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Synthesis of the Nonamannan Residue of a Glycoprotein with High Mannose Content.

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Fig 3 Siinplilicd I-cprexntationof(47th and 48th) degenerate orbitals of the staggered and the eclip~edI . O n l y positions of axial and methyl H are shown. Nodal
plaiic!, bctwccii I{ i n close contact are shown by dashed lines. The orbital energy of
ihe cclipwi coiiforiner I ) Iowcr than that of the staggered conformer by
3.5X kciil imol I . hcc,iusc i t has fewer nodal danes.
CH,--C[N(CH,),],[41 is not a good model of 1 either. This is
because the H atom of the -N(CH,), groups will not occupy the
corresponding axial positions in 1, in order to avoid strong
repulsion between neighboring H atoms (Fig. 4). Finally. it
should be noted that MM3[l4] molecular mechanical calculations. without any MO concept in the underlying principles,
afford 3.98 and 4.38 kcalmol-' for the AE,,, of 1 and CH,C(NH 2 ) 3 . respectively.
[4] J. J Novoa. P. Constans. M.-H. Whmgbo. A i i , y ~ i i . .C . / i w i 1993. 103. 640,
A i ~ g e i i . .C h c m /Fir. Ed Eiigl. 1993. 32. 5XX.
[5] J. J N o ~ ~ oB.
a . Tarron. M -H. Whangbo. J. M.Williams. .I Clieiii Phi > 1991.
95. 5179.
16) J S. Murray. S. Raganathan. P. Politzer. J. Orx. Chriii 1991. 56. 3734
[7] J. S. Murra), P Politrer. J. Org Chmi 1991, 56. 6715
[XI a ) All MEP calculations and H F optimizations used the Ci.iussian 92 program
M . J. Frisch. G. W. Trucks. M . Head-Gordon. P. M. W. Gill. M W. Wens. J. B
Foresman. B G . Johnson. H. B. Schlegcl. M . A Robb. E. S. Replogle. R.
Gomperts. I. L Andres. K. Raghavachari. J. S Binkle!. C. Gonzales. R. L
Martin, D.I Fox. D. J. Defrees. J. Baker. J. 1. P. Stewart. I A . Pople, Gaussian.
Inc.. Pittsburgh. PA. 1992. For CH,. C H F , . and 1. Imixwere values at p
= 0 002 e b o h r - along the C-H bond vector. b) All DFT calculation^ uted the
Gaussian 94 program: M. J. Fi-isch. G.W Trucks. H . H Schlegel. P. M W.
Gill. B. G Johnson. M. A. Robb. J. R. Cheeseman. T A. Keith. G. A. Peterson. J A Montgomery. K . Raghavachari. M. A. A-Laham. V G. Zakrzewski. J V Ortir. J. B. Foresman. J. Cioslowski. H. H Stefanov. A.
Nanakakkara. M Challaconibe. C. Y Peng. P Y Ayal.i. W Chen. M. W
Wons. J. L. Andres, E S. Replogle. R Gomperts. R L Martin. D. J. Fox. J S.
Binkley. D. 1. Defrees. J Baker. J P. Stewart. M Head-Gordon. C. Gonialez.
J. A. Poplc. Gaussian, Inc . Pittsburgh PA. 1995.
[9] Since a C - H . 0 H-bond is significantly weaker than 0 1 1 . '0and 0H - N bonds. we did not include any C - H . . - 0bond in .iny inodel shown in
Figure 1
[lo] At the RHF;.'6-31G* level. the BSSE-uncorrected C - H - 0 bindingenergies
o f C H , . ' . H,Oand CHF, . H,Oare -0.56(Ref [5])and -4 05 k c a l m o l ~ ' .
[ I l l When using MEP as a measure of H-bond donor,accepror ability, we overlooked the dispersion energy contribution t o nonbondcd interactions However, due to the attractive naturc of dispcrsioii energy and bccause more dispersion forces are present in the crystal than in the models. oiir conclusion that
model systems provide the lower limit of the strength of C H. 0 interactions
remains unchanged
[I?] E. Hirota. Y Endo. S. Saito. J. L. Duncan. J Mol. . S p ( w i ~ 1981.
~ . HY. 285.
[I31 '11 The abbreviation BLYP implies that the Becke functional (A. D Becke.
P / T K .RW. A 1988.38.3098) is used for the exchange energ! m d the Lee. Yang.
and Parr functional ( C . Lee. W. Yang, R G. Parr. P / ~ E Rc*i.. R 1988.37, 7x5)
for correlation energy. b)The C-,,-CH, torsioiial barrier ciilculated for ethane
is 2.75 kcalmol-' at the BLYP 6-31G* level and 2.65 kcalmol-' at the BLYP
6-31 + + G** level: for CH,-C(NH,), i t is 5.07 kcalmol I iit the BLYP 631G' level and 4.62 kcalrnol-' at thc BLYP 6-31 + <;** level.
[I41 MM3(92). N . L. Allinger, University of Georgia. Athens. G A
Fig. 4 I!nfaiorablc contact\ between H of CH,-C[N(CH,),],
In summary. we found that 1) the strength of the three CH . . . O H-bonds in 1,3H,O estimated by Novoa et al.
(2.5 kcalmol- ' ) is the lower limit of these interactions and 2)
AE,,, of 1 is equal to or less than 2 kcalmol-' because of the
existence of proximal axial H atoms. Therefore, our results lead
to the conclusion that the unique crystal structure of 1.3 H,O is
a result of the C - H . . . O interactions that overcome the low
rotational barrier of 1 . Furthermore, these results demonstrate
the danger of relying on small model systems for solving delicate
problems of large molecules.
Received: August 7, 1995 [Z8292IE]
German version- Aiigeii. Chei??.1996. IOH. 200 -202
Keywords: hydrogen bonds
semiempirical calculations
molecular electrostatic potential
[ I ] a ) I' Seilcr. ( i R Weimxin. E. D. Glendening. F. Wernhold. V. B. Johnson.
J. D. Dunit/, ~4ii.qcwC/imi. 1987. 9Y. 1216. Aiigiw C h m h i . E d EiigI 1987.
-76. 1175. bl P.Seller. J. D. Dunit7. Heli, Chiin. Acrri 1989. 72. 1125.
[?I R I). Giccn. llr~lro,qcviBoiirling hi. C-H group.^. Wiley, New York. 1974.
(?. R I h i r a j i i .
c . C h i i i . Rp.5. 1991. 74. 290 and references therein J. BernI Ettcr. L Leiserowit7 in Strii~riirfilCoi-rekirioii. V01.2 (Eds: H.-B.
stein. %C
Bui-gi. I D Dunit/). VCH. Weinheim. 1994, pp 431 -507.
I:[. I n the ci-q\tal \trircture of 1.3H,O, each H,Omolecule engaged in C--H " - 0
hydrogeii bonding aI\o forms a hydrogen bond with the N atom o f a nearby I.
Synthesis of the Nonamannan Residue of a
Glycoprotein with High Mannose Content**
Peter Grice, Steven V. Ley,* Jorg Pietruszka, and
Henning W. M. Priepke
AIDS (Acquired Immunodeficiency Syndrome) is a vicious
retroviral disease characterized by immunosupression associated with opportunistic infections, secondary neoplasms, and neurological manifestations. Despite an extensive international
research effort, the viral infection caused by the human
immunodeficiency virus (HIV) remains incurable. In the United
States it is presently the fourth leading cause of mortality for
men between the age of 15 and 54.[']
The heavily glycosylated surface glycoprotein gpl20 plays a
critical role for HIV infection of cells. Gp120 is responsible not
only for the attachment and penetration of target cells, but also
for the antiviral immune response. There is evidence that the
Prof. Dr. S. V. Ley. Di-. P. Grice. Dr I. Pietruszka. Dr H W. M Priepke
University of Cambridge. Department of Chemistry
Lensfield Road. GB-Cambridge CB2 1 EW ( U K )
Telefax: I n t . code +(1223)336-442
Cyclohexane-l .?-diacetals in Synthesis. Part 4 This work wii\ supported by the
BP Research Endowment (to S. V. L.). the Zeneca Strategic Research Fund.
the Deutsche Forschungsgemeinsehaft (postdoctoral fellow\hip to J. P ). and
Schering Agrochemicals Ltd. now AgrEvo. (Schering Fellowrhip i n Bioorganic
Chemistry to H. W M P) Parts 1-3- Ref. [7a- c]
glycans of the viral envelope are possible targets for immunotherapy and/or vaccine development.[’] No less than 29
N-linked oligosaccharides have been identified, the main fraction being of the high mannose type, for example 1,13] a ubiquitous undeca~accharide.~~]
In view of the remarkable activity of
antibodies directed against the mannose residues of HIV-1 glycoprotein gp120 in ~ i t r o , [ the
~ ’ mannan moiety of this glycoprotein is a very attractive synthetic target.“] In this paper we
describe the preparation of the model nonasaccharide 2 with our
CDA methodology (CDA = cyclohexane-l,2-diacetal) for
oligosaccharide assembly.[71
3b, R = TPS
4b, R = T P S
E 0a,R=Bz
8 b , R = Bn
Scheme 1. Building blocks A - E for the synthesis of 2 (schematic representation at
the top right).
2, R ’ = H ,
Recently we reported that the reactivity of glycosyl donors
can be tuned by the selective introduction of different protecting
and leaving groups, thus enabling highly efficient oligosaccharide synthesis.[’] Four levels of reactivity are provided by these
methods. This led us to propose a synthetic plan for 2 including
the five building blocks A - E (Scheme l).l8I We anticipated that
the final step for assembling the nonasaccharide would be the
coupling between an ethylthio pentasaccharide donor and a
tetrasaccharide acceptor unit. The preparation of the two segments should be straightforward, since the CDA group decreases the reactivity of glycosyl donors relative to the per-0-benzylated compounds (reactivity A > B) .[’I In addition, phenylseleno
glycosides are more reactive than the ethylthio analogues (reactivity B > C,E), whereas the 0-glycoside D is virtually unreactive in the presence of iodonium sources.L91
Unfortunately it was not possible to selectively benzylate the
6-position of CDA-protected mannose donors, which would
have led directly to 3a (B) and 4 a (C).r81
Instead we began with
the TPS-protected (TPS = 6-0-tert-butyldiphenylsilyl) analogues 3 b and 4 b and performed appropriate deprotections and
reprotections at later stages. First we synthesized the “common” disaccharide 6 from 5 (A) and 3b in 5 5 % yield
(Scheme 2), by a fast reaction (reaction time less than ten minutes) that is selective towards activation with N-iodosuccinimide/triflic acid (NIS/TfOH). Subsequent protecting group
manipulation (desilylation/benzylation) furnished 7 in 84 YO
yield. Two equivalents of 7 then reacted selectively with 8a (E)
to form the pentasaccharide 9 (80%). The benzoyl group in the
2-position of 8a is essential not only for high a-selectivity in the
following coupling reaction, but also for the successful formation of 9, since the 2-0-benzyl compound 8 b reacted with NIS
faster than disaccharide 7.
(0 VCH
Verlugsgesellschuft mhH, 0-69451 Wrmheim, 1996
Scheme 2. a) NIS/TfOH(cat.). dichloroethane/Et,O (lil), 4A molecular sieves,
5 5 % ; b)TBAFiAcOH(3%),THF,c)NdH,BnBr(Bn = PhCH,),DMF,X4% over
two steps. d) 8 a (0.4 equiv), NIS/TfOH(cdt.), dichloroethane/Et,O (1 : 1). 4A
molecular sieves, 80%.
US70-0833/96/3502-U196:$ 10.00 + .2S/U
Anger. Chem. Inr. Ed. Engl. 1996, 35. No. 2
Next we focused on the synthesis of the trisaccharide 10 for
further elaboration to the tetrasaccharide 11 (Scheme 3). For
the formation of disaccharide 6 the difference in glycosyl reactivity originated from the choice of protecting groups. For the
formation of trisaccharide 10, however, the difference in glycosyl reactivity could be exclusively controlled by changing from
the phenylselenoglycoside 3 b to the ethylthioglycoside 4 b without changing the protecting groups. The desired trisaccharide 10
was thus formed in an excellent yield (80%); after protecting
group manipulation 12 was obtained in 70% yield over two
steps. Finally. tetrasaccharide 11 was formed by activation of 12
in the presence of acceptor 13 with NIS/TfOH and desilylation
with tetrabutylammonium fluoride (TBAF)/acetic acid (66 %
over two steps, Scheme 3).
The final glycosidation step--activation of 9 in the presence
of 11-provided the desired nonasaccharide 14 (Scheme 4).
However, the low 30 % yield of this reaction was disappointing.
More successful preliminary results with other tetrasaccharide
+ 1 2 -
/ o
b, c, d
acceptors indicate that this may be due to a steric mismatch of
the two partners, a phenomenon which has been previously
noted.["] Deprotection of 14 to yield the target molecule 2 was
straightforward. The global cleavage of the CDA groups was
achieved with trifluoroacetic acid/water (20jl) in an acceptable
43% yield (81 % per CDA unit). Debenzoylation mediated by
sodium methoxide in methanol at 55 "C (no reaction at room
temperature) followed by removal of the benzyl groups by catalytic hydrogenation occurred smoothly to afford 2.["]
In summary, we have achieved a short synthesis of the mannan residue of a high mannose type oligosaccharide present on
the viral coat of HIV-1. We efficiently assembled the protected
nonasaccharide 14 from monosaccharide building blocks using
only one promotor system (NIS/TfOH) to activate the different
glycosyl donors and only minor protecting group manipulation.
Furthermore, this synthesis demonstrates that the strategy of
tuning the reactivity of glycosides is a powerful tool for the
concise and rapid preparation of complex oligosaccharides. The
synthesis of a nonasaccharide with a P-0-linker (instead of the
a-0-methyl group) that would permit binding of the glycan to a
protein (hence providing us with a tool for further biological/
medical testing) is currently under investigation.
Received: July 24, 1995 [Z8250IE]
German version: Angen. Chem. 1996. 10R, 206-208
BnO 0
Keywords: AIDS . mannose . oligosaccharide . protecting
Scheme 3. a) NIS/TfOH(cdt.), dichloroethane/Et,O ( l / l ) ~
4 A molecular sieves,
8 0 % ; b) TBAF;AcOH (3%). THF; c) NdH, BnBr, D M E 70% over two steps; d)
12(1.1 equiv). NIS;TfOH(cat.), dichloroethane/Et,O(l/l), 48, molecular sieves: e)
TBAF/AcOH ( 3 % ) in T H E 66% over two steps.
Angew. C ' h r m . I m . Ed. Engl. 1996. 35. N o . 2
Scheme 4. a) NIS/TfOH(cat.), dichloroethane/Et,O ( l / l ) , 4 A molecular sieves,
30%: b) CF,CO,H/H,O (20/1). 5 min, (43%): c) NaOCH, in MeOH, Amherlite
IR 120, ( 5 5 % ) ; d) Pd(OH), on activated charcoal, MeOH, quantitative.
[I] R. S. Cotran, V. Kumar, S. L. Robbins, Robbins Pathologic Busis of Diseuse,
Saunders. Philadelphia, London, 1994, Chap. 6, and references therein.
(21 J:E. S. Hansen, H. Clausen, C . Nielsen, L. S. Teglhjierg. L. L. Hansen, C. M.
Nielsen, E. Dahelsteen, L. Mathiesen, S.-i. Hakomori. J. 0 . Nielsen, J. Virol.
1990, 64, 2833-2840; J:E. S. Hansen, C. Nielsen, M. Arendrup, S. Olofsson.
L. Mathiesen, J. 0. Nielsen, H. Clausen, ihid. 1991, 65. 6461-6467; J.-E. S.
Hansen, C. M. Nielsen, C. Nielsen, P. Heedegaard, L. R. Mathiesen, J. 0 .
VCH Verlugsgesellschuft m b H , 0-65451 Weinherm, 1996
0570-0833~56/3502-0155$10.00+ .25:0
Nielsen, AIDS 1989.3. 635-~641;
A. Kobata, Alfred Benron Symp. 1994. 36,
246-256,J.-E. S. Hansen, H . Clausen. T. Ssrensen, T. White, H.H.Wandall,
ibid. 1994,36,297-310;J.-E. S.Hansen, B. Hofmann, T. Ssrensen, H . Clausen.
ihirl. 1994. 36. 414-427, and references therein.
[3] T. Mizuochi. M. W. Spellman. M. Larkin. J. Solomon, L. J. Basa, T. Feizi,
Biochern. .I 1988,254, 599-603.
[41 H . Lis, N.Sharon, J. B i d . Cliern. 1978.253,3468:E.Li, S.Kornfeld, [hid. 1979.
254, 1600; L. Dorland, H . Ydn Halbeek, J. F. G. Vliegenthart, H . Lls. N.
Sharon. ibid. 1981,256, 7708.
[51 W E.G.Miiller, H . C. Schroder, P. Reuter, A. Maidhof. G. Uhlenbruck, 1.
Winkler, AIDS 1990,4 , 159- 162.
[61 Synthesis of major segments of high mannose glycoproteins: H. Paulsen,
Angew. Chem. 1990,102. 851 -867; Angew. Chnn. I n t . Ed. Engl. 1990,29,823.
and references therein; J. R. Merritt. E. Naisang, B. Fraser-Reid. .IOrg. Cliem.
[7l a) S. V. Ley, H. W M. Priepke, S. L. Wdrriner. Angew. Cliem. 1994,106,24102412;Angew. Chem. Int. Ed. Engl. 1994.33,2290-2292;b) S. V.Ley, H. W. M.
Priepke. ihid. 1994,106, 2412-2414and 1994.33,2292-2294; c) P. Grice, S. V.
Ley, J. Pietruszka, H . W M. Priepke, E. P. E.Walther. Synlerr 1995,781-784;
d) T. Ziegler, Angew. Chem. 1994,106,2362-2365:Angew Cliern.In(. Ed. Engl.
1994,33. 2212-2275.
[XI Preparation of building blocks with full experimental details will be reported in
due course.
[9] S.Mehtd, B. M. Pinto, J. Org. Cheni. 1993,58,3269-3276; H. M. Zuurmond,
P. H. van der Meer, P. A. M. van der Klein, G . A. van der Marel, J. H . van
Boom. J. Carholvdr. Clrem. 1993, 12, 1091-1103; G.H . Veeneman. J. H. van
Boom, Tetrahedron Lett. 1990, 31, 275-278: G . H. Veeneman. S. H. van
Leeuwen, J. H. van Boom, ibid. 1990,31, 1331-1334.
Y.-M. Zhang. A. Brodzky, P. Sinay, G. Saint-Marcoux, B. Perly. Tetruhedron:
Asjmnwtry 1995,6. 1195%1216.
2: ' H N M R (500 MHz, D,O, 297.3 K): 6 = 5.29 (s, 1 H. I-Ha). 5.22 ( s , 1 H,
I - € l J , 5.19 ( s , 1 H, l-HJ, 5.04 (s, 1 H. I-HJ. 4.93 ( s , 3H. l-Hc. I-H,, 1-HJ,
l a R =CH,
l b R = CH(CH&
1 C R = C(CH3)Z
I d R =C,Hs
l e R = CHZ(C6HS)
R = CHzCH(CH3)z
l g R = CH&(CH&
tested these ligands in intermolecular Heck reactions of cyclic
olefins. The reaction between 2,3-dihydrofuran and l-cyclohexenyl triflate, previously reported by Ozawa, Hayashi et a1.,[2b1
was chosen to screen different ligands and catalyst precursors
and to optimize the reaction conditions (Table 1). The best
enantioselectivity and also the highest catalyst activity was observed with the tert-butyldihydrooxazole derivative 1 c. With
3 mol% of catalyst, prepared in situ from [Pd(dba),]['I and
1.S-2 equivalents of ligand 1c, the 2,s-dihydrofuran derivative
2 was formed in high yield and with excellent enantioselectivity
[Eq. (a), Table 11. The corresponding 2,3-dihydrofuran deriva-
4.76(s,1H,l-H,),4.63(s,1H,l-H,),3.40-4.07(m,54H),3.29(s,3H.OCH,): +
13CNMR (100 MHz, D,O): 6 =102.2, 102.2 (2x). 100.9,100.6 (2x), 100.5.
99.4, 98.0 (anomeric C), 54.74 (OCH,); MALDI-TOF-MS: m / z : 1513
( [ M + Na]'). MALDI = matrix-supported laser desorptioniionkation. TOF
= time of flight.
[Pd(dba),] (3 mol%)
l c (6mol%)
C6H8,30 "C, 3 d
Table I . Enantioselective Heck reaction of 2,3-dihydrofuran to give (R)-2 [Eq. (a)].
re ["h]
Yield ["A] [a]
> 99
98 [bl
Chiral Phosphanyldihydrooxazoles in Asymmetric
Catalysis: Enantioselective Heck Reactions**
Olivier Loiseleur, Peter Meier, and Andreas Pfaltz*
The development of enantioselective variants of the Heck
reaction has added a new dimension to this important method
for C-C bond formation.['. 21 Excellent enantioselectivities
have been achieved and several remarkable applications in the
synthesis of complex natural products have been reported.
So far, the most effective ligand for these reactions has been
BINAP." - 31 However, the application range of Pd(B1NAP)
catalysts seems limited to certain classes of substrates and their
activity is often low. In addition, these catalysts promote C = C
bond migration which sometimes leads to useful products but
unfortunately often results in mixtures of isomers. Therefore, it
i s necessary to search for other ligands and catalysts to enhance
the scoDe of enantioselective Heck reactions.
In the course of our work on phosphanyldihydrooxazoles
1,[4-61 which have proven to be effective ligands for enantioselective Pd-t4"*'1 and W-catalyzed[61allylic substitution, we have
Prof. Dr. A. Pfaltz.[+' Dipl.-Chem. 0. Loiseleur, P. Meier
lnstitut fur Organische Chemie der Universitit
St.-Johanns-Ring 19, CH-4056 Basel (Switzerland)
New address: Max-Planck-Institut fur Kohlenforschung
Kaiser-Wilhelm-Platr I , D-45470 Mulheirn an der Ruhr (Germany)
Fax: Int. code +(208)306-2992
Financial support of this work by the Swiss National Science Foundation and
Hoffmann-La Roche AG. Basel. i s gratefully acknowledged.
VCH Verlugsgesellschuft mbH, 0-69451 Weinheim, 1996
sodium carbonate
sodium acetate
[a] Determined by GC with n-tridecane as internal standard. [b] Yield of purified
product: 92%.
tive was not detected, in contrast to the Pd(B1NAP)-catalyzed
reactionrzb1which yields the thermodynamically more stable
2,3-dihydro isomer as the main product with 5 8 % yield and
87 YO ee. With Pd(B1NAP) catalysts, 1,8-bis(dimethylamino)naphthalene (proton sponge) has to be used as base for optimum results, whereas in our case simpler bases such as triethylamine or N,N-diisopropylethylamineare equally effective. Catalysts derived from analogous ligands with less bulky substituents at the stereogenic center are significantly less reactive
and the resulting ee values are slightly lower [ Y conversion/
% ee: 97/98 for 1 c, 24/90 for 1 e, 18/95 for 1 f; proton sponge,
50 "C, other conditions, see Equation (a)].
Similar results were obtained with phenyl and l-cyclopentenyl triflate (Scheme 1). Arylation of 4,7-dihydro-I ,3-dioxepin,
which leads to a masked hydroxyaldehyde, also proceeds with
good enantioselectivity and satisfactory yield. The corresponding Pd(B1NAP)-catalyzed process[2d1 was reported to give
72 'YO ee and 84 YOyield.
The reaction was found to be highly sensitive to traces of
chloride ions and chloroform. No reaction was observed in the
presence of Et4NC1 o r with [(lc)PdCl,]/BuLi as catalyst precur-
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Angen. Chem. I n t . Ed. Engl. 1996,35, No. 2
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contents, synthesis, mannose, residue, nonamannan, high, glycoprotein
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