A new benzoangelicin with strong photobiological activity

Article abstract of DOI:10.1016/S0960-894X(99)00640-X

Benzoangelicins 4-6 were synthesized in good yields from 7-hydroxy-5- methoxy-4-methylcoumarin (1). In the absence of UVA radiation, compounds 5 and 6 were only weakly active against HL60 and HeLa tumour cells; in its presence, compound 6 was 10 times mor

Full text of DOI:10.1016/S0960-894X(99)00640-X

Bioorganic & Medicinal Chemistry Letters 10 (2000) 135±137
A New Benzoangelicin with Strong Photobiological Activity
Lourdes Santana, a Eugenio Uriarte, a,* Lisa Dalla Via b and Ornella Gia b
a
Â
Laboratorio de Quõmica Farmaceutica, Facultad de Farmacia, Universidad de Santiago de Compostela, Spain
Â
Dipartimento Scienze Farmaceutiche, Universita di Padova, Italy
b
Á
Received 18 June 1999; accepted 15 November 1999
AbstractÐBenzoangelicins 4±6 were synthesized in good yields from 7-hydroxy-5-methoxy-4-methylcoumarin (1). In the absence of
UVA radiation, compounds 5 and 6 were only weakly active against HL60 and HeLa tumour cells; in its presence, compound 6 was
10 times more active than the reference compound 8-methoxypsoralen. None of 4±6 exhibited cutaneous phototoxicity. # 2000
Elsevier Science Ltd. All rights reserved.
The furocoumarin family includes members that are
widely used in the photochemotherapy of various skin
diseases.1 The utility of linear furocoumarins (psor-
alens) is limited by the side e€ects deriving from their
ability to crosslink the two strands of DNA by binding
to the thymine residues.2±4 In previous work we pursued
two of the most important strategies put forward to
avoid this e€ect: fusing the furan ring to the coumarin
moiety in [2,3-h] instead of [3,2-g] con®guration so as to
create an `angular' furocoumarin, or angelicin,5 and
fusing a benzene ring to the furan ring.6,7 Although the
®rst attempts to combine these two strategies a€orded
compounds with little activity,8±10 we have now found
that compound 6, a benzoangelicin with a dimethyl-
aminopropyloxy group at position 5, is not only 10
times as e€ective as 8-methoxypsoralen (8-MOP)
against HL60 and HeLa cells, but also appears to lack
the cutaneous phototoxicity of 8-MOP.
replaced with a dimethylaminopropyl group by Wil-
liamson's reaction using either 3-chloro-N,N-dimethyl-
propylamine hydrochloride, sodium hydride and sodium
iodide in re¯uxing DMF (30 min; yield 58% after chro-
matography with chloroform as eluant) or potassium
carbonate and HMPA in re¯uxing acetone (2 h; yield
77%)12 (Scheme 1).
The antiproliferative activity of compounds 4±6 was
evaluated in vitro against human cervix adenocarci-
noma (HeLa) cells and human promyelocytic (HL60)
cells in parallel with that of the reference drug 8-MOP.
Experiments were performed with and without irradia-
tion at 365 nm (0.793 J cm 2) using previously estab-
lished procedures.13 Compound 4 was inactive, and
compounds 5 and 6 were only weakly active in the dark.
Under irradiation, compound 5 was roughly as active as
8-MOP against HL60, and compound 6, which has a
protonable dimethylaminopropyloxy side-chain, was 10
times more active in both cell lines (Table 1). Tests of skin
photosensitizing potency on Dunkin±Hartley depilated
albino guinea pigs, performed as previously reported,13
showed 4±6 to be completely devoid of phototoxicity at
concentrations below 50 mg cm 2, whereas 8-MOP is
Compound 6 was synthesized via angelicins 4 and 5
starting from 7-hydroxy-5-methoxy-4-methylcoumarin
(1), as follows. Compound 4 was obtained from 1 as
described previously6 in an overall yield of 38% (the
step from 2 to 3 gives a 3:2 mixture of 3 and its linear
isomer 6,7,8,9-tetrahydro-5-methoxy-4-methylbenzo-
furo[3,2-g]coumarin). The methoxy group of 4 was
hydrolized for 4 h with a re¯uxing mixture of hydriodic
acid, acetic acid and acetic anhydride to give compound
5 in 97% yield after chromatography with methylene
chloride as eluant.11 The hydroxyl hydrogen was then
2
highly toxic at 10 mg cm (Table 1).
To evaluate the binding of the new benzofurocoumarin
6 to double-stranded DNA, linear ¯ow dichroism (LD)
measurements were performed at a [DNA]/[drug] ratio
of 12.5. A negative band in the chromophore absorption
region of the resulting spectrum (310±380 nm) shows
that 6 adopts a position parallel to the plane of the
DNA bases (not shown). The reduced linear dichroism
value (LDr=LD/Aiso) determined at the wavelength of
*Corresponding author. Fax: +34-981-594912; e-mail: qofuri@usc.es
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(99)00640-X

136
L. Santana et al. / Bioorg. Med. Chem. Lett. 10 (2000) 135±137
Scheme 1. Reagents: (a) 2-chlorocyclohexanone, K2CO3, Me2CO, re¯ux; (b) NaOH, re¯ux; (c) DDQ, benzene, re¯ux; (d) HI, AcOH, Ac2O, re¯ux;
(e) 3-chloro-N,N-dimethylpropylamine, K2CO3, HMPA, Me2CO, re¯ux.
Table 1. Antitumour activity of compounds 4±6 under irradiation at
365 nm
IC50 (mM)a
Compound
HL60
HeLa
Erythema formationb
4
5
>2 0
6.95
0.52
5.4
>2 0
>20
1.12
10
6
8-MOP
+++
aConcentration required to reduce proliferation of tumour cells by
50%.
bSymbols: +++, severe erythema with edema;
, no erythema.
peak absorption by 6, is close to that of the DNA
absorption band at 260 nm, and implies14 a value of
90ꢀ for the angle a de®ning the orientation of the
ligand with respect to the axis of the double helix. The
geometry of the DNA±drug complex is thus consistent
with an intercalative binding mode similar to that of
psoralens15 and angelicins.16
Figure 1. Photobinding of compound 6 and 8-MOP to double-stranded
DNA from calf thymus (nucleotide±drug ratio=75) as a function of
irradiation time.
Quantitative assays of photobinding by tritiated com-
pound 6 to calf thymus DNA showed its photoreactivity
to be signi®cantly less than that of 8-MOP (Fig. 1). This
lack of correlation between cytotoxicity and covalent
interaction with DNA is unprecedented among furo-
coumarin derivatives. The inkling that other molecular
mechanisms, apart from the covalent photoaddition to
the DNA, are involved in the photobiological events
evoked by the furocoumarins, is present in litera-
ture.17,18 Nevertheless, their real contribution has not
been evaluated yet. The peculiar behaviour of com-
pound 6 can be considered an experimental con®rma-
tion of these alternative mechanisms and an evidence of
their importance to determine the biological activity
and, ®nally, the therapeutic e€ects of the furocoumar-
ins. Studies to identify intracellular targets of compound
6 other than DNA are currently in progress.
Acknowledgement
Thanks go to the Xunta de Galicia (XUGA20308B98)
for the partial ®nancial support.
References and Notes
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