Synthesis and Akt inhibitory properties of a 1D-3,4-dideoxyphosphatidylinositol ether lipid

Article abstract of DOI:10.1016/S0040-4039(00)01186-2

1D-3,4-Dideoxyphosphatidylinositol ether lipid 2, a PI analog, was synthesized through a sequence of protection/deprotection protocols and two Barton deoxygenation reactions, starting from L-(-)-quebrachitol. DDPIEL is 18-fold more potent than its monodeoxy counterpart DPIEL in the inhibition of PI3-K. (C) 2000 Published by Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)01186-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 7415–7418
Synthesis and Akt inhibitory properties of a
-3,4-dideoxyphosphatidylinositol ether lipid
1
D
Youhong Hu,a Emmanuelle J. Meuillet,b Lixin Qiao,a Margaret M. Berggren,b
Garth Powisb and Alan P. Kozikowskia,*
aDrug Discovery Program, Department of Neurology, Georgetown University Medical Center, 3970 Reservoir Road,
NW, Washington, DC 20007, USA
bArizona Cancer Center, 1515 North Campbell Avenue, Tucson, AZ 85724, USA
Received 17 May 2000; revised 29 June 2000; accepted 30 June 2000
Abstract
1
D
-3,4-Dideoxyphosphatidylinositol ether lipid 2, a PI analog, was synthesized through a sequence of
protection/deprotection protocols and two Barton deoxygenation reactions, starting from -(−)-quebra-
L
chitol. DDPIEL is 18-fold more potent than its monodeoxy counterpart DPIEL in the inhibition of
PI3-K. © 2000 Published by Elsevier Science Ltd.
The proto-oncogenic serine/threonine kinase Akt (also known as RAC-PK or protein kinase
B (PKB)) is one of the most extensively studied of the PH domain-regulated signaling proteins
acting downstream of PI3-K. Binding of the PH domain of Akt to membrane PI(3)Ps causes the
translocation of Akt to the plasma membrane bringing it into contact with membrane bound
Akt kinase (phosphatidylinositol dependent kinase-1 and 2 (PDK1 and 2)), which phosphory-
lates and activates Akt.1 Akt inhibits apoptosis by phosphorylating a number of downstream
targets. Thus, the inhibition of Akt activation induces cancer cell apoptosis. Three mammalian
isoforms of Akt have been identified, Akt1, Akt2, and Akt3. Akt1 has been found to be
overexpressed in gastric adenocarcinomas, and Akt2 is overexpressed in breast, ovarian, and
pancreatic cancer.2 While the PH domain of Akt binds both PI(3,4)P2 and PI(3,4,5)P3 in vitro,
only PI(3,4)P2 activates Akt.3 Thus, the design and synthesis of PI(3,4)P2 antimetabolites
capable of blocking Akt activation may offer a new approach to the design of anticancer agents
that work by blocking Akt’s ability to repress apoptosis in cancer cells.
* Corresponding author. Tel: 2026870686; fax: 2026875065; e-mail: kozikowa@giccs.georgetown.edu
0040-4039/00/$ - see front matter © 2000 Published by Elsevier Science Ltd.
PII: S0040-4039(00)01186-2

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Figure 1.
In our previous work, 3-deoxy-PI ether lipid 1 (DPIEL, Fig. 1) was found to inhibit PI3-K
(IC50=14.8 5.6 mM) and Akt (IC50=1.5 0.3 mM), and to block the growth of HT-29 colon
cancer cells (IC50=2.1 mM) both in vitro and in tumor xenografts in scid mice. This phospho-
lipid is currently under preclinical development through the RAID program of the National
Cancer Institute (NCI).4 Because of the promising activity exhibited by DPIEL, a PI analog that
cannot be phosphorylated by PI3-K to produce PI(3)P-related metabolites (such as PI(3,4)P2)
due to the absence of the 3-OH group, it was deemed valuable to examine the activity of a PI
analog lacking hydroxyl groups at both positions 3 and 4. The biological effect of the deletion
of this additional hydroxyl group upon Akt and PI3-K activity, and cancer cell growth relative
to DPIEL would provide important SAR data for further lead optimization. In the present
paper we detail the synthesis of 1
D
-3,4-dideoxyphosphatidylinositol ether lipid 2 (DDPIEL)
starting from
(Scheme 1).
L
-quebrachitol and disclose preliminary information on its biological activity
Scheme 1. Synthesis of DDPIEL from
L-quebrachitol. Reagents and conditions: (a) (i) PhCOCl, DMAP (cat.),
pyridine, rt; (ii) CrO3, AcOH, rt; (iii) AcCl, MeOH, reflux; (b) (i) CS2, DBU, MeI, DMF, rt; (ii) n-Bu3SnH, AIBN,
toluene, reflux; (c) (i) K2CO3, MeOH, rt; (ii) 2-methoxypropene, CSA (cat.), DMF, 0 to 60°C; (d) (i) NaH, CS2, MeI,
DMF, rt; (ii) n-Bu3SnH, AIBN, toluene, reflux; (e) p-TsOH (cat.), MeOH–CH2Cl2 (1:5), rt; (f) (i) NaH, BnBr, DMF,
rt; (ii) conc. HCl, MeOH, rt; (g) (i) Bu2SnO, toluene, reflux; (ii) AllylBr, CsF, DMF, −50°C to rt; (h) NaH, BnBr,
DMF; (i) (i) RhCl(PPh)3, DABCO, EtOH, reflux; (ii) 1N HCl, acetone, reflux; (j) (i) BnOP(N-iPr2)2, diisopropyl-
ammonium tetrazolide, CH2Cl2, rt; (ii) 1-O-octadecyl-2-O-Me-sn-glycerol, tetrazole, CH2Cl2, rt; (iii) t-BuOOH,
CH2Cl2, rt; (k) H2, 20% Pd(OH)2/C, t-BuOH, 65 psi

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The five vicinal hydroxyl groups of
L-(−)-quebrachitol 3 were first protected as their
benzoates. Next, using Angyal’s method,5 the methyl group of the resulting pentabenzoate was
converted into a formyl group by oxidation with chromium trioxide in acetic acid. The formyl
group was then removed by treatment with acetyl chloride in methanol to provide 4 bearing a
free hydroxyl at position 4 in 70% yield. Next, the hydroxyl group in 4 was removed by
application of the Barton deoxygenation procedure.6 Accordingly, treatment of 4 with CS2 and
MeI furnished the corresponding S-methyl xanthate intermediate, which was then deoxygenated
homolytically to 5 with n-Bu3SnH. Next, the benzoate groups of 5 were cleaved by the action
of potassium carbonate, and the resulting free hydroxyl groups then reprotected with 2-
methoxypropene to afford the bis-acetonide 6 possessing a free hydroxyl group at position 3
(31% yield). Removal of the hydroxyl group of 6 to give 7 was then effected in the same way
as before by using the Barton reaction. While the treatment of 7 with a catalytic amount of AcCl
in CH2Cl2–MeOH (5:1) for 5 minutes7 gave rise to the corresponding tetraol, exposure of 7 to
a catalytic amount of p-TsOH in CH2Cl2–MeOH (2:1) for 20 min at 0°C furnished the required
diol 8 in 82% yield by selective cleavage of the trans-O-isopropylidene group.
Next, following protocols similar to those previously detailed by our group,8 compound 8 was
reprotected at positions 5, 6 by benzylation, and then the cis-acetonide was removed by acid
hydrolysis to yield 9 in 98% yield. The diol 9 was selectively allylated at position 1 via a
1,2-O-stannylene intermediate to give compound 10 in 86% yield. After benzylation of 10 at
position 2 to afford 11, removal of the allyl group was accomplished in two steps that entailed:
(a) isomerization of the double bond with RhCl(PPh3)3 and DABCO in ethanol, and (b) acidic
hydrolysis of the resulting vinyl ether to afford compound 12 in 69% yield for the two steps. The
intermediate 12 was transformed into the corresponding protected phosphatidylinositol analog
13 in accordance with established protocols in 30% yield.4b,c Finally, hydrogenolysis of the
benzyl groups of compound 13 with 20% Pd(OH)2/C in t-butanol gave the required 1
D-3,4-
dideoxyphosphatidylinositol ether lipid (DDPIEL) 29 in 85% yield.
To evaluate the biological activity of DDPIEL, initial studies examined its ability to block the
growth of NIH 3T3 cells (IC50=2.0 mM; for DPIEL, IC50=4.5 mM). DDPIEL is also a good
inhibitor of Akt with an IC50 of 11.0 2.5 mM; it is about sevenfold less potent than DPIEL
(1.5 0.3 mM). Interestingly, this dideoxy analog was found to be 18-fold more potent (IC50=
0.8 0.1 mM) than the monodeoxy analog DPIEL (IC50=14.8 5.6 mM) in the inhibition of
PI3-K. Further studies of the antiproliferative action of DDPIEL are underway, and these data
will be reported separately.
In conclusion, the present work details the first synthesis of a novel PI analog, namely,
1D
-3,4-dideoxyphosphatidylinositol ether lipid 2, starting from -(−)-quebrachitol as the chiral
L
educt. The synthesis protocol entails a sequence of protection/deprotection protocols and two
Barton deoxygenation reactions. DDPIEL is 18-fold more potent than its monodeoxy counter-
part DPIEL in the inhibition of PI3-K.
Acknowledgements
This work was supported by the National Institutes of Health (Grant No. CA61015) and the
Department of Defense (DAMD 17-93-V-3018).

7418
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9. Compound 12: [h]D=−11.7° (c 0.12, CHCl3/MeOH 1:1); H NMR (300 MHz, CDCl3/CD3OD 1:1, TMS) l 4.14
(m, 3H), 4.00 (t, 1H, J=7.5 Hz), 3.72 (t, 1H, J=9.0 Hz), 3.62–3.41 (br m, 9H), 1.87 (dd, 1H, J=14.4, 3.6 Hz),
1.76 (m, 2H), 1.58 (m, 3H), 1.27 (m, 30H), 0.88 (t, 3H, J=9.3 Hz); 13C NMR (75 MHz, CDCl3/CD3OD 1:1, TMS)
l 82.35, 79.54 (J=6.1 Hz), 74.43, 73.45, 72.42, 69.92, 68.62, 66.54, 58.12, 32.47, 30.91, 30.20, 30.07, 30.03, 29.88,
27.29, 26.57, 26.48, 23.18, 14.29; 31P NMR (121 MHz, CDCl3/CD3OD 1:1, 85% H3PO4) l −0.02.
.