O. J. Donadel et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3536–3539
3537
addition to the TBS group, other common protecting
groups for hydroxyl groups, such as allyl, acetate, and
benzoate, were used to obtain appropriate derivatives.
We report herein the synthesis and preliminary in vitro
inhibitory activity against HL60 human promyelocytic
leukemia cells and MCF7 human breast cancer cells.
These cell lines are included in the National Cancer
Institute anticancer screening program and are widely
found in literature as representative examples of leuke-
mias and solid tumors, respectively.
in a 50% reduction of cellular net growth when com-
pared with values of untreated control cells, the drug
concentration resulting in total growth inhibition
(TGI), and the net loss in 50% of cells following treat-
ment (LC50) denoting cell kill.
The octanol/water partition coefficient expressed in log-
arithmic form (CLOGP) has been widely used in calcu-
lating numerous physical properties such as membrane
transport and water solubility. It is usually calculated
from the sum of partition coefficients of the chemical
fragments composing the molecule. The lipophilicity of
the compounds was evaluated by in silico calculation
based on their chemical structure.14,15 CLOGP values
were calculated to correlate lipophilicity with antitumor
activity.
The synthesis of the compounds used in this study is
outlined in Scheme 1. Tetrahydropyran derivatives 2–
17 were envisioned as being synthesized from the com-
mon precursor alcohol 1,9 which can be obtained from
the commercially available tri-O-acetyl-D-glucal. A first
series of compounds was prepared from nitrile 2. To car-
ry out the synthesis of the nitrile compound 2, a one-car-
bon homologation of the alcohol 1 was performed by a
simple two-step sequence; tosylation and NaCN nucleo-
philic substitution. When compound 2 was submitted to
reduction with DIBAL-H in toluene at low temperature
tetrahydropyran 3 was obtained as a side product and in
low yield. On the contrary, the reduction of 2 with DI-
BAL-H in THF at 0 ꢁC led to aldehyde 4 in 92% yield.
Aldehyde 5 was obtained from nitrile 2 by a three-step
process; deprotection of the silyl ether, O-alkylation
with ally bromide, and reduction with DIBAL-H. The
two-carbon homologation of 4 by a Wittig–Horner reac-
tion afforded the (E)-a,b-unsaturated ester 6. The TBS
of the latter compound was cleaved to give the second-
ary free alcohol 7. The DMAP catalyzed acetylation
and benzoylation of 7 led, in high yields, to the acetyl
and benzoyl esters 8 and 9, respectively. Reduction of
6 with in situ generated alane afforded the allylic alcohol
10.
The CLOGP values together with the growth inhibition
data are listed in Table 1. Taken as a whole, those com-
pounds having a TBS group show larger CLOGP values
and are therefore more lipophilic than the correspond-
ing derivatives without TBS. The growth inhibition re-
sults allow us to classify the compounds according to
their activity profile. The group of active compounds
against HL60 cells comprises seven products, whilst
MCF7 cells were sensitive to nine products. Overall,
the active products showed GI50 values in the range
22–46 and 6.4–86 lM against HL60 and MCF7 cells,
respectively. The breast cancer cell line was more sensi-
tive to the drugs than the leukemia cells. For instance,
compounds 15 and 16 were active against MCF7 cells
but showed no activity against HL60 cells. Compounds
6, 12, and 17 were the only products from the active
group series that reached a TGI value in HL60 cells.
The TGI values for those products were in the range
64–77 lM. For MCF7 cells, compounds 4, 6, 10, 12,
16, and 17 showed TGI values in the range 23–83 lM.
Interestingly, compound 17 was the only product that
reached a LC50 value in both cell lines and therefore,
it appears as the most active compound of the series.
A second series of compounds having one carbon atom
less than their homologues of the previous series was
prepared. Thus, aldehyde 11 was obtained by Swern oxi-
dation of the alcohol 1 in 86% yield. Subsequent Wittig–
Horner reaction led to the (E)-a,b-unsaturated ester 12.
This ester was reduced with alane and the allylic alcohol
13 was obtained. Acid catalyzed deprotection of the
TBS ether gave the diol 14. Finally, the selective protec-
tion of the primary alcohol as a TBS ether yielded the
alcohol 15. In addition, (Z)-a,b-unsaturated ester 16
was prepared by a Wittig–Horner reaction of aldehyde
11 using the Ando reagent.10 Further reduction with DI-
BAL-H in THF at 0 ꢁC provided the (Z) allylic alcohol
17 in good yields.11
When the obtained dose–response parameters are con-
sidered, the following structure–activity relationship is
obtained. In general, those compounds bearing a TBS
protecting group at position 3 of the tetrahydropyran
ring showed significant cytotoxicity in all cell lines
whereas the compounds lacking such functionality were
found inactive. Thus, when the TBS group is replaced
with an allyl group (4 vs 5) the activity is lost. A similar
observation is found when the TBS group is removed (6
vs 7, and 13 vs 14) or substituted by an acetyl (6 vs 8) or
a benzoyl group (6 vs 9).
Cell antiproliferative assays were performed in 96-well
plates using the National Cancer Institute protocol with
slight modifications.12 We screened growth inhibition
and cytotoxicity against HL60 and MCF7 cells after
48 h of stimulation using the sulforhodamine B (SRB)
assay.13 Additionally, treated and control cells were ana-
lyzed by phase contrast microscopy to assess morpho-
logical changes. Three dose–response parameters can
be calculated, when possible, for each experimental
agent from the dose–response curves. Growth inhibition
of 50% (GI50), which is the drug concentration resulting
The presence of a TBS group is not the unique require-
ment for the compounds to induce activity. Inactive
compound 2 led us to consider the substituent at posi-
tion 2 of the tetrahydropyran ring responsible for the
activity exerted by the compounds. This can be seen also
for compounds 13–15. The removal of the TBS group of
active product 13 led to inactive diol 14. When the pri-
mary hydroxyl group was protected with TBS, the
resulting derivative 15 was inactive in HL60 cells and
showed slight activity in MCF7 cells.
Donadel, Osvaldo J.
