A five-component one-pot synthesis of phosphatidylinositol pentamannoside (PIM5)

Article abstract of DOI:10.1016/j.cclet.2017.12.014

A practical and efficient synthesis of phosphatidylinositol pentamannoside (PIM₅) was achieved based on a five-component one-pot sequential glycosylation protocol with exclusive regio- and stereo-selectivity. Two regioselective sequential glycosylations on inositol and p-tolyl thioglycosides as the sole type of building blocks made this protocol to avoid the tedious protective group manipulations. This synthetic strategy provides access to other important glycolipids with similar structures.

Full text of DOI:10.1016/j.cclet.2017.12.014

Accepted Manuscript
Title: A five-component one-pot synthesis of
phosphatidylinositol pentamannoside (PIM5)
Authors: Dong Wang, De-Cai Xiong, Xin-Shan Ye
PII:
DOI:
Reference:
S1001-8417(17)30548-X
https://doi.org/10.1016/j.cclet.2017.12.014
CCLET 4376
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
29-11-2017
6-12-2017
18-12-2017
Please cite this article as: Dong Wang, De-Cai Xiong, Xin-Shan Ye, A five-component
one-pot synthesis of phosphatidylinositol pentamannoside (PIM5), Chinese Chemical
Letters https://doi.org/10.1016/j.cclet.2017.12.014
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Communication
A five-component one-pot synthesis of phosphatidylinositol pentamannoside (PIM5)
Dong Wang, De-Cai Xiong*, Xin-Shan Ye*
State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
Corresponding authors.
E-mail addresses: decai@bjmu.edu.cn (D.C. Xiong); xinshan@bjmu.edu.cn (X.S. Ye)
Graphical Abstract:
A practical and efficient synthesis of phosphatidylinositol pentamannoside (PIM5) was achieved based on a five-component one-
pot sequential glycosylation protocol with exclusive regio- and stereo-selectivity.
ARTICLE INFO
ABSTRACT
Article history:
A practical and efficient synthesis of phosphatidylinositol pentamannoside (PIM5) was achieved
based on a five-component one-pot sequential glycosylation protocol with exclusive regio- and
stereo-selectivity. Two regioselective sequential glycosylations on inositol and p-tolyl
thioglycosides as the sole type of building blocks made this protocol to avoid the tedious
protective group manipulations. This synthetic strategy provides access to other important
glycolipids with similar structures.
Received 29 November 2017
Received in revised form 6 December 2017
Accepted 11 December 2017
Available online
Keywords:
Phosphatidylinositol pentamannoside
Glycosylation
Preactivation
One-pot synthesis
Thioglycoside
Tuberculosis (TB) is a major cause of mortality worldwide [1]. The thick glycolipid-containing cell envelope of M. tuberculosis is
critical for bacterial survival and growth [2]. Among the glycolipids, phosphatidylinositol mannosides (PIMs) and their
hypermannosylated structural relatives (lipomannans and lipoarabinomannans), noncovalently anchor to the plasma membrane and the
outer capsule through palmitate, stearate and tuberculostearate lipid chains, as determinants for modulating the host immune system
and dictating the fate of mycobacteria [3]. The isolation of homogeneous glycolipids from M. tuberculosis is challenging and does not
give access to glycolipid derivatives or substructures. Therefore, chemical synthesis is employed to obtain these glycolipids with
defined structures and high purity, which are suitable for biochemical assays and medical applications. PIMs are the biosynthetic
precursors of lipomannan and lipoarabinomannan [4]. Especially, phosphatidylinositol pentamannoside (PIM5) is similar to the

conserved structure. Thus, PIM5 would be a good synthetic model for the synthesis of tuberculosis-related glycolipids. Elegant
methods or strategies have been developed for the synthesis of PIMs and their related compounds [5-30]. However, to the best of our
knowledge, there has been no report on the synthesis of the pseudo-hexasaccharide chain in PIM5 by using preactivation-based one-pot
glycosylation protocol [31-45]. We describe herein the one-pot sequential assembly of PIM5.
Scheme 1. Retrosynthetic analysis of PIM5.
Our synthetic plan for PIM5 is depicted in Scheme 1. In our initial plan, the pseudo-hexasaccharide 1 was fragmented into six
segments. The core carbohydrate structure 1 would be probably assembled by the preactivation-based one-pot glycosylation protocol.
Since most α-mannosyl would be achieved using 2-O- acylated-mannosyl building blocks by virtue of the neighboring group
participation, the 2-O-acetyl or benzoyl protective groups were equipped to control the α-glycosyl linkages. The benzoyl group was
also used to avoid the acyl migration. To try the one-pot six-component assembly (2 + 6 + 4 + 4 + 5 + 2), the readily perceptible
synthetic issues include the stereoselective glycosylation of blocks 6 and 4 to deliver the necessary 1-6 linkage as well as the
regioselective glycosylation between the equatorial hydroxyl and the axial hydroxyl in the inositol unit 5. Because the preliminary
experiments involving the glycosyl coupling of the benzylated compound 6 and block 4 gave the poor β selectivity, the disaccharide 3
was chosen as an alternative building block. In addition, it has been proved that the regioselective glycosylation of the inositol blocks
can be accomplished using the monosaccharide building blocks step by step [9, 20]. We conceived that it could be also achieved using
the oligosaccharide block via one-pot protocol. Therefore, the one-pot five-component assembly of PIM5 (2 + 3 + 4 + 5 + 2) was
designed. The lipid 7 would be installed in the final stage. The benzyl group and p-methoxybenzyl group would be utilized as the
global protective group and the temporary protective group, respectively.
o
Scheme 2. Synthesis of building blocks 2-4. Reagents and conditions: (a) HClO4/Ac2O, 0 C. (b) HBr/HOAc, r.t. (c) 2,4,6-collidine, MeOH/CH2Cl2,
.
o
reflux. (d) NaOMe/MeOH. (e) NaH, BnBr, DMF. (f) TolSH, BF3 Et2O, CH2Cl2, Ar, 4Å MS, -78 C. (g) TIPSCl, imidazole, DMF. (h) BzCl, Py. (i)
TBAF, THF. (j) Ph2SO, Tf2O, Et2O, 4Å MS, -78 oC, and then 4. (k) 3% (v/v) AcCl, MeOH/CH2Cl2.
Monosaccharide building blocks 2 and 4 were prepared from mannose [14, 30, 46]. As shown in Scheme 2, peracetylation of
mannose and subsequent bromination, followed by the treatment with 2,4,6-collidine and MeOH, afforded orthoester 8. Deacetylation
of 8 which was followed by perbenzylation provided compound 9 in 95% yield. Glycosylation of 9 and p-thiocresol (TolSH) produced
the building block 2 in 65% yield. Compound 8 was subjected to the successive deacetylation, regioselective silylation of the 6-OH
using TIPSCl, and benzylation to furnish compound 10 in 69% yield. The reaction of 10 with TolSH generated thiomannoside 11,
which was smoothly converted into the building block 4 through deacetylation, benzoylation and desilylation. For the preparation of
disaccharide 3, the glycosyl donor 2 was activated at low temperature (-78 °C) with diphenyl sulfoxide and trifluoromethanesulfonic
anhydride (Tf2O), and then the glycosyl acceptor 4 was added to achieve the glycosylation. After a selective deacetylation, the
disaccharide building block 3 was obtained in 80% yield over two steps.

o
Scheme 3. Synthesis of building blocks 5 and 7. Reagents and conditions: (a) TIPSCl, imidazole, DMF, r.t. (b) NaH, BnBr, DMF, 0 C to r.t. (c)
o
TBAF, THF. (d) DMP, CH2Cl2, r.t. (e) K2CO3, Ac2O, MeCN, reflux. (f) Hg(CF3CO2)2, acetone/H2O (4:1), r.t.; then NaOAc (aq.), NaCl (aq.), 0 C to
r.t. (g) NaBH(OAc)3, HOAc/MeCN (1:1), 0 oC to r.t. (h) PPTS, CH2=CHOEt, CH2Cl2. (i) NaOMe/MeOH, reflux. (j) PMBCl, NaH, TBAI, THF, r.t. (k)
PPTS, n-PrOH, r.t. (l) H3PO3, PivCl, Py.
The partially protected myo-inositol 5 was prepared over eleven steps (Scheme 3). Starting from methyl glucopyranoside 12,
compound 13 was obtained by three consecutive steps [47]. The primary hydroxyl group in 13 was oxidized to an aldehyde using
Dess–Martin periodinane (DMP). Then, inositol 14 was readily available from the aldehyde via three-step transformations. The C-2
and C-6 hydroxyl groups in inositol 14 were temporarily masked as ethoxyethyl (EE) ethers. Subsequently, deacetylation, followed by
p-methoxybenzylation and removal of the EE groups under acidic conditions, afforded the building block 5 in 73% yield over four
steps [13]. Finally, the commercially available octadecanol (15) was phosphorylated using H3PO3, pivaloyl chloride (PivCl) and
pyridine to provide the H-phosphonate 7 [48].
With all building blocks in hand, the five-component assembly of fully protected pseudohexasaccharide derivative 1 was attempted
as outlined in Scheme 4. The preactivation of mannoside 2 in dichloromethane at -78 °C by Ph2SO/Tf2O for 10 min, was followed by
the addition of acceptor 3. After stirring for another 15 min at -78 °C, the reaction mixture was gradually warmed up to room
temperature for 120 min, and then cooled down back to -78 °C. Following the similar glycosylation protocol, building blocks 4 and 5
were sequentially added to the reaction mixture. Mannoside donor 2 was then added to the reaction mixture, which was activated by
substoichiometric amount (0.8 equiv) of Tf2O at -78 °C to continue the glycosyl coupling reaction, affording pseudohexasaccharide 1
in 40% isolated yield (see the Supplementary data). It should be noted that the regioselective introduction of tetrasaccharide moiety at
the equatorial hydroxyl position of inositol 5 can be realized. The excellent regioselectivity might come from the small steric hindrance
of 2-OH in acceptor 5 and the bulky tetrasaccharide donor [8]. The structure of 2-O-mannosyl-6-O-tetraglycosyl-inositol 1 was
characterized by extensive NMR experiments (the Supplementary data). Correlations of the anomeric hydrogen (5.58 ppm)/carbon
(98.75 ppm) of the tetraglycosyl unit with the H-6 of inositol (4.07 ppm) and the anomeric hydrogen (5.20 ppm)/carbon (98.80 ppm) of
mono-mannosyl unit with the H-2 of inositol (4.38 ppm) were observed in its gHMBC and NOESY spectra, confirming that the 6-O-
tetraglycosylation and 2-O-mannosylation occurred exclusively on inositol. The α-anomeric configurations of newly-formed glycosyl
linkages were established by the one-bond 13C–1H coupling constant (>170 Hz) of C-1 in the HMBC spectrum.
Scheme 4. One-pot assembly of the pseudohexasaccharide. The values given in parentheses denote the number of equivalents of each reagent.
Next, all acyl protective groups in pseudohexasaccharide 1 were removed with sodium methoxide in methanol, and the free
hydroxyl groups were masked as benzyl ethers to give compound 16. The p-methoxybenzyl group in 16 was removed by treatment
with trifluoroacetic acid to provide 17. The attachment of H-phosphonate 7 to pseudohexasaccharide 17 was carried out by using
pivaloyl chloride, followed by iodine-mediated in situ oxidation and cation exchange, affording compound 18 in 80% isolated yield.
The global hydrogenolysis of the benzyl groups in 18 provided the target PIM5 in 75% yield (Scheme 5).

Scheme 5. Phosphorylation and deprotection. Reagents and conditions: (a) NaOMe/MeOH, r.t. (b) NaH, BnBr, DMF, r.t. (c) 5% TFA/CH2Cl2, r.t. (d)
PivCl, Py, r.t.; then 7. (e) I2, Py/H2O, r.t. then Na2S2O3 (aq.). (f) 10% Pd/C, H2, EtOAc/THF/n-PrOH/H2O.
In conclusion, using
a five-component one-pot sequential glycosylation strategy, we have successfully synthesized
phosphatidylinositol pentamannoside (PIM5), a key structural motif of antigenic glycolipids found on the cell wall of Mycobacterium
tuberculosis. It is noteworthy that p-tolyl thioglycosides as the sole type of building blocks were used in this preactivation-based
glycosylation protocol. In addition, two regioselective sequential glycosylations on inositol further simplified the overall synthetic
route. By means of the same strategy, some other important glycolipids with similar structures such as lipoarabinomannan (LAM) and
glycosylphosphatidylinositol (GPI) anchors could be synthesized to study their structure−activity relationships.
Acknowledgments
This work was financially supported by the National Natural Science Foundation of China (Nos. 21232002, 21572012, and
21772006), Beijing Natural Science Foundation (No. 2142015) and Beijing Higher Education Young Elite Teacher Project (No.
YETP0063).
Supplementary data
Experimental procedures and compound characterization dada. Supplementary data associated with this article can be found, in the
online version, at http://
References
[1] WHO. Tuberculosis factsheet, October 2016, http://www.who.int/mediacentre/factsheets/fs104/en/
[2] P.C. Karakousis, W.R. Bishai, S.E. Dorman, Cell Microbiol. 6 (2004) 105-116.
[3] B. Cao, S.J. Williams, Nat. Prod. Rep. 27 (2010) 919-947.
[4] M.E. Guerin, J. Kordulakova, P.M. Alzari, et al., J. Biol. Chem. 285 (2010) 33577-33583.
[5] C.J.J. Elie, R. Verduyn, C.E. Dreef, et al., J. Carbohydr. Chem. 11 (1992) 715-739.
[6] Y. Watanabe, T. Yamamoto, T. Okazaki, Tetrahedron 53 (1997) 903-918.
[7] A. Stadelmaier, R.R. Schmidt, Carbohydr. Res. 338 (2003) 2557-2569.
[8] A. Stadelmaier, M.B. Biskup, R.R. Schmidt, Eur. J. Org. Chem. 69 (2004) 3292-3303;
[9] K.N. Jayaprakash, J. Lu, B. Fraser-Reid, Bioorg. Med. Chem. Lett. 14 (2004) 3815-3819.
[10] K.N. Jayaprakash, J. Lu, B. Fraser-Reid, Angew. Chem., Int. Ed. 44 (2005) 5894-5898.
[11] B. Fraser-Reid, J. Lu, K.N. Jayprakash, C. Lopez, Tetrahedron: Asymmetry 17 (2006) 2449-2463.
[12] B. Fraser-Reid, S.R. Chaudhuri, K.N. Jayaprakash, et al., J. Org. Chem. 73 (2008) 9732-9743.
[13] X. Liu, B.L. Stocker, P.H. Seeberger, J. Am. Chem. Soc. 128 (2006) 3638-3648.
[14] S. Boonyarattanakalin, X. Liu, M. Michieletti, B. Lepenies, P.H. Seeberger, J. Am. Chem. Soc. 130 (2008) 16791-16799.
[15] P.S. Patil, S.C. Hung, Chem. Eur. J. 15 (2009) 1091-1094.
[16] P.S. Patil, S.C. Hung, Org. Lett. 12 (2010) 2618-2621.
[17] P.S. Patil, T.J. Cheng, M.M.L. Zulueta, et al., Nat. Commun. 6 (2015) 7239.
[18] P.S. Patil, M.M.L. Zulueta, S.C. Hung, J. Chin. Chem. Soc. (Weinheim, Ger.) 61 (2014) 151-162.
[19] G.D. Ainge, J. Hudson, D.S. Larsen, et al., Bioorg. Med. Chem. 14 (2006) 5632-5642.
[20] G.D. Ainge, N.A. Parlane, M. Denis, et al., Bioorg. Med. Chem. 14 (2006) 7615-7624.
[21] B.S. Dyer, J.D. Jones, G.D. Ainge, et al., J. Org. Chem. 72 (2007) 3282-3288.
[22] G.D. Ainge, N.A. Parlane, M. Denis, et al., J. Org. Chem. 72 (2007) 5291-5296.
[23] G.D. Ainge, B.J. Compton, C.M. Hayman, et al., J. Org. Chem. 76 (2011) 4941-4951.
[24] G.D. Ainge, W.J. Martin, B.J. Compton, et al., J. Med. Chem. 54 (2011) 7268-7279.
[25] G.M. Rankin, B.J. Compton, K.A. Johnston, et al., J. Org. Chem. 77 (2012) 6743-6759.
[26] A.M.M. Lee, G.F. Painter, B.J. Compton, D.S. Larsen, J. Org. Chem. 79 (2014) 10916-10931.
[27] A. Ali, M.R. Wenk, M. J. Lear, Tetrahedron Lett. 50 (2009) 5664-5666.
[28] B. Cao, J.M. White, S.J. Williams, Beilstein J. Org. Chem. 7 (2011) 369-376.
[29] J. Gao, Z. Guo, J. Org. Chem. 78 (2013) 12717-12725.
[30] J. Gao, G. Liao, L. Wang, Z. Guo, Org. Lett. 16 (2014) 988-991.
[31] X. Huang, L. Huang, H. Wang, X.S. Ye, Angew. Chem., Int. Ed. 43 (2004) 5221-5224.
[32] Y. Wang, X. Huang, L.H. Zhang, X.S. Ye, Org. Lett. 6 (2004) 4415-4417.
[33] Z. Wang, L. Zhou, K. El-Boubbou, et al., J. Org. Chem. 72 (2007) 6409-6420.
[34] A. Miermont, Y. Zeng, Y. Jing, et al., J. Org. Chem. 72 (2007) 8958-8961.

[35] Y. Zeng, Z. Wang, D. Whitfield, X. Huang, J. Org. Chem. 73 (2008) 7952-7962.
[36] Y. Geng, L.H. Zhang, X.S. Ye, Chem. Commun. 44 (2008) 597-599.
[37] Y.S. Lu, Q. Li, L.H. Zhang, X.S. Ye, Org. Lett. 10 (2008) 3445-3448.
[38] X. Lu, M.N. Kamat, L. Huang, X. Huang, J. Org. Chem. 74 (2009) 7608-7617.
[39] L. Yang, J. Zhu, X.J. Zheng, G. Tai, X.S. Ye, Chem. Eur. J. 17 (2011) 14518-14526.
[40] P. Peng, X.S. Ye, Org. Biomol. Chem. 9 (2011) 616-622.
[41] Y. Geng, Q. Qin, X.S. Ye, J. Org. Chem., 77 (2012), 5255-5270.
[42] L. Yang, Q. Qin, X.S. Ye, Asian J. Org. Chem. 78 (2013) 30-49.
[43] R.Z. Mao, D.C. Xiong, F. Guo, et al., Org. Chem. Front. 3 (2016) 737-743.
[44] Y. Wu, D.C. Xiong, S.C. Chen, et al., Nat. Commun. 8 (2017) 14851.
[45] G.J. Liu, C.Y. Li, X.T. Zhang, et al., Chin. Chem. Lett. (2017) http://dx.doi.org/10.1016/j.cclet.2017.09.034.
[46] B.M. Swarts, Z. Guo, J. Am. Chem. Soc. 132 (2010) 6648-6650.
[47] Z.J. Jia, L. Olsson, B. Fraser-Reid, J. Chem. Soc., Perkin Trans. 1 (1998) 631-632.
[48] C.F. Becker, X. Liu, D. Olschewski, et al., Angew. Chem., Int. Ed. 47 (2008) 8215-8219.