C-Glycosyl Tyrosines. Synthesis and Incorporation into C-Glycopeptides

Article abstract of DOI:10.1021/jo990253e

The synthesis of the Fmoc-protected C-glycosyl tyrosines 1 and 2, together with two other related C-glycosyl tyrosines, has been achieved. Key reactions involved (i) the reaction of a glycal with an organozinc reagent (carrying an aryl iodide function) in the presence of a Lewis acid to establish the C-glycosyl linkage and (ii) subsequent cross coupling of the aryl iodide to an alanyl zinc reagent (in the presence of a Pd(0) catalyst) to complete the construction of the α-amino acid moiety. Using solid-phase peptide synthesis methods, two units of the mannosyl derivative 1 (shown as L-Tyr-[C-Ac₄-α-D-Man]) have been incorporated (with four units of glycine) into the linear hexapeptide 3 which was then converted to the C₂-symmetric cyclic oligopeptide 4.

Full text of DOI:10.1021/jo990253e

J . Org. Chem. 1999, 64, 5453-5462
5453
C-Glycosyl Tyr osin es. Syn th esis a n d In cor p or a tion in to
C-Glycop ep tid es
Alan J . Pearce,† Sharn Ramaya,† Simon N. Thorn,† Graham B. Bloomberg,‡
Daryl S. Walter,§ and Timothy Gallagher*,†
School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK, Department of Biochemistry,
Medical School, University of Bristol, Bristol, BS8 1TD, UK, and Roche Discovery Welwyn,
Welwyn Garden City, AL7 3AY, UK
Received February 10, 1999
The synthesis of the Fmoc-protected C-glycosyl tyrosines 1 and 2, together with two other related
C-glycosyl tyrosines, has been achieved. Key reactions involved (i) the reaction of a glycal with an
organozinc reagent (carrying an aryl iodide function) in the presence of a Lewis acid to establish
the C-glycosyl linkage and (ii) subsequent cross coupling of the aryl iodide to an alanyl zinc reagent
(in the presence of a Pd(0) catalyst) to complete the construction of the R-amino acid moiety. Using
solid-phase peptide synthesis methods, two units of the mannosyl derivative 1 (shown as L-Tyr-
[C-Ac4-R-D-Man]) have been incorporated (with four units of glycine) into the linear hexapeptide 3
which was then converted to the C2-symmetric cyclic oligopeptide 4.
O-Linked glycopeptides represent an extensive and
critically important group of glycoconjugates with the
O-glycosylation of a variety of hydroxylated R-amino
acids, in particular serine and threonine, playing a
significant role in a number of key cellular processes.1
To probe and understand the mechanisms of these
processes, access to effective molecular tools is a prereq-
uisite, and the emergence of C-glycosides2 as chemically
and metabolically stable carbohydrate analogues has led
to interest in the potential of the corresponding C-glycosyl
amino acids. C-Glycosides have already been employed
to mimic both the conformation (structure)3 and biological
profile (function)4 of a variety O-glycoconjugates. C-
Glycosyl amino acids, which could be readily incorporated
into larger and biologically more relevant molecular
frameworks (using established peptide methodologies),
would provide novel tools for studying those carbohydrate-
based interactions associated with O-glycopeptides. As
a consequence, the synthesis of a series of different
C-glycosyl amino acids has been described,5 and more
recently, the development and exploitation of these units
as components for peptide synthesis has been reported.6
In addition to the commonly found serine- and threo-
nine-based linkages, the O-glycosylation of phenolic
units7 (tyrosine and substituted phenylglycine deriva-
tives) is frequently encountered. In a very recent paper,
Meldal and co-workers6e reported a series of phenylala-
nine-containing C-glycosides based on a two-carbon
alkyne linkage; however, C-glycosyl variants of tyrosine
O-glycoconjugates have yet to be described. In this paper
we report the first synthesis of the C-glycosyl tyrosine
(5) A variety of C-glycosyl amino acids have been described: “ano-
meric” R-amino acids (a) Estevez, J . C.; Long, D. D.; Wormald, M. R.;
Dwek, R. A.; Fleet, G. W. J . Tetrahedron Lett. 1995, 36, 8287.
Substituted glycine variants (b) Simchen, G.; Pu¨rkner, E. Synthesis
1990, 525. (c) Colombo, L.; Casiraghi, G.; Pittalis, A.; Rassu, G. J . Org.
Chem. 1991, 56, 3897. (d) Garner, P.; Park, J . M. J . Org. Chem. 1990,
55, 3772. (e) Barrett, A. G. M.; Lebold, S. A. J . Org. Chem. 1990, 55,
3853. Substituted alanine variants. (f) Kessler, H.; Wittmann, V.; Ko¨ck,
M.; Kottenhahn, M. Angew. Chem., Int. Ed. Engl. 1992, 31, 902. (g)
Axon, J . R.; Beckwith, A. L. J . J . Chem. Soc., Chem. Commun. 1995,
549. (h) Gurjar, M. K.; Mainkar, A. S.; Syamala, M. Tetrahedron:
Asymmetry 1993, 4, 2343. (i) Wang, L.; Fu¨gedi, P.; Horne, A. Abstr.
Papers of Am. Chem. Soc. 1996, 212, 25-CARB. C-Linked variants of
serine-based glycopeptides (j) Petrus, L.; BeMiller, J . N. Carbohydr.
Res. 1992, 230, 197. (k) Bertozzi, C. R.; Hoeprich, P. D.; Bednarski,
M. D. J . Org. Chem. 1992, 57, 6092 (see also ref 4). (l) Dorgan, B. J .;
J ackson, R. F. W. Synlett 1996, 859. (m) Lay, L.; Meldal, M.; Nicotra,
F.; Panza, L.; Russo, G. J . Chem. Soc., Chem. Commun. 1997, 1469.
(n) Herpin, T. F.; Motherwell, W. B.; Weibel, J .-M. J . Chem. Soc., Chem.
Commun. 1997, 923. (o) Debenham, S. D.; Debenham, J . S.; Burk, M.
J .; Toone, E. J . J . Am. Chem. Soc. 1997, 119, 9897. (p) Fuchss. T.;
Schmidt, R. R. Synthesis 1998, 753. (q) Urban, D.; Skyrdstrup, T.;
Beau, J .-M. Chem. Commun. 1998, 955. (r) Arya, P.; Ben, R. N.; Qin,
H. Tetrahedron Lett. 1998, 39, 6131. (s) Dondoni, A.; Marra, A.; Massi,
A. Chem. Commun. 1998, 1741. (t) Dondoni, A.; Marra, A.; Massi, A.
Tetrahedron 1998, 54, 2827. (u) Dondoni, A.; Massi, A.; Marra, A.
Tetrahedron Lett. 1998, 39, 6601. (v) Dondoni, A.; Marra, A.; Massi,
A. J . Org. Chem. 1999, 64, 933. More complex glycosyl amino acid
derivatives (w) Hoffmann, M.; Burkhart, F.; Hessler, G.; Kessler, H.
Helv. Chim. Acta 1996, 79, 1519. (x) Wang, L.-X.; Fan, J .-Q.; Lee, Y.
C. Tetrahedron Lett. 1996, 37, 1975. (y) Burkhart, F.; Hoffmann, M.;
Kessler, H. Angew. Chem., Int. Ed. Engl. 1997, 36, 1191.
† School of Chemistry, University of Bristol.
‡ Medical School, University of Bristol.
§ Roche Discovery Welwyn.
(1) Hughes R. G. Glycoproteins; Chapman and Hall: London, 1983.
J entoft, N. Trends Biochem. Sci. 1990, 15, 291. Lis, S.; Sharon, N. Eur.
J . Biochem. 1993, 218, 1. Dwek, R. A. Chem. Rev. 1996, 96, 683.
Meldal, M. In Neoglycoconjugates: Preparation and Application; Lee,
Y. C., Lee, R. T., Eds.; Academic Press: San Diego, CA, 1994; p 145.
Boons, G.-J .; Polt, R. L. In Carbohydrate Chemistry; Boons, G. J ., Ed.;
Blackie: London, 1998; p 223.
(2) Levy D. E.; Tang, C. The Chemistry of C-Glycosides; Elsevier
Science: Oxford, 1995. Postema, M. H. D. Tetrahedron 1992, 48, 8545.
Postema, M. H. D. C-Glycoside Synthesis; CRC Press: London, 1995.
(3) Ravishankar, R.; Surolia, A.; Vijayan, M.; Lim, S.; Kishi, Y. J .
Am. Chem. Soc. 1998, 112, 11297 and references therein. Rubinstein,
G.; Sinay¨, P.; Berthault, P. J . Phy. Chem. A 1997, 101, 2536. Espinosa,
J .-F.; Montero, E.; Vian, A.; Garc´ıa, J . L.; Dietrich, H.; Schmidt, R. R.;
Mart´ın-Lomas, M.; Imberty, A.; Can˜ada, F. J .; J ime´nez-Barbero, J . J .
Am. Chem. Soc. 1998, 120, 1309 and references therein.
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1993, 36, 778. Nagy, J . O.; Wang, P.; Gilbert, J . H.; Schaefer, M. E.;
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35, 4501. Michael, K.; Wittmann, V.; Ko¨nig, W.; Sandow J .; Kessler,
H. Int. J . Pept. Protein Res. 1996, 48, 59. Bertozzi, C. R.; Cook, D. G.;
Kobertz, W. R.; Gonzalez-Scarano, F.; Bednarski, M. D. J . Am. Chem.
Soc. 1992, 114, 10639.
(6) C-Glycosylated dipeptides and related structures are known: (a)
Sutherlin, D. P.; Stark, T. M.; Hughes, R.; Armstrong, R. W. J . Org.
Chem. 1996, 61, 8350. (b) Arya, P.; Dion, S.; Shimizu, G. K. H. Bioorg.
Med. Chem. Lett. 1997, 7, 1537. (c) Wang, L.-X.; Tang, M.; Suzuki, T.;
Kitajima, K.; Inoue, Y.; Inoue, S.; Fan, J .-Q.; Lee, Y. C. J . Am. Chem.
Soc. 1997, 119, 11137. (d) Tedebark, U.; Meldal, M.; Panza, L.; Bock,
K. Tetrahedron Lett. 1998, 39, 1815. (e) Lowary, T.; Meldal, M.;
Helmbolt, A.; Vasella, A.; Bock, K. J . Org. Chem. 1998, 63, 9657.
10.1021/jo990253e CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/03/1999

5454 J . Org. Chem., Vol. 64, No. 15, 1999
Pearce et al.
Sch em e 1a
motif represented by general structure 1. Four structur-
ally distinct C-glycosyl tyrosines 6a , 6b, 6c, and 10 have
been generated and these derivatives are based on
D-mannose, a disaccharide unit, L-rhamnose, and an
unsaturated 2,3-dideoxy furanosyl derivative, respec-
tively. We view a primary role for C-glycosyl amino acids
as building blocks for peptide synthesis, and the success-
ful incorporation of the Fmoc-protected C-mannosyl
tyrosine 11a into representative examples of both linear
and cyclic oligopeptides, using a combination of solid
phase and solution synthesis techniques, is also demon-
strated.
An analysis of C-glycosyl tyrosines 1 offered various
options for synthesis and the route shown in Schemes 1
and 2 represents a convergent and flexible approach to
this class of molecule. The crucial C-glycoside linkage is
established using an organozinc species as a nucleophilic
C-glycosyl “acceptor”,8 and the synthesis of the C-man-
nosyl tyrosine 6a , which has been optimized (23% overall
yield from 2a ), serves to illustrate all aspects of the
strategy that has been developed. Reaction of 3,4,5-tri-
O-acetyl-D-glucal (2a ) (in the presence of BF3‚OEt2) with
the organozinc reagent prepared from 4-iodobenzyl bro-
mide gave 3a as a 3.5:1 mixture of R and â isomers which
were separated by chromatography.9 In a general sense,
the R/â selectivity associated with this C-glycosylation
method does depend on the nature of the glycal compo-
nent, and very high R selectivity has been observed with
a number of substrates8 (see also 9 below). Those factors
responsible for determining this R/â ratio are, however,
unclear, and efforts are underway to both understand and
improve the general level of stereocontrol available with
(7) For occurrence and synthesis of O-glycosyl tyrosines and vari-
ants, see: (a) Williams, D. H.; Rajananda, V.; Williamson, M. P.;
Bojesen, G. Top. Antibiot. Chem. 1980, 5, 119. (b) Kramer, K. J .;
Hopkins, T. L.; Ahmed, R. F.; Mueller, D.; Lookhart, G. Arch. Biochem.
Biophys. 1980, 205, 146. (c) Isobe, M.; Kondo, N.; Imai, K.; Yamashita,
O.; Goto, T. Agric. Biol. Chem. 1981, 45, 687. (d) Lu, P.-W.; Kramer,
K. J .; Seib, P. A.; Mueller, D. D.; Ahmed, R.; Hopkins, T. L. Insect
Biochem. 1982, 12, 377. (e) Messner, P.; Christian, R.; Kolbe, J .; Schulz
G.; Sleytr, U. B. J . Bacteriol. 1992, 174, 2236. (f) Lomako, J .; Lomako,
W. M.; Whelan, W. J . Carbohydr. Res. 1992, 227, 331. (g) Morita, H.;
Yamamiya, T.; Takeya, K.; Itokawa, H. Chem. Pharm. Bull. 1992, 40,
1352. (h) Rodriguez, I. R.; Whelan, W. J . Biochem. Biophys. Res.
Commun. 1985, 132, 829. (i) Ahmad, S. A.; Hopkins, T. L.; Kramer,
K. J . Insect Biochem. Mol. Biol. 1996, 26, 49. (j) J ansson, A. M.; J ensen,
K. J .; Meldal, M.; Lomako, J .; Lomako, W. M.; Olsen C. E.; Bock, K. J .
Chem. Soc., Perkin Trans. 1 1996, 1001. (k) Skelton, N. J .; Harding,
M. M.; Mortishire-Smith, R. J .; Rahman, S. K.; Williams, D. H.; Rance
M. J .; Ruddock, J . C. J . Am. Chem. Soc. 1991, 113, 7522.
a
Key: (a) 4-IC6H4CH2ZnBr, BF3‚OEt2, CH2Cl2, -30 to 0 °C,
0.5 h; (b) 3a , 3b (see text) or 3c, PdCl2(o-Tol3P)2, DMA/THF then
4 in THF, rt to 50 °C, 1 h; (c) NMO, OsO4 (10 mol %), tert-BuOH/
Me2CO/H2O, rt, 24 h. (d) Ac2O, DMAP, py, 0 °C, 0.5 h.
(8) Thorn, S. N.; Gallagher, T. Synlett 1996, 185. For a related
application of this zinc methodology see ref 5l.
this process. With 3a -c, only modest R selectivity was
observed (2 to 3.5:1) but the need to separate isomers at
this first stage did not constitute a major barrier. The
â-C-glycoside isomers are also available, but we have only
pursued the synthesis of C-glycosyl tyrosines using the
R-anomers as this corresponds to the configuration as-
sociated with most of the naturally occurring O-glyco-
peptides of this type.7
Introduction of the R-amino acid moiety into 3a was
achieved using J ackson’s method which involved a Pd-
(0)-mediated coupling with the enantiomerically pure zinc
reagent 4.10,11 We found, however, that the efficiency of
this transformation was sensitive to the conditions used
(9) Stothers, J . B. Carbon-13 NMR Spectroscopy; Academic Press:
New York, 1973; Chapter 3. The numbering system used for both the
C-glycoside adducts (3, 9) and the C-glycopeptides (5, 6, 10-13) is
shown within Scheme 1. Stereochemical assignment of the individual
R and â isomers associated with 3a [and 3b and 3c] was achieved using
13C and 1H NMR as previously described for a series of structurally
related C-glycosides.8 For 3a R isomer: C(6) 69.5; J 5, 6.8 Hz. For 3a
6
â isomer: C(6) δC 74.2; J 5, 9.0 Hz. NOE was observed between C(2)
6
and C(6) in â-isomer only (see Scheme 1 for numbering system). For
other applications of this method, see: Dawe, R. D.; Fraser-Reid, B.
J . Org. Chem. 1984, 49, 522. Orsini, F.; Pelizzoni, F. Carbohydr. Res.
1993, 243, 183. Moineau, C.; Bolitt, V.; Sinou, D. J . Chem. Soc., Chem.
Commun. 1995, 1103. Brakta, M.; Lhoste, P.; Sinou, D. J . Org. Chem.
1989, 54, 1890. Achmatowicz has noted that the magnitude of J 5,6 is
also diagnostic of the “anomeric” configuration in C-glycosides of this
type: Achmatowicz, O.; Bukowski, P. Rocz. Chem. 1973, 47, 99.

C-Glycosyl Tyrosines
J . Org. Chem., Vol. 64, No. 15, 1999 5455
Sch em e 2a
case neither the C-glycosylation step nor the final O-
acetylation procedure has yet been fully optimized.12
We were also interested in generating a C-glycosyl
amino acid based on a pentose derivative. Lewis acid-
mediated reaction of crude di-O-acetyl-D-arabinal (7) with
the zinc reagent derived from 4-iodobenzyl bromide gave
the C-glycoside 9 in 34% isolated yield. This is an
acceptable result, bearing in mind that oxonium ion 8 is
a likely intermediate in this process, together with the
known sensitivity of 7 toward acids.13 Further, C-glyco-
side 9 was obtained as a single stereoisomer, the struc-
ture of which was assigned on the basis of NOE experi-
ments.14 Pd-Mediated cross coupling of 4 with 9 gave the
protected C-furanosyl tyrosine 10 in 78% yield (Scheme
2).15
To realize the potential of C-glycosyl amino acids as
tools for probing the structure and function of carbohy-
drates, including O-glycopeptides, an ability to incorpo-
rate these structural units within larger and more
relevant peptide frameworks is required. With solid-
phase peptide synthesis (SPPS) as the method of choice
for assembling oligopeptides, including O-glycopeptides,16
our aim was to incorporate C-glycosyl tyrosine units
within simple, but nonetheless representative examples
of both linear and cyclic oligopeptides. We chose the cyclic
C-glycopeptide 13 as a target since this is closely related
to a family of C2-symmetric peptides [cyclo(Gly-Xaa-
Gly)2]17,18 which have attracted significant interest and
offer the additional benefit of simple and well-defined
NMR spectra.
a
Key: (a) 4-IC6H4CH2ZnBr, BF3‚OEt2, CH2Cl2, -30 to 0 °C,
0.5 h. (b) PdCl2(o-Tol3P)2, DMA/THF then 4 in THF, rt to 50 °C,
1 h.
and, in the examples that we have studied, our best yields
were obtained when 4 was added to a solution of 3a
already containing the Pd(0) catalyst. These optimized
conditions afforded 5a in 82% yield. Osmium-mediated
dihydroxylation of 5a was highly selective12 leading to
the mannose derivative exclusively, and O-acetylation
gave the fully protected C-mannosyl tyrosine 6a in 48%
overall yield from 5a .
Since tyrosine is found in nature linked to more
elaborate oligosaccharides,7e we have applied this strat-
egy to both the synthesis of a structurally more complex
C-glycosyl amino acid as well as variants derived from
alternative monosaccharide precursors. Starting from
D-maltal (2b), application of the sequence shown in
Scheme 1 led to a disaccharide C-glycosyl tyrosine variant
6b. In this instance, it was more convenient to convert
the intermediate C-glycoside 3b (as a 2:1 mixture of R
and â-isomers) to 5b prior to separation of the R- and
â-C-glycosides. Dihydroxylation of 5b was completely
stereoselective and the fully protected C-[ManR1f4Man]
analogue 6b was obtained in ca. 13% (optimized) overall
yield from D-maltal. Similarly, starting with L-rhamnal
(2c), the chemistry shown in Scheme 1 provided the
L-configured glycosyl tyrosine 6c, although in this latter
To exploit these C-glycosyl amino acid components in
SPPS, access to the appropriately protected monomers
(13) Attempts to rigorously purify 7 by chromatography led to
extensive decompositon to give 2-(acetoxymethyl)furan, and 7 was
prepared and used directly in crude form. The sensitivity of 7 under
acidic C-glycosylation conditions has been noted: Byerley, A. L. J .;
Kenwright, A. M.; Steel, P. G. Tetrahedron Lett. 1996, 37, 9092.
(14) The assignment of the stereochemistry of C-glycoside 9 is
primarily based on NOE experiments and at this time should be viewed
as tentative. Irradiation of 1-H (benzylic CH2) resulted in an enhance-
ment (2%) of 5-H, and irradiation of 6-H resulted in an enhancement
(2%) of 2-H. No enhancement of 5-H was observed on irradiation of
2-H.
(15) Dihydroxylation of 10 results in a mixture of both syn-diol
isomers but only a marginal degree of diastereoselectivity was ob-
served, and this has not been pursued.
(16) Kunz, H. Angew. Chem., Int. Ed. Engl. 1987, 26, 294. Kihlberg
J .; Elofsson, M. Curr. Med. Chem. 1997, 4, 85. Arsequell, G.; Valencia,
G. Tetrahedron: Asymmetry 1997, 8, 2839. For the synthesis of
peptides incorporating glycosylated tyrosine units, see: Varga, L.;
Horvat, S.; Lemieux, C.; Schiller, P. W. Int. J . Pept. Protein Res. 1987,
30, 371. Horvat, S.; Varga L.; Horvat, J . Synthesis 1986, 209. Horvat,
S.; Varga, L.; Horvat, J .; Pfu¨tzner, A.; Suhartono, H.; Ru¨bsamen-
Waigmann, H. Helv. Chim. Acta 1991, 74, 951.
(17) Kopple, K. D.; Go, A.; Logan, R. H.; Savrda, J . J . Am. Chem.
Soc. 1972, 94, 973. Tanizawa, K.; Okumura, K.; Itoh, H.; Hatanaka,
Y.; Kanaoka, Y. Chem. Pharm. Bull. 1986, 34, 4001.
(18) Synthesis of a model cyclic hexapeptide cyclo-[Gly-L-Phe-Gly]2
(14) (Schwyzer, R.; Tun-Kyi, A. Helv. Chim. Acta 1962, 45, 859.
Schwyzer, R.; Carrio´n, J . P.; Gorup, B.; Nolting, H.; Tun-Kyi, A. Helv.
Chim. Acta 1964, 47, 441), which lacks any bulky carbohydrate units,
was carried out by cyclization19 of the corresponding linear hexapeptide
(H-Gly-L-Phe-Gly-Gly-L-Phe-Gly-OH) using HOBt/TBTU. In our hands,
this reaction proceeded in 41% yield as compared to the cyclization of
12 to give 13 (23% yield). Cyclic hexapeptides are also available via
cyclodimerization of a tripeptide unit using azide activation: Kopple,
K. D. J . Pharm. Sci. 1972, 61, 1345. While this method was successfully
applied to the synthesis of the model cyclic hexapeptide (cyclo-[Gly-
L-Phe-Gly]2) 14, it is known that the presence and position of a bulky
aryl amino acid component within the tripeptide unit does influence
the yield of this reaction (Konishi, M.; Yoshida, N.; Izumiya, N. Bull.
Chem. Soc. J pn. 1971, 44, 2801). We were not able to prepare the cyclic
C-glycopeptide derivative 13 using this dimerization methodology and
details of the synthesis and characterization of the precursor linear
tripeptide {H-L-Tyr[C-(Ac4-R-D-Man)]-Gly-Gly-NHNH2} and of 14 are
available in the Supporting Information.
(10) J ackson, R. F. W.; Wishart, N.; Wood, A.; J ames, K.; Wythes,
M. J . J . Org. Chem. 1992, 57, 3397. J ackson, R. F. W.; Turner, D.;
Block, M. H. Synlett 1996, 862. Dunn, M. J .; J ackson, R. F. W.;
Pietruszka, J .; Wishart, N.; Ellis, D.; Wythes, M. J . Synlett 1993, 499.
Fraser, J . L.; J ackson R. F. W.; Porter, B. Synlett 1994, 379.
(11) For other applications of Pd-mediated cross coupling reactions
of organozinc reagents in the synthesis of amino acids, see: Evans, D.
A.; Bach, T. Angew. Chem., Int. Ed. Engl. 1993, 32, 1326. Walker, M.
A.; Kaplita, K. P.; Chen, T.; King, H. D. Synlett 1997, 169. Malan, C.;
Morin, C. Synlett 1996, 167.
(12) Fraser-Reid, B.; Molino, B. F.; Magdzinski, L.; Mootoo, D. R.
J . Org. Chem. 1987, 52, 4505. In the case of 6a we have carried out
the dihydroxylation step (and O-acetylation) prior to the Pd-mediated
coupling of 4 without deleterious effect. However, when applied to the
L-rhamnal-derived C-glycoside 3c, while dihydroxylation/acetylation
of this intermediate proceeded smoothly, the subsequent attempt at
the Pd(0) coupling step (involving 4) surprisingly failed.

5456 J . Org. Chem., Vol. 64, No. 15, 1999
Pearce et al.
Sch em e 3a
11a , that these novel C-glycosyl amino acids will function
as building blocks for the solid-phase synthesis of linear
and cyclic C-glycopeptides.20,21 The chemistry described
in this paper extends the range of C-glycosyl amino acids
available, with these derivatives being important both
in relation to O-glycopeptides (as a means to study the
influence of glycosylation on glycopeptide structure) but
also as novel amino acids in their own right. The robust
nature of the C-linkage offers advantages where the
naturally occurring O-glycoside proves to be sensitive,
and work to extend the applications associated with
C-glycosyl amino acids is continuing.
Exp er im en ta l Section
For general experimental procedures, including details of
HPLC purification methods, and procedures used to generate
activated zinc and Pd/C, see Supporting Information.
4-(5,7-Di-O-acetyl-2,6-an h ydr o-1,3,4-tr ideoxy-â-D-er yth r o-
h ep t-3-en itol-1-yl)iod oben zen e (â-3a ) a n d 4-(5,7-Di-O-
acetyl-2,6-an h ydr o-1,3,4-tr ideoxy-r-D-er yth r o-h ept-3-en itol-
1-yl)iod oben zen e (r-3a ). Zinc dust (4.80 g, 0.08 mol) was
activated according to general procedure A (see Supporting
Information), using dry THF (5 mL), 1,2-dibromoethane (253
µL, 2.94 mmol) and TMSCl (281 µL, 2.21 mmol). A solution of
4-iodobenzyl bromide (10.91 g, 0.04 mol) in dry THF (20 mL)
was added dropwise, over 1 h, to the stirred suspension of
activated zinc at 0 °C under argon in the dark. After addition,
TLC (ethyl acetate-light petroleum, 1:5) indicated no iodide
(Rf 0.8) remained, and the mixture was warmed to room
temperature and allowed to settle. The zincate solution was
transferred away from unreacted zinc via gastight syringe into
a flask purged with argon, and the solvent was removed in
vacuo (bath temp 35 °C). Dry dichloromethane (20 mL) was
added to the residue, and the solution was cooled to -30 °C
under argon in the dark. A solution of tri-O-acetyl-D-glucal (2a )
(5.88 g, 0.02 mol) in dry dichloromethane (10 mL) was added
to the zincate, followed by BF3‚OEt2 (13.3 mL, 0.11 mol). The
mixture was immediately warmed to 0 °C and stirred for 15
min, after which time TLC (ethyl acetate-light petroleum, 1:3)
indicated no glucal (Rf 0.3) and a major product (Rf 0.4). The
reaction mixture was warmed to room temperature, then
diluted with dichloromethane (40 mL), and washed with brine
(40 mL); and the organic layer was dried (Na2SO4) and filtered;
and the solvent was removed in vacuo. The residue was
purified by flash chromatography (ethyl acetate-light petro-
leum, 1:3) to afford the title compounds (7.0 g, 75%) as a 3.5:1
mixture of R:â isomers as determined by 1H NMR analysis.
Further flash chromatography (ethyl acetate-light petroleum,
1:3) afforded pure 4-(5,7-di-O-acetyl-2,6-anhydro-1,3,4-trideoxy-
â-D-erythro-hept-3-enitol-1-yl)iodobenzene (â-3a ), as a colorless
oil: [R]D19 +90.7 (c 1.8, CHCl3); IR (film) 1738vs (CdO), 1486s,
a
Key: (a) H2, 10% Pd/C, MeOH, rt, 1 h. (b) TFA, CH2Cl2, rt, 1
h. (c) FmocOSuc, Et3N, MeCN/H2O, rt, 0.75 h. (d) SPPS (see
Supporting Information). (e) HOBt, DIEA, TBTU (2-(1H-benzot-
riazol-1-yl)-1,1,3,3,-tetramethyluronium tetrafluoroborate), DMF,
rt, 26 h, followed by reverse phase HPLC (see Supporting Informa-
tion).
is mandatory. The conversion of 6a and 6b to the
corresponding Fmoc-protected amino acids 11a (72%
overall yield) and 11b (61% overall yield) was carried out
as shown in Scheme 3. Using Fmoc-Gly-PEG-PS(HMP)
resin, and starting with the C-mannosyl derivative 11a ,
we have achieved the synthesis of hexapeptide 12,
containing two units of C-mannosyl tyrosine (and four
glycine units), which was isolated in 22% yield following
purification by reverse phase HPLC. Linear hexapeptide
12 was then converted to cyclic hexapeptide 13 (isolated
in 23% yield), a transformation that was conducted in
solution using the conditions described by Kessler.19 This
cyclization step18 did not appear to be significantly
impeded by the presence of the bulky C-glycosyl units
and the C2-symmetry of the cyclic derivative 13, which
was evident from 1H NMR, and also served to confirm
the integrity of the linear precursor 12.
1
1369s, 1232s (C-O), 1047s, 1007s cm-1; H NMR (300 MHz,
CDCl3) δ 7.60 (2 H, d, J 8.0, Ar o-I), 6.98 (2 H, d, J 8.0, Ar
m-I), 5.77 (1 H, dt, J 3,4 10.4, J 2,3 ) J 3,5 1.5, 3-H), 5.70 (1 H, dt,
J 3,4 10.4, J 2,4 ) J 4,5 2.0, 4-H), 5.22 (1 H, ddd, J 5,6 9.0, J 4,5 2.0,
J 3,5 1.5, 5-H), 4.36 (1 H, m, 2-H), 4.19 (2 H, m, 7-Ha,b), 3.70 (1
H, ddd, J 5,6 9.0, J 6,7b 5.0, J 6,7a 3.5, 6-H), 2.87 (1 H, dd, J 1a,1b
13.7, J 1a,2 6.6, 1-Ha), 2.72 (1 H, dd, J 1a,1b 13.7, J 1b,2 6.4, 1-Hb),
2.08 (3 H, s, CH3), 2.07 (3 H, s, CH3); 13C NMR (75 MHz,
CDCl3) δ 170.9, 170.3 (2 × COCH3), 137.3 (Ar o-I), 136.9 (Cipso),
131.7 (Ar m-I), 131.6 (3-C), 125.6 (4-C), 91.8 (C-I), 75.2 (2-C),
74.2 (6-C), 65.5 (5-C), 63.5 (7-C), 40.9 (1-C), 21.0, 20.9 (2 ×
COCH3); MS (CI) m/z 431 (M + H+, 15%), 371 [(M + H -
In summary, C-glycosides corresponding to a repre-
sentative series of tyrosine O-glycoconjugates have been
synthesized for the first time. We have also demon-
strated, using the Fmoc-protected C-mannosyl tyrosine
(20) There are a number of incentives for developing the chemistry
of cyclic C-glycopeptides, other than to prove the viability of C-glycosyl
amino acids as peptide building blocks. RA-XIV,7g
a glycosylated
tyrosine-containing cyclic peptide displays antitumor activity, and the
antibiotic ramoplanose7k incorporates an R-linked mannosyl-based
trisaccharide. Recently, glucosylated cyclic hexapeptides have also been
examined as molecular receptors for amino acids.21
(21) Leipert, D.; Nopper, D.; Bauser, M.; Gauglitz, G.; J ung, G.
Angew. Chem., Int. Ed. Engl. 1998, 37, 3308.
(19) For the application of the HOBt/TBTU method for the “head-
to-tail” cyclization of linear hexapeptides, see: Zimmer, S.; Hoffmann,
E.; J ung, G.; Kessler, H. Liebigs. Ann. Chem. 1993, 497.

C-Glycosyl Tyrosines
J . Org. Chem., Vol. 64, No. 15, 1999 5457
AcOH)+, 100], 311 [(M + H - 2AcOH)+, 94), 217 (p-ITol+, 50),
213 [(M - p-ITol)+, 56]; HRMS for C17H20IO5 (M + H+) calcd
431.0356, found 431.0393.
line N-oxide (247 mg, 2.11 mmol) and then OsO4 (2.5 wt % in
tert-BuOH, 2.20 mL, 0.18 mmol) were added to a stirred
solution of NR-(tert-butoxycarbonyl)-C-(4,6-di-O-acetyl-2,3-
dideoxy-R-D-erythro-hex-2-enopyranosyl)-L-tyrosine benzyl es-
ter (5a ) (1.0 g, 1.76 mmol) in acetone-water (5:1, 15 mL) at
room temperature. After 24 h, TLC (ethyl acetate-light
petroleum, 3:2) indicated no starting material (Rf 0.8) and
product (Rf 0.2). Sodium metabisulfite (70 mg, 0.37 mmol) in
water (2 mL) was added, and the mixture was stirred vigor-
ously for 0.5 h. Ethyl acetate (15 mL) was added, and the
mixture was filtered through Celite into a separating funnel
and washed with brine (2 mL). The aqueous layer was
extracted with ethyl acetate (3 × 15 mL), dried (Na2SO4), and
filtered, and the solvent was removed in vacuo. The residue
was purified by flash chromatography (eluent gradient, ethyl
acetate-light petroleum, 2:1 to ethyl acetate) to afford NR-
(tert-butoxycarbonyl)-C-(4,6-di-O-acetyl-R-D-mannopyranosyl)-
L-tyrosine benzyl ester (628 mg, 58%), as a colorless oil. [R]D25
+20.8 (c 1.0, CHCl3); IR (film) 3350br, 2933w, 1734vs (CdO),
1694s (CdO), 1523m, 1368m, 1239s (C-O), 1167m, 1055s
Continued elution gave 4-(5,7-di-O-acetyl-2,6-anhydro-1,3,4-
trideoxy-R-D-erythro-hept-3-enitol-1-yl)iodobenzene (R-3a ), as
19
a colorless oil: [R]D +61.7 (c 1.0, CHCl3); IR (film) 1739vs
(CdO), 1485s, 1370s, 1233s (C-O), 1046s, 1007s cm-1 1H
;
NMR (300 MHz, CDCl3) δ 7.62 (2 H, d, J 8.0, Ar o-I), 7.00 (2
H, d, J 8.0, Ar m-I), 5.89 (1 H, ddd, J 3,4 10.4, J 2,3 2.0, J 3,5 1.5,
3-H), 5.81 (1 H, dt, J 3,4 10.4, J 2,4 ) J 4,5 2.0, 4-H), 5.12 (1 H, m,
5-H), 4.42 (1 H, ddt, J 1a,2 8.0, J 1b,2 6.0, J 2,3 ) J 2,4 2.0, 2-H),
4.22 (1 H, dd, J 7a,7b 11.9, J 6,7a 6.8, 7-Ha), 4.13 (1 H, dd, J 7a,7b
11.9, J 6,7b 3.5, 7-Hb), 4.00 (1 H, td, J 5,6 ) J 6,7a 6.8, J 6,7b 3.5,
6-H), 2.95 (1 H, dd, J 1a,1b 14.0, J 1a,2 8.0, 1-Ha), 2.77 (1 H, dd,
J 1a,1b 14.0, J 1b,2 6.0, 1-Hb), 2.10 (3 H, s, CH3), 2.07 (3 H, s, CH3);
13C NMR (75 MHz, CDCl3) δ 170.8, 170.4 (2 × COCH3), 137.5
(Ar o-I), 137.4 (Cipso), 132.3 (3-C), 131.4 (Ar m-I), 124.2 (4-C),
91.8 (C-I), 72.6 (2-C), 69.5 (6-C), 65.0 (5-C), 62.9 (7-C), 39.0
(1-C), 21.1, 20.8 (2 × COCH3); MS (CI) m/z 431 (M + H+, 1%),
371 [(M + H - AcOH)+, 42], 311 [(M + H - 2AcOH)+, 100),
1
217 (p-ITol+, 38), 213 [(M - p-ITol)+, 20]; HRMS for C17H20
IO5 (M + H+) calcd 431.0356, found 431.0358.
-
cm-1; H NMR (400 MHz, CDCl3) δ 7.35-7.30 (5 H, m, Ph),
7.10 (2 H, d, J 7.2, Ar), 6.97 (2 H, d, J 7.2, Ar), 5.16 (1 H, d, J
12.3, PhCHH′), 5.10 (1 H, d, J 12.3, PhCHH′), 4.99 (2 H, m,
4-H and NH), 4.59 (1 H, dt, J R,ΝΗ 8.0, J R,â ) J R,â′ 6.0, R-H),
4.37 (1 H, dd, J 6a,6b 12.0, J 5,6a 7.0, 6-Ha), 4.15 (1 H, m, 1-H),
4.08 (1 H, dd, J 6a,6b 12.0, J 5,6b 3.0, 6-Hb), 3.98-3.92 (2 H, m,
5-H and 3-H), 3.81 (1 H, t, J 1,2 ) J 2,3 3.7, 2-H), 3.11-2.99 (2
H, m, â-H, â′-H), 2.97-2.84 (2 H, m, γ-H, γ′-H), 2.12 (3 H, s,
COCH3), 1.97 (3 H, s, COCH3), 1.41 (9 H, s, (CH3)3C); 13C NMR
(100 MHz, CDCl3) δ 171.7 (COCH2), 171.2, 170.8 (2 × COCH3),
155.1 (OCON), 136.2, 135.1, 134.1, 129.5, 129.3, 129.2, 129.0,
128.6, 79.9 ((CH3)3C), 76.6, 70.7, 70.6, 70.1, 69.6, 67.1 (1-C,
2-C, 3-C, 4-C, 5-C, PhCH2), 62.4 (6-C), 54.4 (R-C), 37.7, 35.4
(â-C, γ-C), 28.2 ((CH3)3C), 21.0, 20.7 (2 × COCH3); MS (EI)
m/z 498 [(M - BocNH2)+, 20%), 247 (C10H15O7+, 40), 91
(C7H7+, 100), 57 (C4H9+, 75); HRMS for C27H30O9 (M -
BocNH2)+ calcd 498.1890, found 498.1893.
Nr-(ter t-Bu toxycar bon yl)-C-(4,6-di-O-acetyl-2,3-dideoxy-
r-D-er yth r o-h ex-2-en op yr a n osyl)-L-tyr osin e ben zyl ester
(5a ). Zinc dust (1.71 g, 0.03 mol) was activated according to
general procedure A, using dry THF (1.5 mL), 1,2-dibromoet-
hane (90 µL, 1.04 mmol), and TMSCl (100 µL, 0.79 mmol). A
solution of Boc-L-Ala(I)-OBn10 (3.53 g, 8.71 mmol) in dry THF
(4.5 mL) was added to the stirred suspension of activated zinc
at 35 °C under argon in the dark. After 2 h, TLC (ethyl
acetate-light petroleum, 1:3) indicated no iodide (Rf 0.8)
remained, and the mixture was cooled to room temperature
and allowed to settle. Bis(tri-o-tolylphosphine)palladium dichlo-
ride (236 mg, 0.33 mmol) was added to a stirred solution of
(R-3a ) (0.94 g, 2.18 mmol) in dry N,N-dimethylacetamide (3
mL) and dry THF (1 mL) at room temperature under argon.
After 15 min, the zincate solution was transferred away from
unreacted zinc via gastight syringe and added to the yellow
iodobenzene mixture. After 1 h of stirring at room temperature,
the mixture was heated to 50 °C. After 2 h, TLC (ethyl
acetate-light petroleum, 1:3) indicated no iodobenzene (Rf 0.5)
and a major product (Rf 0.2), and the green reaction mixture
was allowed to cool to room temperature. Ethyl acetate (100
mL) was added, the mixture was filtered through Celite into
a separating funnel, then washed with saturated aqueous NH4-
Cl (15 mL), brine (15 mL), dried (Na2SO4) and filtered, and
the solvent was removed in vacuo. The residue was purified
by flash chromatography (eluent gradient, light petroleum to
ethyl acetate-light petroleum, 2:3) to afford NR-(tert-butoxy-
carbonyl)-C-(4,6-di-O-acetyl-2,3-dideoxy-R-D-erythro-hex-2-enopy-
ranosyl)-L-tyrosine benzyl ester (5a ) (1.0 g, 82%), as a colorless
oil: [R]D26 +27.4 (c 1.0, CHCl3); IR (film) 3375br (N-H), 2977w,
1744vs (CdO), 1715vs (CdO), 1500m, 1358m, 1237s (C-O),
NR-(ter t-Bu toxyca r bon yl)-C-(2,3,4,6-tetr a -O-a cetyl-R-D-
m a n n op yr a n osyl)-L-tyr osin e Ben zyl Ester (6a ). Acetic
anhydride (0.48 mL, 5.09 mmol) was added dropwise over 1
min to a stirred solution of NR-(tert-butoxycarbonyl)-C-(4,6-di-
O-acetyl-R-D-mannopyranosyl)-L-tyrosine benzyl ester (628 mg,
1.02 mmol) and DMAP (6.2 mg, 0.05 mmol) in dry pyridine (7
mL) at 0 °C under nitrogen. After 25 min, TLC (ethyl acetate-
light petroleum, 2:1) indicated no diol (Rf 0.2) and product (Rf
0.6), and the reaction was quenched by the addition of water
(2 mL). The mixture was allowed to warm to room tempera-
ture, brine (2 mL) was added, and the aqueous layer was
extracted with ethyl acetate (3 × 15 mL). Combined extracts
were washed with 2 M hydrochloric acid (7 × 5 mL), dried
(Na2SO4), and filtered, and the solvent was removed in vacuo
(toluene azeotrope × 3). The residue was purified by flash
chromatography (eluent gradient, ethyl acetate-light petro-
leum, 2:3 to ethyl acetate-light petroleum, 1:1) to afford NR-
(tert-butoxycarbonyl)-C-(2,3,4,6-tetra-O-acetyl-R-D-mannopy-
ranosyl)-L-tyrosine benzyl ester (6a ) (591 mg, 83%), as a
colorless solid: mp 53-55 °C; analytical chiral HPLC (Rt 23.0
1
1166s, 1050m cm-1; H NMR (400 MHz, CDCl3) δ 7.38-7.28
(5 H, m, Ph), 7.10 (2 H, d, J 7.8, Ar), 6.98 (2 H, d, J 7.8, Ar),
5.87 (1 H, ddd, J 2,3 10.5, J 1,2 2.4, J 2,4 1.6, 2-H), 5.79 (1 H, dt,
J
2,3 10.5, J 1,3 ) J 3,4 2.0, 3-H), 5.20-5.08 (3 H, m, PhCH2, 4-H),
28
5.03 (1 H, br d, J NH,CHR 8.0, NH), 4.61 (1 H, dt, J NH,CHR 8.0,
J CHR,CHâ ) J CHR,CHâ′ 6.0, R-H), 4.41 (1 H, m, J 1,CHγ 8.0, J 1,CHγ′
6.3, J 1,3 2.0, 1-H), 4.23 (1 H, dd, J 6a,6b 11.8, J 5,6a 6.6, 6-Ha), 4.15
(1 H, dd, J 6a,6b 11.8, J 5,6b 3.4, 6-Hb), 3.99 (1 H, td, J 4,5 ) J 5,6a
6.6, J 5,6b 3.4, 5-H), 3.10 (1 H, dd, J CHâ,CHâ′ 8.0, J CHR,CHâ 6.0, â-H),
3.03 (1 H, dd, J CHâ,CHâ′ 8.0, J CHR,CHâ′ 6.0, â′-H), 3.00 (1 H, dd,
min); [R]D +6.6 (c 1.6, CHCl3); IR (KBr) 3370br (N-H),
2976w, 1746vs (CdO), 1716s (CdO), 1515m, 1368s, 1228vs
(C-O), 1165s, 1050s cm-1; UV (CH2Cl2) 229 (ꢀ/dm3 mol-1 mL-1
2 200), 263 (650), 259 (650) nm; 1H NMR (400 MHz, CDCl3) δ
7.38-7.29 (5 H, m, Ph), 7.10 (2 H, d, J 8.0, Ar), 7.00 (2 H, d,
J 8.0, Ar), 5.35 (1 H, dd, J 3,4 9.0, J 2,3 3.2, 3-H), 5.22 (1 H, t, J 1,2
) J 2,3 3.2, 2-H), 5.21 (1 H, t, J 3,4 ) J 4,5 9.0, 4-H), 5.16 (1 H, d,
J 12.0, PhCHH′), 5.10 (1 H, d, J 12.0, PhCHH′), 4.97 (1 H, br
d, J NH,CHR 8.3, NH), 4.61 (1 H, m, R-H), 4.29 (1 H, dd, J 6a,6b
12.0, J 5,6a 6.6, 6-Ha), 4.18 (1 H, ddd, J 1,CHγ 8.8, J 1,CHγ′ 5.9, J 1,2
3.2, 1-H), 4.08 (1 H, dd, J 6a,6b 12.0, J 5,6b 3.0, 6-Hb), 4.02 (1 H,
ddd, J 4,5 9.0, J 5,6a 6.6, J 5,6b 3.0, 5-H), 3.05-3.00 (3 H, m, â-H,
â′-H, γ-H), 2.88 (1 H, dd, J CHγ,CHγ′ 14.5, J 1,CHγ′ 5.9, γ′-H), 2.09
(6 H, s, 2 × COCH3), 2.04 (3 H, s, COCH3), 2.01 (3 H, s,
COCH3), 1.41 (9 H, s, (CH3)3C); 13C NMR (100 MHz, CDCl3) δ
171.1, 170.7, 170.2, 170.1, 169.7 (5 × OCO), 155.1 (OCON),
135.25, 135.2, 134.4, 129.6, 129.2, 128.6, 128.55, 128.5, 80.0
((CH3)3C), 75.8, 70.8, 70.0, 68.8, 67.1, 67.0, 62.4 (6-C), 54.4 (R-
J
CHγ,CHγ′ 13.8, J 1,CHγ 8.0, γ-H), 2.77 (1 H, dd, J CHγ,CHγ′ 13.8, J 1,CHγ′
6.3, γ′-H), 2.09 (3 H, s, COCH3), 2.06 (3 H, s, COCH3), 1.41 (9
H, s, (CH3)3C); 13C NMR (100 MHz, CDCl3) δ 171.6 (COCH2),
170.7, 170.3 (2 × COCH3), 155.0 (OCON), 136.2, 135.1, 134.0,
132.4 (2-C), 129.3, 128.5, 128.42, 128.4, 128.0, 123.9 (3-C), 79.8
((CH3)3C), 72.9, 69.4, 67.0, 65.0, 62.9, 54.3 (R-C), 39.1, 37.7 (â-
C, γ-C), 28.2 ((CH3)3C), 21.0, 20.7 (2 × COCH3); MS (FAB+)
m/z 582 (M + H+, 10%), 482 [(M + H - Boc)+, 40], 213 (10),
91 (C7H7+, 100); HRMS for C32H40NO9 (M + H+) calcd
582.2703, found 582.2672.
Nr-(ter t-Bu t oxyca r b on yl)-C-(4,6-d i-O-a cet yl-r-D-m a n -
n op yr a n osyl)-L-tyr osin e Ben zyl Ester . N-Methylmorpho-

5458 J . Org. Chem., Vol. 64, No. 15, 1999
Pearce et al.
C), 37.8, 35.0 (â-C, γ-C), 28.3 ((CH3)3C), 20.9, 20.8, 20.75, 20.7
(4 × COCH3); MS (FAB+) m/z 700 (M + H+, 10%), 600 [(M +
H - Boc)+, 100]. Anal. Calcd for C36H45NO13: C, 61.8; H, 6.5;
N, 2.0. Found: C, 61.7; H, 6.3; N, 2.2.
(4.5 mL) was added to the stirred suspension of activated zinc
at 35 °C under argon in the dark. After 2.5 h, TLC (ethyl
acetate-light petroleum, 1:3) indicated no iodide (Rf 0.8)
remained, and the mixture was cooled to room temperature
and allowed to settle. Bis(tri-o-tolylphosphine)palladium dichlo-
ride (236 mg, 0.33 mmol) was added to a stirred solution of
4-[(2′,3′,4′,6′-tetra-O-acetyl-R-D-glucopyranosyl)-(1′f5)-(7-O-
acetyl-2,6-anhydro-1,3,4-trideoxy-R,â-D-erythro-hept-3-enitol-
1-yl)]iodobenzene (3b ) (1.50 g, 2.09 mmol) in dry N,N-
dimethylacetamide (3 mL) and dry THF (1 mL) at room
temperature under argon. After 15 min, the zincate solution
was transferred away from unreacted zinc via gastight syringe
and added to the yellow iodoarene mixture. After stirring at
room temperature for 0.5 h the mixture was heated to 55 °C.
After 2 h, TLC (ethyl acetate-light petroleum, 2:3) indicated
no iodobenzene (Rf 0.3) and a major product (Rf 0.2), and the
green reaction mixture was allowed to cool to room tempera-
ture. Ethyl acetate (100 mL) was added; the mixture was
filtered through Celite into a separating funnel and then
washed with saturated aqueous NH4Cl (15 mL), brine (15 mL),
dried (Na2SO4), and filtered; and the solvent was removed in
vacuo. The residue was purified by flash chromatography
(eluent gradient, ethyl acetate-light petroleum, 1:4 to 1:1) to
afford the title compounds (1.46 g, 81%) as a 2:1 mixture of
4-[(2′,3′,4′,6′-Tetr a -O-a cetyl-r-D-glu cop yr a n osyl)-(1′f5)-
(7-O-acetyl-2,6-an h ydr o-1,3,4-tr ideoxy-r,â-D-er yth r o-h ept-
3-en itol-1-yl)]iod oben zen e (3b). Zinc dust (1.78 g, 0.03 mol)
was activated according to general procedure A, using dry THF
(2.0 mL), 1,2-dibromoethane (94 µL, 1.09 mmol) and TMSCl
(104 µL, 0.82 mmol). A solution of 4-iodobenzyl bromide (4.05
g, 13.64 mmol) in dry THF (10 mL) was added dropwise over
1 h to the stirred suspension of activated zinc at 0 °C, under
argon in the dark. After an additional 0.5 h at 0 °C, TLC (ethyl
acetate-light petroleum, 1:5) indicated no iodide (Rf 0.8)
remained, and the mixture was warmed to room temperature
and allowed to settle. The zincate solution was transferred
away from unreacted zinc via gastight syringe into a flask
purged with argon, and the solvent was removed in vacuo (bath
temp 35 °C). Dry dichloromethane (10 mL) was added to the
residue, and the solution was cooled to -30 °C under argon in
the dark. A solution of hexa-O-acetyl-D-maltal (2b) (4.49 g, 8.02
mmol) in dry dichloromethane (10 mL) was added to the
zincate, followed by BF3.OEt2 (4.93 mL, 0.04 mol). The mixture
was warmed to 0 °C after 10 min and stirred for an additional
0.5 h, after which time TLC (ethyl acetate-light petroleum,
1:1) indicated no maltal (Rf 0.5) and a major product (Rf 0.6).
The reaction mixture was warmed to room temperature,
diluted with dichloromethane (40 mL), washed with brine (30
mL); the organic (upper) layer was dried (Na2SO4) and filtered;
and the solvent was removed in vacuo. The residue was
purified by flash chromatography (60H; eluent gradient, 15-
35% ethyl acetate in light petroleum) to afford 4-[(2′,3′,4′,6′-
tetra-O-acetyl-R-D-glucopyranosyl)-(1′f5)-(7-O-acetyl-2,6-an-
h yd r o-1 ,3 ,4 -t r id e oxy-R,â-D -er yt h r o-h e p t -3 -e n it ol-1 -
yl)]iodobenzene (3b) (3.92 g, 67%) as an inseparable 2:1
mixture of R/â isomers as determined by 1H NMR analysis,
as a colorless foam: IR (KBr) 1748vs (CdO), 1368m, 1226vs
(C-O), 1038s cm-1; 1H NMR (300 MHz, CDCl3) δ 7.62 (1.3 H,
d, J 8.3, ArR o-I), 7.60 (0.7 H, d, J 8.3, Arâ o-I), 7.00 (1.3 H, d,
J 8.3, ArR m-I), 6.97 (0.7 H, d, J 8.3, Arâ m-I), 5.89 (0.7 H,
ddd, J 3,4 10.5, J 2,3 2.6, J 3,5 2.0, 3-HR), 5.77 (1 H, m, 4-HR, 3-Hâ),
5.67 (0.3 H, dt, J 3,4 10.5, J 2,4 ) J 4,5 2.0, 4-Hâ), 5.47 (0.7 H, dd,
J 2′,3′ 10.3, J 3′,4′ 9.5, 3′-HR), 5.41 (0.3 H, dd, J 2′,3′ 10.3, J 3′,4′ 9.5,
3′-Hâ), 5.32 (0.7 H, d, J 1′,2′ 3.9, 1′-HR), 5.27 (0.3 H, d, J 1′,2′ 4.0,
1′-Hâ), 5.07 (0.7 H, t, J 3′,4′ ) J 4′,5′ 9.5, 4′-HR), 5.05 (0.3 H, t,
J 3′,4′ ) J 4′,5′ 9.5, 4′-Hâ), 4.85 (0.7 H, dd, J 2′,3′ 10.3, J 1′,2′ 3.9, 2′-
HR), 4.82 (0.3 H, dd, J 2′,3′ 10.3, J 1′,2′ 4.0, 2′-Hâ), 4.40-4.03 (7 H,
m, 2-HR,â, 5-HR,â, 5′-HR,â, 6′-HaR,â, 6′-HbR,â, 7-HaR,â, 7-HbR,â), 3.97
(0.7 H, td, J 5,6 ) J 6,7a 7.0, J 6,7b 5.0, 6-HR), 3.62 (0.3 H, ddd, J 5,6
8.4, J 6,7b 5.7, J 6,7a 2.4, 6-Hâ), 2.94 (0.7 H, dd, J 1a,1b 13.9, J 1a,2
8.6, 1-HaR), 2.84 (0.3 H, dd, J 1a,1b 13.8, J 1a,2 6.6, 1-Haâ), 2.75
(0.7 H, dd, J 1a,1b 13.9, J 1b,2 6.0, 1-HbR), 2.70 (0.3 H, dd, J 1a,1b
13.8, J 1b,2 6.2, 1-Hbâ), 2.09-2.01 (15 H, 8 × s observed but not
all signals were cleanly resolved, COCH3); 13C NMR (75 MHz,
CDCl3) δ 170.7-169.5 (10 × C observed, but not all signals
were not fully resolved, COCH3), 137.4 (ArR o-I), 137.2 (Arâ
o-I), 136.8 (Cipso), 132.4 (3-CR), 131.7 (3-Câ), 131.3 (ArR,â m-I),
124.9 (4-Câ), 123.9 (4-CR), 94.3 (1′-CR), 94.1 (1′-Câ), 91.8 (C-
IR,â), 74.9 (2-Câ), 74.7 (6-Câ), 72.8 (2-CR), 70.8, 70.75 (2′-CR, 2′-
1
R/â isomers as determined by H NMR analysis. Flash chro-
matography (60H; eluent gradient, 15-50% ethyl acetate in
light petroleum) afforded the minor â-isomer (NR-(tert-butoxy-
carbonyl)-C-[(2′,3′,4′,6′-tetra-O-acetyl-R-D-glucopyranosyl)-
(1′f4)-(6-O-acetyl-2,3-dideoxy-â-D-erythro-hex-2-enopyranosyl)]-
L-tyrosine benzyl ester) (480 mg) as a colorless foam: analytical
RPHPLC (0-15 min, linear gradient of 60-100% solvent B
30
in solvent A, Rt 10.2 min); [R]D +105.1 (c 1.0 in CHCl3); IR
(KBr) 3376br (N-H), 2976w, 1748vs (CdO), 1716s (CdO),
1368m, 1229vs (C-O), 1166m, 1040s cm-1;1H NMR (400 MHz,
CDCl3) δ 7.37-7.29 (5 H, m, Ph), 7.08 (2 H, d, J 7.8, Ar), 6.96
(2 H, d, J 7.8, Ar), 5.76 (1 H, m, 2-H), 5.65 (1 H, m, 3-H), 5.41
(1 H, t, J 2′,3′ ) J 3′,4′ 10.0, 3′-H), 5.28 (1 H, d, J 1′,2′ 3.9, 1′-H),
5.17 (1 H, d, J 12.2, PhCHH′), 5.11 (1 H, d, J 12.2, PhCHH′),
5.06 (1 H, t, J 3′,4′ ) J 4′,5′ 10.0, 4′-H), 4.98 (1 H, d, J NH,CHR 7.7,
NH), 4.82 (1 H, dd, J 2′,3′ 10.0, J 1′,2′ 3.9, 2′-H), 4.61 (1 H, dt,
J NH,CHR 7.7, J CHR,CHâ ) J CHR,CHâ′ 6.0, R-H), 4.38 (1 H, dd, J 6a,6b
12.0, J 5,6a 2.4, 6-Ha), 4.28 (1 H, m, 1-H), 4.27-4.05 (5 H, m,
4-H, 5′-H, 6-Hb, 6′-Ha, 6′-Hb), 3.64 (1 H, ddd, J 8.3, J 5.9, J 5,6a
2.4, 5-H), 3.08 (1 H, dd, J CHâ,CHâ′ 14.0, J CHR,CHâ 6.0, â-H), 3.03
(1 H, dd, J CHâ,CHâ′ 14.0, J CHR,CHâ′ 6.0, â′-H), 2.92 (1 H, dd,
J
CHγ,CHγ′ 13.5, J 1,CHγ 6.6, γ-H), 2.66 (1 H, dd, J CHγ,CHγ′ 13.5, J 1,CHγ′
7.3, γ′-H), 2.10, 2.09, 2.03, 2.02, 2.01 (5 × 3 H, s, OCH3), 1.41
(9 H, s, (CH3)3C);13C NMR (100 MHz, CDCl3) δ 171.8 (COCH2),
170.9, 170.7, 170.3, 170.1, 169.6 (5 × COCH3), 155.1 (OCON),
135.9, 135.3, 134.1, 132.1 (2-C), 129.8, 129.5, 129.4, 128.65,
128.6, 124.5 (3-C), 94.1 (1′-C), 80.0 ((CH3)3C), 75.4 (1-C), 74.8
(5-C), 70.8 (2′-C), 70.2 (4-C), 69.9 (3′-C), 68.3 (4′-C), 68.1 (5′-
C), 67.1 (PhCH2), 63.9 (6-C), 61.8 (6′-C), 54.5 (R-C), 41.1 (γ-C),
37.9 (â-C), 28.3 ((CH3)3C), 20.9-20.1 (5 × C, COCH3, signals
not fully resolved); MS (ESI+) m/z 892.4 (M + Na+, 25%), 870.4
(M + H+, 15), 770.3 [(M + H2 - Boc)+, 100]; HRMS for C39H48
NO15 (M + H2 - Boc)+: calcd 770.3024, found 770.3054.
-
Continued elution gave NR-(tert-butoxycarbonyl)-C-[(2′,3′,4′,6′-
tetra-O-acetyl-R-D-glucopyranosyl)-(1′f4)-(6-O-acetyl-2,3-
dideoxy-R-D-erythro-hex-2-enopyranosyl)]-L-tyrosine benzyl es-
ter (5b) (950 mg), as a colorless foam: analytical RPHPLC (0-
15 min, linear gradient of 60-100% solvent B in solvent A, Rt
Câ), 70.1, 70.0, 69,9, 69.8, 68.1, 68.0, (3′-CR,â, 5-CR,â, 5′-CR,â
6-CR), 68.3 (4′-CR), 68.2 (4′-Câ), 63.7, 63.4, 61.8, 61.7 (6′-CR,â
,
,
7-CR,â), 40.8 (1-Câ), 38.9 (1-CR), 21.0, 20.9, 20.8, 20.7, 20.63,
20.6 (10 × C, COCH3); MS (FAB+) m/z 741 (M + Na+, 13%),
719 (M + H+, 2), 169 (100); HRMS for C29H36IO13 (M + H+)
calcd 719.1202, found 719.1201.
30
9.6 min); [R]D +63.8 (c 2.6, CHCl3); IR (KBr) 3378br (N-H),
2977w, 1748vs (CdO), 1716s (CdO), 1368m, 1228vs (C-O),
1
1166m, 1040s cm-1; H NMR (300 MHz, CDCl3) δ 7.40-7.30
Nr-(ter t-Bu toxyca r bon yl)-C-[(2′,3′,4′,6′-tetr a -O-a cetyl-
r-D-glu cop yr a n osyl)-(1′f4)-(6-O-a cetyl-2,3-d id eoxy-â-D-
er yth r o-h ex-2-en op yr a n osyl)]-L-t yr osin e Ben zyl E st er
a n d Nr-(ter t-bu toxyca r bon yl)-C-[(2′,3′,4′,6′-tetr a -O-a cetyl-
r-D-glu cop yr a n osyl)-(1′f4)-(6-O-a cet yl-2,3-d id eoxy-r-D-
er yth r o-h ex-2-en op yr a n osyl)]-L-t yr osin e Ben zyl E st er
(5b). Zinc dust (1.71 g, 0.03 mol) was activated according to
general procedure A, using dry THF (1.5 mL), 1,2-dibromoet-
hane (90 µL, 1.04 mmol), and TMSCl (100 µL, 0.79 mmol). A
solution of Boc-L-Ala(I)-OBn10 (3.5 g, 8.63 mmol) in dry THF
(5 H, m, Ph), 7.11 (2 H, d, J 7.9, Ar), 6.97 (2 H, d, J 7.9, Ar),
5.86 (1 H, ddd, J 2,3 10.5, J 1,2 2.4, J 2,4 1.5, 2-H), 5.75 (1 H, dt,
J 2,3 10.5, J 1,3 ) J 3,4 2.0, 3-H), 5.48 (1 H, dd, J 2′,3′ 10.3, J 3′,4′ 9.6,
3′-H), 5.32 (1 H, d, J 1′,2′ 4.0, 1′-H), 5.18 (1 H, d, J 12.2, PhCHH′),
5.12 (1 H, d, J 12.2, PhCHH′), 5.08 (1 H, t, J 3′,4′ ) J 4′,5′ 9.6,
4′-H), 4.99 (1 H, d, J NH,CHR 7.0, NH), 4.86 (1 H, dd, J 2′,3′ 10.3,
J 1′,2′ 4.0, 2′-H), 4.60 (1 H, m, R-H), 4.37 (1 H, m, 1-H), 4.31-
4.06 (6 H, m, 4-H, 5′-H, 6-Ha, 6-Hb, 6′-Ha, 6′-Hb), 3.96 (1 H, dt,
J 7.0, J 5.0, 5-H), 3.13-3.00 (2 H, m, â-H, â′-H), 2.98 (1 H, dd,
J
CHγ,CHγ′ 13.7, J 1,CHγ 8.0, γ-H), 2.75 (1 H, dd, J CHγ,CHγ′ 13.7, J 1,CHγ′

C-Glycosyl Tyrosines
J . Org. Chem., Vol. 64, No. 15, 1999 5459
6.4, γ′-H), 2.10, 2.09, 2.08, 2.04, 2.03 (5 × 3 H, s, COCH3), 1.41
(9 H, s, (CH3)3C); 13C NMR (75 MHz, CDCl3) δ 171.7 (COCH2),
170.7, 170.6, 170.2, 170.1, 169.6 (5 × COCH3), 155.0 (OCON),
136.4, 135.2, 134.1, 132.6 (2-C), 129.4, 128.6, 128.5, 128.4,
128.0, 123.7 (3-C), 94.3 (1′-C), 79.9 ((CH3)3C), 73.2 (1-C), 70.8
(2′-C), 70.0, 69.95, 69.9, 68.0 (3′-C, 4-C, 5-C, 5′-C), 68.3 (4′-C),
67.1 (PhCH2), 63.5, 61.8 (6-C, 6′-C), 54.4 (R-C), 39.2, 37.9 (â-
C, γ-C), 28.3 ((CH3)3C), 20.8-20.1, (5 × C, COCH3, signals not
cleanly resolved); MS (ESI+) m/z 892.4 (M + Na+, 56%), 870.4
signals not cleanly resolved, COCH3), 155.0 (OCON), 135.3,
135.1, 134.3, 129.5, 129.1, 128.5, 128.4, 128.37, 95.8 (1′-C), 79.8
((CH3)3C), 75.1, 71.4, 71.2, 71.0 (1-C, 3-C, 4-C, 5-C), 70.0 (2′-
C), 69.6 (2-C), 69.5 (3′-C), 68.4 (5′-C), 68.0 (4′-C), 67.0 (PhCH2),
62.9 (6-C), 61.4 (6′-C), 54.4 (R-C), 37.7 (â-C), 35.3 (γ-C), 28.2
((CH3)3C), 20.8, 20.7, 20.65, 20.6, 20.55, 20.5, 20.4 (7 ×
COCH3); δC (75 MHz, C6D6) 171.8 (COCH2), 170.2, 170.1, 170.0,
169.7, 169.6, 169.3 (7 × C, COCH3), 155.3 (OCON), 136.0,
135.8, 134.9, 129.7, 129.6, 128.7, 128.65, 96.4 (1′-C), 79.4
((CH3)3C), 75.8 (1-C), 72.0 (3-C, 4-C), 71.5 (5-C), 70.9 (2′-C),
70.2 (2 × C, 2-C), 70.0 (3′-C), 69.2 (5′-C), 68.9 (4′-C), 66.9
(PhCH2), 63.2 (6′-C), 62.0 (6-C), 55.0 (R-C), 37.9 (â-C), 35.2 (γ-
C), 28.3 ((CH3)3C), 20.8, 20.4, 20.35, 20.3, 20.25, 20.2, 20.1 (7
× COCH3); MS (FAB+) m/z 1011 (M + Na+, 30%), 989 (M +
H+, 5), 888 [(M + H2 - Boc)+, 100]; HRMS for C43H54NO19 (M
+ H2 - Boc)+ calcd 888.3290, found 888.3296.
4′-(5-O-Acetyl-2,6-a n h yd r o-1,3,4,7-tetr a d eoxy-r-L-er yth -
r o-h ep t-3-en itol-1-yl) iod oben zen e (r-3c) a n d 4′-(5-O-
a cetyl-2,6-a n h yd r o-1,3,4,7-tetr a d eoxy-â-L-erythro-h ep t-3-
en itol-1-yl) iod oben zen e (â-3c). Zinc dust (2.95 g, 0.05
mmol) was activated according to general procedure A, using
dry THF (2.5 mL), 1,2-dibromoethane (156 µL, 1.81 mmol),
and TMSCl (172 µL, 1.36 mmol). A solution of 4-iodobenzyl
bromide (6.71 g, 0.02 mmol) in dry THF (10 mL) was added
dropwise, over 1 h, to the stirred suspension of activated zinc
at 0 °C under argon in the dark. After addition was complete,
TLC (ethyl acetate-light petroleum, 1:5) indicated no iodide
(Rf 0.8) remained and the mixture was warmed to room
temperature and allowed to settle. The zincate solution was
transferred away from unreacted zinc via a gastight syringe
into a flask purged with argon, and the solvent was removed
in vacuo (bath temp 35 °C). Dry dichloromethane (10 mL) was
added to the residue, and the solution was cooled to -30 °C
under argon in the dark. A solution of 3,4-di-O-acetyl-L-
rhamnal (2c) (2.85 g, 13 mmol) was added to the zincate,
followed by BF3‚OEt2 (6.52 mL, 0.05 mmol). The mixture was
immediately warmed to 0 oC and stirred for 15 min, after which
time TLC (ethyl acetate-light petroleum, 1:3) indicated no
rhamnal (2c) (Rf 0.4) and a major product (Rf 0.3). The reaction
mixture was warmed to room temperature, then diluted with
dichloromethane (20 mL), and washed with brine (30 mL); the
organic layer was dried (Na2SO4) and filtered; and the solvent
was removed in vacuo. The residue was purified by flash
chromatography (ethyl acetate-light petroleum, 1:9) to afford
(3c) (1.8 g, 37%) as a 2:1 mixture of R/â isomers as determined
by 1H NMR analysis. Further flash chromatography (ethyl
acetate-light petroleum, 1:9) afforded pure 4′-(5-O-acetyl-2,6-
anhydro-1,3,4,7-tetradeoxy-â-L-erythro-hept-3-enitol-1-yl)iodo-
benzene (â-3c), as a colorless oil. [R]D26 -1.1 (c 1.0, CHCl3); IR
(film) 1736vs (CdO), 1484s, 1372s, 1238s (C-O), 1043s, 1007s
cm-1; 1H NMR (300 MHz, CDCl3) δ 7.61 (2 H, d, J 8.4, Ar o-I),
6.99 (2 H, d, J 8.4, Ar m-I), 5.74 (1 H, ddd, J 3,4 10.3, J 2,3 or J 3,5
1.3, J 2,3 or J 3,5 1.7, 3-H), 5.67 (1 H, dt, J 3,4 10.3, J 4,5 and J 2,4
1.8, 4-H), 5.02 (1 H, m, 5-H), 4.31 (1 H, m, 2-H), 3.56 (1 H, dq,
(M + H+, 10), 770.3 [(M + H2 - Boc)+, 100]; HRMS for C39H48
NO15 (M + H2 - Boc)+ calcd 770.3024, found, 770.3018.
-
Nr-(ter t-Bu toxyca r bon yl)-C-[(2′,3′,4′,6′-tetr a -O-a cetyl-
r-D-glu cop yr a n osyl)-(1′f4)-(2,3,6-t r i-O-a cet yl-r-D-m a n -
n op yr a n osyl)]-L-tyr osin e Ben zyl Ester (6b). N-Methyl-
morpholine N-oxide (67 mg, 0.57 mmol) and then OsO4 (2.5
wt % in tert-BuOH, 595 µL, 0.05 mmol) were added to a stirred
solution of NR-(tert-butoxycarbonyl)-C-[(2′,3′,4′,6′-tetra-O-acetyl-
R-D-glucopyranosyl)-(1′f4)-(6-O-acetyl-2,3-dideoxy-R-D-erythro-
hex-2-enopyranosyl)]-L-tyrosine benzyl ester (5b) (413 mg, 0.47
mmol) in acetone-water (5:1, 6 mL) at room temperature.
After 24 h, TLC (ethyl acetate-light petroleum, 3:1) indicated
no starting material (Rf 0.7) and product (Rf 0.2). Sodium
metabisulfite (9 mg, 0.05 mmol) in water (1.0 mL) and Florisil
(60-100 mesh, 50 mg) were added, and the mixture was
stirred vigorously for 0.5 h. Ethyl acetate (50 mL) and brine
(10 mL) were added, and the aqueous layer was extracted with
ethyl acetate (2 × 20 mL). The combined extracts were dried
(Na2SO4) and filtered, and the solvent was removed in vacuo.
The residue was dissolved in dry pyridine (5 mL) and cooled
to 0 °C under nitrogen. DMAP (3 mg, 0.02 mmol) was added,
followed by dropwise addition of acetic anhydride (0.23 mL,
2.44 mmol) over 1 min. After 0.5 h of stirring at 0 °C, the
reaction mixture was warmed to room temperature. After 0.5
h at room temperature, the mixture was cooled to 0 °C and
quenched by the addition of water (2 mL). After the reaction
mixture was warmed to room temperature, brine (3 mL) was
added and the aqueous layer was extracted with ethyl acetate
(3 × 15 mL). The combined extracts were washed with 2 M
hydrochloric acid (7 × 5 mL), dried (Na2SO4), and filtered, and
the solvent was removed in vacuo (toluene azeotrope × 3). The
residue was purified by flash chromatography (ethyl acetate-
light petroleum, 1:1) to afford NR-(tert-butoxycarbonyl)-C-
[(2′,3′,4′,6′-tetra-O-acetyl-R-D-glucopyranosyl)-(1′f4)-(2,3,6-tri-
O-acetyl-R-D-mannopyranosyl)]-L-tyrosine benzyl ester (6b)
(252 mg, 54%), as a colorless foam: [R]D30 +50.8 (c 2.1, CHCl3);
IR (KBr) 3396br (N-H), 2975w, 1748vs (CdO), 1716s (CdO),
1369s, 1239vs (C-O), 1166m, 1041vs cm-1; 1H NMR (300 MHz,
CDCl3) δ 7.39-7.29 (5 H, m, Ph), 7.13 (2 H, d, J 7.6, Ar), 7.00
(2 H, d, J 7.6, Ar), 5.47 (1 H, d, J 1′,2′ 4.1, 1′-H), 5.45 (1 H, t,
J 2′,3′ ) J 3′,4′ 10.0, 3′-H), 5.27 (1 H, dd, J 3,4 7.8, J 2,3 3.0, 3-H),
5.18 (1 H, t, J 1,2 ) J 2,3 3.0, 2-H), 5.17 (1 H, d, J 12.2, PhCHH′),
5.11 (1 H, d, J 12.2, PhCHH′), 5.08 (1 H, t, J 3′,4′ ) J 4′,5′ 10.0,
4′-H), 5.00 (1 H, d, J NH,CHR 7.8, NH), 4.92 (1 H, dd, J 2′,3′ 10.0,
J 1′,2′ 4.1, 2′-H), 4.60 (1 H, dt, J NH,CHR 7.8, J CHR,CHâ ) J CHR,CHâ′
6.0, R-H), 4.35-4.22 (3 H, m, 6-Ha, 6-Hb, 6′-Ha), 4.14-4.01 (5
H, m, 1-H, 4-H, 5-H, 5′-H, 6′-Hb), 3.09 (1 H, dd, J CHâ,CHâ′ 14.0,
J
5,6 5.7, J 6,7 6.2, 6-H), 2.85 (1 H, dd, J 1a,1b 13.7, J 1a,2 6.7, 1-Ha),
2.68 (1 H, dd, J 1a,1b 13.7, J 1b,2 6.6, 1-Hb), 2.07 (3 H, s, COCH3),
1.23 (3 H, d, J 6,7 6.2, CH3); 13C NMR (75 MHz, CDCl3) δ 170.6
(COCH3), 137.2 (Ar o-I, Cipso), 131.7 (Ar m-I), 131.6 (3-C), 126.0
(4-C), 91.8 (C-I), 75.1 (2-C), 72.4 (6-C), 71.0 (5-C), 41.3 (1-C),
21.1 (COCH3), 18.4 (CH3); MS (EI) m/z 373 (M + H+, 3%), 217
(p-ITol+, 88), 95 [(M - (p-ITol) - AcOH)+, 34] HRMS for
J
CHR,CHâ 6.0, â-H), 3.05-2.99 (2 H, m, J CHγ,CHγ′ 14.2, â′-H, γ-H),
2.90 (1 H, dd, J CHγ,CHγ′ 14.2, J 1,CHγ′ 5.6, γ′-H), 2.10, 2.08 (2 × 3
H, s, COCH3), 2.05 (6 H, s, 2 × COCH3), 2.04, 2.03, 2.02 (3 ×
3 H, s, COCH3), 1.42 (9 H, s, (CH3)3C); δH (400 MHz, C6D6)
7.15-6.84 (9 H, m, Ar), 5.90 (1 H, t, J 2′,3′ ) J 3′,4′ 10.0, 3′-H),
5.66 (1 H, d, J 1′,2′ 4.4, 1′-H), 5.49 (1 H, dd, J 3,4 8.0, J 2,3 3.0,
3-H), 5.39 (1 H, t, J 1,2 ) J 2,3 3.0, 2-H), 5.36 (1 H, t, J 3′,4′ ) J 4′,5′
10.0, 4′-H), 5.08 (1 H, dd, J 2′,3′ 10.0, J 1′,2′ 4.4, 2′-H), 5.02 (1 H,
d, J NH,CHR 8.4, NH), 4.95 (1 H, d, J 12.4, PhCHH′), 4.85 (1 H,
d, J 12.4, PhCHH′), 4.70 (1 H, ddd, J NH,CHR 8.4, J CHR,CHâ′ 6.6,
J CHR,CHâ 5.9, R-H), 4.40 (1 H, dd, J 6a,6b 12.1, J 5,6a 5.5, 6-Ha),
4.36-4.29 (3 H, m, 5′-H, 6′-Ha, 6′-Hb), 4.25 (1 H, dd, J 6a,6b 12.1,
J 5,6b 3.0, 6-Hb), 4.18 (1 H, t, J 3,4 ) J 4,5 8.0, 4-H), 4.02 (1 H, m,
1-H), 3.78 (1 H, m, J 5,6b 3.0, 5-H), 2.94 (1 H, dd, J CHâ,CHâ′ 13.9,
J CHR,CHâ 5.9, â-H), 2.80 (1 H, dd, J CHâ,CHâ′ 13.9, J CHR,CHâ′ 6.6,
â′-H),_2.62 (1 H, dd, J CHγ,CHγ′ 14.3, J 1,CHγ 8.8, γ-H), 2.46 (1 H,
dd, J CHγ,CHγ′ 14.3, J 1,CHγ′ 5.9, γ′-H), 1.94, 1.86, 1.77, 1.76, 1.70,
1.68, 1.58 (7 × 3 H, s, COCH3), 1.37 (9 H, s, (CH3)3C); 13C NMR
(100 MHz, CDCl3) δ 171.6 (COCH2), 170.5-169.4 (7 × C,
C
15H17IO3 (M+) calcd 372.0222, found 372.0237. Anal. Calcd
for C15H17IO3: 48.4; H, 4.6. Found: 48.3; H, 4.7.
Continued elution gave 4′-(5-O-acetyl-2,6-anhydro-1,3,4,7-
tetradeoxy-â-L-erythro-hept-3-enitol-1-yl)iodobenzene (R-3c), as
26
a colorless oil: [R]D -107.3 (c 1.2, CHCl3); IR (film) 1732vs
(CdO), 1484s, 1371s, 1238s (C-O), 1041s, 1007s cm-1 1H
;
NMR (300 MHz, CDCl3) δ 7.62 (2 H, d, J 8.2, Ar o-I), 6.98 (2
H, d, J 8.2, Ar m-I), 5.82 (1 H, ddd, J 3,4 10.4, J 2,3 or J 3,5 1.1,
J 2,3 or J 3,5 2.2 3-H), 5.79 (1 H, ddd, J 3,4 10.4, J 4,5 or J 2,4 3.1,
J 4,5 or J 2,4 1.8 4-H), 4.89 (1 H, m, 5-H), 4.34 (1 H, m, 2-H),
3.93 (1 H, dq, J 5,6 5.0, J 6,7 6.2, 6-H), 2.94 (1 H, dd, J 1a,1b 13.7,
J 1a,2 7.5, 1-Ha), 2.75 (1 H, dd, J 1a,1b 13.7, J 1b,2 6.6, 1-Hb), 2.09
(3 H, s, COCH3), 1.23 (3 H, d, J 6,7 6.2, CH3); 13C NMR (75 MHz,
CDCl3) δ 170.7 (COCH3), 137.5 (Ar o-I, Cipso), 131.4 (Ar m-I),

5460 J . Org. Chem., Vol. 64, No. 15, 1999
Pearce et al.
132.7, 123.6 (3-C, 4-C), 91.7 (C-I), 71.2 (2-C), 69.5 (5-C), 68.5
(6-C), 39.6 (1-C), 21.2 (COCH3), 17.0 (CH3); MS (EI) m/z 373
(M + H+, 3%), 217 (p-ITol+, 98) 155 [(M - p-ITol)+, 20], 95
[(M - (p-ITol) - AcOH)+, 98]. Anal. Calcd for C15H17IO3: C,
48.4; H, 4.6. Found: C, 48.3; H, 4.5.
H, m, Ph), 7.08 (2 H, d, J 7.1, Ar), 6.98 (2 H, d, J 7.1, Ar), 5.20
(1H, d, J 12.5, PhCHH), 5.10 (1H, d, J 12.5, PhCHH), 5.02
(1H, bd, J 7.5, NH), 4.85 (1H, t, J 3,4 ) J 4,5 8.3, 4-H), 4.61 (1H,
m, R-H), 4.40 (1H, br, OH), 4.15 (1H, m, 1-H), 3.93 (1 H, dq,
J
4,5 8.3, J 5,6 6.0, 5-H), 3.82 (2H, m, 2-H 3-H), 3.23 (1H, br, OH),
Nr-(ter t-Bu toxyca r bon yl)-C-(4-O-a cetyl-2,3,6-tr id eoxy-
r-L-er yth r o-h ex-2-en op yr a n osyl)-L-tyr osin e Ben zyl Ester
(5c). Zinc dust (586 mg, 8.7 mmol) was activated according to
general procedure A, using dry THF (0.5 mL), 1,2-dibromoet-
hane (29 µL, 0.35 mmol), and TMSCl (33 µL, 0.26 mmol). A
solution of Boc-L-Ala(I)-OBn10 (1.18 g, 2.9 mmol) in dry THF
(1.5 mL) was added to the stirred suspension of activated zinc
at 35 °C under argon in the dark. After 2 h, TLC (ethyl
acetate-light petroleum, 1:3) indicated no iodide (Rf 0.8)
remained, and the mixture was cooled to room temperature
and allowed to settle. Bis(tri-o-tolylphosphine)palladium dichlo-
ride (79 mg, 0.11 mmol) was added to a stirred solution of 4′-
(5-O-acetyl-2,6-anhydro-1,3,4,7-tetradeoxy-R-L-erythro-hept-3-
enitol-1-yl)iodobenzene (3c) (270 mg, 0.73 mmol) in dry N,N-
dimethylacetamide (1 mL) and dry THF (0.5 mL) at room
temperature under argon. After 15 min, the zincate solution
was transferred away from the unreacted zinc via gastight
syringe and added to the yellow iodoarene mixture. After 1 h
of stirring at room temperature, the mixture was heated to
50 °C. After 2 h, TLC (ethyl acetate-light petroleum, 1:3)
indicated no iodobenzene (Rf 0.4) and a major product (Rf 0.3),
and the green reaction mixture was allowed to cool to room
temperature. Ethyl acetate (30 mL) was added, the mixture
was filtered through Celite into a separating funnel, and the
organic extract was washed with saturated aqueous NH4Cl
(5 mL) and brine (5 mL). The organic extracts were dried (Na2-
SO4) and filtered, and the solvent was removed in vacuo. The
residue was purified by flash chromatography (eluent gradient,
light petroleum-ethyl acetate 1:5 to 1:3) to afford NR-(tert-
butoxycarbonyl)-C-(4-O-acetyl-2,3-dideoxy-R-L-erythro-hex-2-
enopyranosyl-L-tyrosine benzyl ester (5c) (314 mg, 83%) as a
colorless oil: [R]D26 -2.5 (c 1.6, CHCl3); IR (CHCl3) 3436br (N-
H), 2975s, 1712vs (CdO), 1509m, 1369m, 1257s (C-O), 1164s,
1048m cm-1; 1H NMR (300 MHz, CDCl3) δ 7.38-7.29 (5 H, m,
Ph), 7.09 (2 H, d, J 7.7, Ar), 6.98 (2 H, d, J 7.7, Ar), 5.85 (1 H,
ddd, J 2,3 11.9, J 1,2 or J 2,4 1.6, J 1,2 or J 2,4 1.1, 2-H), 5.76 (1 H,
ddd, J 2,3 11.9, J 1,3 or J 3,4 1.1, J 1,3 or J 3,4 2.9, 3-H), 5.19-5.08 (2
H, m, PhCH2), 4.98 (1 H, br, d, J NH,CHR 7.6, NH), 4.91 (1 H, m,
4-H), 4.61 (1 H, m, R-H), 4.32 (1 H, m, 1-H), 3.94 (1 H, dq, J 4,5
5.3, J 5,6 6.4, 5-H), 3.05 (2 H, m, â-H, â′-H), 2.99 (1 H, dd, J 1,CHγ
7.2, J CHγ,CHγ′ 13.6, γ-H), 2.75 (1 H, dd, J 1,CHγ′ 7.2, J CHγCHγ′ 13.6,
γ′-H), 2.10 (3 H, s COCH3), 1.41 (9 H, s, (CH3)3C), 1.26 (3 H,
d, J 6.4, CH3); 13C NMR (75 MHz, CDCl3) δ 171.7 (COCH2),
170.7 (COCH3), 155.0 (OCON), 136.3, 135.2, 134.0, 133.0 (2-C
or 3-C), 129.4, 128.5, 128.6, 123.3 (2-C or 3-C), 79.9 ((CH3)3C),
71.6, 69.7 (1-C), 68.4 (4-C), 67.4 (5-C), 54.4, 39.8 (â-C), 37.9
(γ-C), 28.3 ((CH3)3C), 21.2 (COCH3), 17.1 (CH3); MS (FAB+)
m/z 523 (M+, 10%), 425 [(M + H - BOC)+, 44].
3.05 (2H, m, â-H â′-H), 2.95 (1H, dd, J 1,CHγ 7.7, J CHγ,CHγ′ 14.1,
γ-H), 2.90 (1 H, dd, J 1,CHγ′ 7.0, J CHγ,CHγ′ 14.1, γ′-H), 2.14 (3H, s,
COCH3), 1.41 (9H, s, (CH3)3C), 1.21 (3H, d, J 6.0, CH3); 13C
NMR (75 MHz, CDCl3) δ 171.6, 170.2 (2 × OCO), 155.1
(OCON), 136.3, 135.2, 134.2, 129.6, 129.1, 128.6, 80.1 ((CH3)3C),
76.6, 75.8, 70.6, 70.2, 67.9, 67.2, 54.5 (R-C), 37.6, 35.3 (â-C,
γ-C), 29.7 ((CH3)3C), 28.3 (COCH3), 17.7 CH3; MS (CI) m/z 458
(M + H - Boc)+; HRMS for C30H38NO9 (M - H)+ calcd
556.2548, found 556.2547.
Nr-(ter t-Bu toxycar bon yl)-C-(2,3,4-tr i-O-acetyl-r-L-r h am -
n op yr a n osyl)-L-tyr osin e Ben zyl Ester (6c). Acetic anhy-
dride (0.08 mL, 0.83 mmol) was added dropwise over 1 min to
a stirred solution of NR-(tert-butoxycarbonyl)-C-(4-O-acetyl-R-
L-rhamnopyranosyl)-L-tyrosine benzyl ester (92 mg, 0.17 mmol)
and DMAP (1 mg, 0.01 mmol) in dry pyridine (1.0 mL) at 0 °C
under nitrogen. After 1 h at 0 °C, TLC (ethyl acetate-light
petroleum, 2:3) indicated no diol (Rf 0.2) and product (Rf 0.4),
and the reaction was quenched by the addition of water (0.5
mL). The reaction mixture was allowed to warm to room
temperature, brine (0.5 mL) was added, and the aqueous layer
was extracted with ethyl acetate (3 × 3 mL). Combined
extracts were washed with 2 M hydrochloric acid (5 × 1.0 mL),
dried (Na2SO4), and filtered and the solvent was removed in
vacuo (toluene azetrope × 3). The residue was purified by flash
chromatography (ethyl acetate-light petroleum, 2:3) to afford
NR-(tert-butoxycarbonyl)-C-(2,3,4-tri-O-acetyl-R-L-mannopyra-
nosyl)-L-tyrosine benzyl ester (6c) (33 mg, 31%), as a colorless
26
foam: [R]D +1.0 (c 1.9, CHCl3); IR (CHCl3) 3685br (N-H),
3436 (N-H), 1742vs (CdO), 1709 (CdO), 1499m, 1369s, 1256s
(C-O), 1164s, 1050m cm-1; 1H NMR (300 MHz, CDCl3) δ 7.39-
7.29 (5 H, m, Ph), 7.10 (2 H, d, J 7.8, Ar), 6.99 (2 H, d, J 7.8,
Ar), 5.32 (1 H, dd, J 2,3 3.2, J 3,4 9.4 3-H), 5.30 (1 H, t, J 2,3 )J 1,2
3.2, 2-H), 5.19-5.04 (3 H, m, 4-H, PhCH2), 4.98 (1 H, br, d,
J NH,CHR 8.1, NH), 4.61 (1 H, m, R-H), 4.10 (1 H, m, 1-H), 3.90
(1 H, dq, J 4,5 5.6, J 5,6 6.2, 5-H), 3.07-2.99 (2 H, m, â-H, â′-H),
3.04 (1 H, dd, J 1,CHγ 5.1, J CHγ,CHγ′ 14.0, γ-H), 2.90 (1 H, dd, J 1,CHγ′
6.6, J CHγ,CHγ′ 14.0, γ′-H), 2.10, 2.09, 2.02 (3 × 3 H, s, COCH3),
1.41 (9 H, s, (CH3)3C), 1.22 (3 H, d, J 6.2, 6-CH3); 13C NMR
(75 MHz, CDCl3) δ 171.1, 170.7, 170.2, 170.1 (4 × OCO), 155.1
(OCON), 135.25, 135.2, 134.4, 129.7, 129.1, 128.6, 128.55,
128.5, 80.0 ((CH3)3C), 76.2 (1-C), 71.5, 70.3 (PhCH2, 4-C), 69.2
(3-C), 68.5 (2-C), 67.1 (5-C), 54.4 (R-C), 37.8, 35.1 (â-C, γ-C),
28.3 ((CH3)3C), 20.98, 20.89, 20.78 (3 × COCH3), 17.6 CH3; MS
(FAB+) m/z 664 [(M + Na)+, 100%]; HRMS for C34H43NO11 (M)+
calcd 641.2834, found 641.2838.
4-(6-O-Acet yl-2,5-a n h yd r o-1,3,4-t r id eoxy-r-D-glycer o-
h ex-3-en itol-1-yl)iod oben zen e (9). Zinc dust (247 mg, 3.78
mmol) was activated according to general procedure A, using
dry THF (0.75 mL), 1,2-dibromoethane (13 µL, 0.15 mmol),
and TMSCl (14.5 µL, 0.11 mmol). A solution of 4-iodobenzyl
bromide (562 mg, 1.89 mmol) in dry THF (2.5 mL) was added,
dropwise over 1 h, to the stirred suspension of activated zinc
at 0 °C under argon in the dark. After addition, the mixture
was stirred for an additional 0.5 h and then warmed to room
temperature and allowed to settle. The zincate solution was
transferred away from unreacted zinc via gastight syringe into
a flask purged with argon, and the solvent was removed in
vacuo (bath temp 35 °C). Dry dichloromethane (5 mL) was
added to the residue, and the solution was cooled to -30 °C
under argon in the dark. A solution of di-O-acetyl-D-arabinal
(7)22 (223 mg, 1.11 mmol) in dry dichloromethane (1.5 mL) was
added to the zincate, followed by BF3‚OEt2 (0.41 mL, 3.33
mmol). After 10 min, the reaction mixture was warmed to 0
°C and stirred for 0.5 h, after which time TLC (ethyl acetate-
light petroleum, 1:2) indicated no arabinal (Rf 0.1) and a major
product (Rf 0.5). The reaction mixture was warmed to room
temperature, diluted with dichloromethane (10 mL), then
Nr-(ter t-Bu toxyca r bon yl)-C-(4-O-a cetyl-r-L-r h a m n op y-
r a n osyl)-L-tyr osin e Ben zyl Ester . N-Methylmorpholine N-
oxide (27 mg, 0.19 mmol) and then OsO4 (2.5wt % in tert-
BuOH, 0.24 mL, 0.03 mmol) were added to a stirred solution
of NR-(tert-butoxycarbonyl)-C-(4-O-acetyl-2,3,6-trideoxy-R-L-
erythro-hex-2-enopyranosyl-L-tyrosine benzyl ester (5c) (100
mg, 0.19 mmol) in acetone-water (5:1, 1.5 mL) at room
temperature. After 24 h, TLC (ethyl acetate-light petroleum,
3:2) indicated no starting material (Rf 0.6) and product (Rf 0.2).
Sodium metabisulfite (7.3 mg, 0.04 mmol) in water (0.2 mL)
was added, and the mixture was stirred vigorously for 30 min.
Ethyl acetate (2 mL) was added, and the mixture was filtered
through Celite into a separating funnel and washed with brine
(1 mL). The aqueous layer was extracted with ethyl acetate
(3 × 1.5 mL), dried (Na2SO4), and filtered, and the solvent was
removed in vacuo. The residue was purified by flash chroma-
tography (eluent gradient, ethyl acetate-light petroleum 2:1
to 5:1) to afford NR-(tert-butoxycarbonyl)-C-(4-O-acetyl-R-L-
rhamnopyranosyl)-L-tyrosine benzyl ester (62 mg, 58%), as a
colorless foam: [R]D33 -13.7 (c 1.2, CHCl3); IR (CHCl3) 3435br,
2924w, 1732vs (CdO), 1701s (CdO), 1521m, 1369m, 1244s (C-
(22) Cheng, J . C.-Y.; Hacksell U.; Davies, G. D. J . Org. Chem. 1985,
50, 2778.
1
O), 1167m cm-1; H NMR (300 MHz, CDCl3) δ 7.36-7.34 (5

C-Glycosyl Tyrosines
J . Org. Chem., Vol. 64, No. 15, 1999 5461
washed with brine (5 mL), dried (Na2SO4), and filtered, and
the solvent was removed in vacuo. The residue was purified
by flash chromatography (ethyl acetate-light petroleum, 1:5)
to afford 4-(6-O-acetyl-2,5-anhydro-1,3,4-trideoxy-R-D-glycero-
hex-3-enitol-1-yl) iodobenzene (9) (153 mg, 34%), as a colorless
60]; HRMS for C24H28NO5 (M + H2 - Boc)+ calcd 410.1967,
found 410.1982.
Nr-(F lu or en -9-ylm eth oxyca r bon yl)-C-(2,3,4,6-tetr a -O-
a cetyl-r-D-m a n n op yr a n osyl)-L-tyr osin e (11a ). A solution
of NR-(tert-butoxycarbonyl)-C-(2,3,4,6-tetra-O-acetyl-R-D-man-
nopyranosyl)-L-tyrosine benzyl ester (6a ) (439 mg, 0.63 mmol)
in dry methanol (4 mL) was added to a vigorously stirred
suspension of preactivated Pd/C (10%, 40 mg) (prepared
according to general procedure B) in dry MeOH (2 mL) at room
temperature under hydrogen (1 atm). After 1 h, the reaction
mixture was purged with nitrogen filtered through Celite, and
the solvent was removed in vacuo. The crude acid was
dissolved in dry dichloromethane (4.25 mL) and cooled to 0
°C under nitrogen. Trifluoroacetic acid (0.75 mL) was added
dropwise over 1 min, and the solution was stirred for 0.5 h at
0 °C and then warmed to room temperature. After 1 h at room
temperature, TLC (chloroform-ethanol, 3:1) indicated no
starting material (Rf 0.6) and product (Rf 0.3, ninhydrin active).
Toluene (20 mL) was added, and the solvent was removed in
vacuo (toluene azeotrope × 3). The resultant foam was
immediately dissolved in water (5 mL) and acetonitrile (5 mL)
and stirred at room temperature. A solution of FmocOSu (254
mg, 0.75 mmol) in acetonitrile (2 mL) was added followed by
the dropwise addition of Et3N (263 µL, 1.88 mmol) in order to
maintain pH ) 8.5-9.0 (monitored via pH meter). After 45
min, pH remained constant and TLC (chloroform-ethanol, 3:1)
indicated no starting material (Rf 0.3) and a major product
(Rf 0.7). Hydrochloric acid (2 M) was added until pH ) 2, and
then dichloromethane (20 mL) was added. The aqueous layer
was extracted with dichloromethane (2 × 10 mL); combined
extracts were washed with brine (5 mL), dried (Na2SO4), and
filtered; and the solvent was removed in vacuo. The residue
was purified by flash chromatography (eluent gradient, chlo-
roform to chloroform-methanol, 9:1) to afford NR-(fluoren-9-
ylmethoxycarbonyl)-C-(2,3,4,6- tetra-O-acetyl-R-D-mannopyr-
anosyl)-L-tyrosine (11a ) (329 mg, 72%), as a colorless foam:
analytical RPHPLC (isocratic elution, 55% solvent B in solvent
27
oil: [R]D -146.3 (c 1.6 in CHCl3); IR (KBr) 2923w, 2851w,
1736vs (CdO), 1484m, 1231s (C-O), 1088s, 1038s, 1007s cm-1
;
1H NMR (300 MHz, CDCl3) δ 7.59 (2 H, d, J 8.2, Ar o-I), 6.95
(2 H, d, J 8.2, Ar m-I), 5.85 (1 H, dt, J 3,4 6.2, J 2,3 ) J 3,5 2.0,
3-H), 5.71 (1 H, dt, J 3,4 6.2, J 2,4 ) J 4,5 2.0, 4-H), 5.10 (1 H, dtt,
J 2,5 7.5, J 1a,2 ) J 1b,2 6.0, J 2,3 ) J 2,4 2.0, 2-H), 4.91 (1 H, dddt,
J 2,5 7.5, J 5,6b 6.0, J 5,6a 4.0, J 3,5 ) J 4,5 2.0, 5-H), 4.11 (1 H, dd,
J 6a,6b 11.6, J 5,6a 4.0, 6-Ha), 4.03 (1 H, dd, J 6a,6b 11.6, J 5,6b 6.0,
6-Hb), 2.86 (1 H, dd, J 1a,1b 13.6, J 1a,2 6.0, 1-Ha), 2.79 (1 H, dd,
J 1a,1b 13.6, J 1b,2 6.0, 1-Hb), 2.06 (3 H, s, CH3); 13C NMR (75
MHz, CDCl3) δ 170.8 (COCH3), 137.2 (Ar o-I), 137.1 (Cipso),
131.6 (Ar m-I), 131.4 (3-C), 126.7 (4-C), 91.7 (C-I), 86.6 (2-C),
84.1 (5-C), 66.1 (6-C), 41.8 (1-C), 20.9 (COCH3); MS (CI) m/z
359 (M + H+, 0.2%), 299 [(M + H - AcOH)+, 2], 217 (p-ITol+,
15), 83 (100); HRMS for C14H16IO3 (M + H+): calcd 359.0144,
found 359.0138.
The assignment of the stereochemistry of C-glycoside 9 is
primarily based on NOE.14
Nr-r-(ter t-Bu toxyca r bon yl)-C-(5-O-a cetyl-2,3-d id eoxy-
r-D-glycer o-p en t-2-en ofu r a n osyl)-L-tyr osin e Ben zyl Ester
(10). Zinc dust (205 mg, 3.14 mmol) was activated according
to general procedure A, using dry THF (0.5 mL), 1,2-dibromo-
ethane (11 µL, 0.13 mmol), and TMSCl (12 µL, 0.09 mmol). A
solution of Boc-L-Ala(I)-OBn10 (421 mg, 1.04 mmol) in dry THF
(0.75 mL) was added to the stirred suspension of activated zinc
at 35 °C under argon in the dark. After 2.25 h, TLC (ethyl
acetate-light petroleum, 1:3) indicated no iodide (Rf 0.8)
remained, and the mixture was cooled to room temperature
and allowed to settle. Bis(tri-o-tolylphosphine)palladium dichlo-
ride (28 mg, 0.04 mmol) was added to a stirred solution of 4-(6-
O-acetyl-2,5-anhydro-1,3,4-trideoxy-R-D-glycero-hex-3-enitol-1-
yl)iodobenzene (9) (93 mg, 0.26 mmol) in dry N,N-di-
methylacetamide (0.75 mL) and dry THF (0.25 mL) at room
temperature under argon. After 15 min, the zincate solution
was transferred away from unreacted zinc via gastight syringe
and added to the yellow iodobenzene mixture. After 0.5 h of
stirring at room temperature, the mixture was heated to 50
°C. After 1.5 h, TLC (ethyl acetate-light petroleum, 1:3)
indicated no iodoarene (9) (Rf 0.4) and a major product (Rf 0.2),
and the green reaction mixture was allowed to cool to room
temperature. Ethyl acetate (20 mL) was added; the mixture
was filtered through Celite into a separating funnel, then
washed with saturated aqueous NH4Cl (5 mL), brine (5 mL),
dried (Na2SO4), and filtered; and the solvent was removed in
vacuo. The residue was purified by flash chromatography
(eluent gradient, ethyl acetate-light petroleum, 1:9 to 2:3) to
afford NR-(tert-butoxycarbonyl)-C-(5-O-acetyl-2,3-dideoxy-R-D-
glycero-pent-2-enofuranosyl)-L-tyrosine benzyl ester (10) (103
26
A, Rt 6.5 min); [R]D +13.9 (c 3.2, CHCl3); IR (KBr) 3436br,
2952w, 1744vs (CdO), 1517w, 1371s, 1229vs (C-O), 1049s
1
cm-1; H NMR (400 MHz, CDCl3) δ 7.70-7.45 (8 H, m, Fmoc
Ar), 7.40-6.95 (4 H, m, Ar), 5.35 (2 H, m, 3-H and NH), 5.22
(1 H, t, J 3,4 ) J 4,5 9.0, 4-H), 5.19 (1 H, m, 2-H), 4.68 (1 H, m,
R-H), 4.56 (1 H, d, J 7.7, Fmoc CHH), 4.41 (2 H, m, Fmoc CH,
CHH), 4.29 (1 H, dd, J 6a,6b 12.0, J 5,6a 6.3, 6-Ha), 4.20 (1 H, m,
1-H), 4.08 (1 H, dd, J 6a,6b 12.0, J 5,6b 3.0, 6-Hb), 4.00 (1 H, m,
5-H), 3.14 (2 H, m, â-H, â′-H), 3.03 (1 H, dd, J CHγ,CHγ′ 14.0,
J 1,CHγ 8.4, γ-H), 2.93 (1 H, dd, J CHγ,CHγ′ 14.0, J 1,CHγ′ 6.5, γ′-H),
2.09 (6 H, s, 2 × COCH3), 2.08, 2.03 (2 × 3 H, s, COCH3)
(carboxylic acid OH not observed); 13C NMR (100 MHz, CDCl3)
δ 170.8, 170.3, 170.1, 169.7 (5 × C, OCO), 155.5 (OCON), 143.7,
141.3, 129.6, 129.2, 127.8, 127.7, 127.0, 125.0, 120.0 (10 × C,
Ar), 77.3, 75.9, 70.7, 69.9, 68.8, 66.9 (1-C, 2-C, 3-C, 4-C, 5-C,
FmocCH2O), 62.4 (6-C), 47.0 (FmocCH), 34.9 (2 × C, â-C, γ-C),
20.9, 20.75, 20.7, 20.65 (4 × COCH3); MS (FAB+) m/z 754 (M
+ Na+, 80%), 732 (M + H+, 15), 511 [(M + H - Fmoc)+, 15],
179 (C14H11+, 100); HRMS for C39H42NO13 (M + H+) calcd
732.2656, found 732.2638.
30
mg, 78%), as a colorless oil: [R]D -71.9 (c 1.7, CHCl3); IR
(film) 3370br, 2978m, 2934w, 1741vs (CdO), 1715vs (CdO),
1
1515s (CdC), 1367s, 1250vs (C-O), 1165vs, 1087m cm-1; H
Nr-(F lu or en -9-ylm eth oxyca r bon yl)-C-[(2′,3′,4′,6′-tetr a -
O-a cetyl-r-D-glu cop yr a n osyl)-(1′f4)-(2,3,6-tr i-O-a cetyl-r-
D-m a n n op yr a n osyl)]-L-tyr osin e (11b). A solution of NR-(tert-
butoxycarbonyl)-C-[(2′,3′,4′,6′-tetra-O-acetyl-R-D-glucopyranosyl)-
(1′f4)-(2,3,6-tri-O-acetyl-R-D-mannopyranosyl)]-L-tyrosine benzyl
ester (6b) (167 mg, 0.17 mmol) in dry methanol (1 mL) was
added to a vigorously stirred suspension of preactivated Pd/C
(10%, 20 mg, prepared according to general procedure B) in
dry MeOH (1 mL) at room temperature under hydrogen (1
atm). After 0.5 h, the reaction mixture was purged with
nitrogen and filtered through Celite, and the solvent was
removed in vacuo. The residue was dissolved in dry dichlo-
romethane (1.7 mL) and cooled to 0 °C under nitrogen.
Trifluoroacetic acid (0.6 mL) was added dropwise over 1 min;
NMR (300 MHz, CDCl3) δ 7.38-7.28 (5 H, m, Ph), 7.07 (2 H,
d, J 8.0, Ar), 6.97 (2 H, d, J 8.0, Ar), 5.85 (1 H, dt, J 2,3 6.0, J 1,2
) J 2,4 2.0, 2-H), 5.70 (1 H, dt, J 2,3 6.0, J 1,3 ) J 3,4 2.0, 3-H), 5.17
(1 H, d, J 12.5, PhCHH′), 5.10 (1 H, d, J 12.5, PhCHH′), 5.08
(1 H, ddt, J 1,CHγ 5.5, J 1,CHγ′ 7.3, J 1,2 ) J 1,3 2.0, 1-H), 5.02 (1 H,
d, J NH,CHR 8.0, NH), 4.96 (1 H, dddt, J 1,4 7.5, J 4,5b 6.0, J 4,5a 4.0,
J 2,4 ) J 3,4 2.0, 4-H), 4.61 (1 H, dt, J NH,CHR 8.0, J CHR,CHâ
)
J CHR,CHâ′ 6.0, R-H), 4.13 (1 H, dd, J 5a,5b 11.6, J 4,5a 4.0, 5-Ha),
4.04 (1 H, dd, J 5a,5b 11.6, J 4,5b 6.0, 5-Hb), 3.08 (1 H, dd, J CHâ,CHâ′
14.0, J CHR,CHâ 6.0, â-H), 3.02 (1 H, dd, J CHâ,CHâ′ 14.0, J CHR,CHâ′
6.0, â′-H), 2.94 (1 H, dd, J CHγ,CHγ′ 13.4, J 1,CHγ 5.5, γ-H), 2.76 (1
H, dd, J CHγ,CHγ′ 13.4, J 1,CHγ′ 7.3, γ′-H), 2.06 (3 H, s, OCH3), 1.41
(9 H, s, (CH3)3C); 13C NMR (75 MHz, CDCl3) δ 171.8, 170.9 (2
× CdO), 155.1 (OCON), 136.2, 135.2, 133.9, 131.9 (2-C), 129.6,
129.3, 128.6, 128.5, 128.4, 126.3 (3-C), 87.0 (1-C), 84.0 (4-C),
79.9 ((CH3)3C), 67.0 (PhCH2O), 66.3 (5-C), 54.5 (R-C), 42.2 (γ-
C), 37.9 (â-C), 28.3 ((CH3)3C), 20.9 (COCH3); MS (ESI+) m/z
532 (M + Na+, 100%), 510 (M + H+, 5), 410 [(M + H2 - Boc)+,
o
the solution was stirred for 0.5 h at 0 C and then warmed to
room temperature. After 1 h at room temperature, TLC
(chloroform-ethanol, 3:1) indicated no starting material (Rf
0.75) and product (Rf 0.4, ninhydrin active). Toluene (15 mL)

5462 J . Org. Chem., Vol. 64, No. 15, 1999
Pearce et al.
was added, and the solvent was removed in vacuo (toluene
azeotrope × 3). The resultant oil was immediately dissolved
in water (2 mL) and acetonitrile (2 mL) and stirred at room
temperature. A solution of FmocOSu (68 mg, 0.20 mmol) in
acetonitrile (1 mL) was added followed by the dropwise
addition of Et3N in order to maintain pH ) 8.5-9.0 (monitored
via pH meter). After 45 min, the pH remained constant and
TLC (chloroform-ethanol, 3:1) indicated no starting material
(Rf 0.4) and a major product (Rf 0.7). Hydrochloric acid (2 M)
was added until pH ) 2, and then dichloromethane (10 mL)
was added. The aqueous layer was extracted with dichlo-
romethane (2 × 10 mL); combined extracts were washed with
brine (5 mL), dried (Na2SO4), and filtered; and the solvent was
removed in vacuo. The residue was purified by flash chroma-
tography (eluent gradient, chloroform to chloroform-methanol,
9:1) to afford NR-(fluoren-9-ylmethoxycarbonyl)-C-[(2′,3′,4′,6′-
tetra-O-acetyl-R-D-glucopyranosyl)-(1′f4)-(2,3,6-tri-O-acetyl-
R-D-mannopyranosyl)]-L-tyrosine (11b) (105 mg, 61%), as a
5.04 (2 H, m, 4-H, 4′-H), 1.95 (12 H, s, 4 × COCH3), 1.93 (6
H, s, 2 × COCH3), 1.92 (6 H, s, 2 × COCH3); MS (ESI+) m/z
1230 (M + H+, 20%), 615.5 (M + 2H+, 100); HRMS for
C
56H73N6O25 (M + H+) calcd 1229.4625, found 1229.4607.
Continued elution gave H-L-Tyr[C-(Ac4-R-D-Man)]-Gly-Gly-
L-Tyr[C-(Ac4-R-D-Man)]-Gly-OH‚TFA (3.0 mg, 2%, Rt 23.0 min),
as a hygroscopic colorless solid: analytical RPHPLC (0-10
min, linear gradient of 50-80% solvent B in solvent A, Rt 4.9
min); MS (ESI+) m/z 1173 (M + H+, 85%), 586.9 (M + 2H+,
100); HRMS for C54H70N5O24 (M + H+) calcd 1172.4411, found
1172.4380. Due to the small amount of material available, this
product was not characterized further.
cyclo-{Gly-L-Tyr [C-(Ac4-r-D-Ma n )]-Gly}2 (13). H-Gly-L-
Tyr[C-(Ac4-R-D-Man)]-Gly-Gly-L-Tyr[C-(Ac4-R-D-Man)]-Gly-OH‚
TFA (12) (18.0 mg, 0.01 mmol) was dissolved in dry DMF (9.7
mL) and mixed with HOBt (5.9 mg, 0.04 mmol) and TBTU
(14.1 mg, 0.04 mmol) at room temperature under nitrogen.
Diisopropylethylamine (97 µL) was added, and the solution
was stirred. After 26 h, the solvent was removed in vacuo, and
ether (10 mL) was added to precipitate a gum. The ether was
decanted, and the gum was purified by preparative RPHPLC
(0-10 min, isocratic elution of 30% solvent B in solvent A, then
10-20 min, linear gradient of 30-67% solvent B in solvent A,
eluting at 3.2 mL min-1) to afford cyclo-{Gly-L-Tyr[C-(Ac4-R-
D-Man)]-Gly}2 (13) (4 mg, 23%, Rt 18.4 min), as a hygroscopic
colorless gum: analytical RPHPLC (0-10 min, linear gradient
30
colorless foam: [R]D +56.2 (c 2.8, CHCl3); IR (KBr) 3432br,
1747vs (CdO), 1652m, 1371m, 1240vs (C-O), 1041s cm-1; 1H
NMR (300 MHz, CDCl3) δ 7.71-6.99 (12 H, m, Ar), 5.46 (1 H,
d, J 1′,2′ 4.0, 1′-H), 5.44 (1 H, t, J 2′,3′ ) J 3′,4′ 10.0, 3′-H), 5.24 (1
H, br m, 3-H), 5.15 (1 H, br m, 2-H), 5.08 (1 H, t, J 3′,4′ ) J 4′,5′
10.0, 4′-H), 4.91 (1 H, dd, J 2′,3′ 10.0, J 1′,2′ 4.0, 2′-H), 4.56-3.90
(12 H, br m, R-H, 1-H, 4-H, 5-H, 5′-H, 6-Ha,b, 6′-Ha,b, Fmoc CH,
Fmoc CH2), 3.20-2.80 (4 H, m, â-H, â′-H, γ-H, γ′-H), 2.09, 2.06,
2.04, 2.02, 2.01 (21 H, 5 × s, COCH3); 13C NMR (100 MHz,
CDCl3) δ 170.6, 170.5, 170.3, 170.1, 170.0, 169.9, 169.5 (8 ×
C, CdO), 148.1 (OCON), 143.7, 141.1, 135.2, 135.1, 135.0,
129.5, 129.2, 127.6, 127.0, 119.9 (10 × C, Ar), 95.8 (1′-C), 71.4,
71.2, 71.0 (4 × C, 1-C, 3-C, 4-C, 5-C), 70.0, 69.9, 69.6 (2-C,
2′-C, 3′-C), 68.4 (5′-C), 68.0 (4′-C), 67.0 (FmocCH2O), 63.0, 61.4
(6-C, 6′-C), 56.9 (R-C), 46.9 (FmocCH), 35.1 (2 × C, γ-C, â-C),
20.9, 20.8, 20.7, 20.65, 20.6, 20.56, 20.5 (7 × COCH3); MS
(FAB+) m/z 1058.6 (M + K+, 17%), 1042.5 (M + Na+, 21),
1020.6 (M + H+, 63); HRMS for C51H58NO21 (M + H+) calcd
1020.3501, found 1020.3494.
1
of 50-80% solvent B in solvent A, Rt 4.5 min); H NMR (400
MHz, DMSO-d6) (structure numbered as described by Ko-
pple17) δ 8.52 (2 H, d, J 6.3, 2(5)-NH), 8.46 (2 H, t, J 6.0, 3(6)-
NH), 7.55 (2 H, t, J 4.4, 1(4)-NH), 7.23-7.10 (8 H, m, Ar), 5.37
(2 H, dd, J 3,4 9.0, J 2,3 3.0, 3-H), 5.15 (2 H, t, J 1,2 ) J 2,3 3.0,
2-H), 5.05 (2 H, t, J 3,4 ) J 4,5 9.0, 4-H), 4.25-4.11 (6 H, m, R-H,
5-H, 6-Ha), 4.07 (2 H, ddd, J 1,CHγ 9.3, J 1,CHγ′ 6.0, J 1,2 3.0, 1-H),
3.97 (2 H, m, 6-Hb), 3.84 (2 H, dd, J 3(6)-H
16.6, J 3(6)-H
a
b
a
,3(6)-H
,3(6)-NH
6.0, 3(6)-Ha), 3.80 (2 H, dd, J 1(4)-H
16.6, J 1(4)-H
16.6, J 1(4)-H
a
b
a
,1(4)-H
,1(4)-NH
4.4, 1(4)-Ha), 3.71 (2 H, dd, J 1(4)-H
a
b
b
,1(4)-H
,1(4)-NH
4.4, 1(4)-Hb), 3.50 (2 H, m, 3(6)-Hb), 3.11 (2 H, dd, J CHγ,CHγ′
14.0, J 1,CHγ 9.3, γ-H), 3.03 (2 H, J CHâ,CHâ′ 13.7, J CHR,CHâ 5.0, â-H),
2.95 (2 H, dd, J CHγ,CHγ′ 14.0, J 1,CHγ′ 6.0, γ′-H), 2.82 (2 H,
H-Gly-L-Tyr [C-(Ac4-r-D-Ma n )]-Gly-Gly-L-Tyr [C-(Ac4-r-
D-Ma n )]-Gly-OH‚TF A (12) a n d H-L-Tyr [C-(Ac4-r-D-Ma n )]-
Gly-Gly-L-Tyr [C-(Ac4-r-D-Man )]-Gly-OH‚TFA. Synthesis was
achieved by SPPS according to general procedure C (see
Supporting Information), using Fmoc-Gly-PEG-PS (HMP)
resin (0.105 mmol). Couplings with NR-(fluoren-9-ylmethoxy-
carbonyl)-C-(2,3,4,6-tetra-O-acetyl-R-D-mannopyranosyl)-L-ty-
rosine (11) were performed using a 2-fold excess, with O-(1H-
benzotriazol-1-yl)-N,N,N′,N′-tetramethyluroniumhexafluorophosphate,
1-hydroxybenzotriazole (1.0 equiv), and N-methylmorpholine
(2.0 equiv) for a fixed coupling time of 1 h. Purification of the
crude peptide (48 mg) by preparative RPHPLC {0-30 min,
linear gradient of 30-42% solvent B in solvent A (see Sup-
porting Information), eluting at 2.0 mL min-1} afforded H-Gly-
L-Tyr[C-(Ac4-R-D-Man)]-Gly-Gly-L-Tyr[C-(Ac4-R-D-Man)]-Gly-
OH‚TFA (12) (29.0 mg, 21%, Rt 20.3 min), as a hygroscopic
colorless solid: analytical RPHPLC (0-10 min, linear gradient
J
CHâ,CHâ′ 13.7, J CHR,CHâ′ 9.3, â′-H), 2.06 (6 H, s, 2 × OCH3), 2.05
(6 H, s, 2 × OCH3), 1.96 (6 H, s, 2 × OCH3), 1.93 (6 H, s, 2 ×
OCH3); MS (ESI+) m/z 1211.7 (M + H+, 100%), 1169.5 [(M +
H - C2H2O)+, 40], 606.3 (M + 2H+, 4).
Ack n ow led gm en t. We thank EPSRC for support
(A.J .P., S.R., S.N.T.) and Roche Discovery Welwyn for
a CASE studentship (to A.J .P.).
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal procedures, including details of SPPS and HPLC purifica-
1
tion methods, copies of H and 13C NMR spectra, character-
ization data for cyclic peptide 13 (COSY, VT-NMR, and NH
proton dependence, and ESI+ mass data), and synthesis and
characterization of {H-L-Tyr[C-(Ac4-R-D-Man)]-Gly-Gly-NHNH2}
14. This material is available free of charge via the Internet
at http://pubs.acs.org.
1
of 50-80% solvent B in solvent A, Rt 4.6 min); H NMR (300
MHz, DMSO-d6, partial data) δ 8.67 (1 H, d, J 7.9, NH), 8.47
(1 H, t, J 6.0, NH), 8.39 (1 H, t, J 6.0, NH), 8.15 (1 H, d, J 8.2,
NH), 7.97 (1 H, t, J 6.0, NH), 7.88 (2 H, br s, NH2), 7.16 (8 H,
m, Ar), 5.34 (2 H, m, 3-H, 3′-H), 5.14 (2 H, m, 2-H, 2′-H),
J O990253E