Thermal atropisomerism of teicoplanin aglycon derivatives: Preparation of the P,P,P and M,P,P atropisomers of the teicoplanin aglycon via selective equilibration of the DE ring system

Article abstract of DOI:10.1021/ja002376i

The degradation of teicoplanin to a series of key aglycon derivatives, including those containing a cleaved FG ring system, and a study of their thermal atropisomerism are detailed. In all cases, selective equilibration of the DE ring system was observed to provide a 1:1 mixture of P:M atropisomers under conditions in which the AB and CD atropisomer stereochemistry were unaffected. The DE atropisomer equilibration was found to occur with an E(a) of 29.3 and 24.8-25.2 kcal/mol for 6a (FG ring system intact) and 10/12 (cleaved FG ring system), respectively, which is comparable to that of a vancomycin aglycon DE ring system (E(a) = 23.6 kcal/mol) and more facile than the CD (E(a) = 30.4 kcal/mol) or O-methylated AB ring system (E(a) = 37.8 kcal/mol). Consistent with intuitive expectations, the intact teicoplanin FG ring system slowed the rate of isomerization, contributing ca. 4.0 kcal/mol to the E(a) (6a vs 10), and the bulky C₂³ substituent on teicoplanin acyclo FG derivatives had a much less significant effect, contributing only 1-1.5 kcal/mol to the E(a) relative to the vancomycin aglycon. Neither precludes selective equilibration of the DE ring system, and neither had an effect on the thermodynamic ratio of the resulting atropisomers (1:1). Resynthesis of the teicoplanin aglycon (P,P,P-2) from 8 as a prelude to the synthesis of the teicoplanin aglycon unnatural DE atropisomer (M,P,P-17) from 13 is described and provides the final stages of a teicoplanin aglycon total synthesis and a key structural analogue. The comparative evaluation of 2 and 17 revealed that the DE atropisomer stereochemistry substantially impacts the antimicrobial activity (2 > 17, 50-fold) and the binding affinity for N,N'-Ac₂-L-Lys-D-Ala-D-Ala (2 > 17, K(a) = 2.4 x 10⁶ vs 1.9 x 10⁴ M^-1, 125 times).

Full text of DOI:10.1021/ja002376i

J. Am. Chem. Soc. 2000, 122, 10047-10055
10047
Thermal Atropisomerism of Teicoplanin Aglycon Derivatives:
Preparation of the P,P,P and M,P,P Atropisomers of the Teicoplanin
Aglycon via Selective Equilibration of the DE Ring System
Dale L. Boger,* Jian-Hui Weng, Susumu Miyazaki, J. Jeffrey McAtee, Steven L. Castle,
Seong Heon Kim, Yoshiki Mori, Olivier Rogel, Harald Strittmatter, and Qing Jin
Contribution from the Department of Chemistry and The Skaggs Institute for Chemical Biology,
The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
ReceiVed June 30, 2000
Abstract: The degradation of teicoplanin to a series of key aglycon derivatives, including those containing a
cleaved FG ring system, and a study of their thermal atropisomerism are detailed. In all cases, selective
equilibration of the DE ring system was observed to provide a 1:1 mixture of P:M atropisomers under conditions
in which the AB and CD atropisomer stereochemistry were unaffected. The DE atropisomer equilibration was
found to occur with an Ea of 29.3 and 24.8-25.2 kcal/mol for 6a (FG ring system intact) and 10/12 (cleaved
FG ring system), respectively, which is comparable to that of a vancomycin aglycon DE ring system (Ea )
23.6 kcal/mol) and more facile than the CD (Ea ) 30.4 kcal/mol) or O-methylated AB ring system (Ea ) 37.8
kcal/mol). Consistent with intuitive expectations, the intact teicoplanin FG ring system slowed the rate of
isomerization, contributing ca. 4.0 kcal/mol to the Ea (6a vs 10), and the bulky C23 substituent on teicoplanin
acyclo FG derivatives had a much less significant effect, contributing only 1-1.5 kcal/mol to the Ea relative
to the vancomycin aglycon. Neither precludes selective equilibration of the DE ring system, and neither had
an effect on the thermodynamic ratio of the resulting atropisomers (1:1). Resynthesis of the teicoplanin aglycon
(P,P,P-2) from 8 as a prelude to the synthesis of the teicoplanin aglycon unnatural DE atropisomer (M,P,P-
17) from 13 is described and provides the final stages of a teicoplanin aglycon total synthesis and a key
structural analogue. The comparative evaluation of 2 and 17 revealed that the DE atropisomer stereochemistry
substantially impacts the antimicrobial activity (2 > 17, 50-fold) and the binding affinity for N,N′-Ac2-L-
Lys-D-Ala-D-Ala (2 > 17, Ka ) 2.4 × 106 vs 1.9 × 104 M-1, 125 times).
Teicoplanin (1, Figure 1) is a complex of five closely related
natural products isolated from Actinoplanes teichomyceticus1,2
(ATCC 31121) that are related to vancomycin.3-8 It is 2-20-
fold more potent than vancomycin against Gram-positive
bacteria,9,10 possesses a lower toxicity than vancomycin,1,11,12
exhibits a longer half-life in man (40 h vs 6 h),13,14 and is easier
(1) Parenti, F.; Beretta, G.; Berti, M.; Arioti, V. J. Antibiot. 1978, 31,
276.
(2) Hunt, A. H.; Molloy, R. M.; Occolowitz, J. L.; Marconi, G. G.;
Debono, M. J. Am. Chem. Soc. 1984, 106, 4891. Barna, J. C. J.; Williams,
D. H.; Stone, D. J. M.; Leung, T.-W. C.; Doddrell, D. M. J. Am. Chem.
Soc. 1984, 106, 4895.
(3) McCormick, M. H.; Stark, W. M.; Pittenger, G. E.; Pittenger, R. C.;
McGuire, J. M. Antibiot. Annu. 1955-1956, 606.
(4) Harris, C. M.; Kopecka, H.; Harris, T. M. J. Am. Chem. Soc. 1983,
105, 6915. Sheldrick, G. M.; Jones, P. G.; Kennard, O.; Williams, D. H.;
Smith, G. A. Nature 1978, 271, 223. Williams, D. H.; Kalman, J. R. J. Am.
Chem. Soc. 1977, 99, 2768. Williamson, M. P.; Williams, D. H. J. Am.
Chem. Soc. 1981, 103, 6580.
(5) Malabarba, A.; Nicas, T. I.; Thompson, R. C. Med. Res. ReV. 1997,
17, 69.
(6) Wiedemann, B.; Grimm, H. In Antibiotics in Laboratory Medicine;
Lorian, V., Ed.; Williams and Wilkins: Baltimore, 1996; pp 900-1168.
(7) Williams, D. H.; Bardsley, B. Angew. Chem., Int. Ed. Engl. 1999,
38, 1172.
(8) Walsh, C. T.; Fisher, S. L.; Park, I.-S.; Prahalad, M.; Wu, Z. Chem.
Biol. 1996, 3, 21.
(9) Varaldo, P. E.; Debbia, E.; Schito, G. C. Antimicrob. Agents
Chemother. 1983, 23, 402.
Figure 1.
(10) Barry, A. L.; Thornsberry, C.; Jones, R. N. J. Clin. Microbiol. 1986,
23, 100.
(11) De Lalla, F.; Tramarin, A. Drug Saf. 1995, 13, 317.
(12) Greenwood, D. J. Antimicrob. Chemother. 1988, 21 (Suppl. A), 1.
to administer15 and monitor.16 The teicoplanin aglycon bears
the identical ABCD ring system and the same ABCDE
atropisomer stereochemistry of vancomycin but contains a DE
10.1021/ja002376i CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/03/2000

10048 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
Boger et al.
ring system that lacks the sensitive â-hydroxy group of the
E-ring-substituted phenylalanine (residue 2) and incorporates
an especially racemization-prone substituted phenylglycine
(residue 3).17 Most significantly, it contains the additional 14-
membered diaryl ether FG ring system that is not found in
vancomycin. We recently disclosed a total synthesis18-22 of the
vancomycin aglycon, complementary to those of Evans and
Nicolaou, which enlisted a defined order to the introduction of
its CD, AB, and DE ring systems, which permits selective
thermal atropisomerism of the newly formed ring systems or
their immediate precursors.23-27 In addition to the diastereo-
selection that was achieved in each of the ring closures, this
order permitted the recycling of any undesired atropisomer for
each ring system and provided a means for reliable control of
the stereochemistry throughout the synthesis, funneling all
synthetic material into the natural atropisomer. A special
attraction of this approach was the recognition that the common
ABCD ring system of vancomycin, and teicoplanin could serve
as a key intermediate to both classes of natural products.
(13) Verbist, L.; Tjandramaga, B.; Hendrickx, B.; Van Hecken, A.; Van
Melle, P.; Verbesselt, R.; Verhaegaen, J.; De Schepper, P. J. Antimicrob.
Agents Chemother. 1984, 26, 881.
(14) Benet, L. Z.; Williams, R. L. In The Pharmacological Basis of
Therapeutics, 8th ed.; Gilman, A. G., Rall, T. W., Nies, A. S., Taylor, P.,
Eds.; Pergamon: New York, 1990; pp 1650-1735.
(15) Graninger, W.; Presterl, E.; Wenisch, C.; Schwameis, E.; Breyer,
S.; Vukovich, T. Drugs 1997, 54 (Suppl. 6), 21.
(16) Brogden, R. N.; Peters, D. H. Drugs 1994, 47, 823.
(17) Barna, J. C. J.; Williams, D. H.; Strazzolini, P.; Malabarba, A.;
Leung, T.-W. C. J. Antibiot. 1984, 37, 1204.
(18) Nicolaou, K. C.; Boddy, C. N. C.; Brase, S.; Winssinger, N. Angew.
Chem., Int. Ed. Engl. 1999, 38, 2096.
Prior to implementing this approach for teicoplanin20 and in
efforts to address a concern over its viability, we examined the
thermal atropisomerism of a series of teicoplanin aglycon
derivatives. The added constraints that the teicoplanin FG ring
system imposes on the conformational properties of the structure
were not clear, and it was expected to have a significant impact
on the ease of DE atropisomerism and could also alter the
thermodynamic atropisomer preference. Optimally, the DE ring
system would be capable of selective isomerism without
affecting the AB or CD atropisomer stereochemistry. Anticipat-
ing that the constraints of the FG ring system might preclude
selective thermal DE atropisomer equilibration, we examined
derivatives of the teicoplanin aglycon containing both the intact
and cleaved FG ring system. This approach provided the added
benefit that we could establish the relative sensitivity of both
types of derivatives toward C23 epimerization, which is known
to be especially facile for teicoplanin derivatives.17
Herein we provide details of studies that have defined
conditions suitable for selective teicoplanin DE versus CD or
AB atropisomerism and that provided appropriately function-
alized teicoplanin aglycon derivatives which served as relay
intermediates in a total synthesis of the natural product. Thus,
thermal atropisomerism of 6a or 10 and 12 provided 1:1
mixtures of the P,P,P and M,P,P-atropisomers 13, 14, and 15,
respectively, in which the DE atropisomers selectively equili-
brate. We also describe the conversion of 8 to the teicoplanin
aglycon, which constitutes the final stages of its total synthesis
and the conversion of M,P,P-13 to M,P,P-17, the corresponding
teicoplanin aglycon which possesses the unnatural DE antro-
pisomer stereochemistry.
(19) Rao, A. V. R.; Gurjar, M. K.; Reddy, K. L.; Rao, A. S. Chem. ReV.
1995, 95, 2135.
Teicoplanin Degradation. The degradation of 1 to a series
of aglucoteicoplanin derivatives is summarized in Scheme 1.
The removal of the three carbohydrates was accomplished by
treatment with 10% concentrated HCl-HOAc (80 °C, 1 h)29
or 80% aqueous H2SO4, DMSO (85-90 °C, 30 h).30 Although
the aglycon 2 could be isolated in pure form by semipreparative
reverse-phase HPLC, it proved to be more convenient to carry
the crude material forward without purification. N-Boc formation
(Boc2O, NaHCO3, DMF, 25 °C), followed by methyl ester
formation (CH3I, NaHCO3, DMF, 25 °C) conducted in situ
without isolation of the carboxylic acid 3, provided 4a (50%
overall from 1). Exhaustive methylation of the six phenols
(CH3I, K2CO3, DMF, 25 °C) and O-silylation of the C36 alcohol
of 5a (CF3CONMeTBS, CH3CN, 45 °C) afforded 6a. Methyl
ester reduction (LiBH4, (MeO)3B, THF, 45 °C), followed by
MEM protection of the primary alcohol 7 (MEMCl, i-Pr2NEt,
CH2Cl2, 25 °C), provided 8. This sequence was also conducted
with formation of the benzyl versus methyl ester (PhCH2Br,
NaHCO3, 45% overall from 1), providing 4b, an intermediate
which is often easier to purify than 4a.
(20) Vancomycin aglycon: Boger, D. L.; Miyazaki, S.; Kim, S. H.; Wu,
J. H.; Loiseleur, O.; Castle, S. L. J. Am. Chem. Soc. 1999, 121, 3226. Boger,
D. L.; Miyazaki, S.; Kim, S. H.; Wu, J. H.; Castle, S. L.; Loiseleur, O.;
Jin, Q. J. Am. Chem. Soc. 1999, 121, 10004. Teicoplanin aglycon: Boger,
D. L.; Kim, S. H.; Miyazaki, S.; Strittmatter, H.; Weng, J.-H.; Mori, Y.;
Rogel, O.; Castle, S. L.; McAtee, J. J. J. Am. Chem. Soc. 2000, 122, 7416.
(21) Orienticin C aglycon: Evans, D. A.; Barrow, J. C.; Watson, P. S.;
Ratz, A. M.; Dinsmore, C. J.; Evrard, D. A.; DeVries, K. M.; Ellman, J.
A.; Rychnovsky, S. D.; Lacour, J. J. Am. Chem. Soc. 1997, 119, 3419.
Evans, D. A.; Dinsmore, C. J.; Ratz, A. M.; Evrard, D. A.; Barrow, J. C.
J. Am. Chem. Soc. 1997, 119, 3417. Vancomycin aglycon: Evans, D. A.;
Wood, M. R.; Trotter, B. W.; Richardson, T. I.; Barrow, J. C.; Katz, J. L.
Angew. Chem., Int. Ed. Engl. 1998, 37, 2700. Evans, D. A.; Dinsmore, C.
J.; Watson, P. S.; Wood, M. R.; Richardson, T. I.; Trotter, B. W.; Katz, J.
L. Angew. Chem., Int. Ed. Engl. 1998, 37, 2704.
(22) Nicolaou, K. C.; Li, H.; Boddy, C. N. C.; Ramanjulu, J. M.; Yue,
T.-Y.; Natarajan, S.; Chu, X.-J.; Brase, S.; Rubsam, F. Chem. Eur. J. 1999,
5, 2584. Nicolaou, K. C.; Boddy, C. N. C.; Li, H.; Koumbis, A. E.; Hughes,
R.; Natarajan, S.; Jain, N. F.; Ramanjulu, J. M.; Brase, S.; Solomon, M. E.
Chem. Eur. J. 1999, 5, 2602. Nicolaou, K. C.; Koumbis, A. E.; Takayanagi,
M.; Natarajan, S.; Jain, N. F.; Bando, T.; Li, H.; Hughes, R. Chem. Eur. J.
1999, 5, 2622. Nicolaou, K. C.; Mitchell, H. J.; Jain, N. F.; Bando, T.;
Hughes, R.; Winssinger, N.; Natarajan, S.; Koumbis, A. E. Chem. Eur. J.
1999, 5, 2648. Nicolaou, K. C.; Mitchell, H. J.; Jain, N. F.; Winssinger,
N.; Hughes, R.; Bando, T. Angew. Chem., Int. Ed. Engl. 1999, 38, 240.
Nicolaou, K. C.; Takayanagi, M.; Jain, N. F.; Natarajan, S.; Koumbis, A.
E.; Bando, T.; Ramanjulu, J. M. Angew. Chem., Int. Ed. Engl. 1998, 37,
2717. Nicolaou, K. C.; Natarajan, S.; Li, H.; Jain, N. F.; Hughes, R.;
Solomon, M. E.; Ramanjulu, J. M.; Boddy, C. N. C.; Takayanagi, M. Angew.
Chem., Int. Ed. Engl. 1998, 37, 2708. Nicolaou, K. C.; Jain, N. F.;
Nataranjan, S.; Hughes, R.; Solomon, M. E.; Li, H.; Ramanjulu, J. M.;
Takayanagi, M.; Koumbis, A. E.; Bando, T. Angew. Chem., Int. Ed. Engl.
1998, 37, 2714.
For access to derivatives that lack the FG ring system, the
N-terminus amide was reductively cleaved following a modi-
fication to protocols disclosed in studies conducted on N-Boc
aglucoteicoplanin.31 Thus, treatment of 8 with LiBH4 (10%
H2O-EtOH, 25 °C) cleanly led to reductive cleavage of the
FG ring system at the N-terminus amide to provide 9 (66%,
(23) Boger, D. L.; Borzilleri, R. M.; Nukui, S.; Beresis, R. T. J. Org.
Chem. 1997, 62, 4721. Boger, D. L.; Borzilleri, R. M.; Nukui, S. Bioorg.
Med. Chem. Lett. 1995, 5, 3091.
(24) Boger, D. L.; Castle, S. L.; Miyazaki, S.; Wu, J. H.; Beresis, R. T.;
Loiseleur, O. J. Org. Chem. 1999, 64, 70.
(25) Boger, D. L.; Loiseleur, O.; Castle, S. L.; Beresis, R. T.; Wu, J. H.
Bioorg. Med. Chem. Lett. 1997, 7, 3199.
(26) Boger, D. L.; Beresis, R. T.; Loiseleur, O.; Wu, J. H.; Castle, S. L.
Bioorg. Med. Chem. Lett. 1998, 8, 721.
(28) The natural AB atropisomers within the ABCD and ABCDE ring
systems of vancomycin are also the thermodynamically most stable (g 95:
5) ensuring that the DE equilibration does not affect the AB stereochemistry.
(29) Malabarba, A.; Ferrari, P.; Gallo, G. G.; Kettenring, J.; Cavalleri,
B. J. Antibiot. 1986, 39, 1430.
(30) We thank Dr. A. Malabarba and Dr. G. Panzon (Lepetit Research
Center, Via R. Lepetit 34, 21040 Geranzano, Italy) for providing this
procedure.
(27) Boger, D. L.; Miyazaki, S.; Loiseleur, O.; Beresis, R. T.; Castle, S.
L.; Wu, J. H.; Jin, Q. J. Am. Chem. Soc. 1998, 120, 8920.
(31) Malabarba, A.; Ciabatti, R.; Kettenring, J.; Ferrari, P.; Vekey, K.;
Bellasio, E.; Denaro, M. J. Org. Chem. 1996, 61, 2137.

Teicoplanin Aglycon DeriVatiVes
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10049
Scheme 1
Figure 2.
phenols, but also for the C36 secondary alcohol which was found
to suffer a thermally slow retro aldol reaction within the
vancomycin aglycon.27 Clean, selective equilibration of the DE
atropisomers was observed for 6a under relatively mild condi-
tions (130-150 °C, o-Cl2C6H4), which provided a 1:1 mixture
of 6a and 13 without detectable isomerization of either the AB
or CD ring system atropisomers (Figure 2).28 The thermal
equilibration occurs with a greater Ea (29.3 kcal/mol vs 23.6
kcal/mol) and longer half-life (140 °C, 1.6 vs 0.8 h) than the
vancomycin aglycon DE equilibration, which also provided a
1:1 mixture of P:M atropisomers.27 Thus, the teicoplanin FG
ring system, including the sterically bulky C23 side chain, does
slow the rate of atropisomerism, but it does not preclude
selective equilibration of the DE ring system; nor does it alter
the atropisomer thermodynamic ratio. The isolation of 13 and
its thermal reequilibration with 6a established their relation-
ship as interconverting atropisomers. Diagnostic of the DE
atropisomer stereochemistry, the 2D 1H-1H NMR (Roesy,
CD3OD, 600 MHz, 313 K) of 6a revealed natural atropisomer
NOEs corresponding to C3â2-H (δ 3.00)/C5b2-H (δ 7.41) (s,
strong), C3R2-H (3.31)/C5a2-H (7.36) (s) and C4a4-H (5.68)/
C6b2-H (7.03,) (w, weak), and C4a4-H (5.68)/C5a2-H (7.36)
(w), whereas 13 revealed unnatural atropisomer NOEs corre-
sponding to C3R2-H (3.34)/C5b2-H (7.25) (m, medium),
C3â2-H (2.95)/C5a2-H (7.58) (m), and C4a4-H (5.66)/C5b2-H
(7.25) (w). Diagnostic NOE cross-peaks indicative of the CD
Scheme 1). However, the conversion was much lower following
the conditions disclosed for N-Boc aglucoteicoplanin (NaBH4,
10% H2O-EtOH, 25 °C, 72 h)31 in which substantial competi-
3
3
tive C2 epimerization of 8 (50%), generation of the C2
epimerized reductive cleavage product,32 and further reduction
products were observed.
In studies related to synthetic efforts on teicoplanin, the
liberated free amine in 9 was protected as the Boc derivative
10 (Boc2O, NaHCO3, CH2Cl2), the Troc derivative 11 (TrocCl,
NaHCO3, CH2Cl2), and the Teoc derivative 12 (Teoc-OBt,
Et3N, dioxane-H2O).
Thermal Atropisomerism. Given the anticipated thermal
instability of teicoplanin and the fact that it is a mixture of five
components, no effort was made to study the thermal equilibra-
tion of 1. The thermal isomerization of 6a was examined in
detail, and it contains protecting groups not only for the
C-terminus carboxylic acid, the N-terminus amine, and all six
6
and AB ring system stereochemistry were unperturbed: C3 -
6
6
5
H/C5a6-H, C2 -H/C5a6-H, C4a5-H/C2 -H, C2 -H/C4a5-H,
5
6
and C2 -H/C2 -H.
These observed NOEs and assignments for 6a and related
structures were analogous to those that Malabarba29 made on
the teicoplanin aglycon. In addition, 2 (DMF-d7, 500 MHz, 323
1
1
K) exhibited a C2 -H/C4b1-H NOE much stronger than C2 -
H/C4a1-H, a C4a1-H/C4a3-H NOE but no C4b1-H/C4a3-H
(32) The identity of this product was examined by independent synthesis;
see Scheme 5.
NOE, and C2 -H exhibited a NOE with C4b3-H but not with
3

10050 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
Boger et al.
either the AB or CD ring system atropisomers was observed.
Thus, the added conformational constraints of 6a relative to 10
imposed by the FG ring system resulted in a greater barrier to
thermal isomerism. Isolation of the unnatural DE atropisomer
14 and its thermal reequilibration with 10 established the
relationship of 10 and 14 as interconverting atropisomers.
Diagnostic of the DE atropisomer stereochemistry, the 2D 1H-
1H NMR (Roesy, CD3OD, 500 MHz, 313 K) of 10 revealed
natural atropisomer NOEs corresponding to C3R2-H (3.41)/
C5a2-H (7.42) (s), whereas 14 revealed unnatural atropisomer
NOEs corresponding to C3R2-H (3.34)/C5b2-H (7.25) (m),
C3â2-H (2.95)/C5a2-H(7.58) (m), and C4a4-H (5.66)/C5b2-H
(7.25) (w). Diagnostic NOE cross-peaks indicative of the CD
6
and AB ring system stereochemistry were unperturbed: C3 -
6
6
5
5
H/C5a6-H, C2 -H/C5a6-H, C4a5-H/C2 -H, and C2 -H/C4a
-
H.
The corresponding N-Teoc derivative 12 behaved similarly
(130-150 °C, o-Cl2C6H4), providing a 1:1 mixture of P:M DE
atropisomers with no evidence of AB or CD ring system
isomerism (Figure 3), but the N-Troc derivative 11 preferentially
closed to the imino carbamate A33 faster than DE ring system
equilibration. Diagnostic of the DE atropisomer stereochemistry
for the equilibration of 12, the 2D 1H-1H NMR (Rosey,
CD3OD, 500 MHz, 313 K) of 12 revealed natural atropisomer
NOEs corresponding to C3R2-H (3.43)/C5a2-H (7.51) (s),
whereas 15 revealed unnatural atropisomer NOEs corresponding
to C3R2-H (3.44)/C5b2-H (7.34) (m), C3â2-H (2.89)/C5a2-H
(7.50) (w), and C4a4-H (5.76)/C6b2-H (7.28) (w). NOE cross-
peaks indicative of the CD and AB ring system stereochemistry
6
6
were unperturbed: C3 -H/C5a6-H, C2 -H/C5a6-H, C4a5-H/
C2 -H, and C2 -H/C4a5-H.
6
5
Although not investigated in detail, initial attempts at the
thermal equilibration of 9 led to conversion to a second product
(o-Cl2C6H4) that did not reequilibrate with 9 and most likely
constitutes an epimerized diastereomer. However, the equilibra-
tion could be conducted in DMSO, albeit with some degradation,
resulting in a 70% recovery of a 1:1 mixture of DE ring system
atropisomers at 130 °C: Ea ) 27.6 kcal/mol, t1/2 ) 1.1 h (120
°C), 0.45 h (130 °C), and 0.16 h (140 °C).
Finally, studies conducted with 5a revealed that its DE
atropisomerism, even in nonpolar solvents (o-Cl2C6H4) which
suppress retro aldol cleavage of the CD ring system,27 did not
proceed sufficiently well at the lower temperatures (130 °C) to
permit respectable rates of equilibration or product recoveries.
Instead, an unidentified product was observed that possessed
the same molecular weight and the same diagnostic NOEs as
5a, but that exhibited chemical shift perturbations in C6b6-H
Figure 3.
C4a3-H. Similarly, 8 (DMSO-d6, 600 MHz, 333 K) exhibited
1
1
C2 -H/C4a1-H and C2 -H/C4b1-H NOEs, a C4a1-H/C4a3-H
5
and C6 -OMe. Thus, useful interconversions do not appear to
NOE but no C4b1-H/C4a3-H NOE, and C2 -H exhibited a
3
be possible with 5a.
NOE with C4b3-H, but not with C4a3-H. These observations
suggest a well-defined FG conformation for 2 and related
compounds in polar aprotic solvents which has not been
previously established for teicoplanin or a teicoplanin aglycon
derivative. The behavior of 8 and, presumably, related agents
Synthesis of the Teicoplanin Aglycon from 8. The prepara-
6
tion of the teicoplanin aglycon from 8 or its corresponding C3
free alcohol 16 was conducted to establish the final steps of a
total synthesis and as a prelude to preparing the teicoplanin
aglycon unnatural DE atropisomer (Scheme 3). Thus, C36 OTBS
deprotection enlisting Bu4NF in the presence of HOAc (10
equiv) cleanly provided the secondary alcohol 16 (88%) without
competitive retro aldol ring cleavage.27 Reprotection of 16 as
its C36 OTBS ether (CF3CONMeTBS, CH3CN, 50 °C), followed
by aqueous acid workup, provided 8 (87%). MEM deprotection
(B-bromocatecholborane, CH2Cl2, 0 °C), followed by reprotec-
tion of the N-terminus amine with Boc2O (aqueous NaHCO3,
25 °C), provided 7 (76% for 2 steps). Two-step alcohol oxidation
(Dess-Martin periodinane, CH2Cl2; NaClO2, DMSO-H2O in
3
was slightly different in CD3OD (313 K, 500 MHz), with C2 -H
exhibiting NOEs with both C4a3-H and C4b3-H, C2 -H
1
exhibiting NOEs with both C4a1-H and C4b1-H but still
exhibiting only a C4a1-H/C4a3-H NOE and no C4b1-H/C4a3-H
NOE.
The analogous thermal equilibration of 10 which contains
the cleaved FG ring system occurred with greater ease, requiring
temperatures of 130-150 °C (o-Cl2C6H4) and proceeding with
an Ea of 24.8 kcal/mol and t1/2 of 0.84 h (140 °C) or 1.78 h
(130 °C), which produced a separable 1:1 mixture of DE ring
system atropisomers (Figure 3). No detectable isomerism of
(33) Full characterization is provided in Supporting Information.

Teicoplanin Aglycon DeriVatiVes
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10051
Scheme 2
Scheme 4
Scheme 3
treatment of the purified carboxylic acid 6c with AlBr3-EtSH
(25 °C, 3 h), which served to deprotect the six aryl methyl ethers,
6
the C3 OTBS ether, and the N-terminus Boc, to provide 2
(48%).
Preparation of the Teicoplanin Aglycon Unnatural DE
Atropisomer 17. Following the route detailed for 2, 13 was
obtained from preparative thermal isomerism of 6a and con-
verted to 17, aglucoteicoplanin that possesses the unnatural
M-atropisomer of the DE ring system. Thus, treatment of 13
with A1Br3 (EtSH, 25 °C, 3 h) led to exhaustive deprotection
of the nine protecting groups and provided 17 directly (41%)
(Scheme 4).
The unnatural DE atropisomer of the teicoplanin aglycon (17)
was compared to the natural teicoplanin aglycon 2 in representa-
tive antimicrobial assays and in cell free binding assays with
N,N′-diacetyl-L-Lys-D-Ala-D-Ala and N,N′-diacetyl-L-Lys-D-
Ala-D-Lac. In the antimicrobial assays, 17 was found to be 50
times less potent than 2 (Table 1). Unlike teicoplanin itself, both
its aglycon 2, as well as 17, exhibited diminished activity against
Van B Enterococcus faecalis.
The binding of 2 and 17 with both N,N′-Ac2-L-Lys-D-Ala-
D-Ala and N,N′-Ac2-L-Lys-D-Ala-D-Lac was examined fol-
lowing established protocols (Table 2). The binding of 17 with
the D-Ala-D-Ala ligand was reduced 125 times relative to the
natural teicoplanin aglycon (2), indicating that the DE atrop-
isomer stereochemistry substantially impacts the tripeptide
binding affinity. This observation is consistent with the relative
antimicrobial potency of the two compounds. Both 2 and 17,
like vancomycin, exhibited very substantial reductions in binding
affinity to the D-Ala-D-Lac ligand that were consistent with
their loss of antimicrobial activity against vancomycin resistant
strains of E. faecalis.
the presence of resorcinol) provided the carboxylic acid, which
was esterified upon treatment with TMSCHN2 (20% MeOH-
toluene, 25 °C) to afford 6a (74% for 3 steps). The use of
resorcinol in DMSO-H2O proved to be superior to isobutene/
t-BuOH and prevented competitive aromatic chlorination under
6
the reaction conditions. Deprotection of the C3 OTBS ether
(Bu4NF-HOAc, THF, 25 °C, 78%), followed by exhaustive
deprotection of 5a enlisting AlBr3-EtSH (25 °C, 3 h, 46%),21
which served to cleave the six aryl methyl ethers, the C-terminus
methyl ester, and the N-terminus Boc group, provided the
teicoplanin aglycon identical in all respects with authentic
material.34
These observations may help clarify the role of the residue 2
chlorine substituent. Recent proposals have suggested a role for
promoting antibiotic dimerization enhancing the cooperative
D-Ala-D-Ala binding.35 However, teicoplanin represents the
exception for which antibiotic dimerization is not observed.
A more concise sequence for the final conversions, which
eliminates two steps and improves the overall conversion, en-
tailed two-step alcohol oxidation of 7 (Dess-Martin periodi-
nane, CH2Cl2; NaClO2, DMSO-H2O in the presence of
resorcinol) to provide the carboxylic acid 6c (79%) and direct
(34) The resynthesis of the teicoplanin aglycon from 8 and 11 confirmed
that 9-12 possess the natural C2 stereochemistry.
(35) Gerhard, U.; Mackay, J. P.; Maplestone, R. A.; Williams, D. H. J.
Am. Chem. Soc. 1993, 115, 232.
3

10052 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
Table 1. Antimicrobial Activity
Boger et al.
MIC (µg/mL)
Enterococcus faecium
Staphylococcus aureus
Enterococcus faecalis
compound
vancomycin
1, teicoplanin
2, teicoplanin aglycon
17
(ATCC 25923)
(ATCC 35667)
vanco. resist.
Van A (BM 4166)
Van B (ATCC 51299)
1.25
0.15
e0.30
16
2.5
1.25
1.25
66
500
60
>640
>534
2850
2560
>640
>534
125
1.25
10
534
Table 2. Association Constantsa
Ka, M-1
ligand
vancomycin
2, teicoplanin aglycon
17
N,N'-Ac2-L-Lys-D-Ala-D-Ala
N,N'-Ac2-L-Lys-D-Ala-D-Lac
3.1 × 105
2.4 × 106
1.9 × 104
3.3 × 102b
2.0 × 102
4.8 × 102
a 0.11 mM compound, 25 °C, 0.02 M sodium citrate, pH ) 5.1. Perkins, H. R. Biochem. J. 1969, 111, 195. Nieto, M.; Perkins, H. R. Biochem.
J. 1971, 123, 773. Scrimin, P., et al. J. Org. Chem. 1996, 61, 6268. b Popieniek, P. H.; Pratt, R. F. Anal. Biochem. 1987, 165, 108.
Scheme 5
Instead, enhancement of its antimicrobial properties is derived
from the membrane-anchoring effects provided by the residue
4 glucosamine acyl lipid. That the reduction in the antimicrobial
activity of 17 correlated with its reduced binding affinity for
D-Ala-D-Ala with an antibiotic that does not dimerize suggests
a primary, direct role for the residue 2 chlorine. The distinct
behavior of 17 vs 2 may be derived from a chlorine-enhanced
D-Ala-D-Ala binding of 2, a chlorine-diminished binding of
17, or a combination of the two effects. The binding of the
corresponding DE dechloro teicoplanin aglycon with N,N′-Ac2-
L-Lys-D-Ala-D-Ala has been examined in the work of Mala-
barba36 and was found to exhibit a Ka ) 3.5 × 104 M-1, which
is only slightly greater than that of 17 (1-2 times) and
approximately 70-fold lower than the teicoplanin aglycon. Thus,
the residue 2 chlorine, with only the natural atropisomer
stereochemistry, enhances the D-Ala-D-Ala binding affinity
relative to its removal (70 times) and its incorporation with the
unnatural stereochemistry has little additional effect (1.8 times,
125 times total). This is a direct effect on the binding affinity
of the teicoplanin monomer and is independent of any additional
role the substituent might play in promoting dimerization of
other antibiotics in the class, or its role in orienting the residue
4-bound carbohydrates.
Teicoplanin Aglycon Epimerization. In studies leading to
the structure elucidation of teicoplanin, Williams and co-
workers17 detailed a facile C23 epimerization that occurs under
mild conditions (3% aqueous NaHCO3, 80 °C, 5 h or 20%
n-BuNH2-CH3OH, 80 °C, 3-6 h) to provide the unnatural C2
(R)-isomer as the near exclusive product of the equilibration.
basic conditions of 3% K2CO3 in 33% H2O-EtOH, even at 45
°C, produced a 3:1 mixture of 19:9 with the unnatural C23 (R)-
diastereomer predominating. Thus, the ease of epimerization
3
of 9 is lower than 8, and the preference for the unnatural C2
3
(R) versus (S) diastereomer appears to be less pronounced, and
this observation has significant strategic implications in the
planning of a total synthesis of the teicoplanin aglycon.
However, both 8 and 9 epimerize with an ease that should raise
concerns in synthetic efforts. Notably, 19 was identical to the
epimerized reduction product that was derived from reductive
cleavage of 8 with NaBH4 (10% H2O-EtOH, 26%). In the case
Although equilibrated diastereomer ratios were not reported, the
3
unnatural C2 (R)-diastereomers were isolated in yields up to
80%. Consequently, we examined the analogous epimerization
of 8 and 9 to provide an in-house sense of their relative ease of
isomerization and to provide authentic samples for comparison.
Thus, while exposure of 8 to 1% NaHCO3 in 33% H2O-EtOH
at 25 °C or 50 °C (5 h) had no effect, its exposure at 80 °C (30
1
of both 18 and 19, the H NMR chemical shifts most affected
3
4
by the epimerization were C2 -H and C2 -H and the exact
site of epimerization was not unambiguously established in our
studies. That of 18 might be safely extrapolated from the work
of Williams,17 and that of 19 deduced from correlation with
the epimerized reduction product. However, no effort was made
to unambiguously establish the assignments, and it is possible
3
min) led to a presumed C2 epimerization to 18 (52%) and a
second additional minor isomer (16%) whose structure was not
established, with only a trace of 8 remaining (g 95:5 18:8)
(Scheme 5). By contrast, 9 epimerized more slowly, and a 4-h
versus 30-min exposure of 9 to 1% NaHCO3 in 33% H2O-
EtOH at 80 °C led to a 1:1.7 mixture of 9:19, and 19 appears
to possess the unnatural C23 (R)-stereochemistry. More vigorous
4
3
that they could involve C2 versus C2 epimerization.
Discussion. Most remarkable of the observations is the ease
of the teicoplanin DE atropisomerism and the relative lack of
impact the constraints of the additional 14-membered FG ring
system have on the rate of isomerism or the thermodynamic
(36) Malabarba, A.; Spreafico, F.; Ferrari, P.; Kettenring, J.; Strazzolini,
P.; Tarzia, G.; Pallanza, R.; Berti, M.; Cavalleri, B. J. Antibiot. 1989, 42,
1684.

Teicoplanin Aglycon DeriVatiVes
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10053
ring systems isomerizes much more readily than the O-
methylated AB ring system 21, but is comparable to its isolated
acyclic biaryl precursor. In contrast, the isolated AB ring system
bearing the free phenols isomerizes even at room temperature.21
Unlike the deprotected natural AB ring system (g 95:5) or its
cyclic biaryl precursor (3:1),20 the CD ring system (1:1) and
both the vancomycin DE (1:1) and teicoplanin DE ring systems
(1:1) exhibit no thermodynamic atropisomer preference.
Experimental Section
4a. Teicoplanin37 (1, 1.32 g) in HOAc (90 mL) was treated with
conc. HCl (10 mL), and the resulting mixture was stirred at 80 °C for
1 h. The reaction mixture was poured into Et2O (700 mL), and the
resulting precipitate was collected by filtration, washed with EtOAc
(200 mL) and dried under vacuum to afford aglucoteicoplanin (2) as a
crude residue. A solution of the crude 2 in DMF (15 mL) was treated
sequentially with NaHCO3 (159 mg, 1.89 mmol) and Boc2O (276 mg,
1.26 mmol) at 0 °C. The reaction mixture was slowly warmed to 25
°C and stirred for 5 h before the dropwise addition of CH3I (0.158
mL, 2.54 mmol) at 25 °C. The reaction mixture was stirred at 25 °C
under Ar for 8 h. The mixture was cooled to 0 °C; quenched by the
addition of H2O (40 mL), followed by 10% aqueous HCl (5 mL); and
extracted with EtOAc (2 × 100 mL). The combined organic layers
were washed with H2O (30 mL) and saturated aqueous NaCl (30 mL),
dried (Na2SO4), and concentrated in vacuo. Chromatography (SiO2, 2.5
× 20 cm, 14% CH3OH-CHCl3) afforded 4a33 (509 mg, 50% for 3
steps) as a white film.
4b. Teicoplanin37 (1, 5.2 g) was dissolved in 41.6 mL of DMSO
and 1.04 mL of 80% aqueous H2SO4 (v/v). The solution was warmed
at 85 °C for 30 h, cooled to 25 °C, and 65 mL of H2O was added.
Activated charcoal (520 mg) was added to the cloudy solution, which
was stirred for 1 h and filtered. The filtrate was neutralized (pH 7)
under stirring by the addition of 10% aqueous NaOH, and the
suspension that was obtained was cooled and left overnight at 5 °C.
The solid was collected by filtration and dried under vacuum overnight
to provide 4.8 g of crude teicoplanin aglycon. A sample of crude 2
(100 mg) prepared as described above was purified by semipreparative
reverse-phase HPLC (Nova Pak C18, 2.5 × 10 cm, CH3CN-0.07%
TFA/H2O 18:82, 10 mL/min, tR ) 20 min) to afford pure agluco-
teicoplanin (2, 29.0 mg) as a white film.33 The crude aglycon was placed
in DMF (15 mL) and treated with NaHCO3 (697 mg, 8.3 mmol) and
Boc2O (905 mg, 4.15 mmol) at 25 °C for 2 h before NaHCO3 (600
mg, 7.14 mmol) and benzyl bromide (3.31 mL, 27.8 mmol) were added.
The mixture was stirred at 25 °C for 10 h, cooled to 0 °C, and 936 µL
of HOAc was added to neutralize the mixture (pH 7). Most of the DMF
was removed in vacuo, H2O (50 mL) was added, and the mixture was
extracted with EtOAc (3 × 100 mL). The combined organic layers
were washed with H2O (3 × 100 mL) and saturated aqueous NaCl (50
mL), dried (Na2SO4), filtered, and concentrated in vacuo. Chromatog-
raphy (SiO2, 7 × 20 cm, 10-15% MeOH-CH2Cl2 gradient elution)
afforded 4b33 (1.74 g, 45% for 3 steps) as a white solid.
Figure 4.
3: from 4b. 1 mg of 10% Pd/C was placed in MeOH (0.5 mL) and
the mixture was saturated with H2. A solution of 4b (10 mg, 7.21 µmol)
in MeOH (0.5 mL) was added and the mixture was stirred under 1 atm
H2 at 25 °C for 12 h. The Pd/C was removed by filtration through
Celite, and the solvent was evaporated in vacuo to afford 333 (8.9 mg,
95%) as a white powder.
5a. A solution of 4a (509 mg, 0.387 mmol) in DMF (4 mL) was
treated sequentially with K2CO3 (535 mg, 3.87 mmol) and CH3I (0.48
mL, 7.8 mmol). The reaction mixture was stirred at 25 °C for 4.5 h,
diluted with EtOAc (100 mL), cooled to 0 °C, quenched by the addition
of 10% aqueous HCl (80 mL) at 0 °C, and extracted with EtOAc (2 ×
50 mL). The combined organic layers were washed with H2O (40 mL)
and saturated aqueous NaCl (30 mL), dried (Na2SO4), and concentrated
in vacuo. Chromatography (SiO2, 2.5 × 20 cm, 6% CH3OH-CHCl3
gradient elution) afforded 5a33 (275 mg, 51%) as a white solid.
5b. A solution of 4b (740 mg, 0.54 mmol) at 0 °C in DMF (8.5
mL) was treated with K2CO3 (723 mg, 5.4 mmol) and CH3I (0.663
ratio of atropisomers. Summarized in Figure 4 are the com-
parison parameters that have been established to date on related
systems. Considering the relative substituent effects (NO2 faster
than Cl),23 the isolated teicoplanin and vancomycin 16-
membered DE ring systems isomerize with essentially the same
ease (22 versus 23). The constraints of the intact FG ring system
substantially slow the rate of DE ring system equilibration,
3
whereas the bulky C2 substituent of FG acyclo teicoplanin
derivatives has only a modest effect (6a versus 10 relative to
24). However, neither precludes selective DE ring system
equilibration. The isomerism of the DE ring system in both
teicoplanin and vancomycin is slowed by the fusion with the
ABCD ring system by roughly 3.6-6.0 kcal/mol. Remarkably,
each of these interconversions is substantially faster than the
isomerism of the isolated 16-membered CD ring system 20, even
without the constraints of the AB ring system, and the origin
of these distinctions is not obvious. Similarly, each of the DE
(37) Purchased from Advanced Separation Technologies Inc.

10054 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
Boger et al.
mL, 10.8 mmol). The mixture was stirred at 25 °C for 2 h, cooled to
0 °C, and 0.4 mL of HOAc was added (pH ∼ 7). Most of the DMF
was removed in vacuo, H2O (30 mL) was added, and the mixture was
extracted with EtOAc (3 × 80 mL). The combined organic layers were
washed with H2O (3 × 80 mL) and saturated aqueous NaCl (40 mL),
dried (Na2SO4), filtered, and concentrated in vacuo. Chromatography
(SiO2, 3.0 × 20 cm, 5% MeOH-CH2Cl2) provided 5b33 (692 mg, 88%)
as a white solid.
10. A solution of 9 (2.4 mg, 1.5 µmol) in anhydrous CH2Cl2 (0.2
mL) was treated sequentially with NaHCO3 (0.2 mg, 2.4 µmol) and
Boc2O (0.4 mg, 1.8 µmol) at 25 °C. The mixture was stirred at 25 °C
for 3 h, cooled to 0 °C, and 1% aqueous HOAc was added to adjust
the pH ) 7. The mixture was extracted with CH2Cl2, and the CH2Cl2
phase was washed with saturated aqueous NaCl, dried (Na2SO4), and
concentrated in vacuo. PTLC (SiO2, 5% MeOH-CH2Cl2) afforded 1033
(2.5 mg, 98%) as a white powder.
11. A solution of 9 (7.5 mg, 4.8 µmol) in anhydrous CH2Cl2 (0.5
mL) was treated sequentially with NaHCO3 (0.4 mg, 5.2 µmol) and
TrocCl (0.72 µL, 5.3 µmol) at 25 °C. The mixture was stirred at 25 °C
for 14 h, cooled to 0 °C, and 1% aqueous HOAc was added to adjust
to pH ) 7. The mixture was extracted with CH2Cl2, and the CH2Cl2
phase was washed with saturated aqueous NaCl, dried (Na2SO4), and
concentrated in vacuo. Chromatography (SiO2, 0.7 × 6 cm, 5%
MeOH-CH2Cl2) yielded 1133 (7.8 mg, 94%) as a white solid.
12. A solution of 9 (8.9 mg, 6.4 µmol) in 50% dioxane-H2O was
treated sequentially with Et3N (1.3 µL, 9.5 µmol) and Teoc-OBt (2.7
mg, 9.5 µmol) at 25 °C. The mixture was stirred at 25 °C for 3 h before
it was concentrated in vacuo. The residue was dissolved in EtOAc (20
mL), and the EtOAc phase was washed with 10% aqueous citric acid
(2 × 10 mL), H2O (5 mL), and saturated aqueous NaCl (5 mL); dried
(Na2SO4); and concentrated in vacuo. Chromatography (SiO2, 0.7 × 6
cm, 5% MeOH-CH2Cl2) yielded 1233 (7.9 mg, 81%) as a white solid.
16. A solution of 8 (10.8 mg, 6.9 µmol) in THF (300 µL) was treated
with n-Bu4NF-HOAc (1:1.2, 1 M solution in THF, 69 µL, 69 µmol)
at 25 °C. The mixture was stirred at 25 °C for 15.5 h and quenched by
the addition of 1% aqueous HCl (5 mL) at 0 °C. The resulting mixture
was stirred at 25 °C for 2 h and extracted with EtOAc (2 × 15 mL).
The combined organic layers were washed with H2O (2 × 15 mL) and
saturated aqueous NaCl (10 mL), dried (Na2SO4), and concentrated in
vacuo. PTLC (SiO2, 9% CH3OH-CHCl3) afforded 1633 (8.8 mg, 88%)
as a white film.
6a. A solution of 5a (219 mg, 0.16 mmol) in anhydrous CH3CN (4
mL) was treated with CF3CONMeTBS (1.12 mL, 4.76 mmol) under
Ar, and the resulting mixture was stirred at 45 °C for 13 h. The reaction
mixture was poured into EtOAc-20% aqueous citric acid (3:1, 40 mL)
and stirred at 25 °C for 30 min. The two layers were separated, and
the aqueous phase was extracted with EtOAc (2 × 100 mL). The
combined organic layers were washed with saturated aqueous NaHCO3
(40 mL) and saturated aqueous NaCl (30 mL), dried (Na2SO4), and
concentrated in vacuo. Chromatography (SiO2, 2.5 × 20 cm, 50-75%
EtOAc-hexane gradient elution) afforded 6a33 (190 mg, 80%) as a
white film.
6b. A solution of 5b (692 mg, 0.47 mmol) in anhydrous CH3CN
(15 mL) was treated with CF3CONMeTBS (2 mL, 8.48 mmol) at 45
°C for 11 h. The reaction mixture was cooled to 25 °C, and 3 mL of
EtOAc and 1 mL of 5% aqueous citric acid were added. The mixture
was stirred for 5 min at 25 °C. The organic phase was washed with
saturated aqueous NaCl, dried (Na2SO4), filtered, and concentrated in
vacuo. Chromatography (SiO2, 3.0 × 20 cm, 0-2% MeOH-CH2Cl2
gradient elution) yielded 6b33 (628 mg, 84%) as a white solid.
6c. A 2-mg sample of 10% Pd/C was placed in EtOH (0.5 mL), and
the mixture was saturated with H2. A sample of 6b (9 mg, 5.7 µmol)
was added, and the mixture was stirred under 1 atm H2 at 25 °C for 12
h. The Pd/C was removed by filtration, and the solvent was evaporated
in vacuo to provide 6c33(5.4 mg, 64%) as a pale yellow powder.
7: from 6a. A solution of 6a (36.7 mg, 24 µmol) in anhydrous
THF (2 mL) was treated sequentially with LiBH4 (2 M solution in THF,
0.486 mL, 0.97 mmol) and (MeO)3B (32.7 µL, 0.29 mmol) at 0 °C.
The reaction mixture was stirred at 45 °C for 9 h, cooled to 0 °C,
quenched by the addition of 10% aqueous HCl (10 mL), and extracted
with EtOAc (2 × 50 mL). The combined organic layers were washed
with H2O (10 mL) and saturated aqueous NaCl (20 mL), dried (Na2SO4),
and concentrated in vacuo. Chromatography (SiO2, 2.5 × 10 cm, 75-
80% EtOAc-hexane gradient elution) afforded 733 (27.6 mg, 77%) as
a white solid.
Preparation of 8 from 16. A solution of 16 (1.8 mg, 1.24 µmol) in
anhydrous CH3CN (0.2 mL) was treated with CF3CONMeTBS (14.6
µL, 61.8 µmol) under Ar, and the resulting mixture was stirred at 50
°C for 13 h. The reaction mixture was poured into EtOAc-20%
aqueous citric acid (3:1, 10 mL) and stirred at 25 °C for 1 h. The two
layers were separated, and the aqueous phase was extracted with EtOAc
(2 × 10 mL). The combined organic layers were washed with saturated
aqueous NaHCO3 (5 mL) and saturated aqueous NaCl (5 mL), dried
(Na2SO4), and concentrated in vacuo. PTLC (SiO2, 80% EtOAc-
hexane) afforded 833 (1.7 mg, 87%) as a white film.
7: from 6b. A solution of 6b (360 mg, 0.23 mmol) in anhydrous
THF (15 mL) was treated sequentially with LiBH4 (2 M solution in
THF, 4.51 mL, 9.02 mmol) and (MeO)3B (306 µL, 2.7 mmol) at 0 °C.
The reaction mixture was stirred at 45 °C for 12 h, cooled to 0 °C,
quenched by the addition of 5% aqueous HCl (10 mL), and extracted
with EtOAc (2 × 50 mL). The combined organic layers were washed
with H2O (10 mL) and saturated aqueous NaCl (20 mL), dried (Na2SO4),
and concentrated in vacuo. Chromatography (SiO2, 3.0 × 20 cm, 75-
80% EtOAc-hexane gradient elution) afforded 733 (213 mg, 63%) as
a white solid.
Preparation of 7 from 8. A solution of 8 (6.1 mg, 3.8 µmol) in
anhydrous CH2Cl2 (0.3 mL) was treated with B-bromocatecholborane
(0.2 M in CH2Cl2, 195 µL, 37.8 µmol) at 0 °C for 2.5 h under Ar. The
reaction mixture was poured into saturated aqueous NaHCO3 (5 mL)
and stirred for 30 min. The two layers were separated, and the aqueous
phase was extracted with EtOAc (2 × 30 mL). The combined organic
layers were washed with saturated aqueous NaCl (10 mL), dried
(Na2SO4), and concentrated in vacuo. The resulting amino alcohol was
dissolved in THF (0.6 mL), and saturated aqueous NaHCO3 (145 µL),
followed by Boc2O (2.5 mg, 11.3 µmol), was added. The reaction
mixture was stirred at 25 °C for 1 h, diluted with EtOAc (5 mL), and
quenched by the addition of 1% aqueous HCl (5 mL) at 0 °C. The two
layers were separated and the aqueous phase was extracted with EtOAc
(3 × 20 mL). The combined organic layers were washed with saturated
aqueous NaCl (10 mL), dried (Na2SO4), and concentrated in vacuo.
PTLC (SiO2, 80% EtOAc-hexane) afforded 733 (4.3 mg, 76%) as a
white film.
Preparation of 6a from 7. A solution of 7 (2.9 mg, 2.0 µmol) in
anhydrous CH2Cl2 (0.6 mL) was treated with Dess-Martin periodinane
(8.3 mg, 20 µmol) at 25 °C for 3 h. The reaction mixture was diluted
with EtOAc (5 mL) and quenched by the addition of saturated aqueous
NaHCO3-10% aqueous Na2S2O3 (1:1, 1 mL). The two layers were
separated and the aqueous phase was extracted with EtOAc (2 × 10
mL). The combined organic layers were washed with saturated aqueous
NaHCO3 (4 mL) and saturated aqueous NaCl (4 mL), dried (Na2SO4),
and concentrated in vacuo. The resulting aldehyde in DMSO (0.4 mL)
was treated sequentially with resorcinol (2.2 mg, 20 µmol) and a
solution of NaClO2 (80%, 1.1 mg, 10 µmol) and NaH2PO4‚2H2O (1.36
8. A solution of 7 (80.0 mg, 54 µmol) in anhydrous CH2Cl2 (2 mL)
was treated sequentially with i-Pr2NEt (564 µL, 3.24 mmol) and
MEMCl (277 µL, 2.43 mmol) at 0 °C. The reaction mixture was stirred
at 25 °C for 13 h, diluted with EtOAc (50 mL), cooled to 0 °C,
quenched by the addition of 1% aqueous HCl (10 mL), and extracted
with EtOAc (2 × 10 mL). The combined organic layers were washed
with H2O (10 mL) and saturated aqueous NaCl (20 mL), dried (Na2SO4),
and concentrated in vacuo. Chromatography (SiO2, 1.5 × 15 cm,
0-75% EtOAc-hexane gradient elution) afforded 833 (72.2 mg, 92%)
as a white solid.
9. A solution of 8 (15.8 mg, 0.0l mmol) in 10% H2O-EtOH (333
µL) was treated with LiBH4 (9.0 mg, 0.41 mmol), and the mixture
was stirred at 25 °C for 48 h. A solution of 1% HOAc-EtOH was
added to adjust pH ) 7, then EtOAc (30 mL) and saturated aqueous
NH4Cl were added. The organic phase was dried (Na2SO4) and
concentrated in vacuo. Chromatography (SiO2, 1.5 × 10 cm, 5-10%
MeOH-CH2Cl2 gradient elution) afforded 933 (10.4 mg, 66%) as a
white solid.

Teicoplanin Aglycon DeriVatiVes
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10055
mg, 10 µmol) in H2O (0.1 mL). The reaction mixture was stirred at 25
°C for 30 min, diluted with EtOAc (10 mL), and quenched by the
addition of 1% aqueous HCl (2 mL) at 0 °C. The two layers were
separated and the aqueous phase was extracted with EtOAc (2 × 10
mL). The combined organic layers were washed with H2O (5 mL) and
saturated aqueous NaCl (5 mL), dried (Na2SO4), and concentrated in
vacuo. PTLC (SiO2, 9% CH3OH-CHCl3) afforded the carboxylic acid,
which was dissolved in toluene/CH3OH (5:1, 1.2 mL) and treated with
TMSCHN2 (2.0 M solution in hexane) until the yellow color persisted.
The mixture was stirred at 25 °C for 30 min, and concentrated in vacuo.
PTLC (SiO2, 75% EtOAc-hexane) afforded 6a33 (2.2 mg, 74%) as a
white film.
crude mixture was washed with Et2O (3 × 0.5 mL) and CH2Cl2 (3 ×
0.5 mL) to give a white solid. The solid was purified by semipreparative
reverse-phase HPLC (Nova Pak C18, 2.5 × 10 cm, CH3CN-0.07%
TFA/H2O 17:83, 10 mL/min, tR ) 24.0 min) to afford pure 1733 (1.4
mg, 41%) as a white powder.
Thermal Interconversion of the Atropisomers 6a and 13. A
solution of 6a (6.3 mg, 4.2 µmol) in o-dichlorobenzene (0.6 mL) was
warmed to 150 °C for 9 h. The solvent was removed under a stream of
N2. PTLC (SiO2, 3% MeOH-CH2Cl2, developed two times) afforded
2.9 mg (46%) of pure 1333 as a white film and 3.0 mg (48%) of
recovered 6a as a white film.
Thermal Interconversion of the Atropisomers 10 and 14. A
solution of 10 (6.8 mg, 4.1 µmol) in o-dichlorobenzene (0.6 mL) was
warmed to 140 °C for 10 h. The solvent was removed under a stream
of N2. PTLC (SiO2, 3% MeOH-CH2Cl2, developed three times)
afforded 1433(2.9 mg, 43%) and recovered 10 (3.5 mg, 51%). Longer
equilibration time provided an equilibrium 1:1 ratio of 10:14.
Thermal Interconversion of the Atropisomers 12 and 15. A
solution of 12 (6.1 mg, 3.5 µmol) in o-dichlorobenzene (0.6 mL) was
warmed to 140 °C for 10 h. The solvent was removed under a stream
of N2. PTLC (SiO2, 3% MeOH-CH2Cl2, developed three times)
afforded 1533(2.5 mg, 41%) and recovered 12 (3.1 mg, 51%). Longer
equilibration time provided an equilibrium 1:1 ratio of 12:15.
Thermal Interconversion of the DE Atropisomers of 9. A solution
of 9 (2.0 mg, 1.27 µmol) in DMSO-d6 (0.4 mL) was warmed to 130
°C for 2 h. The solvent was removed under a stream of N2. PTLC
(SiO2, MeOH-CH2Cl2-EtOAc 1:4.5:4.5, developed two times) af-
forded the DE atropisomer of 933 (0.7 mg, 35%) as a white powder
and recovered 9 (0.7 mg, 35%) as a white powder.
Epimerization of 8 to 18. A solution of 8 (3.1 mg, 1.98 µmol) in
33% H2O-EtOH (3 mL) was treated with 30 mg of NaHCO3. The
mixture was stirred at 80 °C for 30 min and concentrated in vacuo.
The mixture was dissolved in EtOAc (10 mL) and H2O (5 mL), and
the H2O phase was extracted with EtOAc (3 × 5 mL). The combined
organic phase was washed with H2O (2 × 5 mL) and saturated aqueous
NaCl, dried (Na2SO4), and concentrated in vacuo. PTLC (SiO2, 5%
CH3OH-CH2Cl2, developed two times) afforded 1833 (1.6 mg, 52%)
as a white powder. HPLC (Nova PakC18, 3.9 × 300 mm, CH3CN-
0.07% TFA/H2O 75:25, 1.0 mL/min) of the crude mixture revealed a
95:5 mixture of 18 (tR ) 5.30 min) and 8 (tR ) 8.96 min).
Preparation of 5a from 6a. A solution of 6a (6.2 mg, 4.1 µmol) in
THF (200 µL) was treated with n-Bu4NF-HOAc (1:1.2, 1 M solution
in THF, 41 µL, 41 µmol) at 25 °C. The resulting mixture was stirred
at 25 °C for 15 h, diluted with EtOAc (5 mL), and quenched by the
addition of 1% aqueous HCl (2 mL) at 0 °C. The resulting mixture
was extracted with EtOAc (2 × 10 mL), and the combined organic
layers were washed with H2O (5 mL) and saturated aqueous NaCl (5
mL), dried (Na2SO4), and concentrated in vacuo. PTLC (SiO2, 6%
CH3OH-CHCl3) afforded 5a33 (4.4 mg, 78%) as a white film.
Preparation of 2 from 5a. A vial charged with 5a (9.8 mg, 7.0
µmol) was treated with AlBr3 (63 mg, 0.24 mmol) in EtSH (0.5 mL)
under Ar. The resulting mixture was stirred at 25 °C for 3 h, diluted
with CHCl3 (0.5 mL), cooled to 0 °C, and quenched by addition of
MeOH (0.1 mL). The solvent was removed by a stream of N2. The
crude mixture was purified by PTLC (SiO2, EtOAc-MeOH-H2O (5:
2.5:1)) and semipreparative reverse phase HPLC (Nova Pak C18, 2.5
× 10 cm, CH3CN-0.07% TFA/H2O 18:82, 10 mL/min, tR ) 20 min)
to afford pure aglucoteicoplanin 233 (4.2 mg, 46%) as a white film.
Preparation of 6c from 7. A solution of 7 (3.9 mg, 2.6 µmol) in
anhydrous CH2Cl2 (1.0 mL) was treated with Dess-Martin periodinane
(11 mg, 26.0 µmol) at 25 °C for 1 h. The reaction mixture was diluted
with EtOAc (5 mL) and quenched by the addition of saturated aqueous
NaHCO3-10% aqueous Na2S2O3 (1:1, 1 mL). The two layers were
separated and the aqueous phase was extracted with EtOAc (2 × 10
mL). The combined organic layers were washed with saturated aqueous
NaHCO3 (4 mL) and saturated aqueous NaCl (4 mL), dried (Na2SO4),
and concentrated in vacuo. The resulting aldehyde in DMSO (0.5 mL)
was treated sequentially with resorcinol (6.1 mg, 55.4 µmol) and a
solution of NaH2PO4‚2H2O (3.0 mg, 19.36 µmol) in H2O (2 mL) and
NaClO2 (80%, 1.6 mg, 22.1 µmol) in H2O (0.2 mL). The reaction
mixture was stirred at 25 °C for 1 h, diluted with EtOAc (10 mL), and
quenched by the addition of 1% aqueous HCl (2 mL) at 0 °C. The two
layers were separated and the aqueous phase was extracted with EtOAc
(2 × 10 mL). The combined organic layers were washed with H2O (5
mL) and saturated aqueous NaCl (5 mL), dried (Na2SO4), and
concentrated in vacuo. PTLC (SiO2, 10% CH3OH-CH2Cl2) afforded
6c33 (3.1 mg, 79%).
Epimerization of 9 to 19. A solution of 9 (5.0 mg, 3.2 µmol) in
33% H2O-EtOH (1 mL) was treated with 10.0 mg of NaHCO3. The
mixture was stirred at 80 °C for 4 h and concentrated in vacuo. The
mixture was dissolved in EtOAc (10 mL) and H2O (5 mL), and the
H2O phase was extracted with EtOAc (3 × 5 mL). The combined
organic phase was washed with H2O (2 × 5 mL), saturated aqueous
NaCl, dried (Na2SO4), and concentrated in vacuo. PTLC (SiO2, 5%
CH3OH-CH2Cl2, developed 3×) to afford 1933 (1.5 mg, 30%) as a
white solid and 0.9 mg of recovered 9.
Preparation of 2 from 6c. A flask charged with AlBr3 (125 mg,
0.47 mmol) was treated with anhydrous EtSH (2.0 mL). After the
mixture was stirred for 10 min, 6c (21.4 mg, 14.3 µmol) was added.
The resulting mixture was stirred at 25 °C for 3 h, cooled to 0 °C, and
quenched by addition of MeOH (2 mL). The solvents were removed
in vacuo. The crude mixture was washed with ether (3 × 1 mL) and
CH2Cl2 (3 × 1 mL) to yield a white solid. The solid was purified by
semipreparative reverse-phase HPLC (Nova Pak C18, 2.5 × 10 cm,
CH3CN-0.07% TFA/H2O 18:82, 10 mL/min, tR ) 20 min) to afford
pure aglucoteicoplanin 233 (8.4 mg, 48%) as a white powder.
Preparation of 17 from 13. A vial charged with AlBr3 (49.0 mg,
0.18 mmol) was treated with anhydrous EtSH (0.5 mL) under Ar. After
the mixture was stirred for 10 min at room temperature, 13 (4.0 mg,
2.9 µmol) was added. The resulting mixture was stirred at 25 °C for 3
h, cooled to 0 °C, diluted with CH2Cl2, and quenched by the addition
of MeOH (1 mL). The solvent was removed by a stream of N2. The
Acknowledgment. We gratefully acknowledge the financial
support of the NIH (CA41101) and The Skaggs Institute for
Chemical Biology, the sabbatical leaves of S.M. (Japan Tabacco,
1997-1999) and Y.M. (Mitsubishi-Tokyo Pharmaceuticals,
Inc., 1999-2001), the award of a Novartis Stiftung to H.S.,
and the award of a NIH postdoctoral fellowship (J.J.M., AI
10367). We wish to thank Drs. Laura B. Pasternack and Dee-
Hua Huang for assistance with the 2D NMR studies.
Supporting Information Available: Full characterization
data for 2, 3, 4a, 4b, 5a, 5b, 6a, 6b, 6c, 7-19, and A are
provided (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
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