Synthetic studies towards the development of psoralen-acidic retinoid conjugates and hybrids

Article abstract of DOI:10.1055/s-0028-1083189

The chemical modification of trioxsalen using electrophilic aromatic substitution reactions, followed by either Wittig or Heck reactions or Suzuki coupling, allowed for ready access to C4′ modified trioxsalen derivatives that were successfully used for th

Full text of DOI:10.1055/s-0028-1083189

PAPER
3433
Synthetic Studies towards the Development of Psoralen–Acidic Retinoid
Conjugates and Hybrids
P
soralen–Acidic Retin
a
r
i
H
ybrid
a
s
Militsopoulou, Stavros E. Bariamis, Constantinos M. Athanassopoulos, Dionissios Papaioannou*
Laboratory of Synthetic Organic Chemistry, Department of Chemistry, University of Patras, 26500 Patras, Greece
Fax +30(261)0997156; E-mail: dapapaio@chemistry.upatras.gr
Received 27 May 2008; revised 21 July 2008
provides ready access to PACs of type 5 with superior
Abstract: The chemical modification of trioxsalen using electro-
philic aromatic substitution reactions, followed by either Wittig or
Heck reactions or Suzuki coupling, allowed for ready access to C4¢
modified trioxsalen derivatives that were successfully used for the
preparation of a variety of trioxsalen conjugates with acitretin of ei-
ther the polyamine or the ester type and trioxsalen–acitretin hybrids.
biological properties than the parent retinoids.12
Application of this chemistry to psoralens, would of
course lead to symmetric PACs, for example, of type 6, or
asymmetric PACs like 8, an example of psoralen–acidic
retinoid PACs, provided that the necessary trioxsalen-
derived SAE 7 were available. As examples of conjugates
of the EC type, the esters 9 and 10 were envisaged. Final-
ly, the trioxsalen derivatives 11–13 were considered as
examples of the trioxsalen–acitretin HYs. It was anticipat-
ed that the synthesis of all these projected compounds
would depend on further functionalization of trioxsalen
through electrophilic aromatic substitution reactions.
Key words: electrophilic aromatic substitution, Heck reaction,
psoralen–retinoid conjugation, Suzuki coupling, Wittig reaction
Psoralens, like 4,5¢,8-trimethylpsoralen (trioxsalen, 1) and
8-methoxypsoralen (2, Figure 1), are commonly used in
combination with ultraviolet A light radiation for the sys-
temic treatment by photochemotherapy (PUVA) of skin
hyperproliferative diseases like psoriasis.1–4 However,
PUVA is associated with important acute and chronic side
effects.1,4 On the other hand, acitretin (3), a second gener-
ation acidic retinoid, is the drug of choice for the systemic
treatment of certain types of psoriasis.1,5,6 Acitretin is a
potent teratogen and is also associated with various other,
dose dependent, side effects, which can prevent the use of
higher, more efficacious, therapeutic doses in some pa-
tients.5 However, combination therapies have now
evolved which, by using two different antipsoriatic agents
concurrently, allow for lower doses and result in reduced
side effects.6–8 They are particularly useful for inducing
rapid remission of psoriasis. A very successful example of
this type of multi-modality therapeutic strategy, coined as
RePUVA therapy, is the combination of acitretin, used as
the ‘accelerator’ of the clinical response and PUVA, con-
sidered as the ‘maintainer’.
Rapoport et al. reported that the chloromethylation of tri-
oxsalen (1) leads to 4¢-(chloromethyl)trioxsalen13 (14,
Scheme 1), which is a key intermediate in the synthesis of
other 4¢-substituted trioxsalens14 (e.g., the alcohol 15)
with superior photoreactivity with DNA and RNA than
the parent compound. We envisaged that these intermedi-
ates will also serve our purpose for the synthesis of triox-
salen bearing various side chains at C4¢. Thus, treatment
of trioxsalen (1) with 1,3,5-trioxane in concentrated hy-
drochloric acid15 at room temperature for 12 hours pro-
duced the chloride 14 in 70% yield. This was then
hydrolyzed in dioxane–water (6:1) at 80 °C for 24 hours
to give alcohol 1513a in 49% yield. Furthermore, manga-
nese(IV) oxide mediated oxidation of alcohol 15 in
dichloromethane at room temperature for 12 hours pro-
vided the aldehyde 1616 in 83% yield.
Aldehyde 16 could be also prepared directly from chloride
14, though in 35% yield, by treating the latter with the sys-
tem K2HPO4/KH2PO4/NaBr in anhydrous dimethyl
sulfoxide17 at 80 °C for 12 hours. Furthermore, oxidation
of aldehyde 16 with oxone18 in N,N-dimethylformamide,
at 45 °C for two days, provided the corresponding carbox-
ylic acid 18 in 73% yield. In addition, the bromide 1719
and the methyl ketone 19 were readily obtained in 82%
and 62% yields, respectively, on treating trioxsalen (1)
with either bromine in dichloromethane at room tempera-
ture for three hours or acetic anhydride in the presence of
tin(IV) chloride20 at room temperature for three days.
Compound 19 was further a-brominated with bromine in
glacial acetic acid (r.t., 2 d) to give a-bromo ketone 20 in
52% yield. Compounds 16, 17, and 20 were projected as
key intermediates in the synthesis of trioxsalen deriva-
tives 21 and 24, of HYs 11–13, and of EC 10.
We therefore considered it of interest to examine the pos-
sibility of incorporating psoralen and retinoid units in a
single molecule. We envisaged that this can be accom-
plished through the following three molecular entities: a
polyamine conjugate (PAC),9 an ester conjugate (EC),10
or a hybrid (HY).11 In the present studies, we have chosen
trioxsalen (1) and acitretin (3) as the psoralen and retinoid
units, respectively, and spermine (SPM) for the formation
of the polyamine conjugates. It has been recently shown
that the direct reaction of the isolable succinimidyl active
esters (SAEs, e.g., 4) of acidic retinoids with spermine,
SYNTHESIS 2008, No. 21, pp 3433–3442
x
x.
x
x
.
2
0
0
8
Advanced online publication: 16.10.2008
DOI: 10.1055/s-0028-1083189; Art ID: T08808SS
© Georg Thieme Verlag Stuttgart · New York

3434
M. Militsopoulou et al.
PAPER
Aci
Tra
X
O
O
OSu
X
O
X
O
X
O
O
O
O
Y
MeO
1: X = Y = Me
3: X = OH
4: R = OSu
7
2: X = H, Y = OMe
O
H
H
N
N
X
Y
N
N
H
O
H
O
O
O
OMe
SPM : X = Y = H
9: X = CH2
10: X = COCH2
5: X = Y = Aci
6: X = Y = Tra
8: X = Tra, Y = Aci
O
O
OH
OH
O
OH
O
O
O
O
O
O
O
O
O
12
11
13
Figure 1 Structures of compounds encountered in the present work
Condensation of 4¢-formyltrioxsalen (16) with (tert-but- 84% yield. In contrast, 4¢-acetyltrioxsalen (19) failed to
oxycarbonylmethylene)triphenylphosphorane in reflux- react with either (tert-butoxycarbonylmethylene)triphe-
ing chloroform for two hours gave ester 21 (Scheme 2) in nylphosphorane or diethyl (tert-butoxycarbonylmeth-
Br2, CH2Cl2
25 °C, 3 h
Br
82%
O
O
O
17
1,3,5-trioxane,
concd HCl
25 °C, 12 h
H2O, 1,4-dioxane
80 °C, 24 h
OH
Cl
70%
49%
O
O
O
O
O
O
O
O
O
O
1
14
15
MnO2, CH2Cl2
25 °C, 12 h
83%
K2HPO4, KH2PO4,
NaBr, DMSO
80 °C, 12 h
H
Ac2O, SnCl4
25 °C, 3 d
O
62%
O
O
O
35%
O
O
O
19
16
Br2, AcOH
25 °C, 2 d
52%
oxone, DMF
45 °C, 2 d
73%
O
OH
Br
O
O
O
O
O
O
O
18
20
Scheme 1 Functionalization of trioxsalen at C4¢ using electrophilic aromatic substitution reactions
Synthesis 2008, No. 21, 3433–3442 © Thieme Stuttgart · New York

PAPER
Psoralen–Acidic Retinoid Conjugates and Hybrids
3435
yl)phosphonate in order to give the corresponding tio 3.6:1, in 62% yield. The thus obtained aldehyde 23 was
unsaturated ester. In an attempt to improve the synthesis then entered into a second Wittig reaction (CHCl3, reflux,
of 21, we subjected the bromide 17 and tert-butyl acrylate 3 h) with (tert-butoxycarbonylmethylene)triphenylphos-
to a Heck reaction.21 Indeed, this reaction gave ester 21 in phorane to give, in 65% yield, the corresponding unsatur-
74%, thus, 21 was available from trioxsalen (1) in two ated ester 24 (only the E,E-isomer is drawn) also as an
steps in 61% overall yield.
inseparable mixture (TLC) of diastereomeric esters. The
E,E-isomer 24 was the major product and was obtained
pure through crystallization in 49% yield. Finally, trifluo-
roacetic acid mediated deprotection of ester 24 at room
temperature for 1.5 hours provided unexceptionally HY
11 in 89% yield.
Removal of the tert-butyl protecting group was routinely
effected by treating ester 21 with a 50% solution of tri-
fluoroacetic acid in dichloromethane22 at room tempera-
ture for two hours to give the unsaturated acid 22 in 95%
yield. This acid was finally converted to the correspond-
ing SAE 7 in 71% yield, upon treatment with N-hydroxy- Bromide 17 was a valuable intermediate in the synthesis
succinimide (HOSu) and diispropylcarbodiimide in N,N- of the other two HYs, namely 12 and 13, using the Suzuki
dimethylformamide initially at 120 °C for 15 minutes and coupling as the key reaction. Thus, the commercially
then at room temperature for 12 hours.
available 4-formylphenylboronic acid was first converted
into the corresponding pinacolyl ester (FPBPE)24 in 92%
yield and then coupled with bromide 17 under typical
Suzuki reaction conditions24 to give aldehyde 25 in 86%
yield. This aldehyde, upon oxidation with Oxone18 in
N,N-dimethylformamide at 50 °C for three days, gave HY
4¢-Formyltrioxsalen (16) could be also converted into the
unsaturated ester 24 using two sequential Wittig reactions.
The first one with the Trippett’s reagent,23 was a sluggish
reaction and produced the unsaturated aldehyde 23 as an
inseparable mixture (TLC) of E- and Z-isomers, in the ra-
Br
X
O
O
O
O
O
O
O
17
CH2=CHCO2t-Bu,
Pd(OAc)2, Et3N,
(o-tolyl)3P, DMF
90 °C, 2 d
22: X = OH
7: X = OSu
DIC/HOSu, DMF
120 °C, 15 min
then 25 °C, 12 h
O
O
B
50% TFA in CH2Cl2
25 °C, 2 h
71%
86%
(FPBPE)
O
74%
95%
K2CO3,
PdCl2(dppf), THF
67 °C, 1 d
Ot-Bu
O
Ph3P=CHCO2t-Bu,
CHCl3
X
61 °C, 2 h
O
O
84%
O
O
O
O
O
O
O
O
O
16
21
25: X = H
Oxone, DMF
50 °C, 3 d
12: X = OH
Ph3P=CHCHO, CHCl3
61 °C, 24 h
57%
62%
[25]
Ph3P=CHCO2t-Bu, CHCl3
61 °C, 12 h
42%
Ph3P=CHCO2t-Bu,
CHCl3
X
X
H
61 °C, 3 h
O
O
O
49%
O
O
O
O
O
O
23
24: X = Ot-Bu
11: X = OH
O
O
O
50% TFA in CH2Cl2
25 °C, 1.5 h
26: X = Ot-Bu
13: X = OH
50% TFA in CH2Cl2
25 °C, 1 h
89%
82%
Scheme 2 Synthesis of the trioxsalen–acitretin HYs 11–13 and of the key intermediate 7 for the preparation of PACs
Synthesis 2008, No. 21, 3433–3442 © Thieme Stuttgart · New York

3436
M. Militsopoulou et al.
PAPER
12 in 57% yield, whereas upon Wittig reaction with (tert- N1,N5,N9-tris(tert-butoxycarbonyl)spermine25 (27) with
butoxycarbonylmethylene)triphenylphosphorane in re- SAE 7 in the presence of N,N-diisopropylethylamine pro-
fluxing chloroform for 12 hours, produced 26 in 53% vided the fully protected monoamide 28 (Scheme 3) in
yield, as an inseparable mixture of E and Z isomers (only 82% yield, which upon trifluoroacetic acid mediated
the E isomer is drawn). Pure (E)-26 was obtained in 42% deprotection, gave the spermine monoamide 29. This was
yield through crystallization. This ester, upon routine trif- then coupled with SAE 412 in the presence of N,N-diiso-
luoroacetic acid mediated deprotection, gave rise to HY propylethylamine in N,N-dimethylformamide at room
13 in 82% yield.
temperature for two hours to produce the asymmetric
PAC 8 in 86% yield. Finally, the halides 14 and 20 were
reacted with acitretin in N,N-dimethylformamide/chloro-
form in the presence of N,N-diisopropylethylamine at 60
°C (16 h) and room temperature (3 h) to give ECs 9 and
10 in 71% and 65% yields, respectively.
The acitretin–trioxsalen conjugates of the polyamine or
the ester type were prepared as follows. Direct reaction of
SAE 7 with spermine in dichloromethane at room temper-
ature for one hour produced the symmetric PAC 6
(Scheme 3) in 96% yield. On the other hand, reaction of
O
O
O
O
H
N
H
N
N
N
H
O
H
O
6
O
O
[SPM]
96%
7, CH2Cl2
25 °C, 1 h
X
N
H
N
SPM: X = H
27: X = Boc
[ref. 25]
H2N
N
X
X
[27]
7, DIPEA,
DMF–CHCl3
25 °C, 2 h
82%
O
Boc
N
O
H
O
N
N
H
N
Boc
Boc
O
28
50% TFA in CH2Cl2
25 °C, 1 h
CF3CO2
NH3
CF3CO2
O
O
H2
N
O
N
N
H
H2
O
29
CF3CO2
4, DIPEA, DMF
25 °C, 2 h
86%
OMe
O
O
O
H
N
H
N
N
N
H
H
8
O
O
3, DIPEA,
DMF–CHCl3
O
25–60 °C, 3–16 h
X
X
Y
O
65–71%
O
O
O
O
O
O
OMe
14: X = CH2, Y = Cl
20: X = COCH2, Y = Br
9: X = CH2
10: X = COCH2
Scheme 3 Synthesis of PACs and ECs incorporating acitretin and trioxsalen units
Synthesis 2008, No. 21, 3433–3442 © Thieme Stuttgart · New York

PAPER
Psoralen–Acidic Retinoid Conjugates and Hybrids
3437
residue that was recrystallized (EtOAc) to obtain pure 14 (1.74 g
70%) as a white solid; mp 214–216 °C; Rf = 0.31 (B).
intermediates useful for the production of acidic retinoid– IR (KBr): 1729, 1702, 1630, 1595 cm–1.
In summary, the present study showed that electrophilic
aromatic substitution reactions of psoralens can provide
1H NMR (CDCl3): d = 7.57 (s, 1 H), 6.25 (s, 1 H), 4.74 (s, 2 H), 2.56
polyamine–psoralen type conjugates, esters of acidic ret-
inoids with psoralen-derived alcohols, and psoralen–
acidic retinoid hybrids. Application of the present meth-
odology to the preparation of other examples of conju-
gates, suitable for structure–activity relationship studies,
as well as the biological evaluation of new compounds in
various cellular targets are currently in progress.
(s, 3 H), 2.52 (s, 6 H).
13C NMR (CDCl3): d = 161.2, 155.2, 154.6, 153.1, 149.4, 123.9,
116.4, 113.1, 112.2, 111.2, 109.5, 36.2, 19.4, 12.3, 8.5.
GC-MS (EI, 20 eV): tR = 12.12 min; m/z (%) = 278 (41, [M + 2]),
276 (14, [M]), 241 (100, [M – Cl]).
Anal. Calcd for C15H13ClO3: C, 65.11; H, 4.74. Found: C, 65.25; H,
4.56.
Melting points were determined with a Buchi SMP-20 apparatus
and are uncorrected. IR spectra were recorded for KBr pellets on a
Perkin Elmer 16PC FT-IR spectrophotometer. H NMR spectra
4¢-(Hydroxymethyl)trioxsalen (15)
1
Chloride 14 (0.84 g, 3 mmol) was suspended in 1,4-dioxane (25
mL) and H2O (4 mL) and heated at 80 °C for 24 h. The resulting
mixture was diluted with H2O and extracted with CHCl3 (2 ×). The
combined organic layers were washed with H2O (3 ×), dried
(Na2SO4), and evaporated to leave a residue. Flash column chroma-
tography (F) gave pure 15 (0.39 g, 49%) as a white solid; mp 222–
225 °C; Rf = 0.37 (F).
were obtained at 400.13 MHz and 13C NMR spectra at 100.62 MHz
on a Bruker DPX spectrometer; TMS was used as reference. The as-
signments of the 1H NMR spectra were based on chemical shift ar-
guments, analysis of coupling patterns and signal intensities
whereas the 13C NMR spectra were assigned taking into consider-
ation chemical shift arguments. ESI-MS were recorded at 30V, on
a Micromass-Platform LC spectrometer using MeOH as solvent.
HRMS experiments were carried out in hybrid Q-Star Pulsar-i
(MDS Sciex Applied Biosystems, Toronto, Canada) mass spec-
trometer equipped with an ion spray ionization source. LC-MS
(ESI) were recorded on a Waters 2695 separation module, fitted
with a LiChrosphere 100 RP-8 endcapped column (5 mm, 125 × 4
mm), with a Waters 2996 Diode array detector tandem to Waters
Micromass ZQ. GC analyses were performed on an Agilent Tech-
nologies 6890N gas chromatograph fitted with a capillary column
(30.0 m; 250 mm; 0.25 mm nominal) having as stationary phase HP-
5MS 5% phenyl methyl siloxane. Carrier gas flow-rate: 26.4 mL
min–1 He; injection port temperature 300 °C; program: 70–300 °C
at 14.45 min. EI-MS were recorded at 20 eV on an Agilent Technol-
ogies 5975B instrument, tandem to the above mentioned GC spec-
trometer. Microanalyses were performed on a Carlo Erba EA 1108
CHNS elemental analyzer in the Laboratory of Instrumental Analy-
sis of the University of Patras. Flash column chromatography was
performed on Merck silica gel 60 (230–400 mesh) and TLC on 60
Merck 60F254 films (0.2 mm) precoated on Al foil. Spots were visu-
alized with UV light at 254 nm and the ninhydrin (where applicable)
or charring agents. The eluent systems used were: (A) toluene, (B)
toluene–EtOAc (9:1), (C) toluene–EtOAc (8:2), (D) toluene–
EtOAc (7:3), (E) toluene–EtOAc (1:1), (F) EtOAc, (G) CHCl3, (H)
CHCl3–MeOH (95:5), (I) CHCl3–MeOH (9:1), (J) CHCl3–MeOH
(8:2), (K) CHCl3–MeOH–concd NH3 (9:1:0.1), (L) CHCl3–MeOH–
concd NH3 (8:2:0.2), (M) CHCl3–MeOH–concd NH3 (7:3:0.3), (N)
CHCl3–MeOH–glacial AcOH (9:1:0.1). All solvents (Merck) were
dried and/or purified according to standard procedures prior to use.
Anhyd Na2SO4 was used for drying solns and subsequently solvents
were routinely removed at ca. 40 °C under reduced pressure (water
aspirator). Trioxsalen (1) and acitretin (3) were purchased from
CHEMOS GmbH. All other reagents employed in the present work
were purchased from either Aldrich or Fluka and used without fur-
ther purification. With the exception of TFA-mediated deprotec-
tion, all other reactions were routinely carried out under an
atmosphere of argon.
IR (KBr): 3396, 1695, 1639, 1592 cm–1.
1H NMR (CDCl3): d = 7.65 (s, 1 H), 6.25 (unresolved q, 1 H) 4.82
(d, J = 3.6 Hz, 2 H), 2.58 (s, 3 H), 2.514 (s, 3 H), 2.509 (d, J = 0.8
Hz, 3 H).
13C NMR (CDCl3): d = 161.5, 154.7, 154.3, 153.3, 149.2, 124.8,
116.2, 114.4, 109.2, 112.8, 111.5, 55.5, 19.3, 12.2, 8.5.
GC-MS (EI, 20 eV): tR = 12.31 min; m/z (%) = 258 (100, [M]), 241
(26, [M – OH]), 229 (17, [M – HCO]), 212 (23, [241 – HCO]).
Anal. Calcd for C15H14O4: C, 69.76; H, 5.46. Found: C, 69.91; H,
5.32.
4¢-Formyltrioxsalen (16)
From chloride 14: A suspension of chloride 14 (1.66 g, 6 mmol) in
anhyd DMSO (30 mL) was stirred at 80 °C for 10 min. To the re-
sulting soln were added sequentially K2HPO4 (1.26 g), KH2PO4
(0.25 g), and NaBr (0.07 g) and stirring was continued at this tem-
perature for 12 h. The mixture was diluted with H2O (30 mL) and
extracted with CHCl3 ( 2 × 70 mL). The combined organic layers
were washed with brine (2 × 30 mL), dried (Na2SO4), and evaporat-
ed to give a residue that was dissolved in a small volume of CHCl3
and flash column chromatographed (D). The fractions containing
the product were pooled and evaporated to leave crystalline 16 (0.54
g, 35%).
From alcohol 15: To a soln of alcohol 15 (0.31 g, 1.2 mmol) in
CH2Cl2 (60 mL) was added activated MnO2 powder (4 g, 46 mmol)
and the resulting mixture was stirred at r.t. for 12 h. Filtration
through Celite and evaporation of the solvent left pure white crys-
talline 16 (0.25 g, 83%). This was identical in all respects with the
same product obtained from chloride 14; mp 228–230 °C; Rf = 0.41
(D).
IR (KBr): 2850, 1727, 1713, 1671, 1596 cm–1.
1H NMR (CDCl3): d = 10.23 (s, 1 H), 8.19 (s, 1 H), 6.29 (s, 1 H),
2.83 (s, 3 H), 2.59 (s, 3 H), 2.53 (s, 3 H).
13C NMR (CDCl3): d = 184.8, 168.4, 161.0, 154.5, 153.4, 150.2,
4¢-(Chloromethyl)trioxsalen (14)
120.8, 118.1, 117.9, 114.6, 113.8, 109.8, 19.6, 13.3, 8.7.
1,3,5-Trioxane (0.71 g, 7.9 mmol) was suspended in concd HCl (45
mL) at r.t. under vigorous stirring and then trioxsalen (1, 2.05 g, 9
mmol) was added portionwise over 20 min. Vigorous stirring was
continued at r.t. for 12 h and then the mixture was diluted with H2O
(120 mL) and extracted with CHCl3. The organic phase was washed
H2O (3 ×), dried (Na2SO4), and evaporated to dryness to give a solid
GC-MS (EI, 20 eV): tR = 11.96 min; m/z (%) = 256 (100, [M]), 228
(54, [M – CO]), 227 (49, [M – HCO]), 199 (25, [227 – CO]).
Anal. Calcd for C15H12O4: C, 70.31; H, 4.72. Found: C, 70.19; H,
4.85
Synthesis 2008, No. 21, 3433–3442 © Thieme Stuttgart · New York

3438
M. Militsopoulou et al.
PAPER
4¢-Bromotrioxsalen (17)
1H NMR (DMSO-d6): d = 8.09 (s, 1 H), 6.40 (unresolved q, 1 H),
To a soln of trioxsalen (1, 0.46 g, 2 mmol) in anhyd CH2Cl2 (10 mL)
was added dropwise Br2 (0.11 mL, 2.2 mmol). Stirring was contin-
ued at r.t. for 3 h and the resulting suspension was diluted with Et2O
(10 mL) and refrigerated. The precipitated product was filtered,
washed with cold Et2O, and dried in vacuo to give pure bromide 17
(0.5 g, 82%) as a white solid; mp 243–245 °C; Rf = 0.32 (B).
4.95 (s, 2 H), 2.86 (s, 3 H), 2.51 (s, 3 H), 2.48 (s, 3 H).
13C NMR (DMSO-d6): d = 193.7, 166.1, 160.4, 154.3, 153.7, 149.2,
122.5, 117.2, 115.9, 114.4, 113.3, 108.5, 31.5, 19.3, 16.1, 8.8.
GC-MS (EI, 20 eV): tR = 13.72 min; m/z (%) = 350 and 348 (100,
[M]), 335 and 333 (42, [M – CH3]), 270 (77, [MH – Br]), 269 (43,
[M – Br]), 255 (54, [M – CH2Br]), 241 (77, [M – Br – CO]), 227
(40, [M – Br – CH2CO]).
IR (KBr): 1717, 1706, 1634, 1613, 1591 cm–1.
1H NMR (CDCl3): d = 7.42 (s, 1 H), 6.27 (s, 1 H), 2.56 (s, 3 H), 2.52
(s, 3 H), 2.51 (s, 3 H).
13C NMR (CDCl3): d = 161.1, 153.9, 153.8, 152.9, 149.7, 124.6,
116.7, 113.4, 111.2, 109.5, 94.5, 19.3, 12.6, 8.5.
Anal. Calcd for C16H13BrO4: C, 55.04; H, 3.75. Found: C, 54.34; H,
3.59.
tert-Butyl (E)-3-(Trioxsalen-4¢-yl)propenoate (21)
From aldehyde 16: Aldehyde 16 (0.54 g, 2.1 mmol) was treated
with Ph3P=CHCO2t-Bu (0.88 g, 2.4 mmol) in refluxing anhyd
CHCl3 (3 mL) for 2 h. Flash column chromatography (C) of the re-
sulting mixture gave pure 21 (0.62 g, 84%) as a white solid.
GC-MS (EI, 20 eV): tR = 11.65 min; m/z (%) = 306 and 308 (100,
[M]), 280 and 278 (37, [M – CO]), 279 and 277 (38, [M – HCO]),
199 (20, [280 and 278] – Br), 128 (37, [C10H8]).
Anal. Calcd for C14H11BrO3: C, 54.75; H, 3.61. Found: C, 54.98; H,
3.46.
From bromide 17: A mixture of bromide 17 (0.31 g, 1 mmol), tert-
butyl acrylate (0.29 mL, 2 mmol), Pd(OAc)2 (0.034g, 0.15 mmol),
tri(o-tolyl)phosphine (0.114 g, 0.37 mmol), and Et3N (1.7 mL, 12
mmol) in DMF (8 mL) was degassed, brought to 90 °C (bath tem-
perature) and vigorously stirred at this temperature for 1 d. The mix-
ture was then passed through a short Celite pad. The precipitate was
washed with a small volume of DMF and the filtrate was diluted
with CHCl3. The organic phase was washed with H2O (2 ×), dried
(Na2SO4), and evaporated to a small volume. This was directly ap-
plied to a flash column and elution (A) gave pure 21 (0.26 g, 74%
yield) with identical physical and spectral data to the sample ob-
tained from 16; mp 207–209 °C, Rf = 0.55 (C).
Trioxsalen-4¢-carboxylic Acid (18)
To aldehyde 16 (0.22 g, 0.84 mmol) in anhyd DMF (2.5 mL) was
added Oxone (0.65 g, 1.06 mmol) and the resulting suspension was
stirred at 45 °C for 2 d and then diluted with CHCl3. The organic
layer was washed with H2O (2 ×), dried, and evaporated to leave a
solid residue. Flash column chromatography (H) gave pure 18 (0.17
g, 73%) as a white solid; mp 162–164 °C; Rf = 0.36 (H).
IR (KBr): 3200–2500, 1738, 1656, 1618, 1590 cm–1.
1H NMR (CDCl3): d = 12.03 (br s, OH), 7.82 (s, 1 H), 6.21 (s, 1 H),
2.42 (s, 3 H), 2.32 (s, 3 H), 1.71 (s, 3 H).
IR (KBr): 1736, 1712, 1636, 1600 cm–1.
1H NMR (CDCl3): d = 7.73 (s, 1 H), 7.70 (d, J = 16.0 Hz, 1 H), 6.40
(d, J = 16.0 Hz, 1 H), 6.24 (s, 1 H), 2.62 (s, 3 H), 2.59 (s, 3 H), 2.56
(s, 3 H), 1.58 (s, 9 H).
13C NMR (CDCl3): d = 166.6, 161.1, 159.7, 154.8, 153.0, 149.5,
133.4, 122.6, 119.3, 116.6, 113.4, 112.6, 112.5, 109.7, 80.8, 28.3,
19.2, 16.4, 8.6.
MS (ESI, 30 eV): m/z = 311.25 [M + K], 295.10 [M + Na], 273.04
[MH], 255.01 [MH – H2O].
Anal. Calcd for C15H12O5: C, 66.17; H, 4.44. Found: C, 66.25; H,
4.28.
4¢-Acetyltrioxsalen (19)
To a suspension of trioxsalen (1, 0.69 g, 3 mmol) in Ac2O (6 mL)
was added SnCl4 (0.26 mL, 2.2 mmol). The resulting mixture was
stirred at r.t. for 3 d, then treated with ice-cold H2O (30 mL) and fi-
nally extracted with CHCl3 (50 mL). The organic layer was washed
with H2O, dried (Na2SO4), and evaporated to leave a residue, which
was crystallized (EtOAc) to give pure 19 (0.5 g, 62%) as a white
solid; mp 211–213 °C; Rf = 0.26 (C).
MS (ESI, 30 eV): m/z = 733.41 [2 M + Na], 393.21 [M + K], 377.22
[M + Na], 355.25 [MH].
Anal. Calcd for C21H22O5: C, 71.17; H, 6.26. Found: C, 71.02; H,
6.40.
(E)-3-(Trioxsalen-4¢-yl)propenoic Acid (22)
A soln of ester 21 (0.7 g, 2 mmol) in TFA (7 mL) and CH2Cl2 (7
mL) was kept at 0 °C for 2 h, whereby deprotection was complete
(TLC). The mixture was evaporated to dryness under reduced pres-
sure, triturated (Et2O, 10 mL) and refrigerated overnight to effected
precipitation of acid 22. The precipitate was filtered, washed (ice-
cold Et2O), and dried under reduced pressure to give pure 22 (0.5 g,
95%) as a white solid; mp 357 °C (dec.); Rf = 0.24 (I).
IR (KBr): 1718, 1659, 1600 cm–1.
1H NMR (CDCl3): d = 8.13 (s, 1 H), 6.27 (s, 1 H), 2.85 (s, 3 H), 2.65
(s, 3 H), 2.58 (s, 3 H), 2.54 (s, 3 H).
13C NMR (CDCl3): d = 193.5, 163.6, 161.1, 153.9, 153.0, 149.6,
122.5, 117.9, 117.3, 114.7, 113.4, 109.3, 30.8, 19.3, 15.7, 8.5.
GC-MS (EI, 20 eV): tR = 12.33 min; m/z (%) = 270 (100, [M]), 255
(77, [M – CH3]), 241 (15, [M – HCO]), 227 (52, [M – CH3CO]).
IR (KBr): 3150–2500, 1729, 1688, 1627, 1599 cm–1.
MS (ESI, 30 eV): m/z = 321.27 [M + Na], 299.22 [MH], 281.21
[MH – H2O], 253.08 [MH –(H2O + CO)].
Anal. Calcd for C16H14O4: C, 71.10; H, 5.22. Found: C, 70.95; H,
5.34.
Anal. Calcd for C17H14O5: C, 68.45; H, 4.73. Found: C, 68.31; H,
4.52.
4¢-(Bromoacetyl)trioxsalen (20)
To a magnetically stirred suspension of ketone 19 (0.27 g, 1 mmol)
in glacial AcOH (2 mL), kept at 10 °C, was added dropwise Br2
(0.05 mL, 1 mmol). After 5 min, the cooling bath was removed and
the mixture was allowed to attain r.t. where it was kept for 2 d. It
was then diluted with CHCl3 (20 mL) and washed with ice-cold 5%
aq NaHCO3 soln (2 ×) and H2O (2 ×), dried (Na2SO4), and evapo-
rated to give a residue that was subjected to flash column chroma-
tography (B) to give pure 20 (0.18 g, 52%) as a light-brown solid;
mp 236–237 °C; Rf = 0.19 (B).
Succinimidyl (E)-3-(Trioxsalen-4¢-yl)propenoate (7)
To a suspension of acid 22 (0.45 g, 1.5 mmol) and HOSu (0.35 g, 3
mmol) in anhyd DMF (12 mL) was added DIC (0.27 mL, 1.7 mmol)
with vigorous stirring. The resulting mixture was heated to 120 °C
for 15 min, whereby complete soln occurred, and then left overnight
at r.t. The mixture was cooled to 0 °C for 15 min and filtered and the
precipitate was washed initially with cold DMF and then Et2O and
dried under reduced pressure to give pure 7 (0.42 g 71%) as a white
solid; mp 277 °C (dec.); Rf = 0.53 (F).
IR (KBr): 1721, 1703, 1671, 1599 cm–1.
Synthesis 2008, No. 21, 3433–3442 © Thieme Stuttgart · New York

PAPER
Psoralen–Acidic Retinoid Conjugates and Hybrids
3439
IR (KBr): 1766, 1736, 1712, 1630, 1600 cm–1.
nally, the mixture was refluxed for 1 d and then filtered through a
pad of Celite. The filtrate was evaporated and residue was subjected
to flash column chromatography (G) to give pure product that crys-
tallized upon addition of Et2O. The crystalline product was filtered,
washed on the filter, and dried under reduced pressure to give pure
25 (0.16 g, 86%) as a white solid; mp 268–269 °C; Rf = 0.29 (G).
1H NMR (DMSO-d6): d = 7.92 (d, J = 16.0 Hz, 1 H), 7.89 (s, 1 H),
6.88 (d, J = 16.0 Hz, 1 H), 6.29 (s, 1 H), 2.91–2.80 (m, 4 H), 2.63
(s, 3 H), 2.46 (s, 3 H), 2.37 (s, 3 H).
13C NMR (DMSO-d6): d = 171.3, 164.4, 163.9, 163.5, 155.2, 154.8,
149.9, 140.2, 121.9, 117.6, 115.0, 113.6, 113.2, 111.5, 109.4, 26.4,
19.9, 13.7, 9.1.
IR (KBr): 1766, 1736, 1712, 1630, 1600 cm–1.
1H NMR (CDCl3): d = 10.10 (s, 1 H), 8.05 (d, J = 8.0 Hz, 2 H), 7.69
(d, J = 8.0 Hz, 2 H), 7.56 (s, 1 H), 6.26 (s, 1 H), 2.64 (s, 3 H), 2.61
(s, 3 H), 2.46 (s, 3 H).
13C NMR (CDCl3): d = 191.4, 161.2, 154.7, 154.1, 152.9, 149.5,
138.7, 135.3, 129.3, 124.4, 116.6, 116.3, 113.2, 111.2, 109.6, 19.2,
13.1, 8.5.
MS (ESI, 30 eV): m/z = 434.15 [M + K], 418.19 [M + Na], 396.19
[MH].
Anal. Calcd for C21H17NO7: C, 63.80; H, 4.33; N, 3.54. Found: C,
63.60; H, 4.21; N, 3.75
tert-Butyl (2E,4E)-5-(Trioxsalen-4¢-yl)penta-2,4-dienoate (24)
A soln of aldehyde 16 (0.39 g, 1.5 mmol) and Trippett’s reagent
(0.84 g, 2.7 mmol) in anhyd CHCl3 (2 mL) was heated at reflux for
24 h. The solvent was evaporated and the residue was subjected to
flash column chromatography (D) to give unreacted aldehyde 16
(0.22 g ) and an inseparable mixture of (E)- and (Z)-3-(trioxsalen-
4¢-yl)propenal (23) (0.1 g) in the ratio 3.6:1 (relative intensity of
formyl proton chemical shifts at d = 9.72 and 9.66). The isolated un-
reacted aldehyde 16 was resubjected to treatment with Trippett’s re-
agent as above to provide a further quantity of 23 (0.09 g) and
unreacted aldehyde 16 (0.1 g ); the totally yield of 23 based on the
unreacted aldehyde 16 was 62%. Compound 23 was then used as
such in the next step as follows. A soln of aldehyde 23 (0.19 g, 0.67
mmol) and Ph3P=CHCO2t-Bu (0.31 g, 0.81 mmol) in anhyd CHCl3
(1 mL) was heated at reflux for 3 h. Flash column chromatography
(B) of the resulting mixture provided an also inseparable (TLC and
flash column chromatography) mixture of isomeric esters 24 (0.17
g, 65%). Crystallization (EtOAc) gave pure (E,E)-24 (0.13 g, 49%);
mp 217–218 °C; Rf = 0.24 (B).
GC-MS (EI, 20 eV): tR = 12.57 min; m/z (%) = 332 (100, [M]), 304
(48, [M – CO]).
Anal. Calcd for C21H16O4: C, 75.89; H, 4.85. Found: C, 75.68; H,
5.02.
4-(Trioxsalen-4¢-yl)benzoic Acid (12)
A suspension of aldehyde 25 (0.1 g, 0.3 mmol) in DMF (1 mL) and
Oxone (0.21 g, 0.33 mmol) was stirred at 50 °C for 3 d. The result-
ing mixture was directly applied to a flash column chromatography
column and eluted (N) to give pure 12 (0.06 g, 57%) as a white sol-
id; mp 250 °C (dec.); Rf = 0.38 (I).
IR (KBr): 3150–2500, 1737, 1691 cm–1.
1H NMR (DMSO-d6, 50 °C): d = 8.09 (d, J = 8.4 Hz, 2 H), 7.71 (d,
J = 8.4 Hz, 2 H), 7.67 (s, 1 H), 6.33 (s, 1 H), 2.58 (s, 3 H), 2.48 (s,
3 H), 2.45 (s, 3 H).
13C NMR (DMSO-d6, 50 °C): d = 167.8, 160.4, 154.5, 154.3, 154.3,
149.1, 135.9, 130.5, 129.1, 124.0, 116.6, 116.3, 112.9, 112.7,
108.7, 19.1, 13.5, 8.7.
IR (KBr): 1715, 1703, 1633, 1610, 1594 cm–1.
1H NMR (CDCl3): d = 7.73 (s, 1 H), 7.38 (dd, J = 15.2, 9.6 Hz, 1 H),
6.95–6.84 (m, 2 H), 6.28 (unresolved q, 1 H), 5.84 (d, J = 15.2 Hz,
1 H), 2.59 (s, 3 H), 2.58 (s, 3 H), 2.53 (unresolved d, 3 H), 1.53 (s,
9 H).
13C NMR (CDCl3): d = 166.3, 161.0, 157.3, 154.8, 152.7, 149.5,
143.7, 129.3, 126.6, 122.9, 116.5, 113.7, 113.3, 112.2, 109.6, 80.3,
28.2, 19.2, 12.8, 8.4.
MS (ESI, 30 eV): m/z = 371.20 [M + Na], 349.23 [MH], 331.24
[MH – H2O].
Anal. Calcd for C21H16O5: C, 72.41; H, 4.63. Found: C, 72.25; H,
4.56.
tert-Butyl (E)-3-[4-(Trioxsalen-4¢-yl)phenyl]propenoate (26)
A soln of aldehyde 25 (0.23 g, 0.7 mmol) and Ph3P=CHCO2t-Bu
(0.34 g, 0.9 mmol) in anhyd CHCl3 (1.5 mL) was heated at 60 °C
for 12 h and then directly applied to a flash column chromatography
column and eluted (B) to provide ester 26 (0.16 g, 53%) as an insep-
arable mixture of E- and Z-isomers in the ratio 9:1. Crystallization
(EtOAc) gave pure (E)-26 (0.13 g, 42%) as white crystals; mp 198–
200 °C; Rf = 0.25 (B).
MS (ESI, 30 eV): m/z = 783.28 [2 M + Na], 403.16 [M + Na],
381.21 [MH], 325.13 [M – (CH3)2CCH2].
Anal. Calcd for C23H24O5: C, 72.61; H, 6.36. Found: C, 72.34; H,
6.13
(2E,4E)-5-(Trioxsalen-4¢-yl)penta-2,4-dienoic Acid (11)
IR (KBr): 1715, 1703, 1633, 1610, 1594 cm–1.
To an ice-cold soln of TFA–CH2Cl2 (1:1, 2 mL) was added ester 24
(0.1 g, 0.27 mmol) with stirring. Stirring was continued at this tem-
perature for 15 min and at r.t. for 1.5 h. Evaporation of the volatile
components under reduced pressure left a residue which was tritu-
rated (Et2O) and cooled overnight. The solid was filtered, washed
(ice-cold Et2O), and dried in vacuo to give pure acid 11 (0.08 g,
89%) as a yellow solid; mp 357 °C (dec.); Rf = 0.39 (E).
1H NMR (CDCl3): d = 7.65 (d, J = 16.0 Hz, 1 H), 7.64 (d, J = 8.4
Hz, 2 H), 7.56 (s, 1 H), 7.52 (d, J = 8.4 Hz, 2 H), 6.44 (d, J = 16.0
Hz, 1 H), 6.25 (unresolved q, 1 H), 2.62 (s, 3 H), 2.58 (s, 3 H), 2.46
(unresolved d, 3 H), 1.56 (s, 9 H).
13C NMR (CDCl3): d = 166.4, 161.4, 154.8, 153.6, 153.2, 149.5,
142.9, 134.0, 129.3, 128.7, 124.9, 120.7, 116.7, 116.5, 113.2, 111.6,
109.5, 80.9, 28.4, 19.4, 13.2, 8.6.
IR (KBr): 3150–2500, 1731, 1682, 1651, 1596 cm–1.
MS (ESI, 30 eV): m/z = 362.20 [M + K], 325.29 [MH].
MS (ESI, 30 eV): m/z = 883.32 [2 M + Na], 453.16 [M + Na],
431.14 [MH], 375.13 [M – C(CH3)3].
Anal. Calcd for C19H16O5: C, 70.36; H, 4.97. Found: C, 70.58; H,
4.85.
Anal. Calcd for C27H26O5: C, 75.33; H, 6.09. Found: C, 75.01; H,
6.22.
4-(Trioxsalen-4¢-yl)benzaldehyde (25)
To a soln of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzal-
dehyde (0.16 g, 0.7 mmol) and bromide 17 (0.17 g, 0.56 mmol) in
anhyd THF (5 mL), K2CO3 (0.23 g, 1.7 mmol) was added and the
resulting mixture was degassed. Then PdCl2(dppf) (0.033 g, 0.04
mmol) was added and the resulting mixture was again degassed. Fi-
(E)-4-(Trioxsalen-4¢-yl)cinnamic Acid (13)
To an ice-cold soln of TFA–CH2Cl2 (1:1, 2 mL) was added ester 26
(0.1 g, 0.24 mmol) with stirring. Stirring was continued at this tem-
perature for 15 min and at r.t. for 1 h. The volatile components were
evaporated under reduced pressure to give a residue that was tritu-
Synthesis 2008, No. 21, 3433–3442 © Thieme Stuttgart · New York

3440
M. Militsopoulou et al.
PAPER
rated (Et2O) and cooled overnight. The solid was filtered, washed
(ice-cold Et2O), and dried in vacuo to give pure 13 (0.07 g, 82%)
white solid; mp 298 °C (dec.); Rf = 0.34 (F).
IR (KBr): 3200–2500, 1707, 1685, 1626, 1605, 1595 cm–1.
rated (Et2O) and cooled overnight. Et2O was decanted and the oily
residue was treated once again in the same way with Et2O. The oily
residue was finally converted into a foam in vacuo. Compound 29
thus obtained had Rf = 0.22 (M).
MS (ESI, 30 eV): m/z = 521.53 [M + K], 505.58 [M + Na], 483.54
[MH], 281.22 [MH – SPM], 253.15 [MH – SPM – CO], 203.28
[SPM + H].
1H NMR (DMSO-d6, 50 °C): d = 7.86 (d, J = 8.4 Hz, 2 H), 7.72 (s,
1 H), 7.68 (d, J = 16.0 Hz, 1 H), 7.67 (d, J = 8.4 Hz, 2 H), 6.59 (d,
J = 16.0 Hz, 1 H), 6.35 (unresolved q, 1 H), 2.60 (s, 3 H), 2.55 (s, 3
H), 2.47 (s, 3 H).
13C NMR (DMSO-d6, 50 °C): d = 168.0, 160.5, 154.2, 149.2, 145.5,
143.8, 133.8, 133.6, 130.5, 130.3, 129.3, 124.3, 119.9, 116.7, 116.4,
112.8, 112.7, 108.7, 19.1, 13.5, 8.8.
This material was used as such into the next experiment as follows.
It was dissolved in anhyd DMF (0.3 mL) and then was added se-
quentially SAE 4 (0.05 g, 0.11 mmol) and dropwise i-Pr2NEt (0.1
mL, 0.6 mmol). The mixture was stirred at r.t. for 2 h and then di-
luted with CHCl3 (20 mL). The resulting soln was washed 5% aq
NaHCO3 soln (2 ×) and H2O (2 ×), dried (Na2SO4), and evaporated
to give a residue that subjected to flash column chromatography
(initially K then M). The fractions containing the product were
pooled, washed several times with H2O, and the organic layer was
then dried (Na2SO4) and finally evaporated in vacuo leaving pure
conjugate 8 (0.08 g, 86%) as a yellow foam; Rf = 0.35 (M).
MS (ESI, 30 eV): m/z = 771.32 [2 M + Na], 413.26 [M + K], 397.22
[M + Na], 375.27 [MH], 357.27 [MH – H2O].
Anal. Calcd for C23H18O5: C, 73.79; H, 4.85. Found: C, 73.94; H,
4.72.
N1,N12-Bis[(E)-3-(trioxsalen-4¢-yl)propenoyl]spermine (6)
To a soln of spermine (0.051 g, 0.25 mmol) in anhyd CH2Cl2 (5 mL)
was added succinimidyl ester 7 (0.20 g, 0.5 mmol). After stirring for
5 min, the resulting mixture turned into a soln and then a precipitate
began to fall. The reaction was complete after 1 h at r.t. and the pre-
cipitated product was filtered and washed (CH2Cl2) and finally
dried under reduced pressure to give pure product. Conjugate 6 was
isolated as the corresponding bishydroxysuccinimidate salt (0.24 g,
96%); mp 181–182 °C; Rf = 0.19 (L).
IR (Nujol): 3410, 3290, 1734, 1718, 1710, 1700, 1662, 1654, 1647,
1636, 1617, 1600 cm–1.
1H NMR (DMSO-d6): d = 8.31 (s, 1 H), 8.35–8.17 (m, 1 H), 8.07–
7.89 (m, 1 H), 7.81 (s, 1 H), 7.48 (d, J = 16.0 Hz, 1 H), 6.91 (dd,
J = 15.2, 11.2 Hz, 1 H), 6.74 (d, J = 16.0 Hz, 1 H), 6.66 (s, 1 H),
6.63 (d, J = 16.0 Hz, 1 H), 6.35 (s, 1 H), 6.33 (d, J = 16 Hz, 1 H),
6.26 (d, J = 9.2 Hz, 1 H), 6.23 (d, J = 16 Hz, 1 H), 5.81 (s, 1 H), 3.74
(s, 3 H), 3.291 (q, J = 7.2 Hz, 2 H), 3.17–3.11 (m, 2 H), 2.61–2.54
(m, 5 H), 2.53 (s, 3 H), 2.53–2.47 (m, 6 H), 2.43 (s, 3 H), 2.26 (s, 3
H), 2.19 (s, 3 H), 2.15, (s, 3 H), 2.04 (s, 6 H), 1.80 (s, 1 H), 1.65
(quint, J = 6.8 Hz, 2 H), 1.55 (quint, J = 6.8 Hz, 2 H), 1.51–1.38 (m,
4 H).
13C NMR (CDCl3): d = 167.6, 166.7, 161.2, 159.1, 156.4, 154.9,
153.4, 149.6, 148.2, 138.4, 138.3, 136.3, 136.0, 130.5, 130.0, 129.5,
128.9, 128.3, 123.1, 122.9, 122.1, 121.1, 116.7, 113.2, 112.9, 112.7,
110.2, 109.6, 66.2, 55.7, 49.3, 49.2, 47.4, 47.2, 38.4, 37.9, 29.8,
28.9, 27.7, 21.5, 19.5, 17.6, 14.1, 13.7, 13.0, 11.9, 8.8.
IR (KBr): 3421, 3250, 2950–2650, 1698, 1669, 1651, 1625, 1599
cm–1.
1H NMR (DMSO-d6, 45 °C): d = 8.49 (unresolved t, 2 H), 7.74 (s,
1 H), 7.42 (d, J = 16.0 Hz, 2 H), 6.85 (d, J = 16.0 Hz, 2 H), 6.18 (s,
2 H), 3.77 (br s), 3.27 (q, J = 6.0 Hz, 4 H), 2.67 (t, J = 6.8 Hz, 4 H),
2.63–2.56 (m, 4 H), 2.55 (s, 6 H), 2.54 (s, 6 H) 2.49–2.45 (m, 8 H),
2.39 (s, 6 H), 1.70 (quint, J = 6.8 Hz, 4 H), 1.57–1.50 (m, 4 H).
13C NMR (DMSO-d6, 45 °C): d = 173.4, 165.7, 160.3, 158.9, 154.3,
149.0, 128.1, 122.7, 122.5, 116.6, 113.6, 112.8, 112.7, 108.5, 49.1,
46.8, 37.3, 29.4, 27.5, 25.7, 19.5, 12.9, 8.6.
MS (ESI, 30 eV): m/z = 829.13 [M + K], 813.29 [M + Na], 791.26
[MH],
437.23
[AciNH(CH2)3NH(CH2)4],
409.13
[Tra-
MS (ESI, 30 eV): m/z = 785.43 [M + Na], 763.61 [MH],
409.33[TraNH(CH2)3NH(CH2)4], 338.31 [TraNH(CH2)3], 281.19
[Tra], 253.12 [Tra – CO], 237.09 [Tra – CO – C2H2].
NH(CH2)3NH(CH2)4], 366.20 [AciNH(CH2)3], 338.17 [Tra-
NH(CH2)3], 309.22 [Aci], 281.07 [Tra or Aci – CO].
HRMS (ESI): m/z [M + H] calcd for C48H63N4O6: 791.4747; found
791.4790.
HRMS (ESI): m/z [M + H] calcd for C44H52N4O8: 763.3706; found
763.3750.
Anal. Calcd for C52H60N6O14: C, 62.89; H, 6.09; N, 8.46. Found: C,
62.55; H, 5.93; N, 8.77
(Trioxsalen-4¢-yl)methyl Acitretinate (9)
To a soln of acitretin (3, 0.07 g, 0.2 mmol) in anhyd DMF (0.4 mL)
and CHCl3 (0.2 mL) was added dropwise i-Pr2NEt (0.04 mL, 0.22
mmol) followed after 5 min by the chloride 14 (0.08 g, 0.30 mmol).
The mixture was heated at 60 °C for 16 h and then diluted with
CHCl3 (20 mL). The resulting soln was washed with 5% aq
NaHCO3 soln (2 ×) and H2O (2 ×), dried (Na2SO4), and evaporated
to give a residue that was subjected to flash column chromatogra-
phy (C) to give pure 9 (0.08 g, 71%) as a yellow solid; mp 164–165
°C; Rf = 0.51 (C).
N1,N4,N9-Tris(tert-butoxycarbonyl)-N12-[(E)-3-(trioxsalen-4¢-
yl)propenoyl]spermine (28)
To a soln of SPM derivative 27 (0.28 g, 0.55 mmol) and i-Pr2NEt
(0.1 mL, 0.55 mmol) in DMF (0.25 mL) and CHCl3 (0.25 mL) was
added SAE 7 (0.2 g, 0.5 mmol). The resulting suspension was
stirred at r.t. for 2 h. The resulting soln was diluted with CHCl3 (20
mL) and washed with 5% aq NaHCO3 soln (2 ×) and H2O (2 ×). The
organic layer was dried (Na2SO4), evaporated to dryness, and the
residue thus obtained was subjected to flash column chromatogra-
phy (F) to provide pure 28 (0.32 g, 82%) as a foam; Rf = 0.25 (F).
IR (KBr): 1731, 1707, 1654, 1636, 1596 cm–1.
1H NMR (CDCl3): d = 7.62 (s, 1 H), 7.03 (dd, J = 15.2, 11.6 Hz, 1
H), 6.69 (d, J = 16.0 Hz, 1 H), 6.59 (s, 1 H), 6.28 (d, J = 15.2 Hz, 1
H), 6.25 (s, 1 H), 6.23 (d, J = 16.0 Hz, 1 H), 6.17 (d, J = 11.2 Hz, 1
H), 5.78 (s, 1 H), 5.27 (s, 2 H), 3.81 (s, 3 H), 2.57 (s, 3 H), 2.56 (s,
3 H), 2.51 (s, 3 H), 2.39 (s, 3 H), 2.29 (s, 3 H), 2.22 (s, 3 H), 2.14 (s,
3 H), 2.10 (s, 3 H).
13C NMR (CDCl3): d = 167.1, 161.5, 156.4, 156.3, 154.8, 153.8,
153.3, 149.5, 139.8, 138.2, 136.0, 135.4, 134.0, 131.4, 130.2, 129.9,
129.0, 124.9, 123.0, 118.1, 116.5, 113.1, 111.6, 111.1, 110.2, 109.4,
55.7, 21.5, 19.4, 17.6, 14.2, 13.1, 12.5, 12.0, 8.6.
MS (ESI, 30 eV): m/z = 805.60 [M + Na], 783.58 [MH], 683.64
[MH – Boc], 583.53 [MH – 2 Boc], 483.51 [MH – 3 Boc], 281.20
[MH – Boc3SPM].
N1-Acitretinyl-N12-[(E)-3-(trioxsalen-4¢-yl)propenoyl]spermine
(8)
Amide 28 (0.32 g, 0.4 mmol) was added to an ice-cold soln of TFA–
CH2Cl2 (1:1, 4 mL) with stirring. Stirring was continued at this tem-
perature for 15 min and at r.t. for 1 h. The volatile components were
evaporated under reduced pressure to give a residue that was tritu-
Synthesis 2008, No. 21, 3433–3442 © Thieme Stuttgart · New York

PAPER
Psoralen–Acidic Retinoid Conjugates and Hybrids
3441
LC-MS (ESI): tR = 26.22 min, m/z (%) = 1133.69 (5, [2 MH]),
589.30 (5, [M + Na]), 567.28 (100, [MH]).
(8) Van der Kerkhof, P. C. M. Clin. Exp. Dermatol. 2001, 26,
356; and references cited therein.
(9) For a review on PACs see for example: (a) Karygiannis, G.;
Papaioannou, D. Eur. J. Org. Chem. 2000, 1841. For some
recent examples of medicinally interesting PACs see:
(b) Camps, P.; Formosa, X.; Muñoz-Torrero, D.; Petrignet,
J.; Badia, A.; Clos, M. V. J. Med. Chem. 2005, 48, 1701.
(c) Cholody, W. M.; Kosakowska-Cholody, T.;
HRMS (ESI): m/z [M + H] calcd for C36H39O6: 567.2746; found
567.2759.
Anal. Calcd for C36H38O6: C, 76.30; H, 6.76. Found: C, 76.55; H,
6.49.
2-Oxo-2-(trioxsalen-4¢-yl)ethyl Acitretinate (10)
Hollingshead, M. G.; Hariprakasha, H. K.; Michejda, C. J.
J. Med. Chem. 2005, 48, 4474. (d) Nagarajan, M.; Morrell,
A.; Antony, S.; Kohlhagen, G.; Agama, K.; Pommier, Y.;
Ragazzon, P. A.; Garbett, N. C.; Chaires, J. B.;
Hollingshead, M.; Cushman, M. J. Med. Chem. 2006, 49,
5129. (e) Oves, D.; Fernández, S.; Verlinden, L.; Bouillon,
R.; Verstuyf, A.; Ferrero, M.; Gotor, V. Bioorg. Med. Chem.
2006, 14, 7512. (f) Battaglia, A.; Guerrini, A.; Baldelli, E.;
Fontana, G.; Varchi, G.; Samori, C.; Bombardelli, E.
Tetrahedron Lett. 2006, 47, 2667. (g) Wu, D.; Ji, S.; Wu,
Y.; Ju, Y.; Zhao, Y. Bioorg. Med. Chem. Lett. 2007, 17,
2983. For the recent development of an a-methylene-g-
butyrolactone-psoralen bisamide heterodimer see:
To a soln of acitretin (3, 0.07 g, 0.2 mmol) in anhyd DMF (0.1 mL)
and CHCl3 (0.3 mL) was added dropwise i-Pr2NEt (0.04 mL, 0.22
mmol) followed after 5 min by the bromide 20 (0.1 g, 0.3 mmol).
The mixture was kept at r.t. for 3 h and then diluted with CHCl3 (20
mL). The resulting soln was washed with 5% aq NaHCO3 soln (2 ×)
and H2O (2 ×), dried (Na2SO4), and evaporated to give a residue that
was subjected to flash column chromatography (B) to obtain pure
10 (0.08 g, 65%) as a yellow solid; mp 194–195 °C, Rf = 0.29 (B).
IR (KBr): 1730, 1718, 1710, 1684, 1676, 1654, 1636, 1600 cm–1.
1H NMR (CDCl3): d = 8.07 (s, 1 H), 7.09 (dd, J = 15.2, 11.2 Hz, 1
H), 6.71 (d, J = 16.0 Hz, 1 H), 6.60 (s, 1 H), 6.37 (d, J = 15.2 Hz, 1
H), 6.28 (s, 1 H), 6.26 (d, J = 16.0 Hz, 1 H), 6.23 (d, J = 11.2 Hz, 1
H), 5.99 (s, 1 H), 5.25 (s, 2 H), 3.82 (s, 3 H), 2.86 (s, 3 H), 2.59 (s,
3 H), 2.51 (s, 3 H), 2.41 (s, 3 H), 2.30 (s, 3 H), 2.24 (s, 3 H), 2.15 (s,
3 H), 2.12 (s, 3 H).
13C NMR (CDCl3): d = 189.2, 166.3, 164.2, 161.0, 156.5, 155.2,
154.3, 153.3, 149.9, 140.0, 138.2, 136.1, 135.4, 134.1, 131.3, 130.3,
129.9, 129.1, 128.4, 123.0, 122.1, 117.7, 117.6, 117.1, 114.7, 113.8,
110.2, 109.8, 67.4, 55.7, 21.5, 19.4, 17.6, 16.1, 14.3, 13.1, 12.0, 8.7.
(h) Ropp, S.; Guy, J.; Berl, V.; Bischoff, P.; Lepoittevin,
J.-P. Bioorg. Med. Chem. 2004, 12, 3619.
(10) For a recent example of an EC prodrug see: (a) Zakharian,
T. Y.; Seryshev, A.; Sitharaman, B.; Gilbert, B. E.; Knight,
V.; Wilson, B. E. J. Am. Chem. Soc. 2005, 127, 12508. See
also: (b) Walsh, J. J.; Coughlan, D.; Heneghan, N.; Gaynor,
C.; Bell, A. Bioorg. Med. Chem. Lett. 2007, 17, 3599.
(11) Tietze, L. F.; Bell, H. P.; Chandrasekhar, S. Angew. Chem.
Int. Ed. 2003, 42, 3996; and references cited therein.
(12) Papaioannou, D.; Drainas, D.; Tsambaos, D. WO
2004,018,001, 2004; Chem. Abstr. 2004, 140, 235912.
(13) (a) Isaacs, S. T.; Shen, C.-K. J.; Hearst, J. E.; Rapoport, H.
Biochemistry 1977, 16, 1058. (b) Kim, K.; Matsuura, K.;
Kimizuka, N. Bioorg. Med. Chem. 2007, 15, 4311.
(14) For selected examples of other psoralen derivatives, their
synthesis and mode of action, see ref. 4 above and:
(a) Oliveira, A. M. A. G.; Raposo, M. M. M.; Oloveira-
Campos, A. M. F.; Machado, A. E. H.; Puapairoj, P.; Pedro,
M.; Nascimento, M. S. J.; Portela, C.; Afonso, C.; Pinto, M.
Eur. J. Med. Chem. 2006, 41, 367. (b) Chimichi, S.;
Boccalini, M.; Cosimelli, B.; Viola, G.; Vedaldi, D.;
Dall’Acqua, F. Tetrahedron 2002, 58, 4859. (c) Traven, V.
F.; Kravtcenko, D. V.; Chibisova, T. A.; Shorshnev, S. V.;
Eliason, R.; Wakefield, D. H. Heterocycl. Commun. 1996, 2,
345. (d) Besson, T.; Ruiz, N.; Coudert, G.; Guillaumet, G.
Tetrahedron 1995, 51, 3197. (e) Bisagni, E. J. Photochem.
Photobiol., B 1992, 14, 23; and references cited therein.
(f) Zubía, E.; Luis, F. R.; Massanet, G. M.; Collado, I. G.
Tetrahedron 1992, 48, 4239. (g) Confalone, P. N.;
LC-MS (ESI): tR = 24.18 min, m/z (%) = 1189.95 (6, [2 MH],
617.05 (18, [M + Na]), 595.29 (100, [MH]).
HRMS (ESI): m/z [M + H] calcd for C37H39O7: 595.2695; found:
595.2731.
Anal. Calcd for C37H38O7 (594.69): C, 74.73; H, 6.44. Found: C,
74.41; H, 6.76.
Acknowledgment
We thank the European Social Fund (ESF), Operational Program
for Educational and Vocational Training II (EPEAEK II) and parti-
cularly the Program PYTHAGORAS II for funding the above work,
as well as Prof. G. Sindona and Prof. A. Napoli, from the Depart-
ment of Chemistry of University of Calabria (Italy), for the kind
provision of the HRMS analyses.
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Synthesis 2008, No. 21, 3433–3442 © Thieme Stuttgart · New York