼12.5 Hz, H-6a); 3.09 (H-6b);

2.66 (H-11); 3.29 (H-13); 3.52 (H-14); 3.51 (H-15); 4.92 (d,

J¼10.2 Hz, H-20); 3.13 (H-21); 2.75 (dd, J¼17.5þ7.9 Hz,

H-23a); 2.36 (dd, J¼17.5þ5.4 Hz, H-23b); 4.17 (dd,

J¼7.9þ5.4 Hz, H-24); 5.13 (d, J¼9.9 Hz, H-26); 5.25 (d,

J¼9.7 Hz, H-29); 2.94 (H-32); 3.40 (H-33); 1.01 (d, 3H,

J¼6.7 Hz, 11-Me); 1.74 (s, 3H, 19-Me); 1.62 (s, 3H,

27-Me); 0.07, 20.03, (s, each 3H, Si–Me), 0.06 (s, 6H, Si–

Me); 0.89 (s, 18H, (CH₃)₃); 3.82 (s, 3H, 10-OMe); 5.48 (s,

9-OH); d (E-isomer, ppm): 5.00 (br s, H-2); 4.56 (d,

J¼13.5 Hz, H-6a); 2.98 (H-6b); 2.35 (H-11); 3.20 (H-13);

3.48 (H-14); 3.44 (H-15); 4.69 (d, J¼10.0 Hz, H-20); 3.31

(H-21); 2.85 (dd, J¼14.7þ10.0 Hz, H-23a); 2.28 (dd,

J¼14.7þ4.4 Hz, H-23b); 4.08 (dd, J¼10.0þ4.4 Hz,

H-24); 5.19 (d, J¼8.0 Hz, H-26); 5.31 (d, J¼8.6 Hz,

H-29); 2.94 (H-32); 3.40 (H-33); 0.93 (d, 3H, J¼6.6 Hz,

11-Me); 1.83 (s, 3H, 19-Me); 1.55 (s, 3H, 27-Me); 0.07,

0.02, (s, each 3H, Si–Me), 0.01 (s, 6H, Si–Me); 0.87, 0.85

(s, each 9H, (CH₃)₃); 3.62 (s, 3H, 10-OMe); 4.20 (br s,

9-OH).

75.32 (C14); 77.59 (C15); 35.33 (C16); 28.11 (C17); 48.07

(C18); 139.10 (C19); 123.59 (C20); 55.13 (C21); 209.58

(C22); 45.91 (br) (C23); 67.81 (C24); 39.88 (C25); 80.63

(br) (C26); 131.73 (C27); 12.46 (C28); 133.5 br (C29);

35.06 (C30); 36.40 (C31); 84.18 (C32); 75.16 (C33); 33.92

(C34); 30.81 (C35); 23.52 (C36); 11.61 (C37); 53.00 (10-

OMe); 56.35 (13-OMe); 57.49 (15-OMe); 57.88 (32-OMe);

15.41 (11-Me); 20.31 (17-Me); 17.83 (19-Me); 9.34 (25-

Me); 25.93, 25.86, 18.14, 18.06, 24.24, 24.34, 24.52,

1

24.75 (2£TBDMS). H NMR (CDCl₃, selected data), d

(ppm): H2 absent; 3.94 (d, J¼13.9 Hz, H-6_eq); 3.23 (m,

overlapped, H-6_ax); 2.68 (m, H-11); 3.24 (m, H-13); 3.37

(m, H-14); 3.46 (ddd, J¼9.4þ4.6þ1.3 Hz, H-15); 4.87 (d,

J¼9.7 Hz, H-20); 3.14 (m, H-21); 2.60 (dd,

J¼17.8þ5.3 Hz, H-23a); 2.44 (dd, J¼17.8þ6.6 Hz,

H-23b); 4.16 (ctd, J¼6.1þ1.5 Hz, H-24); 5.13 (d,

J¼7.6 Hz, H-26); 5.24 (d, J¼8.7 Hz, H-29); 2.25 (m,

H-30); 2.92 (m, H-32); 3.38 (m, H-33); 0.82 (t, J¼7.3 Hz,

CH₃-37); 0.07, 0.06, 0.02, 20.07 (4s, 24H, 24-

Si(t.Bu)Me₂þ32-Si(t.Bu)Me₂); 0.88, 0.85 (2s, 18H,

24-Si(tBu)Me₂þ32-Si(tBu)Me₂); ,4.0 (s, very broad,

9-OH); 3.80 (s, 10-OMe); 0.92 (d, 3H, J¼6.9 Hz, 11-Me);

3.31 (s, 3H, 13-OMe); 3.36 (s, 3H, 15-OMe); 1.70 (s, 3H,

19-Me); 1.59 (s, 3H, 27-Me); 3.38 (s, 3H, 32-OMe).

4.2.4. Compound 6a. CHN (C₅₅H₉₉NO₁₃Si₂) calcd: 63.61/

9.61/1.35, found: 63.39/9.58/1.21. HRMS (MþNa; calcd/

found): 1060.6553/1060.6549. ¹³C NMR (CD₃OD, single

rotamer), d (ppm): 169.55 (C1); 53.39 (C2); 26.18 (C3);

20.50 (C4); 24.53 (C5); 43.41 (C6); 170.14 (C8); 81.54

(C9); 172.05 (C10); 35.75 (C11); 32.99 (C12); 79.71 (C13);

74.26 (C14); 77.90 (C15); 37.36 (C16); 27.63 (C17); 46.74

(C18); 139.82 (C19); 122.36 (C20); 55.44 (C21); 210.37

(C22); 44.3 br (C23); 69.03 (C24); 39.96 (C25); 78.8 (C26);

132.07 (C27); 11.95 (C28); 132.7br (C29); 34.84 (C30);

36.03 (C31); 84.13 (C32); 75.06 (C33); 33.57 (C34); 30.62

(C35); 23.29 (C36); 10.63 (C37); 55.44 (13-OMe); 57.14

(15-OMe); 56.76 (32-OMe); 13.55 (11-Me); 19.25 (17-Me);

16.92 (19-Me); 8.57 (25-Me); 25.09, 24.99, 17.57, 17.48,

25.46, 25.56, 25.65, 25.89 (2£TBDMS). ¹H NMR

(CD₃OD, selected data), d (ppm): 5.15 (br d, J¼4.5 Hz,

H-2); 4.31 (d, J¼12.5 Hz, H-6a); 3.10 (ddd, J¼12.5þ

12.5þ2.9 Hz, H-6b); 2.53 (H-11); 3.30 (H-13); 3.56 (dd,

J¼5.7þ3.9 Hz, H-14); 3.51 (H-15); 4.94 (d, J¼9.9 Hz,

H-20); 3.26 (H-21); 2.71 (br dd, J¼17.0þ5.2 Hz, H-23a);

2.48 (dd, J¼17.0þ6.0 Hz, H-23b); 4.21 (ddd, J¼6.0þ

5.2þ2.6 Hz, H-24); 5.23 (H-26); 5.23 (H-29); 3.00 (ddd,

J¼11.2þ8.5þ4.5 Hz, H-32); 3.43 (H-33); 1.07 (d, 3H,

J¼6.6 Hz, 11-Me); 1.75 (s, 3H, 19-Me); 1.65 (d, 3H,

J¼1.2 Hz, 27-Me); 0.09, 0.08, 0.07, 20.01 (s, each 3H,

Si–Me); 0.90, 0.89 (s, each 9H, (CH₃)₃).

4.2.2. Compound 5b. CHN (C₅₆H₁₀₁NO₁₃Si₂) calcd: 63.90/

9.67/1.33, found: 63.72/9.61/1.28. HRMS (MþNa; calcd/

found): 1074.6709/1074.6716. ¹³C NMR (CDCl₃, single

rotamer), d (ppm): 169.68 (C1); 53.32 (C2); 25.97 (C3);

20.59 (C4); 25.13 (C5); 44.28 (C6); 168.25 (C8); 82.17

(C9); 172.92 (C10); 36.66 (C11); 34.53 (C12); 79.64 (C13);

75.31 (C14); 77.59 (C15); 35.35 (C16); 28.06 (C17); 48.07

(C18); 139.09 (C19); 123.60 (C20); 55.15 (C21); 209.60

(C22); 45.83 (C23); 67.85 (C24); 39.93 (C25); 80.56 (C26);

131.74 (C27); 12.49 (C28); 134.92 (C29); 35.07 (C30);

36.41 (C31); 84.19 (C32); 75.17 (C33); 33.93 (C34); 30.82

(C35); 23.54 (C36); 11.62 (C37); 52.99 (10-OMe); 56.37

(13-OMe); 57.50 (15-OMe); 57.88 (32-OMe); 15.43 (11-

Me); 20.32 (17-Me); 17.82 (19-Me); 9.37 (25-Me); 25.93,

25.87, 18.15, 18.06, 24.33, 24.52, 24.74 (2£TBDMS). ¹H

NMR (CDCl₃, selected data), d (ppm): 5.27 (d, J¼4.8 Hz,

H-2); 3.97 (d, J¼13.5 Hz, H-6a); 3.24 (H-6b); 2.69 (H-11);

3.26 (H-13); 3.40 (H-14); 3.46 (ddd, J¼9.4þ4.6þ1.7 Hz,

H-15); 4.88 (d, J¼9.9 Hz, H-20); 3.15 (H-21); 2.60 (dd,

J¼17.5þ5.5 Hz, H-23a); 2.46 (dd, J¼17.5þ6.5 Hz,

H-23b); 4.17 (ddd, J¼6.5þ5.5þ2.1 Hz, H-24); 5.13 (d,

J¼7.5 Hz, H-26); 5.24 (d, J¼8.9 Hz, H-29); 2.93 (ddd,

J¼11.4þ8.5þ4.6 Hz, H-32); 3.40 (H-33); 0.93 (d, 3H,

J¼6.7 Hz, 11-Me); 1.71 (d, 3H, J¼1.2 Hz, 19-Me); 1.60 (d,

3H, J¼1.2 Hz, 27-Me); 0.08, 0.06, 0.03, 20.06 (s, each 3H,

Si–Me); 0.89, 0.86 (s, each 9H, (CH₃)₃); 4.06 (br s, 9-OH);

3.80 (s, 3H, 10-OMe).

4.2.5. Compound 6b. CHN (C₅₅H₉₉NO₁₃Si₂) calcd: 63.61/

9.61/1.35, found: 63.40/9.54/1.39. HRMS (MþNa; calcd/

found): 1060.6553/1060.6551. ¹³C NMR (CDCl₃, mixture

of rotamers .9:1), d (major rotamer, ppm): 170.19 (C1);

55.38 (C2); 26.23 (C3); 21.57 (C4); 25.30 (C5); 45.87 (C6);

173.83 (C8); 83.48 (C9); 173.35 (C10); 40.57 (C11); 33.92

(C12); 78.03 (C13); 74.10 (C14); 77.27 (C15); 34.40 (C16);

25.86 (C17); 47.20 (C18); 137.33 (C19); 122.14 (C20);

54.53 (C21); 208.88 (C22); 49.41 (C23); 68.22 (C24); 42.65

(C25); 79.22 (C26); 130.54 (C27); 13.77 (C28); 130.54

(C29); 34.94 (C30); 36.49 (C31); 84.13 (C32); 75.10 (C33);

4.2.3. Compound 2-deuterio-5b. ¹³C NMR (CDCl₃, single

rotamer), d (ppm): 169.67 (C1); 53.10 (C2); 25.9 (br) (C3);

20.53 (C4); 25.13 (C5); 44.24 (C6); 168.23 (C8); 82.15

(C9); 172.92 (C10); 36.64 (C11); 34.56 (C12); 79.59 (C13);

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

5975

33.73 (C34); 30.95 (C35); 22.74 (C36); 11.76 (C37); 56.22

(13-OMe); 57.09 (15-OMe); 57.99 (32-OMe); 13.77

(11-Me); 20.62 (17-Me); 18.92 (19-Me); 10.61 (25-Me);

2£25.86, 18.13, 17.95, 24.52, 24.57, 24.68, 24.73

DMSO¼6:1), d (ppm): 164.50 (C1); 72.05 (C2); 30.27

(C3); 20.72 (C4); 23.55 (C5); 37.59 (C6); 170.46 (C8);

76.25 (C9); 204.24 (C10); 34.18 (C11); 31.79 (C12); 78.64

(C13); 73.66 (C14); 78.67 (C15); 37.07 (C16); 27.13 (C17);

48.18 (C18); 139.42 (C19); 124.08 (C20); 55.46 (C21);

209.97 (C22); 46.25 (C23); 66.82 (C24); 38.75 (C25); 84.90

(C26); 130.76 (C27); 11.9 (C28); 134.45 (C29); 34.84

(C30); 34.68 (C31); 83.89 (C32); 73.19 (C33); 31.71 (C34);

30.24 (C35); 22.56 (C36); 11.38 (C37); 56.11 (13-OMe);

58.55 (15-OMe); 56.43 (32-OMe); 14.89 (11-Me); 20.69

1

(2£TBDMS). H NMR (CDCl₃, selected data), d (major

rotamer, ppm): 5.65 (m, H-2); 5.20 (d, J¼12.4 Hz, H-6_eq);

2.75 (ct, J¼12.6 Hz, H-6_ax); 2.60 (m, H-11); 3.28 (m,

H-13); 3.54 (m, H-14); 3.51 (m, H-15); 4.95 (d, J¼10.9 Hz,

H-20); 3.22 (m, H-21); 2.89 (dd, J¼18.8þ7.9 Hz, H-23a);

2.24 (dd, J¼18.8þ2.2 Hz, H-23b); 4.20 (ctd,

J¼8.4þ2.5 Hz, H-24); 4.54 (s, broad, H-26); 5.02 (d,

J¼8.8 Hz, H-29); 2.22 (m, H-30); 2.95 (m, H-32); 3.40 (m,

H-33); 0.79 (t, J¼7.4 Hz, CH₃-37); 0.08, 0.07, 0.06, 0.01,

0.89, 0.87 (6s, 42H, 2£TBDMS); 4.53 (s, 9-OH); 13.5

(broad, 10-COOH); 0.96 (d, 3H, J¼6.9 Hz, 11-Me); 3.30 (s,

3H, 13-OMe); 3.02 (s, very broad, 14-OH); 3.32 (s, 3H, 15-

OMe); 1.78 (s, 3H, 19-Me); 1.49 (s, 3H, 27-Me); 3.40 (s,

3H, 32-OMe).

1

(17-Me); 16.47 (19-Me); 9.03 (25-Me). H NMR (CDCl₃/

d₆-DMSO¼6:1, selected data), d (ppm): 2.50 (br d,

J¼13.5 Hz, H-3a); 2.00 (H-3b); 4.35 (br dd,

J¼13.7þ3.0 Hz, H-6a); 3.07 (H-6b); 2.44 (H-11); 3.59

(H-13); 3.54 (H-14); 3.29 (H-15); 4.78 (d, J¼10.4 Hz, H-

20); 3.21 (ddd, J¼10.4þ8.4þ5.5 Hz, H-21); 2.79 (dd,

J¼16.1þ8.6 Hz, H-23a); 2.45 (H-23b); 3.99 (ddd,

J¼7.9þ5.5þ1.7 Hz, H-24); 5.17 (d, J¼9.0 Hz, H-26);

5.36 (d, J¼9.2 Hz, H-29); 3.02 (ddd, J¼11.5þ

8.8þ4.3 Hz, H-32); 3.39 (H-33); 0.87 (d, 3H, J¼7.1 Hz,

11-Me); 1.77 (s, 3H, 19-Me); 1.62 (s, 3H, 27-Me).

4.2.6. Compound 7. HRMS (MþNa; calcd/found):

1042.6447/1042.644. ¹³C NMR (CDCl₃), d (ppm): 163.89

(C1); 72.86 (C2); 33.19 (C3); 20.67 (C4); 23.72 (C5); 37.28

(C6); 170.54 (C8); 203.27 (C9); 76.70 (C10); 33.92 (C11);

30.00 (C12); 77.94 (C13); 71.81 (C14); 79.48 (C15); 39.42

(C16); 26.35 (C17); 47.79 (C18); 140.21 (C19); 123.88

(C20); 56.42 (C21); 208.50 (C22); 47.35 (C23); 68.10

(C24); 39.31 (C25); 86.06 (C26); 130.93 (C27); 11.03

(C28); 137.59 (C29); 35.17 (C30); 36.13 (C31); 84.08

(C32); 75.12 (C33); 33.85 (C34); 30.64 (C35); 22.21 (C36);

11.48 (C37); 55.12 (13-OMe); 59.74 (15-OMe); 57.91 (32-

OMe); 16.94 (11-Me); 20.50 (17-Me); 16.16 (19-Me); 9.59

(25-Me); 25.87, 25.83, 18.16, 18.04, 23.78, 24.27, 24.51,

4.2.8. Compound 9. A solution of 1.5₀g (1.44 mmol) 6a and

0.70 g (3 equiv., 4.33 mmol) 1,1 -carbonyldiimidazole

(CDI) and 5 mg (2.8 mol%) 4-dimethylaminopyridine

(DMAP) in 25 ml dichloromethane was stirred for 2 h at

room temperature. For work up the mixture was partitioned

between ethyl acetate and 1 N-hydrochloric acid. The

organic layer was separated, washed with brine, dried over

anhydrous sodium sulfate and evaporated to dryness at

reduced pressure. The residual foam was subjected to ﬂash

column chromatography (silica gel, toluene/ethyl

acetate¼5:1) to give 1.37 g (93%) 9 as amorphous powder.

CHN (C₅₅H₉₇NO₁₂Si₂) calcd: 64.73/9.58/1.37, found:

64.59/9.40/1.21. HRMS (MþNa; calcd/found): 1042.6447/

1042.6441. ¹³C NMR (CDCl₃, mixture of rotamers ,1:9), d

(major rotamer, ppm): 168.50 (C1); 56.94 (C2); 27.78 (C3);

20.15 (C4); 24.97 (C5); 41.54 (C6); 169.89 (C8); 80.79

(C9); 168.22 (C10); 33.36 (C11); 36.42 (C12); 76.55 (C13);

80.51 (C14); 76.5 br (C15); 31.66 (C16); 25.98 (C17); 49.20

(C18); 136.34 (C19); 125.89 (C20); 53.23 (C21); 212.98

(C22); 46.46 (C23); 70.45 (C24); 42.04 (C25); 76.5 br

(C26); 133.88 (C27); 12.47 (C28); 132.62 (C29); 34.90

(C30); 36.41 (C31); 84.18 (C32); 75.13 (C33); 33.91 (C34);

30.60 (C35); 25.44 (C36); 11.45 (C37); 57.31 (13-OMe);

56.32 (15-OMe); 57.83 (32-OMe); 17.93 (11-Me); 21.30

(17-Me); 15.96 (19-Me); 11.81 (25-Me); 26.00, 25.86,

18.14, 17.96, 24.39, 24.52, 24.75 (2£TBDMS). ¹H NMR

(CDCl₃, selected data), d (major rotamer, ppm): 4.14 (br s);

4.48 (d, J¼13.3 Hz, H-6a); 3.85 (br dd, J¼13.3þ13.3 Hz,

H-6b); 2.06 (H-11); 3.49 (H-13); 4.63 (d, J¼8.7 Hz, H-14);

3.59 (d, J¼11.4 Hz, H-15); 4.94 (d, J¼9.7 Hz, H-20); 3.33

(H-21); 3.02 (d, J¼19.1 Hz, H-23a); 2.63 (dd,

J¼19.1þ8.7 Hz, H-23b); 4.13 (H-24); 5.57 (s, H-26); 5.24

(d, J¼9.2 Hz, H-29); 2.93 (ddd, J¼11.4þ8.6þ4.6 Hz,

H-32); 3.38 (H-33); 0.92 (d, 3H, J¼6.3 Hz, 11-Me); 1.36

(s, 3H, 19-Me); 1.63 (s, 3H, 27-Me); 0.07, 0.06 (s, each 3H,

Si–Me); 0.03 (s, 6H, Si–Me); 0.89, 0.82 (s, each 9H,

(CH₃)₃); 5.49 (br s, 9-OH).

1

24.73 (2£TBDMS). H NMR (CDCl₃, selected data), d

(ppm): 2.47 (br d, J¼13.6 Hz, H-3a); 1.48 (H-3b); 4.36 (dd,

J¼13.4þ4.8 Hz, H-6a); 3.20 (H-6b); 2.52 (H-11); 3.87

(H-13); 3.88 (H-14); 3.22 (H-15); 4.72 (d, J¼10.8 Hz,

H-20); 3.24 (H-21); 2.82 (dd, J¼15.0þ11.1 Hz, H-23a);

2.17 (dd, J¼15.0þ4.1 Hz, H-23b); 4.11 (dd, J¼11.1þ

4.1 Hz, H-24); 5.17 (d, J¼10.6 Hz, H-26); 5.36 (d,

J¼8.9 Hz, H-29); 2.95 (ddd, J¼11.2þ8.5þ4.5 Hz, H-32);

3.40 (H-33); 0.76 (d, 3H, J¼7.3 Hz, 11-Me); 1.82 (s, 3H,

19-Me); 1.62 (s, 3H, 27-Me); 0.08, 0.07 (s, each 3H, Si–

Me); 0.01 (s, 6H, Si–Me); 0.89, 0.85 (s, each 9H, (CH₃)₃);

4.25 (s, 10-OH); 2.42 (s, 14-OH).

4.2.7. Compound 8. To a solution of 3.0 g (2.94 mmol) 7 in

120 ml acetonitrile were added 10 ml aqueous hydrogen

ﬂuoride (40 w/w%). The mixture was stirred for 6 h at room

temperature and then partitioned between ethyl acetate and

a saturated solution of aqueous sodium hydrogen carbonate.

The organic layer was separated, washed with brine, dried

over anhydrous sodium sulfate and evaporated at reduced

pressure. Flash column chromatography (silica gel, ethyl

acetate) provided 2.07 g (89%) 8 as amorphous powder.

1.0 g of the amorphous material was dissolved in 5 ml

methanol and water (,10 ml) was added until the solution

got slightly turbid. The solution was ﬁltered through a

Whatman^wglass ﬁlter (type GF) and the clear solution was

allowed to stand at room temperature for 2 weeks. The

crystals thereby formed were used for X-ray analysis. CHN

(C₄₃H₆₉NO₁₂, from the amorphous powder) calcd: 65.21/

8.78/1.77, found: 64.92/8.43/1.59. HRMS (MþNa; calcd/

found): 814.4714/814.4719. ¹³C NMR (CDCl₃/d₆-

4.2.9. Compounds 11a and 11b. To a solution of 20 g

(17.62 mmol) 14,24,33-tris-OTBDMS-ascomycin 10 in

250 ml tetrahydrofuran were added 15 ml water and 20 g

5976

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

(15.3 equiv., 270 mmol) calcium hydroxide and the

resultant suspension was stirred for 30 min at room

temperature (TLC-monitoring revealed completion of the

reaction in ,5 min). For work up the mixture was

partitioned between ethyl acetate (800 ml) and 1 N-

hydrochloric acid (200 ml). The organic layer was separ-

ated, washed twice with brine, dried over anhydrous sodium

sulfate and evaporated to dryness at reduced pressure. The

residue was dissolved in 200 ml dichloromethane and

titrated with an approx. 1 M ethereal solution of diazo-

methane until the characteristic yellow colour remained.

After evaporation at reduced pressure the mixture of 11a,b

was subjected to ﬂash column chromatography (silica gel,

cyclohexane/ethyl acetate¼10:1) to give 17.69 g (86%) 11a

and 514 mg (2.5%) 11b as amorphous powders.

31.57/30.68 (C12); 84.75/85.5 br (C13); 76.34/n.d. (C14);

79.24/78.72 (C15); 41.49/n.d. (C16); 27.00/26.41 (C17);

46.56/46.90 (C18); 140.49/139.96 (C19); 123.75/123.75

(C20); 56.24/57.77 (C21); 211.78/208.73 (C22); 42.74/

47.92 (C23); 72.29/67.87 (C24); 41.90/39.25 (C25);

77.08/82.6 br (C26); 132.70/131.20 (C27); 14.38/11.05

(C28); 130.37/136.58 (C29); 34.94/35.17 (C30);

36.65/36.13 (C31); 84.12/84.12 (C32); 75.10/75.08 (C33);

33.77/33.92 (C34); 30.93/n.d. (C35); 22.83/22.68 (C36);

11.47/11.47 (C37); 52.95/52.94 (10-OMe); 56.95/55.89

(13-OMe); 60.88/60.88 (15-OMe); 57.98/n.d. (32-OMe);

15.977n.d. (11-Me); 20.56/20.2 br (17-Me); 16.60/16.10

(19-Me); 10.06/n.d. (25-Me); 26.09, 26.00, 25.92, 25.86,

18.41, 18.13, 17.88, 24.47, 24.52, 24.72, 24.93

(3£TBDMS). ¹H NMR (CDCl₃, selected data), d (Z-isomer,

ppm): 5.31 (br s, H-2); 4.22 (d, J¼14.5 Hz, H-6a); 2.90

(H-6b); 2.51 (H-11); 3.30 (H-13); 3.67 (d, J¼8.4 Hz, H-14);

3.05 (H-15); 4.83 (d, J¼10.2 Hz, H-20); 3.14 (ddd,

J¼10.2þ9.7þ4.2 Hz, H-21); 2.57 (dd, J¼14.1þ9.5 Hz,

H-23a); 2.16 (H-23b); 4.03 (br d, J¼9.5 Hz, H-24); 5.15

(H-26); 5.14 (d, J¼9.8 Hz, H-29); 2.94 (H-32); 3.40 (H-33);

0.94 (d, 3H, J¼6.9 Hz, 11-Me); 1.71 (s, 3H, 19-Me); 1.65 (s,

3H, 27-Me); 0.08, 0.07 (s, each 6H, Si–Me), 0.03, 20.05 (s,

each 3H, Si–Me); 0.90, 0.89, 0.88 (s, each 9H, (CH₃)₃);

3.81 (s, 3H, 10-OCH₃); d (E-isomer, ppm): 5.14 (H-2); 4.43

(d, J¼13.2 Hz, H-6a); 3.12 (H-6b); 3.65 (H-14); 2.92

(H-15); 4.57 (d, J¼10.2 Hz, H-20); 3.25 (H-21); 2.84

(H-23a); 2.19 (H-23b); 4.10 (H-24); 5.20 (d, J¼10.0 Hz,

H-26); 5.35 (d, J¼9.0 Hz, H-29); 2.94 (H-32); 3.40 (H-33);

1.80 (s, 3H, 19-Me); 1.55 (s, 3H, 27-Me); 0.08 (s, 9H, Si–

Me), 0.07 (s, 6H, Si–Me), 0.02 (s, 3H, Si–Me); 0.90, 0.89,

0.88 (s, each 9H, (CH₃)₃); 3.84 (s, 3H, 10-OCH₃).

4.2.10. Compound 11a. CHN (C₆₂H₁₁₅NO₁₃Si₃) calcd:

63.82/9.93/1.20, found: 63.73/9.82/1.00. HRMS (MþNa;

calcd/found): 1188.7574/1188.7578. ¹³C NMR (CDCl₃,

Z/E,3:7), d (Z(only selected data due to extreme signal

broadening)/E-isomer, ppm): n.d./168.32 (C1); 53.53/56.35

(C2); n.d./28.50 (C3); n.d./20.95 (C4); n.d./25.07 (C5);

43.14/41.81 (C6); n.d./168,45 (C8); 82.44/81.88 (C9);

n.d./171.84 (C10); n.d./39.59 (C11); n.d./31.77 (C12);

81.33/85.89 (C13); 76.98/76.14 (C14); 79.46/78.16 (C15);

n.d./42.29 (C16); n.d./26.54 (C17); 46.50/46.70 (C18); n.d./

140.39 (C19); n.d./123.38 (C20); n.d./56.59 (C21);

n.d./209.07 (C22); n.d./48.29 (C23); n.d./68.24 (C24);

n.d./39.59 (C25); n.d./84.16 (C26); n.d./131.21 (C27);

12.64/11.10 (C28); n.d./136.61 (C29); 35.03/35.13 (C30);

36.48/36.15 (C31); n.d./84.10 (C32); n.d./75.12 (C33); n.d./

33.87 (C34); 30.84/30.65 (C35); 23.37/23.10 (C36); 11.54/

11.54 (C37); 53.11/52.70 (10-OMe); n.d./55.85 (13-OMe);

60.20/60.38 (15-OMe); 57.84/57.84 (32-OMe); 14.74/13.82

(11-Me); 20.42/20.14 (17-Me); 16.61/16.14 (19-Me);

n.d./9.19 (25-Me); 26.03, 25.86, 25.78, 18.42, 18.14,

18.03, 23.67, 24.35, 24.52, 24.75 (3£TBDMS). ¹H

NMR (CDCl₃, selected data), d (Z-isomer, ppm): 5.16

(H-2); 4.08 (H-6a); 3.35 (H-6b); 2.50 (H-11); 3.72 (d,

J¼8.4 Hz, H-14); 4.87 (d, J¼10.2 Hz, H-20); 3.19 (H21);

2.47 (H-23a); 2.42 (H-23b); 4.08 (H-24); 2.95 (ddd,

J¼11.3þ8.5þ4.4 Hz, H-32); 3.40 (H-33); 1.06 (d, 3H,

J¼6.6 Hz, 11-Me); 1.72 (s, 3H, 19-Me); 1.62 (s, 3H,

27-Me); 0.90, 0.89,0.85 (s, each 9H, (CH₃)₃); 0.07, 0.06,

0.06 (s, each 6H, Si–Me); 3.84 (s, 3H, 10-OCH₃); d (E-

isomer, ppm): 4.99 (br s, H-2); 4.58 (H-6a); 3.04 (H-6b);

2.20 (H-11); 2.85 (H-13); 3.67 (d, J¼8.4 Hz, H-14); 3.05

(H-15); 4.60 (d, J¼9.8 Hz, H-20); 3.30 (H-21); 2.84 (dd,

J¼14.8þ10.8 Hz, H-23a); 2.24 (dd, J¼14.8þ4.1 Hz,

H-23b); 4.09 (dd, J¼10.8þ4.1 Hz, H-24); 5.14 (d,

J¼10.3 Hz, H-26); 5.31 (d, J¼8.9 Hz, H-29); 2.95 (ddd,

J¼11.3þ8.5þ4.4 Hz, H-32); 3.40 (H-33); 0.95 (d, 3H,

J¼6.6 Hz, 11-Me); 1.83 (s, 3H, 19-Me); 1.55 (s, 3H, 27-

Me); 0.90, 0.89,0.85 (s, each 9H, (CH₃)₃); 0.08, 0.07, 0.02

(s, each 6H, Si–Me); 3.62 (s, 3H, 10-OCH₃); 5.43 (s, 9-OH).

4.2.12. Compound 12a. A suspension of 2.0 g (1.71 mmol)

11a and 1.9 g (15 equiv., 25.7 mmol) calcium hydroxide in

50 ml tetrahydrofuran and 10 ml water was stirred for 40 h

at room temperature. For work up the mixture was

partitioned between ethyl acetate and 1 N-hydrochloric

acid. The organic layer was separated, washed with brine,

dried over anhydrous sodium sulfate and evaporated to

dryness at reduced pressure to give 1.9 g (96%) 12a as an

amorphous powder which required no further puriﬁcation.

HRMS (MþNa; calcd/found): 1174.7418/1174.7413. ¹³C

NMR (CDCl₃, mixture of rotamers ,1:9), d (major rotamer,

selected data, ppm): n.d. (C1); 57.18 (C2); 28.63 (C3); 20.79

(C4); 25.24 (C5); 42.62 (C6); n.d. (C8); 83.53 (C9); n.d.

(C10); 40.37 (C11); 31.72 (C12); n.d. (C13); 75.16 (C14);

79.58 (C15); 41.19 (C16); 27.18 (C17); 47.25 (C18); 140.19

(C19); 123.42 (C20); 56.42 (C21); 209.20 (C22); 48.58

(C23); 68.45 (C24); 39.89 (C25); 84.14 (C26); 131.37

(C27); n.d. (C28); n.d. (C29); 35.14 (C30); 36.20 (C31);

84.14 (C32); 75.16 (C33); 33.91 (C34); 30.67 (C35); 23.09

(C36); 11.53 (C37); 55.79 (13-OMe); 60.13 (15-OMe);

57.84 (32-OMe); 14.05 (11-Me); 20.04 (17-Me); 16.11 (19-

Me); 8.8 br (25-Me); 26.05, 25.94, 25.87, 25.82, 18.30,

18.15, 18.03, 23.77, 24.30, 24.52, 24.74, 24.79

1

4.2.11. Compound 11b. CHN (C₆₂H₁₁₅NO₁₃Si₃) calcd:

63.82/9.93/1.20, found: 63.63/9.89/1.01. HRMS (MþNa;

calcd/found): 1188.7574/1188.7580. ¹³C NMR (CDCl₃,

Z/E¼4:1), d (Z/E-isomer, ppm): 169.02/169.78 (C1);

53.84/55.89 (C2); 26.23/n.d. (C3); 20.97/n.d. (C4); 25.33/

25.05 (C5); 43.72/39.96 (C6); 167.39/166.49 (C8);

83.13/81.74 (C9); 172.99/173.35 (C10); 38.60/n.d. (C11);

(3£TBDMS). H NMR (CDCl₃, selected data), d (major

rotamer, ppm): 5.73 (br s, H-2); 4.53 (H-6a); 3.26 (H-6b);

2.26 (H-11); 3.00 (H-13); 3.71 (d, J¼7.9 Hz, H-14); 2.90

(H-15); 4.57 (H-20); 3.19 (H-21); 2.87 (dd,

J¼14.7þ10.8 Hz, H-23a); 2.20 (H-23b); 4.09 (dd,

J¼11.0þ3.3 Hz, H-24); 5.15 (H-26); 5.32 (H-29); 2.95

(ddd, J¼11.4þ8.7þ4.6 Hz, H-32); 3.39 (H-33); 0.94 (d, 3H,

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

5977

J¼6.8 Hz, 11-Me); 1.80 (s, 3H, 19-Me); 1.54 (s, 3H, 27-

Me); 0.08, 0.01 (s, each 6H, Si–Me), 0.07, 0.06 (s, each 3H,

Si–Me); 0.90, 0.86 (s, each 9H, (CH₃)₃), 0.89 (s, 18H,

(CH₃)₃); 6.66 (br s, COOH).

(79%) 12a as amorphous powder. HRMS (MþNa; calcd/

found): 846.4980/846.4975. ¹³C NMR (CDCl₃, Z/E¼1:1), d

(Z/E-isomer, ppm): 169.51/n.d. (C1); 54.33/56.8 br (C2);

26.16/n.d. (C3); 20.74/n.d. (C4); 25.02/24.9 br (C5); 44.12/

41.61 (C6); 168.90/n.d. (C8); 81.85/n.d. (C9); 171.96/n.d.

(C10); 33.56/n.d. (C11); 30.42/n.d. (C12); 79.42/77.67

(C13); 72.86/n.d. (C14); 77.67/76.83 (C15); 36.53/35.17

(C16); 29.92/27.86 (C17); 47.65/48.78 (C18); 139.48/139.3

br (C19); 123.92/124.47 (C20); 54.48/n.d. (C21); 211.71/

n.d. (C22); 45.41/45.65 (C23); 66.67n.d. (C24); 38.73/39.42

(C25); 82.54/n.d. (C26); 130.94/131.41 (C27); 12.34/13.3

br (C28); 133.86/130.49 (C29); 34.96^p/34.90^p(C30);

34.51/34.74 (C31); 84.17/84.17 (C32); 73.49/73.49 (C33);

31.22/31.22 (C34); 30.62/30.53 (C35); 23.70/n.d. (C36);

11.69^p/11.57^p(C37); 52.84/53.4 br (10-OMe); 57.65/56.14

(13-OMe); 57.97/n.d. (15-OMe); 56.48/56.48 (32-OMe);

15.26/19.76 (11-Me); 19.74/21.3 br (17-Me); 18.28/16.3 br

4.2.13. Compound 12b. Starting from 0.35 g (0.3 mmol)

11b, the reaction was performed as described above to give

0.33 g (96%) 12b. CHN (C₆₁H₁₁₃NO₁₃Si₃) calcd:

63.55/9.88/1.21, found: 63.55/9.70/1.21. HRMS (MþNa;

calcd/found): 1174.7418/1174.7420. ¹³C NMR (CDCl₃,

Z/E¼3:1), d (Z/E-isomer, ppm): 168.16/169.18 (C1);

55.31/57.05 (C2); 27.09/28.63 (C3); 21.17/20.38 (C4);

25.01/24.94 (C5); 45.25/40.96 (C6); 171.86/172.84 (C8);

83.97/81.26 (C9); n.d./n.d. (C10); 41.50/42.97 (C11);

30.44/30.00 (C12); 80.55/79.54 (C13); 75.68/74.85 (C14);

82.05/84.53 (C15); 40.67/41.11 (C16); 29.21/27.28 (C17);

47.26/47.26 (C18); 139.41/139.88 (C19); 124.00/123.87

(C20); 55.86/56.21 (C21); 209.75/208.95 (C22);

43.15/48.20 (C23); 70.36/67.90 (C24); 34.98/39.30 (C25);

78.10/83.33 (C26); 132.33/130.98 (C27); 13.68/11.04

(C28); 131.10/136.95 (C29); 34.93/35.18 (C30);

36.45/36.19 (C31); 84.09/84.15 (C32); 75.09/75.17 (C33);

33.83/33.92 (C34); 30.84/30.65 (C35); 24.44/22.88 (C36);

11.65/11.50 (C37); 60.48/60.18 (13-OMe); 56.10/55.86

(15-OMe); 57.87/57.87 (32-OMe); 14.06/15.98 (11-Me);

21.35/20.01 (17-Me); 17.05/16.41 (19-Me); 10.89/8.64

(25-Me); 25.95, 25.86, 25.81, 18.30, 18.15, 18.03, 23.68,

24.36, 24.47, 24.52, 24.62, 24.76 (3£TBDMS). ¹H

NMR (CDCl₃, selected data), d (Z-isomer, ppm): 5.30 (br s,

H-2); 4.56 (H-6a); 3.25 (H-6b); 1.81 (H-11); 3.00 (H-13);

3.74 (d, J¼7.9 Hz, H-14); 2.95 (H-15); 4.60 (H-20); 3.27

(H-21); 2.85 (dd, J¼15.0þ11.1 Hz, H-23a); 2.20 (H-23b);

4.09 (dd, J¼11.1þ3.8 Hz, H-24); 5.19 (d, J¼10.9 Hz,

H-26); 5.35 (d, J¼9.0 Hz, H-29); 2.93 (H-32); 3.39

(H-33); 1.12 (d, 3H, J¼7.0 Hz, 11-Me); 1.81 (s, 3H, 19-

Me); 1.55 (s, 3H, 27-Me); 0.90 (s, 18H, Si–Me); 0.0–0.1

(overlapped, (CH₃)₃); d (E-isomer, ppm): 5.11 (H-2); 4.96

(br d, J¼13.0 Hz, H-6a); 3.13 (H-6b); 1.85 (H-11); 3.18

(H-13); 3.72 (d, J¼7.9 Hz, H-14); 3.02 (H-15); 5.05 (d,

J¼10.3 Hz, H-20); 3.13 (H-21); 2.51 (dd, J¼17.0þ7.4 Hz,

H-23a); 2.44 (dd, J¼17.0þ4.0 Hz, H-23b); 4.16 (H-24);

5.14 (H-26); 5.11 (H-29); 2.93 (H-32); 3.39 (H-33); 0.97 (d,

3H, J¼7.0 Hz, 11-Me); 1.71 (s, 3H, 19-Me); 1.59 (s, 3H,

27-Me); 0.90 (s, 18H, Si–Me); 0.0–0.1 (overlapped,

(CH₃)₃).

1

(19-Me); 9.20/8.7 br (25-Me). H NMR (CDCl₃, selected

data), d (Z-isomer, ppm): 5.31 (d, J¼5 Hz, H-2); 4.08 (d,

J¼13.3 Hz, H-6a); 3.00 (H-6b); 2.66 (H-11); 3.30 (H-13);

3.38 (H-14); 3.49 (H-15); 4.99 (d, J¼9.8 Hz, H-20); 3.09

(H-21); 2.64 (dd, J¼18.3þ4.7 Hz, H-23a); 2.48 (dd,

J¼18.3þ8.4 Hz, H-23b); 3.98 (H-24); 5.10 (d, J¼8.5 Hz,

H-26); 5.29 (d, J¼10.0 Hz, H-29); 2.98 (H-32); 3.40 (H-33);

1.01 (d, 3H, J¼6.5 Hz, 11-Me); 1.72 (s, 3H, 19-Me); 1.58 (s,

3H, 27-Me); 3.81 (s, 3H, 10-OMe); 5.53 (br s, OH); 4.62 (br

s, OH); d (E-isomer, ppm): 4.88 (br s, H-2); 2.66 (H-11);

3.35 (H-13)^p; 3.38 (H-14); 3.30 (H-15)^p; 4.94 (br s, H-20);

2.75 (dd, J¼16.8þ5.8 Hz, H-23a); 2.60 (H-23b); 5.07 (d,

J¼9.5 Hz, H-29); 2.98 (H-32); 3.40 (H-33); 0.97 (d,

J¼6.5 Hz, 11-Me); 1.64 (s, 3H, 19-Me); 1.58 (s, 3H, 27-

Me); 3.71 (br s, 3H, 10-OMe); 5.72 (br s, OH); 4.58 (br s,

OH); ( p ) opposite assignment possible.

4.2.15. Compound 13b. Starting from 0.9 g (0.86 mmol) 5b

or 0.1 g (0.086 mmol) 11b the deprotections were carried as

described above to give 0.64 g (93%) or 81 mg (89%) 13b

as amorphous powders. HRMS (MþNa; calcd/found):

846.4980/846.4972. ¹³C NMR (CDCl₃, single rotamer), d

(ppm): 169.92 (C1); 53.26 (C2); 25.25 (C3); 20.89 (C4);

25.15 (C5); 45.06 (C6); 168.28 (C8); 81.55 (C9); 172.46

(C10); 37.48 (C11); 33.99 or 33.93 (C12); 81.07 (C13);

75.68 (C14); 76.91 (C15); 33.99 or 33.93 (C16); 27.34

(C17); 49.19 (C18); 138.31 (C19); 125.09 (C20); 54.53

(C21); 211.92 (C22); 46.43 (C23); 66.04 (C24); 38.73

(C25); 83.78 (C26); 130.56 (C27); 12.03 (C28); 134.44

(C29); 34.99 (C30); 34.44 (C31); 84.25 (C32); 73.49 (C33);

31.27 (C34); 30.35 (C35); 23.18 (C36); 11.55 (C37); 52.68

(10-OMe); 57.26 (13-OMe); 56.93 (15-OMe); 56.38 (32-

OMe); 17.17 (11-Me); 20.95 (17-Me); 16.86 (19-Me); 9.65

(25-Me). ¹H NMR (CDCl₃, selected data), d (ppm): 5.32 (d,

J¼4.9 Hz, H-2); 3.88 (br d, J¼14.2 Hz, H-6a); 3.02 (br dd,

J¼14.2þ13.5 Hz, H-6b); 2.65 (H-11); 3.17 (H-13); 3.17

(H-14); 3.37 (H-15); 4.80 (d, J¼9.9 Hz, H-20); 3.17 (H-21);

2.62 (H-23a); 2.55 (dd, J¼18.6þ9.1 Hz, H-23b); 3.96 (br d,

J,9 Hz, H-24); 4.93 (d, J¼9.4 Hz, H-26); 5.36 (d,

J¼9.0 Hz, H-29); 2.98 (H-32); 3.41 (H-33); 1.02 (d, 3H,

J¼6.9 Hz, 11-Me); 1.70 (s, 3H, 19-Me); 1.49 (s, 3H, 27-

Me); 4.75 (br s, 9-OH); 3.83 (s, 3H, 10-OCH₃).

4.2.14. Compound 13a. (1) from 5a. To a solution of 2.1 g

(2 mmol) 5a in 100 ml acetonitrile were added 9 ml aqueous

hydrogen ﬂuoride (40 w/w%). The mixture was stirred for

5 h at room temperature and then partitioned between ethyl

acetate and a saturated solution of aqueous sodium

hydrogen carbonate. The organic layer was separated,

washed with brine, dried over anhydrous sodium sulfate

and evaporated at reduced pressure. Flash column chroma-

tography (silica gel, ethyl acetate) provided 1.50 g (93%) of

analytically pure 13a as amorphous powder. 1.0 g of the

amorphous powder was dissolved in 30 ml tetrahydrofuran

and concentrated to a volume of about 15 ml and the

resulting clear solution was stored for 1 week at 4 8C. The

crystals formed thereof (0.4 g) were used for X-ray analysis.

(2) from 11a. Starting from 0.4 g (0.34 mmol) 11a, the

reaction, work up and puriﬁcation was performed as

described above (reaction time 7 h) to provide 0.22 g

4.2.16. Compounds 14-17 and 5b. (a) from 4. To a

magnetically stirred solution of 5.0 g (4.9 mmol) 24,33-bis-

OTBDMS-ascomycin 4, 500 mg (0.39 equiv., 1.9 mmol)

5978

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

18-crown-6 and 3.48 g (5 equiv., 24.5 mmol, 1.53 ml)

iodomethane in 150 ml tetrahydrofuran were added 0.41 g

(1.5 equiv.; 7.35 mmol) powdered potassium hydroxide.

After stirring for 40 min at room temperature, the mixture

was partitioned between ethyl acetate (500 ml) and 1 N-

hydrochloric acid (100 ml). The organic layer was washed

with brine, dried over anhydrous sodium sulfate and

evaporated at reduced pressure. Separation by ﬂash column

found): 1056.6604/1056.6603. ¹³C NMR (CDCl₃, mixture

of rotamers¼1:4), d (major rotamer, ppm): 169.92 (C1);

56.03 (C2); 28.02 (C3); 21.00 (C4); 25.17 (C5); 39.77 (C6);

165.39 (C8); 103.13 (C9); 209.31 (C10); 39.17 (C11); 39.59

(C12); 77.68 (C13); 78.67 (C14); 77.2 br (C15); 35.65

(C16); 25.7 br (C17); 40.2 br (C18); 139.17 (C19); 123.70

(C20); 56.03 (C21); 212.5 br (C22); n.d. (C23); 70.8 br

(C24); 41.43 (C25); 78.67 (C26); 132.18 (C27); 12.6 br

(C28); 134.5 br (C29); 35.04 (C30); 36.29 (C31); 84.09

(C32); 75.09 (C33); 33.85 (C34); 30.67 (C35); 23.66 (C36);

11.26 (C37); 55.25 (9-OMe); 57.13 (13-OMe); 56.15 (15-

OMe); 57.84 (32-OMe); 16.92 (11-Me); 19.87 (17-Me);

15.88 (19-Me); 10.65 (25-Me); 25.86, 18.14, 17.94, 24.10,

24.46, 24.52, 24.74 (2£TBDMS). ¹H NMR (CDCl₃,

selected data), d (major rotamer, ppm): 5.59 (br d,

J¼4.5 Hz, H-2); 4.37 (d, J¼13.5 Hz, H-6a); 2.84 (br s,

H-6b); 2.94 (H-11); 3.42 (H-13); 3.49 (H-14); 3.62 (H-15);

4.68 (d, J¼10.3 Hz, H-20); 3.30 (H-21); 2.57 (br s, H-23a);

2.27 (H-23b); 4.05 (ddd, J¼6.6þ6.6þ2.3 Hz, H-24); 5.22

(H-26); 5.32 (d, J¼9.1 Hz, H-29); 2.94 (H-32); 3.38 (H-33);

1.19 (d, 3H, J¼6.6 Hz, 11-Me); 1.74 (s, 3H, 19-Me); 1.59 (s,

3H, 27-Me); 0.07, 0.06, 0.02, 0.01 (s, each 3H, Si–Me);

0.89, 0.87 (s, each 9H, (CH₃)₃); 3.62 (s, 3H, 9-OMe); d

(minor rotamer, ppm): 5.10 (H-2); 2.94 (H-11); 4.91 (d,

J¼10.0 Hz, H-20); 3.20 (H-21); 2.75 (dd, J¼17.5þ5.5 Hz,

H-23a); 2.36 (dd, J¼17.5þ5.9 Hz, H-23b); 4.28 (H-24);

5.22 (H-29); 2.94 (H-32); 3.38 (H-33); 1.15 (d, 3H,

J¼6.6 Hz, 11-Me); 0.06, 0.05, 0.05, 0.01 (s, each 3H, Si–

Me); 0.88, 0.85 (s, each 9H, (CH₃)₃); 3.32 (s, 3H, 9-OMe).

chromatography

(silica

gel,

gradient/toluene/ethyl

acetate¼7:1 to 2:1) afforded 0.96 g (19%) 15, 0.26 g (5%)

16, 0.46 g (9%) 14, 1.52 g (30%) 17 and 0.77 g (15%) 5b (in

the given order) as amorphous powders. (b) from 7. Starting

from 0.5 g 7 (0.49 mmol) the reaction and work up was

performed as described above to give a mixture of 17 and

5b. Flash column chromatography (toluene/ethyl

acetate¼3:1) afforded 213 mg (42%) 17 and 103 mg

(20%) 5b, respectively (Scheme 4).

4.2.17. Compound 14. CHN (C₅₆H₉₉NO₁₂Si₂) calcd:

65.01/9.65/1.35, found: 65.33/9.45/1.21. HRMS (MþNa;

calcd/found): 1056.6604/1056.6605. ¹³C NMR (CDCl₃,

Z/E¼3:1), d (Z/E-isomer, ppm): 168.93/168.93 (C1);

50.81/56.17 (C2); 26.70/27.74 (C3); 21.21/20.72 (C4);

25.034/25.55 (C5); 43.1 br/38.35 (C6); 164.99/165.91

(C8); 196.54/196.54 (C9); 100.31/100.95 (C10); 32.35/

31.29 (C11); 32.81/30.65 (C12); 74.02/74.21 (C13);

76.16/76.72 (C14); 76.98/79.48 (C15); 35.31/36.78 (C16);

26.55/28.55 (C17); 47.46/42.5 br (C18); 141.13/134.86

(C19); 121.45/126.61 (C20); 56.39/55.61 (C21);

211.15/210.66 (C22); 43.49/50.2 (C23); 72.54/67.87

(C24); 41.55/39.30 (C25); 76.16/82.8 br (C26); 133.28/

131.08 (C27); 13.72/11.6 br (C28); 130.8 br/136.4 br (C29);

34.97/35.16 (C30); 36.54/36.14 (C31); 84.17/84.17 (C32);

75.15/75.15 (C33); 33.92/33.92 (C34); 35.31/35.31 (C35);

22.61/24.50 (C36); 11.31/11.65 (C37); 49.17/48.95 (10-

OMe); 56.49/55.16 (13-OMe); 57.05/60.05 (15-OMe);

57.86/57.77 (32-OMe); 15.01/15.88 (11-Me); 18.55/21.46

(17-Me); 15.96/19.4 br (19-Me); 10.12/9.78 (25-Me); 25.86,

25.83, 18.13, 18.01, 17.87, 24.09, 24.51, 24.75, 24.99

(2£TBDMS). ¹H NMR (CDCl₃, selected data), d (Z-isomer,

ppm): 5.14 (d, J¼6.0 Hz, H-2); 3.40 (H-6a); 3.32 (H-6b);

2.10 (H-11); 3.45 (H-13); 3.62 (dd, J¼9.5þ1.6 Hz, H-14);

3.43 (H-15); 4.74 (d, J¼10.2 Hz, H-20); 3.19 (ddd,

J¼10.0þ10.0þ4.2 Hz, H-21); 2.39 (H-23a); 2.24 (H-23b);

4.08 (ddd, J¼9.0þ3.4þ3.4 Hz, H-24); 5.27 (br s, H-26);

5.12 (d, J¼9.4 Hz, H-29); 2.93 (ddd, J¼11.2þ8.5þ4.4 Hz,

H-32); 3.37 (H-33); 1.05 (d, 3H, J¼6.9 Hz, 11-Me); 1.62 (s,

3H, 19-Me); 1.61 (s, 3H, 27-Me); 0.07, 0.06, 0.01, 20.06 (s,

each 3H, Si–Me); 0.88, 0.87 (s, each 9H, (CH₃)₃); 3.38 (s,

3H, 10-OMe); d (E-isomer, ppm): 4.26 (d, J¼5.4 Hz, H-2);

4.38 (br dd, J¼13.0þ3.4 Hz, H-6a); 3.20 (H-6b); 2.10

(H-11); 3.37 (H-13); 3.73 (H-14); 3.76 (H-15); 4.94 (d,

J¼10.1 Hz, H-20); 3.34 (H-21); 2.93 (H-23a); 2.35 (H-23b);

4.12 (dd, J¼10.2þ4.3 Hz, H-24); 5.22 (d, J¼10.2 Hz,

H-26); 5.33 (d, J¼9.0 Hz, H-29); 2.93 (ddd,

J¼11.2þ8.5þ4.4 Hz, H-32); 3.37 (H-33); 1.09 (d, 3H,

J¼6.8 Hz, 11-Me); 1.74 (d, 3H, J¼1.2 Hz, 19-Me); 1.53 (d,

3H, J¼1.2 Hz, 27-Me); 0.07, 0.06, 0.02, 0.01 (s, each 3H,

Si–Me); 0.89, 0.87 (s, each 9H, (CH₃)₃); 3.34 (s, 3H,

10-OMe).

4.2.19. Compound 16. CHN (C₅₆H₉₉NO₁₂Si₂) calcd: 65.01/

9.65/1.35, found: 65.06/9.57/1.17. HRMS (MþNa; calcd/

found): 1056.6604/1056.6603. ¹³C NMR (CDCl₃), d (ppm):

170.58 (C1); 73.17 (C2); 28.11 (C3); 21.58 (C4); 23.42

(C5); 39.71 (C6); 166.4 (C8); 99.04 (C9); 80.28 (C10);

33.36 (C11); 34.15 (C12); n.d. (C13); 75.06 (C14); 78.46

(C15); n.d. (C16); 27.97 (C17); 38.7 br (C18); 136.3 br

(C19); 124.71 (C20); 54.04 (C21); ,214 br (C22); n.d.

(C23); n.d. (C24); n.d. (C25); n.d. (C26); 131.2 br (C27);

13.8 br (C28); 127.9 br (C29); 35.35 (C30); 36.38 (C31);

84.22 (C32); 75.23 (C33); 33.99 (C34); 30.85 (C35); 25.14

(C36); 11.88 (C37); 54.41 (9-OMe); ,58 br (13-OMe);

56.04 (15-OMe); 57.63 (32-OMe); 17.9 br (11-Me); 21.46

(17-Me); 17.58 (19-Me); 10.04 (25-Me); 25.85, 25.84,

18.17, 18.00, 24.16, 24.53, 24.82 (2£TBDMS). ¹H NMR

(CDCl₃, selected data), d (ppm): 2.19 (d, J¼13.7 Hz, H-3a);

2.02 (H-3b); 4.01 (d, J¼12.5 Hz, H-6a); 2.57 (br s, H-6b);

1.71 (H-11); 3.02 (br s, H-13); 3.68 (br d, J,9.0 Hz, H-14);

3.50 (br s, H-15); 4.97 (d, J¼8.5 Hz, H-20); 3.40 (H-21);

4.22 (br s, H-24); 4.83 (br s, H-26); 5.41 (br d, J¼6.5 Hz, H-

29); 2.96 (ddd, J¼11.4þ8.5þ4.6 Hz, H-32); 3.38 (H-33);

0.97 (br s, 3H, 11-Me); 1.74 (s, 3H, 19-Me); 1.61 (s, 3H, 27-

Me); 0.06, 0.06, 0.04, 0.01 (s, each 3H, Si–Me); 0.88, 0.86

(s, each 9H, (CH₃)₃); 3.77 (s, 3H, 9-OMe); 3.69 (s, 10-OH).

4.2.20. Compound 17. CHN (C₅₆H₉₉NO₁₂Si₂) calcd: 65.01/

9.65/1.35, found: 64.70/9.54/1.23. HRMS (MþNa; calcd/

found): 1056.6604/1056.6599. ¹³C NMR (CDCl₃), d (ppm):

163.87 (C1); 72.44 (C2); 31.82 (C3); 20.40 (C4); 24.33

(C5); 37.24 (C6); 168.06 (C8); 204.20 (C9); 84.34 (C10);

34.21 (C11); 30.33 (C12); 79.46 (C13); 74.07 (C14); 78.83

(C15); 39.06 (C16); 26.69 (C17); 47.73 (C18); 140.31

(C19); 123.72 (C20); 56.20 (C21); 208.67 (C22); 47.32

4.2.18. Compound 15. CHN (C₅₆H₉₉NO₁₂Si₂) calcd: 65.01/

9.65/1.35, found: 64.78/9.59/1.30. HRMS (MþNa; calcd/

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

5979

(C23); 67.98 (C24); 39.30 (C25); 86.26 (C26); 130.76

(C27); 11.11 (C28); 137.65 (C29); 35.17 (C30); 36.09

(C31); 84.07 (C32); 75.09 (C33); 33.84 (C34); 30.60 (C35);

22.31 (C36); 11.47 (C37); 54.26 (10-OMe); 57.10 (13-

OMe); 59.60 (15-OMe); 57.88 (32-OMe); 16.45^p(11-Me);

20.50 (17-Me); 16.41^p(19-Me); 9.89 (25-Me); 25.86, 25.83,

18.15, 18.04, 23.83, 24.28, 24.52, 24.74 (2£TBDMS).

¹H NMR (CDCl₃), d (ppm): 2.44 (br d, J¼12.5 Hz, H-3a);

1.42 (H-3b); 4.44 (br dd, J¼13.0þ3.0 Hz, H-6a); 3.23

(H-6b); 2.57 (H-11); 3.57 (H-13); 3.68 (dd, J¼7.0þ3.6 Hz,

H-14); 3.26 (H-15); 4.73 (d, J¼10.7 Hz, H-20); 3.23

(H-21); 2.80 (dd, J¼15.0þ10.5 Hz, H-23a); 2.21 (dd,

J¼15.0þ4.5 Hz, H-23b); 4.10 (dd, J¼10.5þ4.5 Hz,

H-24); 5.10 (d, J¼10.4 Hz, H-26); 5.36 (d, J¼9.0 Hz,

H-29); 2.95 (ddd, J¼11.3þ8.6þ4.5 Hz, H-32); 3.40 (H-33);

0.80 (d, 3H, J¼7.5 Hz, 11-Me); 1.82 (s, 3H, 19-Me); 1.60 (s,

3H, 27-Me); 0.07, 0.06, 0.01, 0.00 (s, each 3H, Si–Me);

0.89, 0.85 (s, each 9H, (CH₃)₃); 3.16 (s, 3H, 10-OMe).

(MþNa; calcd/found): 786.4768/786.4757. ¹³C NMR

(CDCl₃, hemiketal form/ketone form¼5:1), d (hemiketal/

ketone, ppm): 169.81 or 169.73/169.43 (C1); 56.92/52.63

(C2); 28.39/26.11 (C3); 21.06/21.29 (C4); 25.57/25.20

(C5); 42.05/44.38 (C6); 169.81 or 169.73/166.55 (C8);

97.64/202.68 (C10); 37.10/40.08 (C11); 32.31/32.21 (C12);

73.48/80.79 (C13); 73.11/73.19 (C14); 75.94/78.09 (C15);

32.86/35.58 (C16); 25.11/27.55 (C17); 49.34/48.51 (C18);

139.01/138.56 (C19); 123.84/124.76 (C20); 53.76/55.11

(C21); 213.94/211.87 (C22); 47.51/45.35 (C23); 67.01/

69.94 (C24); 41.90/38.50 (C25); 78.31/82.79 (C26); 132.51/

130.92 (C27); 13.53/12.46 (C28); 130.61/133.47 (C29);

34.92/34.99 (C30); 34.73/34.49 (C31); 84.17/84.21 (C32);

73.52/73.52 (C33); 31.22/31.21 (C34); 30.54/30.41 (C35);

24.43/23.29 (C36); 11.55/11.61 (C37); 55.89/57.35 (13-

OMe); 57.84/57.05 (15-OMe); 56.50/56.43 (32-OMe);

15.75/14.70 (11-Me); 20.09/21.04 (17-Me); 14.70/14.78

(19-Me); 9.77/9.84 (25-Me). ¹H NMR (CDCl₃, selected

data), d (hemiketal form, ppm): 5.53 (s, H-2); 4.40 (d,

J¼13.0 Hz, H-6a); 3.05 (br dd, J¼13.0þ13.0 Hz, H-6b);

1.79 (H-11); 3.49 (H-13); 3.83 (H-14); 3.54 (ddd,

J¼11.2þ5.0þ2.1 Hz, H-15); 4.88 (d, J¼10.1 Hz); 3.41

(H-21); 2.98 (dd, J¼14.8þ4.0 Hz, H-23a); 2.53 (dd,

J¼14.8þ9.0 Hz, H-23b); 3.80 (H-24); 5.25 (s, H-26); 5.27

(d, J¼9.2 Hz, H-29); 2.99 (H-32); 3.40 (H-33); 0.80 (d, 3H,

J¼6.6 Hz, 11-Me); 1.54 (s, 3H, 19-Me); 1.62 (s, 3H, 27-

Me); 5.62 (s, 10-OH); d (ketone form, ppm): 5.21 (d,

J¼5.5 Hz, H-2); 3.80 (H-6a); 3.00 (H-6b); 3.40 (H-11); 3.80

(H-14); 3.26 (H-15); 4.85 (d, J¼10.2 Hz, H-20); 3.39

(H-21); 2.71 (dd, J¼18.0þ3.3 Hz, H-23a); 2.53 (H-23b);

3.98 (H-24); 5.08 (d, J¼8.0 Hz, H-26); 5.32 (d, J¼9.3 Hz,

H-29); 2.99 (H-32); 3.40 (H-33); 1.21 (d, 3H, J¼7.0 Hz, 11-

Me); 1.59 (s, 3H, 19-Me); 1.57 (s, 3H, 27-Me).

4.2.21. Compound 18. (a) from 6a. To a solution of 0.5 g

(0.48 mmol) hydroxy acid 6a in 30 ml benzene were added

1.0 g (4.7 equiv., 2.26 mmol) lead tetra acetate in one

portion. The resultant suspension was stirred for 30 min at

room temperature and then partitioned between ethyl

acetate and a saturated aqueous sodium hydrogen carbonate

solution. The aqueous layer was removed and the organic

layer was washed twice with brine, dried over sodium

sulfate and evaporated to dryness at reduced pressure. The

residue was subjected to a short ﬂash column chromato-

graphy to give 0.46 g (96%) 18 as an amorphous powder.

(b) from 6b. Starting from 0.5 g 6b the reaction, work up

and puriﬁcation was performed as described above to give

0.47 g (98%) 18, CHN (C₅₄H₉₇NO₁₁Si₂) calcd: 65.35/9.85/

1.41, found: 65.30/9.83/1.22. HRMS (MþNa; calcd/found):

1014.6498/1014.6508. ¹³C NMR (CDCl₃, single rotamer), d

(ppm): 169.74 (C1); 57.00 (C2); 27.53 (C3); 20.65 (C4);

25.85 (C5); 42.8 br (C6); 169.39 (C8); 97.43 (C10); 36.69

(C11); 32.71 (C12); 73.72 (C13); 72.87 (C14); 75.59 (C15);

31.84 (C16); 25.56 (C17); 49.65 (C18); 137.2 br (C19);

123.37 (C20); 54.40 (C21); 210.86 (C22); 46.4 br (C23);

70.40 (C24); 39.4 br (C25); n.d. (C26); n.d. (C27); 10.9 br

(C28); 135.35 (C29); 35.06 (C30); 36.25 (C31); 84.27

(C32); 75.11 (C33); 34.02 (C34); 30.65 (C35); 25.79 (C36);

11.44 (C37); 56.21 (13-OMe); 57.23 (15-OMe); 57.75 (32-

OMe); 15.77 (11-Me); 20.08 (17-Me); 14.43 (19-Me); 10.9

br (25-Me); 25.93, 25.79, 18.13, 18.04, 24.11, 24.52,

4.2.23. Compounds 20a and 20b. (a) from 12a. A small

glass tube was charged with 0.5 g (0.43 mmol) 12a and a

magnetic stirring bar and immersed in a preheated (160 8C)

oil bath. After approx. 2 min, carbon dioxide formation

occurred in the clear liquid which ceased after two

additional minutes. After 8 min, the mixture was cooled

down to room temperature, diluted in 3 ml dichloromethane

and subjected to ﬂash column chromatography (silica gel,

dichloromethane/acetone¼20:1) to give after evaporation

and drying of the relevant fractions at high vacuum 0.36 g

(74%) 20a and 63 mg (13%) 20b as amorphous powders. (b)

from 12b. Starting from 100 mg (0.087 mmol) 12b, the

decarboxylation was performed as described above to give

78 mg (81%) 20a and 10 mg (10%) 20b.

1

24.75 (2£TBDMS). H NMR (CDCl₃, selected data), d

(ppm): 5.37 (H-2); 4.47 (br d, J¼13.0 Hz, H-6a); 2.76

(H-6b); 1.82 (H-11); 2.07 (ddd, J¼12.3þ4.6þ4.6 Hz, H-

12a); 3.39 (H-13); 3.81 (dd, J¼9.7þ1.8 Hz, H-14); 3.54

(ddd, J¼11.5þ4.7þ1.4 Hz, H-15); 5.05 (br s, H-20); 3.31

(H-21); 2.72 (br s, H-23a); 2.54 (br s, H-23b); 4.00 (br s,

H-24); 5.05 (br s, H-26); 5.35 (d, J¼8.7 Hz, H-29); 2.92

(ddd, J¼11.2þ8.5þ4.5 Hz, H-32); 3.40 (H-33); 0.81 (d, 3H,

J¼6.6 Hz, 11-Me); 1.52 (s, 3H, 19-Me); 1.46 (s, 3H,

27-Me); 0.07, 0.06, 0.05, 0.03 (s, each 3H, Si–Me); 0.88,

0.85 (s, each 9H, (CH₃)₃); 5.64 (10-OH).

4.2.24. Compound 20a. CHN (C₆₀H₁₁₃NO₁₁Si₃) calcd:

64.99/10.27/1.26, found: 65.20/10.05/1.22. HRMS (MþNa;

calcd/found): 1130.7519/1130.7525. ¹³C NMR (CDCl₃,

Z/E¼1:2), d (Z/E-isomer, ppm): 169.73/169.34 (C1);

52.88/54.66 (C2); 26.60/27.50 (C3); 21.01/20.32 (C4);

26.38/24.68 (C5); 43.60/40.01 (C6); 172.99/174.20 (C8);

71.50/69.05 (C10); 34.40/33.04 (C11); 33.41/32.23 (C12);

79.64/79.72 (C13); 78.11/72.67 (C14); 80.36/81.53 (C15);

40.69/37.28 (C16); 31.20/32.33 (C17); 47.08/45.88 (C18);

139.16/140.91 (C19); 124.10/123.43 (C20); 54.88/55.20

(C21); 208.80/209.65 (C22); 45.88/47.92 (C23); 68.37/

67.52 (C24); 39.21/38.58 (C25); 81.74/83.13 (C26); 131.65/

130.81 (C27); 12.04/11.58 (C28); 135.30/136.76 (C29);

35.01/35.15 (C30); 36.23/36.15 (C31); 84.09/84.09 (C32);

4.2.22. Compound 19. Starting from 0.3 g (0.27 mmol) 21

or 0.4 g (0.4 mmol) 18, the deprotection and work up was

performed as described above for 13a to give after a ﬂash

column chromatography (silica gel, ethyl acetate) 0.17 g

(82%) or 0.24 g (78%) 19 as amorphous powders. HRMS

5980

K. Baumann et al. / Tetrahedron 60 (2004) 5965–5981

75.11/75.11 (C33); 33.88/33.88 (C34); 30.73/30.66 (C35);

23.34/23.36 (C36); 11.49/11.49 (C37); 59.92/55.83 (13-

OMe); 57.11/58.26 (15-OMe); 57.84/57.90 (32-OMe);

12.98/13.82 (11-Me); 20.23/21.33 (17-Me); 16.54/18.54

(19-Me); 11.49/9.70 (25-Me); 26.14, 26.00, 25.91, 25.86,

25.85, 18.15, 18.06, 18.02, 23.62, 24.16, 24.34, 24.52,

24.75, 24.90 (3£TBDMS). ¹H NMR (CDCl₃, selected

data), d (Z-isomer, ppm): 5.39 (d, J¼4.8 Hz, H-2); 3.73 (br

d, J¼13.3 Hz, H-6a); 3.20 (H-6b); 4.40 (d, J¼2.1 Hz,

H-10); 1.85 (H-11); 3.27 (H-13); 3.71 (dd, J¼8.0þ1.4 Hz,

H-14); 3.29 (H-15); 4.78 (d, J¼10.5 Hz, H-20); 3.19 (H-21);

acetone¼50:1) to afford 0.26 g (87%) 21. (b) from 20b.

Starting from 45 mg (0.041 mmol) 20b and applying the

same reaction conditions and work up as described above

provided 38 mg (84%) 21 as amorphous powder: CHN

(C₆₀H₁₁₁NO₁₁Si₃) calcd: 65.11/10.11/1.27, found: 65.00/

9.92/1.15. HRMS (MþNa; calcd/found): 1128.7363/

1128.7363. ¹³C NMR (CDCl₃, mixture of rotamers .9:1),

d (major rotamer, ppm): 168.84 (C1); 51.36 (C2); 25.53

(C3); 20.65 (C4); 25.73 (C5); 44.58 (C6); 167.08 (C8);

203.70 (C10); 40.46 (C11); 31.78 (C12); 82.37 (C13); 75.75

(C14); 78.24 (C15); 42.93 (C16); 26.56 (C17); 46.40 (C18);

139.92 (C19); 123.48 (C20); 55.79 (C21); 208.97 (C22);

47.73 (C23); 67.70 (C24); 38.75 (C25); 82.95 (C26); 130.87

(C27); 11.25 (C28); 136.17 (C29); 35.08 (C30); 36.27

(C31); 84.19 (C32); 75.18 (C33); 34.03 (C34); 30.72 (C35);

23.61 (C36); 11.69 (C37); 56.85 (13-OMe); 61.09 (15-

OMe); 57.78 (32-OMe); 16.48 (11-Me); 20.54 (17-Me);

16.02 (19-Me); 8.87 (25-Me); 26.05, 25.87, 25.73, 18.41,

18.18, 18.05, 23.95, 24.17, 24.40, 24.49, 24.74, 24.85

2.78 (dd,

J¼17.4þ8.0 Hz,

H-23a);

2.36

(dd,

J¼17.4þ4.6 Hz, H-23b); 4.14 (ddd, J¼8.0þ4.6þ2.3 Hz,

H-24); 5.19 (d, J¼8.7 Hz, H-26); 5.27 (d, J¼8.9 Hz, H-29);

2.95 (H-32); 3.40 (H-33); 0.79 (d, 3H, J¼6.6 Hz, 11-Me);

1.78 (s, 3H, 19-Me); 1.57 (s, 3H, 27-Me); 0.10, 0.09, 0.08,

0.06, 0.05, 0.01 (s, each 3H, Si–Me); 0.92, 0.89, 0.88 (s,

each 9H, (CH₃)₃); d (E-isomer, ppm): 4.46 (d, J¼5.1 Hz,

H-2); 4.39 (d, J¼12.0 Hz, H-6a); 3.16 (H-6b); 4.22 (s,

H-10); 1.85 (H-11); 3.27 (H-13); 3.95 (dd, J¼8.0þ1.6 Hz,

H-14); 3.08 (H-15); 4.66 (d, J¼10.3 Hz, H-20); 3.23 (H-21);

2.85 (dd, J¼16.7þ10.3 Hz, H-23a); 2.31 (dd,

J¼16.7þ4.0 Hz, H-23b); 4.09 (ddd, J¼10.3þ4.0þ1.4 Hz,

H-24); 5.16 (d, J¼9.6 Hz, H-26); 5.34 (d, J¼8.7 Hz, H-29);

2.95 (H-32); 3.40 (H-33); 0.80 (d, 3H, J¼6.6 Hz, 11-Me);

1.80 (d, 3H, J¼1.0 Hz, 19-Me); 1.64 (d, 3H, J¼1.1 Hz, 27-

Me); 0.09, 0.08, 0.08, 0.07, 0.02, 0.01 (s, each 3H, Si–Me);

0.91, 0.89, 0.87 (s, each 9H, (CH₃)₃).

1

(3£TBDMS). H NMR (CDCl₃, selected data), d (major

rotamer, ppm): 5.24 (br d, J¼4.0 Hz, H-2); 3.43 (H-6a);

3.05 (ddd, J¼13.8þ13.8þ2.8 Hz, H-6b); 3.28 (H-11); 2.13

(dd, J¼14.7þ10.5 Hz, H-12a); 2.79 (d, J¼9.6 Hz, H-13);

3.63 (d, J¼9.2 Hz, H-14); 3.20 (H-15); 4.61 (d, J¼10.3 Hz,

H-20); 3.22 (H-21); 2.87 (dd, J¼16.0þ9.9 Hz, H-23a); 2.22

(dd, J¼16.0þ4.0 Hz, H-23b); 4.17 (dd, J¼9.9þ4.0 Hz,

H-24); 4.92 (d, J¼9.9 Hz, H-26); 5.35 (d, J¼8.7 Hz, H-29);

2.93 (ddd, J¼11.2þ8.5þ4.4 Hz, H-32); 3.40 (H-33); 1.19

(d, 3H, J¼7.6 Hz, 11-Me); 1.78 (s, 3H, 19-Me); 1.44 (s, 3H,

27-Me); 0.10, 0.08, 0.06, 0.03 (s, each 3H, Si–Me), 0.07 (s,

6H, Si–Me); 0.93, 0.89, 0.88 (s, each 9H, (CH₃)₃).

4.2.25. Compound 20b. CHN (C₆₀H₁₁₃NO₁₁Si₃) calcd:

64.99/10.27/1.26, found: 65.22/10.11/1.25. HRMS (MþNa;

calcd/found): 1130.7519/1130.7520. ¹³C NMR (CDCl₃,

mixture of rotamers .9:1), d (major rotamer, ppm):

168.69 (C1); 53.13 (C2); 26.40 (C3); 21.24 (C4); 25.06

(C5); 43.16 (C6); 174.94 (C8); 72.56 (C10); 34.96 (C11);

29.96 (C12); 83.35 (C13); 75.01 (C14); 79.53 (C15); 42.61

(C16); 27.48 (C17); 48.01 (C18); 139.66 (C19); 123.57

(C20); 55.16 (C21); 210.21 (C22); 45.83 (C23); 68.99

(C24); 40.53 (C25); 78.70 (C26); 132.34 (C27); 13.70

(C28); 131.17 (C29); 34.96 (C30); 36.61 (C31); 84.14

(C32); 75.17 (C33); 33.87 (C34); 30.95 (C35); 23.55 (C36);

11.50 (C37); 56.68 (13-OMe); 60.64 (15-OMe); 57.99 (32-

OMe); 21.31 (11-Me); 20.27 (17-Me); 15.97 (19-Me); 9.71

(25-Me); 25.99, 25.86, 25.80, 18.39, 18.16, 17.97

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¨

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Chapter 27.

Article Doi

On the reactivity of ascomycin at the binding domain. Part 2: Hydroxide mediated rearrangement reactions

DOI: 10.1016/j.tet.2004.05.028

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