Synthesis of chroman aldehydes that inhibit HIV

Article abstract of DOI:10.1016/j.bmcl.2011.01.031

Chroman aldehydes bearing an acetyl group plus alkoxyl or hydroxyl groups inhibit HIV infectivity in HeLa37 cells.

Full text of DOI:10.1016/j.bmcl.2011.01.031

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1399–1401
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of chroman aldehydes that inhibit HIV
George A. Kraus a, , John Mengwasser a, Wendy Maury b, ChoonSeok Oh b
⇑
a Department of Chemistry, Iowa State University, Ames, IA 50011, USA
b Department of Microbiology, University of Iowa, Iowa City, IA 52242, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Chroman aldehydes bearing an acetyl group plus alkoxyl or hydroxyl groups inhibit HIV infectivity in
Received 16 November 2010
Revised 6 January 2011
Accepted 7 January 2011
Available online 14 January 2011
HeLa37 cells.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Antiviral
Chroman
Aldehyde
HIV
As a result of a concerted effort to identify natural products that
inhibit HIV, a wealth of useful natural product leads have been re-
ported.1 Several small molecular weight natural products have
been discovered that inhibit viruses.2 In 2003, Lee and coworkers
isolated aldehyde 1, shown in Figure 1, from Desmos dumosus and
evaluated it for inhibition of HIV replication in H9 lymphocyte
cells.3 Remarkably, 1 demonstrated potent anti-HIV activity with
CHO
CHO
OH
HO
OMe
Me
O
O
OH
Me
Ph
O
OH
Ph
O
1
2
an ability to inhibit 50% of HIV replication (IC50) at 0.022 lg/mL
and with a large therapeutic index (TI) of 489. Lawinal (2) is a re-
lated antiviral aldehyde.3 As part of an effort to identify useful
antiviral agents,4,5 we report herein the synthesis of chroman alde-
hydes related to 1 and 2.
Figure 1. Structures of small molecule antiviral agents.
compounds that inhibited 50% and 90% of HIV infectivity (IC50
and IC90) are shown in Table 1. In parallel, the cytotoxicity of each
compound at those same concentrations was appraised. At concen-
Chroman 3 was available in one pot from phloroglucinol and
isoprene in 69% yield after modification of a literature procedure.6
As shown in Scheme 1, acetylation of 3 with acetic anhydride affor-
ded a mixture of 4, 5 and 67 in 86% yield. Chromatography yielded
a mixture of 4 and 5 in 82% yield and diketone 6 in 4% yield. Ketone
4 could be readily separated from 5 by recrystallization. Formula-
trations as high as 100 lg/mL, little cytotoxicity was observed with
any of the compounds except compound 12 which had significant
cytotoxicity at the higher concentrations tested. The fourteen car-
bon compounds 7, 8 and 11 gave the lowest IC50 values between 30
8
tion of 4 with dichloromethyl methyl ether and TiCl4 produced
and 40 lM.
keto aldehyde 7 in 62% yield.
We investigated the HeLa37 cell cytotoxicity associated with
compound 7 in further detail to obtain a therapeutic index (TI)
for the 14 carbon compound that gave the lowest IC50 values. We
found that the concentration of compound that killed 50% or 90%
To better understand the effects of structure on activity, we
prepared dialdehyde 9 from 3 and ether 10 from 8. As shown in
Scheme 2, oxidation of
7
with DDQ9 in benzene produced
chromene 11. Benzoylation followed by rearrangement to a beta-
diketone generated diketone 12.
of cells (LC50 or LC90) of compound 7 was 145 and 258 lM, respec-
tively (Fig. 2).
Assessment of antiviral activity of the compounds: Compounds
6–12 were evaluated for their ability to inhibit HIV infectivity in
HeLa37 cells as previously described.10 The concentration of
We found that all compounds had inhibitory activity against
HIV. The 14 carbon compounds, compounds 7, 8 and 11, were most
efficacious with a range of IC50 values from 30 to 40
pound 7 that had the lowest IC50 values was also analyzed in detail
for cytotoxicity, giving a LC50 of 145 M, resulting in a TI of about
5. Compounds 8 and 11 that had slightly poorer IC50 may have
lM. Com-
l
⇑
Corresponding author. Tel.: +1 515 294 7794; fax: +1 515 294 0105.
E-mail address: gakraus@iastate.edu (G.A. Kraus).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.01.031

1400
G. A. Kraus et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1399–1401
O
O
HO
O
Ac2O
HO
O
HO
O
HO
O
BF3-Et2O
86%
O
O
+
+
OH
OH
OH
OH
3
4
5
6
TiCl4, MeOCHCl2
62%
TiCl4, MeOCHCl2
56%
TiCl4, MeOCHCl2
31%
O
O
CHO
CHO
t-BuOK
MeI
HO
O
HO
O
MeO
OHC
O
HO
OHC
O
O
10%
OHC
OH
OH
OMe
OH
10
9
7
8
Scheme 1. Synthesis of analogs.
CHO
CHO
CHO
HO
O
HO
O
HO
O
DDQ
2%
PhCOCl
O
O
O
tBuOK
21%
OH
OH
11
OH
Ph
7
12
O
Scheme 2. Derivatives of aldehyde 7.
Table 1
was the least active, indicating that an aldehyde moiety is neces-
sary for good activity. Interestingly, the O-methylated derivative
of aldehyde 8 showed good activity. Diketone 12, the closest analog
to 1, exhibited good activity but had the highest cytotoxicity.
In summary, we synthesized a series of aromatic aldehydes that
are related to naturally derived aldehydes 1 and 2.13 We evaluated
the ability of these compounds to inhibit HIV infectivity. Although
several aldehydes showed inhibitory activity, none of the com-
pounds showed an IC50 value or a therapeutic index comparable
to compound 1.
Anti-HIV activity and cytotoxicity of synthesized phlorogluconols
Compound
Cytotoxicity (
l
M)
HIV-1 Infection (lM)
LC50
LC90
IC50
IC90
7
6
8
9
10
11
12
145
258
N/D
N/D
N/D
N/D
N/D
N/D
30.2
>100
39.8
77.3
55.3
34.6
40.7
85
>100
>100
>100
>100
>100
84.2
>100
85.6
>100
>100
98.2
86.6
Acknowledgment
Cell Viability
Studies were supported by funds provided by NIH P50
AT004155.
HIV-1(NL4-3)
100
References and notes
1. Gambari, R.; Lampronti, I. In Advances in Phytomedicine; Lead Molecules from
Natural Products; Hassan Khan, M. T., Ahter, A., Eds.; Elsevier, 2006; Vol. 2, p
299.
2. Liu, T.; Li, A. X.; Miao, Y. P.; Wu, K. Z.; Ma, Y. Chin. Chem. Lett 2009, 20(11), 1386.
3. Wu, J.-H.; Wang, X.-H.; Yi, Y.-H.; Lee, K.-H. Bioorg. Med. Chem. Lett. 2003, 13(10),
1813.
50
0
1
10
100
1000
Compound 7 (µM)
4. Maury, W.; Price, J. P.; Brindley, M. A.; Oh, C. S.; Neighbors, J. D.; Wiemer, D. F.;
Wills, N.; Carpenter, S.; Hauck, C.; Murphy, P.; Widrlechner, M. P.; Delate, K.;
Kumar, G.; Kraus, G. A.; Rizshsky, L.; Nikolau, B. Virol. J. 2009, 6, 101.
5. Kraus, G. A.; Yuan, Y.; Kempema, A. Molecules 2009, 14(2), 807.
6. Kalena, G. P.; Jain, A.; Banerji, A. Molecules 1997, 2, 100.
7. Donnelly, W. J.; Shannon, P. V. R. J. Chem. Soc., Perkin Trans. 1 1972, 25.
8. Nakagawa-Goto, K.; Lee, K.-H. Tetrahedron Lett. 2006, 47(47), 8263.
9. Ahluwalia, V. K.; Jolly, R. S. Synlett 1982, 74.
Figure 2. A dose response curve of the ability of compound 7 to inhibit HIV-1 NL4-3
infectivity. Cytotoxicity in HeLa37 cells of compound 7 is also shown. All studies
were performed in triplicate three independent times. Shown are the means and
standard errors of the means.
10. Platt, E. J.; Wehrly, K.; Kuhmann, S. E.; Chesebro, B.; Kabat, D. J. Virol. 1998, 72,
2855.
11. Reed-Inderbitzin, E.; Maury, W. Virology 2003, 314, 680.
12. Ahluwalia, V. K.; Arora, K. K.; Jolly, R. S. J. Chem. Soc., Perkin Trans. 1 1982, 335.
similar TIs as compound 7. The TI of our lead compound was signif-
icantly smaller than that reported by Wu et al. for compound 1,3
due to apparently reduced antiviral activity of compound 7. How-
ever, it should be noted that in our studies we assessed the antivi-
ral viral activity during a single round of infection, whereas
compound 1 was assess for the ability to inhibit multiple rounds
of HIV infectivity.
13. 2,2-Dimethyl-5,7-dihydroxychroman (3):
A 100-mL round bottom flask
equipped with stir bar was charged with phloroglucinol dihydrate
a
(500.9 mg, 3.97 mmol) followed by 1,4-dioxane (10 mL) and Amberlyst 15
(1.5 g). The resulting heterogeneous mixture was cooled to 0 °C, and then
isoprene (600 mL, 6.0 mmol) was added over 5 min. The reaction vessel was
next equipped with a reflux condenser and heated to 101 °C. After 17 h, the
reaction mixture was cooled to rt, filtered through Celite, and the catalyst was
washed with hot acetone. The filtrate was concentrated in vacuo to afford a
Our other compounds had either higher IC50 values for HIV inhi-
bition or LC50 values for cytotoxicity below 100 lM. The diketone 6

G. A. Kraus et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1399–1401
1401
0.885 mmol) was added in drops over 5 min. The resulting red solution was sponta-
neously warmed to rt and then stirred for 10 h. It was then cooled to 0 °C, slowly
quenched with ice-cold water (5 mL), and stirred for 1 h. CH2Cl2 was then distilled
off using a rotary evaporator. The purplish slurry was dissolved in EtOAc (20 mL)
and poured into a separatory funnel. The organic phase was washed with water
(3 Â 20 mL) and brine (1 Â 20 mL) then dried over MgSO4, filtered and concentrated
to give a dark purplish-brown residue. It was purified by column chromatography
(EtOAc–hexanes) to give 9 (23 mg, 31%) as a white solid. 1H NMR (300 MHz, CDCl3)
d 10.16 (s, 1H), 10.04 (s, 1H), 3.59 (t, J = 6.4 Hz, 2H), 1.82 (t, J = 6.4 Hz, 2H), 1.42 (s,
6H). 13C (100 MHz, CDCl3) d 192.1, 168.9, 168.1, 163.3, 104.1, 103.7, 100.0, 78.3,
31.4, 26.7, 12.1. HSMS, Calcd for C13H14O5: 250.08412, Found 250.08458.
light yellow solid, which was purified by column chromatography (hexanes/
EtOAc = 9:1 ? 1:1) to first give a mixture of two compounds, which were
separated on
a silica gel column eluted with toluene. The first fraction
gave 2,2,8,8-tetramethyl-2,3,4,8,9,10-hexahydropyrano[2,3-f]chromen-5-ol 13
(54 mg). The second fraction gave 2,2,8,8-tetramethyl-2,3,4,6,7,8-hexahydro-
pyrano[3,2-g]chromen-5-ol 14 (50 mg), spectral data matched the lit.12
O
O
HO
O
8-Acetyl-5,7-dimethoxy-2,2-dimethylchroman-6-carbaldehyde (10):
bottom flask equipped with a stir bar was charged with 8 (55.3 mg, 0.209 mmol) fol-
lowed by THF (2 mL) and t-BuOH (0.5 mL). The resulting mixture was cooled to 0 °C
A 50-mL round
OH
O
13
14
and then t-BuOK (56.4 mg, 0.502 mmol) was added all at once. MeI (65 lL,
1.05 mmol) was added in drops over 1 min. The ice bath was removed to allow
the resulting yellow slurry to warm to rt; then it was warmed to 40 °C for 2 h. After
cooling to rt, the mixture was quenched with water and acidified with 1 N HCl. The
mixture was extracted twice with EtOAc. The combined organic layers were washed
with brine, dried over MgSO4 and concentrated. The residue was purified by column
chromatography on SiO2 (EtOAc–hexanes) to obtain 10 (6.3 mg, 10%). 1H NMR
(400 MHz, CDCl3) d 10.23 (s, 1H), 3.86 (s, 3H), 3.84 (s, 3H), 2.73 (t, J = 6.4 Hz, 2H),
1.82 (t, J = 6.4 Hz, 2H), 1.36 (s, 6H).
2,2-Dimethyl-5,7-dihydroxychroman 3 was isolated (536 mg, 69%) as colorless nee-
dles from benzene, mp 163–164 °C (lit.,12 163–164 °C). The final fraction contained
recovered phloroglucinol (85.6 mg).
Synthesis of 4, 5, and 6 by the acetylation of 3: A 50-mL round bottom flask equipped
with a stir bar was charged with 2,2-dimethyl-5,7-dihydroxychroman (3) (1.70 g,
8.77 mmol) followed by AcOH (18.4 mL) and Ac2O (0.91 mL, 9.65 mmol). The result-
ing mixture was stirred vigorously and warmed to 40 °C until it was homogeneous,
and then BF3ÁOEt2 (1.17 mL, 9.21 mmol) was added over 1 min. The resulting red
mixture was warmed to 100 °C. After 10 hours at that temperature, the mixture
was cooled to 0 °C, quenched with water (10 mL) and poured into a separatory fun-
nel containing EtOAc (25 mL). The phases were separated and the aqueous phase
was extracted with EtOAc (3 Â 25 mL) and 5% MeOH/EtOAc (5 Â 20 mL). The com-
bined organic fractions were washed with water (2 Â 25 mL) and brine
(1 Â 25 mL), dried over MgSO4, filtered and concentrated in vacuo. The pale orange
solid was purified by chromatography. Elution with hexanes/EtOAc (50:1) gave
6,8-diacetyl-2,2-dimethylchroman-5,7-diol (6) (97.6 mg, 4%) as a pale yellow nee-
dles, mp 129–130 °C (lit.7 131–132.5 °C); 1H NMR (400 MHz, CDCl3) d 2.71 (s, 3H),
2.64 (s, 3H), 2.60 (t, J = 6.8 Hz, 2H), 1.82 (t, J = 6.8 Hz, 2H), 1.42 (s, 3H). Elution with
hexanes/EtOAc (5:1) gave a 1:1 mixture (by 1H NMR) of 6-acetyl-2,2-dimethylchro-
man-5,7-diol 4 and 8-acetyl-2,2-dimethylchroman (5) (1.68 g, 81.4%). Crystallization
from benzene first gave 4 as a yellow solid, mp 230–230.5 °C (lit.7 230 °C); 1H NMR
(400 MHz, acetone-d6) d 5.87 (s, 1H), 2.61 (s, 3H), 2.53 (t, J = 6.8 Hz, 2H), 1.78 (t,
J = 6.8 Hz, 2H), 1.30 (s, 6H). The mother liquor was concentrated and the yellow res-
idue afforded 5 as a yellow solid from benzene.
6-Acetyl-2,2-dimethyl-8-formylchromen-5,7-diol (11):
A slurry of 7 (75.9 mg,
0.287 mmol) and DDQ (71.7 mg, 0.316 mmol) in benzene (3 mL) was heated at
100 °C in a sealed tube for 20 h. Then the mixture was filtered through Celite. Ben-
zene was used to rinse the reaction flask and wash the filter pad. The filtrate was
concentrated, and then the residue was purified by column chromatography on
SiO2 to obtain 11 (1.6 mg, 2%). 1H NMR (400 MHz, CDCl3) d 13.15 (s, 1H), 10.20 (s,
1H), 6.61 (d, J = 10 Hz, 1H), 5.51 (d, J = 10 Hz, 1H), 6.68 (s, 3H), 1.55 (s, 6H). 13C
NMR (100 MHz, CDCl3) d 203.6, 192.7, 178.3, 170.9, 164.6, 124.8, 115.4, 104.8,
104.3, 101.1, 80.7, 33.2, 28.8. HRMS Calcd for C14H14O5: 262.0841, Found 262.0846.
6-(1,3-Dioxo-3-phenylpropyl)-2,2-dimethyl-8-formylchroman-5,7-diol (12): Potassium
tert-butoxide (100 mg, 0.82 mmol) was suspended in t-BuOH (1.5 mL) and anhy-
drous THF (5 mL), and then cooled to À10 °C. A solution of 7 (58.1 mg, 0.22 mmol)
in anhydrous THF (5 mL) was added. After stirring at À10 °C for 15 min, benzoyl
chloride (0.512 mL, 0.44 mmol) was added. The ice bath was removed, and the mix-
ture warmed to rt. Then the mixture was heated at reflux for 5 h. After cooling to rt,
the mixture was quenched with water and acidified with 1 N HCl. The mixture was
extracted twice with EtOAc. The combined organic layers were washed with brine,
dried over MgSO4 and concentrated. The residue was purified by column chromatog-
raphy on SiO2 (EtOAc–hexanes 1:19) to obtain 12 (17 mg, 21%) as a mixture of tau-
tomers. 1H NMR (300 MHz, CDCl3) d 10.03 (s, 1H, CHO, for enol form), 9.95 (s, 0.73H,
CHO, for 1,3-diketo form), 7.97–7.92 (m, ArH, for both forms), 7.65 (s, olefin for enol
form), 7.53–7.44 (m, ArH, for both forms), 4.68 (s, 2H, C(O)CH2C(O) for 1,3-diketo
form), 2.63–2.57 (m, CH2, for both forms), 1.86–1.81 (m, CH2, for both forms), 1.40
(s, 6H, 2 Â CH3, for enol form) 1.39 (s, 6H, 2xCH3, CH3 for 1,3-diketo form); HRMS
Calcd for C21H20O6: 368.126, Found 368.126.
Virus infectivity studies: Single round infectivity studies in HeLa37 cells were used to
assess antiviral activity of the compounds. Approximately 250 infectious particles of
a X4-tropic HIV strain that is lab adapted (NL4-3) were combined with serial dilu-
tions of the compounds. Increasing amounts of vehicle, DMSO, were observed to re-
sult in cell cytotoxicity with 0.5% DMSO resulting in about 5% reduction in cell
viability. Thus, in these studies, we never exceeded 0.5% DMSO in the cultures and
a dose response curve from 0.05% to 0.5% DMSO was performed independently.
The effect on cell viability of the DMSO concentrations was subtracted from the inhi-
bition observed in the presence of each compound. The extract and virus mix was
added to 5 Â 104 cells/well of HeLa37 cells in a 48-well format resulting in a multi-
plicity of infection (MOI) of ꢀ0.005 as previously described.11 The infections were
maintained for 40 h. Cells were fixed with 75% acetone/25% water and immuno-
stained for HIV antigens using human anti-HIV antisera. HIV antigen positive cells
were enumerated in the cultures. The findings for each compound were normalized
to control levels at that same concentration of DMSO. IC50 and IC90 concentrations
were determined using TABLECURVE software (Systat Academic).
8-Acetyl-2,2-dimethylchroman (5): mp 150–151 °C (lit.,7 150 °C) 1H NMR (400 MHz,
acetone-d6) d 5.94 (s, 1H), 2.57 (t, partially obscured, J = 6.8 Hz, 2H), 2.55 (s, 3H),
1.76 (t, J = 6.8 Hz, 2H), 1.37 (s, 6H).
6-Acetyl-2,2-dimethyl-8-formylchroman-5,7-diol (7): A 100-mL round bottom flask
equipped with a stir bar was charged with 4 (620.9 mg, 2.63 mmol) followed by
anhydrous CH2Cl2 (50 mL). The resulting mixture was cooled to À78 °C and then
TiCl4 (1.5 mL, 13.4 mmol) was added. This mixture was treated with Cl2CHOMe
(2.26 mL, 25.0 mmol). The resulting red solution was spontaneously warmed to rt
and then stirred for 10 h. Then it was cooled to 0 °C, slowly quenched with ice-cold
water (10 mL), stirred for 1 h and poured into a separatory funnel. The organic phase
was washed with water (3 Â 25 mL) and brine (1 Â 25 mL), dried over MgSO4, fil-
tered and concentrated in vacuo. The residue was purified by column chromatogra-
phy. Elution with 2% EtOAc and 98% hexanes gave 7 (427.2 mg, 62%) as yellow
prisms, mp 102–104 °C. 1H NMR (400 MHz, CDCl3) d 10.00 (s, 1H), 2.69 (s, 3H),
2.56 (t, J = 6.8 Hz, 2H) 1.82 (t, J = 6.8 Hz, 2H), 1.39 (s, 6H).%). 13C NMR (100 MHz,
CDCl3) d 203.7, 191.8, 171.0, 168.3, 161.8, 103.9, 103.4, 100.3, 77.8, 32.6, 31.5,
26.6, 15.5. HRMS, Calcd for C14H16O5: 264.0998, Found: 264.1004.
8-Acetyl-5,7-dihydroxy-2,2-dimethylchroman-6-carboxaldehyde (8): The reaction of 5
under conditions identical to those used for the formulation of 4 provided product
8. Pale yellow needles, mp 131–134 °C. 1H NMR (400 MHz, CDCl3) d 13.23 (s, 1H),
10.18 (s, 1H), 3.63 (s, 3H), 2.60 (t, partially obscured, J = 6.8 Hz, 2H), 1.83 (t,
J = 6.8 Hz, 2H), 1.44 (s, 6H). 13C NMR (100 MHz, CDCl3)
d 203.4, 192.3, 169.7,
167.3, 163.0, 104.4, 104.2, 99.6, 78.4, 33.2, 31.1, 26.9, 15.3.
5,7-Dihydroxy-2,2-dimethylchroman-6,8-dicarbaldehyde (9): A 100-mL round bottom
flask equipped with a stir bar was charged with 3 (57 mg, 0.295 mmol) followed
by anhydrous CH2Cl2 (10 mL). The mixture was gently warmed and vigorously stir-
Cell viability studies: Cells were plated and treated with compounds as described
above for the infectivity assays. Forty hours following treatment, cell viability
was monitored by ATPLite Assay (Packard Biosciences) per manufacturer’s
instructions.
red to fully dissolve the starting material. Next, Cl2CHOMe (160
added to the reaction mixture at rt. After cooling to À78 °C, TiCl4 (98
l
L, 1.77 mmol) was
L,
l