J. Am. Chem. Soc. 2000, 122, 8097-8098
8097
Supramolecular Structures of Novel
Carbohydrate-Based Phospholipids
Geoffrey S. Hird, Thomas J. McIntosh,† and
Mark W. Grinstaff*,‡
Department of Chemistry
Paul M. Gross Chemical Laboratory
Duke UniVersity, Durham North Carolina 27708
Department of Cell Biology, Duke UniVersity Medical Center
Durham, North Carolina 27710
Figure 1. 1,2-Dilauroyl-sn-glycero-3-phosphocholine (DLPC) (A) and
methyl-2,3-di-O-lauroyl-â-D-ribo-5-phosphocholine (DLRPC) (B).
Scheme 1. Synthetic Scheme for DLRPCa
ReceiVed May 17, 2000
ReVised Manuscript ReceiVed July 7, 2000
Conventional glycerol-based phospholipids such as phosphati-
dylcholines self-assemble in water as spherical three-dimensional
self-closed structures known as liposomes.1-4 The potential
applications of liposomes are numerous and include their uses as
drug delivery vehicles, gene transfection agents, ultrasound phase
contrast agents, carriers for dyes and fragrances, as well as models
and tools for membrane structure and function studies.5-12 Current
modifications of phospholipid structure are limited to the hydro-
phobic tails, hydrophilic headgroups, and structural variations of
the glycerol backbone.12-20 Consequently, alteration of the
conventional glycerol backbone by complete substitution provides
new opportunities for (1) assessing supramolecular structure
formation and (2) attaching macromolecules or ligands for
biological targeting. Herein we report the synthesis and physical
characterization of a novel carbohydrate phospholipid, that is an
analogue of 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC)
(A) (Figure 1), where glycerol is replaced by ribose (B). These
new phospholipids spontaneously form three-dimensional su-
pramolecular structures in aqueous solution.
a a) TrCl, C5H5N, 3 h, 120 °C, b) DCC, DMAP, lauric acid, DMF, 48
h, 60 °C, c) acetic acid, H2O, 12 h, 50 °C, d) 2-cyanoethyl diisopropyl-
chlorophosphoramidite, DiPEA, CH2Cl2, 2 h, 22 °C, e) tetrazole, choline
chloride, I2, ACN, 3 h, 22 °C, f) TEA (aq), 3 h, 22 °C.
chromatography in 87% yield with an eluent of 3% methanol/
chloroform. Next, a DCC coupling with DMAP and lauric acid
in DMF afforded compound 3. The compound was purified on a
silica gel column with the eluent of 9/1 hexane/ethyl acetate, and
then immediately dissolved in aqueous acetic acid to remove the
trityl protecting group. Compound 4 was subsequently purified
by silica gel column chromatography (eluent 7/3 hexane/ethyl
acetate) with an overall yield of 41% from 2 to 4. The synthesis
of compound 5 was accomplished by first reacting 4 with
2-cyanoethyl diisopropylchlorophosphoramidite followed by ad-
dition of choline chloride. The phosphorus(III) compound was
subsequently oxidized to phosphorus(V) by I2. Finally, the
cyanoethyl protecting group of 6 was removed by dissolving the
mixture in 0.14 M (aq) TEA and stirring for 3 h. at room
temperature. Compound 7 was isolated after alumina (65/25
chloroform/methanol; 65/25/4 chloroform/methanol/H2O), Sepha-
dex G-10 size exclusion (50/50 chloroform/methanol), and
reverse-phase C-18 Sep Pak chromatography (10/90 methanol/
chloroform). The overall yield for these three steps (d-f) was
33.5%.21
These molecules self-assemble into liposome-like structures in
aqueous solution; we call these supramolecular structures “car-
bohydrosomes” since the structures are carbohydrate analogues
of glycerol-based liposomes.22 A light micrograph of carbohy-
drosomes budding off of a thin film of DLRPC is shown in Figure
2 (bar ) 20 µm). We are able to prepare carbohydrosomes with
sizes ranging from 0.2 to 15 µm. A typical procedure for 0.2 µm
vesicles involves forming a thin film of DLRPC in a 100 mL
round-bottom flask by dissolving 5 mg of 7 in chloroform and
subsequently removing the solvent by rotoevaporation.23 Phos-
Methyl-2,3-di-O-lauroyl-â-D-ribo-5-phosphocholine, 7 (DL-
RPC), was synthesized as shown in Scheme 1. The first step
involved protecting the primary hydroxide of 1 using trityl
chloride. Purification of 2 was accomplished by silica gel column
† Duke University Medical Center.
‡ Duke University.
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(21) The final product was characterized by HR-FAB mass spectrometry
((M-H)+ theoretical ) 694.4659, observed ) 694.4653) as well as 1H NMR,
13C NMR, and 31P-NMR. Complete experimental details are found in the
Supporting Information.
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10.1021/ja001653i CCC: $19.00 © 2000 American Chemical Society
Published on Web 08/06/2000