Coumarin derivatives and method for synthesizing 5'-methyl psoralens therefrom

Two species of a coumarin derivative are disclosed, both of which may be produced from a 7-hydroxycoumarin precursor. The one species is an oxime and the other is a .beta.-haloallyl ester. A method for making a psoralen compound in high yield comprises treating these coumarin derivatives with an acid to fuse a furan ring thereto, and recovering a 5'-methyl psoralen therefrom. The 5'-methyl psoralen may be produced in up to about 70% overall yield with respect to the 7-hydroxycoumarin precursor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to psoralen compounds, and more particularly to 
5'-methyl psoralens synthesized from coumarin derivatives having a common 
hydroxycoumarin precursor. 
2. Prior Art 
Psoralens are the linear isomers of the furocoumarin family and they occur 
naturally in certain fruits and seeds, e.g., Ammi majus and Psoralea 
corylifolia. Extracts of these fruits and seeds have been used since 
ancient times as dermal sensitizing agents in the treatment of vitiligo. 
Topical application of psoralen extracts, followed by irradiation with 
light, results in a stimulation of melanin production, thus producing a 
dermal "tanning" effect. 
In recent years, psoralens have been utilized in the photo-chemotherapy of 
psoriasis. In such treatment, psoralens are administered orally or 
topically to a patient. Subsequently, the skin is exposed to ultra-violet 
radiation. A high percentage of remissions of the disease occur after such 
treatment. 
With increasing study of, and interest in, molecular biology, the psoralens 
have been investigated with respect to their ability to form covalent 
bonds with nucleic acids. Because of their planar structure, psoralens can 
intercalate between the base pairs in the double helix molecular structure 
of nucleic acids. Upon irradiation with light of the proper wavelength, 
the psoralens may form covalent bonds with pyrimidine nucleotides that 
occur as integral entities of nucleic acid strands. Achieving covalently 
bonded psoralen bridges or crosslinks between the nucleic acid strands of 
the double helix presents another tool for use in studying, in vivo, 
secondary structures of nucleic acids. In addition, the psoralens provide 
a means for inactivating viruses for the purpose of vaccine production, 
and also as potential chemotherapeutic agents. The covalently bonded 
psoralens act as inhibitors of DNA replication and thus have the potential 
to slow down, or stop, the replication process. The covalent bond can only 
be produced in a two step process by first intercalating the psoralen into 
the nucleic acid helix, and second by exposing those sites to 
electromagnetic radiation. Thus, it is immediately apparent that the 
covalent bonding can be controlled both temporally and spacially. 
4,5',8-trimethylpsoralen and its derivatives have drawn particular 
attention as effective photoreactive cross-linking reagents for nucleic 
acids. These 5'-methylpsoralens may be synthesized from the readily 
available hydroxy-coumarins. However, the prior known synthesizers have 
proceeded only moderately or poorly, and the yields of 5'-methylpsoralen 
therefrom have been relatively low. For example, one approach has been 
reported by K. D. Kaufman, J. Org. Chem., Vol. 26, 117 (1961), which 
utilizes Claisen rearrangement of 7-allyoxycoumarins. The last step 
thereof requires use of alkali and gives an overall yield from 
hydroxycoumarin of 28%. 
Accordingly, a good and general method for synthesizing 5'-methylpsoralens 
in high yield has been hiterto lacking. 
SUMMARY OF THE INVENTION 
The present invention is concerned with a coumarin derivative having two 
species and a method for synthesizing 5'-methylpsoralens in high yield. 
In one aspect of the present invention, a method for making a 
5'-methylpsoralen compound comprises the steps of providing a coumarin 
derivative selected either from an oxime species or a haloallyl ester 
species thereof. The coumarin derivative is then treated with an acid or 
mixture of acids at a predetermined temperature. Such treatment fuses a 
furano ring moiety to the coumarin derivative. A resultant product, 
produced in high yield, is 5'-methylpsoralen. 
The oxime species and the haloallyl ester species of the coumarin 
derivative are both provided from a 7-hydroxycoumarin precursor. The 
inventive method yields 5'-methylpsoralens of from about 40% to about 70% 
overall with respect to the 7-hydroxycoumarin. 
Other aspects and advantages of the invention will become apparent from the 
following description and appended claims. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The basic psoralen structure (and ring numbering therefor) is 
##STR1## 
while the two most widely known and widely used derivatives are 8-methoxy 
psoralen (commonly called -methoxsalen): 
##STR2## 
and 4,5',8-trimethyl psoralen (commonly called -trioxsalen): 
##STR3## 
The 5'-methylpsoralen trioxsalen is particularly useful as a pigmentation 
agent (a photosensitizer), and a number of useful psoralens may be further 
synthesized therefrom. For example, 4'-adducts of trioxsalen are disclosed 
by U.S. Pat. No. 4,124,598, issued Nov. 7, 1978, inventors John E. Hearst, 
et al., which adducts are conveniently synthesized from trioxsalen. 
Psoralens are members of the furocoumarin family as they include a furano 
moiety fused to a coumarin moiety. The basic coumarin structure is 
##STR4## 
while the basic furan structure is 
##STR5## 
7-hydroxycoumarins are readily commercially available and have the basic 
structure 
##STR6## 
A variety of organic radicals are known as substituents at the 4 and 8 
locations. The new coumarin derivatives are derived from these precursor 
7-hydroxycoumarins, are useful for making 5'-methylpsoralens, and are of 
two species. 
One species, sometimes hereinafter referred to as the oxime species or as 
derivative (2), is a 7-coumaryl oxime having the structure 
##STR7## 
wherein R.sub.1 and R.sub.2 may be a variety of organic radicals known to 
the art, for example, alkyl, aryl and alkyl-aryl; R.sub.1 and R.sub.2 may 
also be hydrogen, and R.sub.2 may be an alkoxy, and, R.sub.3 and R.sub.4 
are various alkyls and may also be hydrogen. 
The other species, sometimes hereinafter referred to as to the 
.beta.-haloallyl species or as derivative (1), is a haloallyl ester 
coumarin derivative having the structure 
##STR8## 
wherein R.sub.1 ' and R.sub.2 ' are as previously described for R.sub.1 
and R.sub.2 of the oxime species; In addition, R.sub.2 ' can be formyl or 
acyl, for example, acetyl; and, X is a halogen. 
Specific examples of the new coumarin derivatives are 
7-acetoxy-6-(.beta.-chloroallyl)-4,8-dimethylcourmarin (of the 
.beta.-haloallyl species): 
##STR9## 
And, acetone 0-7-(4,8-dimethylcoumaryl)oxime (of the oxime species): 
##STR10## 
The oxime and the .beta.-haloallyl species of the coumarin derivatives are 
useful as intermediates in the production of 5'-methylpsoralens. Their use 
to produce 5'-methyl psoralens shall hereinafter be more specifically 
described. Both species are novel compounds in their own right; the 
synthesis of the .beta.-haloallyl species (Examples I-III), and then of 
the oxime species (Examples IV-VI) shall now be described. 
Synthesis Of The Coumarin Derivatives 
For convenience, all syntheses are presented as specific examples, but it 
should be understood that larger or smaller quantities may be produced in 
accordance with the methods set forth. Also, variations in the methods set 
forth will become apparent to those skilled in the art. All temperatures 
hereinafter reported are in centigrade, T.sub.b is bath temperature and 
T.sub.i is internal temperature.

EXAMPLE I 
Crude 7-.beta.-Chloroallyloxy)-4,8-dimethylcoumarin 
4,8-dimethyl-7-hydroxycoumarin (19.0 g, 0.10 mol) and DMF (143 ml, dried 
over 4 A sieves) were heated at 70.degree. (T.sub.b) with mechanical 
stirring until the 4,8-dimethyl-7-hydroxycoumarin dissolved; then benzene 
(143 ml), K.sub.2 CO.sub.3 (18.7 g, 0.13 mol), KI (0.86 g, 5 mmol) and 
2,3-dichloro-1-propene (13.1 g, 0.118 mol, bp 92.degree.-93.degree. ) were 
added in the order given. The mixture was mechanically stirred at 
80.degree.-85.degree. (T.sub.b) for 11 h, cooled, and evaporated at 15 mm 
to remove benzene, then at 0.1 mm to remove DMF. The residue was diluted 
with CHCl.sub.3 (400 ml) and washed with water (55 ml). The aqueous layer 
was extracted further with CHCl.sub.3 (100 ml), and the combined extracts 
were washed with 1 M NaOH (400 ml), then with saturated NaCl (400 ml), and 
dried. Evaporation gave 26.3 g (99%) of solid, giving on TLC (CH.sub.2 
Cl.sub.2) one spot corresponding in R.sub.f with 
7-(.beta.-chloroallyloxy)-4,8-dimethylcoumarin, which was purified as 
described in Example II, below. 
EXAMPLE II 
Purified 7-(.beta.-Chloroallyloxy)-4,8-dimethylcoumarin 
1.33 g (7 mmol) of 4,8-dimethyl-7-hydroxycoumarin was converted to the 
product as described by Example I and then purified for analysis as 
follows. 
Chromatography on silica gel (15 g) with CHCl.sub.3 yielded a residue (1.82 
g, 98%) which was recrystallized from CHCl.sub.3 /hexanes to give after 
collection of three crops 1.67 g (90%) of 
7-.beta.-chloroallyloxy)-4,8-dimethylcoumarin: mp 117.degree.-118.degree.; 
NMR .delta. 2.37 (3H, s), 2.38 (3H, d, J=2 Hz), 4.68 (2H, m), 5.55 (2H, m, 
J.sub.gem =7 Hz), 6.14 (1H, m), 6.82 (1H, d, J=9 Hz), 7.44 (1H, d, J=9 
Hz); UV (95% C.sub.2 H.sub.5 OH).lambda..sub.max 244 nm (.epsilon. 3920), 
254 (4120), 319 (14,600). 
Anal. Calcd for C.sub.14 H.sub.13 O.sub.3 Cl: C, 63.5; H, 5.0. Found: C, 
63.7; H, 5.1. 
EXAMPLE III 
7-Acetoxy-6-(.beta.-chloroallyl)-4,8-dimethylcoumarin 
A portion of the purified 7-(.beta.-chloroallyloxy)-4,8-dimethylcoumarin of 
Example II, (264 mg, 1.0 mmol) was added to p-diisopropylbenzene (4 ml, 
refluxed over Na for 16 hr, then distilled from Na) and acetic anhydride 
(0.4 ml). This mixture was refluxed (T.sub.i 195.degree. ) under argon for 
26 h. The cooled reaction mixture was diluted with CHCl.sub.3 (5 ml), 
washed with water (10 ml) and then with NaHCO.sub.3 (10 ml), dried and 
evaporated at 15 mm to remove CHCl.sub.3, then at 0.1 mm/50.degree. to 
remove p-diisopropylbenzene. The residue was chromatographed on silica gel 
(2.8 g) eluting with CH.sub.2 Cl.sub.2 to yield a residue (300 mg) which 
was recrystallized from CHCl.sub.3 /hexanes to give 
7-acetoxy-6-(.beta.-chloroallyl)-4,8-dimethylcoumarin (185 mg, 60%): mp 
161.degree.-162.degree.; NMR .delta. 2.27 (3H, s) 2.38 (3H, s), 2.42 (3H, 
d, J=2 Hz), 3.64 (2H, broad s), 5.25 (2H, m, J.sub.gem =11 Hz), 6.28 (1H, 
m), 7.40 (1H, broad s); UV (95% C.sub.2 H.sub.5 OH).lambda..sub.max 244 nm 
(sh, .epsilon. 7090), 278 (11,800), 315 (6900). 
Analysis Calculated for C.sub.16 H.sub.15 O.sub.4 Cl: C, 62.7; H, 4.9. 
Found: C, 62.6; H, 5.0. 
EXAMPLE IV 
7-Aminoxy-4,8-dimethylcoumarin 
Sodium hydride (220 mg, 50% NaH in oil dispersion) was diluted and stirred 
with dry hexane (6 ml). The mixture was allowed to settle and the hexane 
was drawn off. This process was repeated twice, then the residue was dried 
by sweeping N.sub.2 through the flask while stirring. To the residue (142 
mg, 5.9 mmol NaH) was added DMF (13 ml, distilled from CaH.sub.2) and the 
mixture was cooled in an ice-water bath. 4,8-dimethyl-7-hydroxycoumarin 
(1.12 g, 5.9 mmol) in DMF (11 ml) was added dropwise over 5 min while 
maintaining T.sub.i at 5.degree.-10.degree. to form the anionic form of 
the hydroxycoumarin. The cooling bath was removed after 0.5 h, and 
0-(2,4-dinitrophenyl)hydroxylamine (588 mg, 2.95 mmol) in DMF (7 ml) was 
added over 3 min. The solution was stirred for 3 h and then added with 
stirring and cooling to a solution of water (175 ml) and saturated 
NaHCO.sub.3 (42 ml) followed by extraction with CHCl.sub.3 (1.times.175 ml 
plus 2.times.75 ml). The combined extracts were cooled to 
5.degree.-10.degree. and washed with cold 1 M NaOH (175 ml) and then with 
saturated NaHCO.sub.3 (100 ml), dried and evaporated to a residue (0.42 g, 
69%). This material was compared by TLC and spectral studies with verified 
7-aminoxy-4,8-dimethylcoumarin from Example V below, and found to be 
identical therewith. 
EXAMPLE V 
Verification of 7-aminoxy-4,8-dimethylcoumarin 
64 mg of material was prepared as described by Example IV, and was 
recrystallized from absolute ethanol to yield 50 mg of fine needles: mp 
155.degree.-156.degree. (dec); NMR (DMSO-d.sub.6) .delta. 2.20 (3H, s), 
2.42 (3H, d, J=2 Hz), 6.18 (1H, m), 7.22 (2H, br s), 7.44 (1H, d, J=9 Hz), 
7.62 (1H, d, J=9 Hz); UV (95% C.sub.2 H.sub.5 OH).lambda..sub.max 247 nm 
(.epsilon. 3720), 256 (3690), 324 (16,200). 
Analysis Calculated for C.sub.11 H.sub.11 NO.sub.3 : C, 64.4; H, 5.4; N, 
6.8. Found: C, 64.1; H, 5.4; N, 7.1. 
EXAMPLE VI 
Acetone 0-7-(4,8-dimethylcoumaryl)oxime 
205 mg (1.0 mmol) of the 7-aminoxy-4,8-dimethylcoumarin of Example IV was 
combined with absolute ethanol (10 ml), acetone (64 mg, 0.081 ml, 1.1 
mmol) and conc. HCl (2 drops) in the order given and stirred. Within 5 min 
this heterogeneous mixture had become homogeneous, and within another 10 
min it was heterogeneous. After 1 h the mixture was evaporated to a 
residue (237 mg) which was chromatographed on silica gel (2 g) with 
CH.sub.2 Cl.sub.2 to yield a residue which on recrystallization from 
absolute ethanol yielded 211 mg (86%) of acetone 
0-7-(4,8-dimethylcoumaryl)oxime: mp 129.degree.-130.degree. (dec.); NMR 
.delta. 2.08 (3H, s), 2.15 (3H, s) 2.3 (3H, s), 2.40 (3H, d, J=2 Hz), 6.08 
(1H, m), 7.38 (2H, s); UV (95% C.sub.2 H.sub.5 OH).lambda..sub.max 248 nm 
(.epsilon. 5880), 257 (5830), 323 (18,400). 
Analysis Calculated for C.sub.14 H.sub.15 NO.sub.3 : C, 68.6; H, 6.2; N, 
5.7. Found: C, 68.5; H, 6.2; N, 5.7. 
Thus, Examples I-III may be summarized by the following general reaction 
schematic, Scheme A (wherein R.sub.1 ', R.sub.2 ' and X are as have been 
previously described, and "derivative (1)" represents the .beta.-haloallyl 
species in accordance with the present invention). 
##STR11## 
The intermediate compound of Scheme A, above, is normally a 
.beta.-haloallyl either which does not require extensive purification for 
conversion to derivative (1), although chromatography is recommended. 
Where the intermediate compound is to be a chloroallyl ether, the 
preferred alkylating agent is 2,3-dichloro-1-propene. When R.sub.2 ' is 
formyl or acetyl the acetic anhydride may be omitted in the rearrangement 
step and thus the product (i.e., derivative (1)) will be phenol rather 
than its acetate. 
Examples IV-VI may be summarized by the following general reaction scheme, 
Scheme B (wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are as have been 
previously described, and "derivative (2)" represents the oxime species in 
accordance with the present invention). 
##STR12## 
A large number of ketones or aldehydes are suitable for use in reaction 
Scheme B, and R.sub.3, R.sub.4 will derive from the particular ketone or 
aldehyde utilized. For example, when acetone is utilized, R.sub.4 =H and 
R.sub.3 =CH.sub.3. Conversion of the phenol, or 7-hydroxycoumarin in 
Scheme B with the aminating reagent (preferably 
0-(2,4-dinitrophenyl)hydroxylamine) may be by a 1:1 mole ratio; however, 
better yield can be obtained with an excess of 7-hydroxycoumarin, 
preferably wherein the 7-hydroxycoumarin is a 2:1 mole ratio with respect 
to aminating reagent. 
METHOD FOR MAKING PSORALENS 
Broadly, a method for making a 5'-methyl psoralen in accordance with the 
present invention comprises treating derivative (1) or derivative (2), as 
represented above, with sufficient of an acid or mixture of acids at a 
predetermined temperature range to fuse a furano ring moiety thereto. When 
derivative (1) is provided, the treating is with sulfuric acid of a 
concentration not greater than about 85%, more preferably from about 70% 
to about 80%, most preferably at about 70%, the treating being at a 
temperature of from about 0.degree. C. to about 25.degree. C., to form a 
5'-methyl psoralen. The 5'-methyl psoralen reaction product from such 
treatment is recoverable in high, overall yield with respect to the 
hydroxycoumarin precursor, which precursor is common to both derivatives 
(1) and (2). The inventive method shall now be more particularly described 
for derivatives (1) and (2) respectively. 
Examples VI-IX illustrate the method, or aspects thereof, when derivative 
(1) is provided. Similarly, Examples X-XII illustrate the method, or 
aspects thereof, when derivative (2) is provided. 
EXAMPLE VI 
Treatment of derivative (1), wherein R.sub.1 '=--CH.sub.3, R.sub.2 
'=--CH.sub.3 and X=--Cl, with concentrated H.sub.2 SO.sub.4 at room 
temperature (about 18.degree. to about 25.degree. ) led to rapid 
consumption of derivative (1), but no product could be isolated. 
EXAMPLE VII 
Treatment of derivative (1), wherein R.sub.1 '=CH.sub.3, R.sub.2 
'=--CH.sub.3 and X=--Cl, with 90% H.sub.2 SO.sub.4 at from about 
0.degree.-5.degree. allowed for isolation of two products as follows. 
To 90% (v/v) sulfuric acid (4 ml) at 0.degree.-5.degree. (T.sub.i) was 
added with magnetic stirring derivative (1) [100 mg, 0.32 mmol] over 1.5 
min. After 10 min the solution was added dropwise over 1 min to 30 ml 
water with rapid stirring and cooling. The mixture was extracted with 
CHCl.sub.3 (2.times.10 ml), and the combined extracts were dried and 
evaporated to yield a residue (56 mg) which was chromatographed on 
kieselgel (6 g) with CHCl.sub.3 to yield 4,5',8-trimethylpsoralen (18 mg) 
and a dimer (29 mg): NMR .delta. 1.87 (3H, s), 2.32 (3H, d, J=2 Hz), 2.38 
(3H, s), 2.42 (3H, d, J=2 Hz), 2.52 (3H, s), 2.58 (3H, s), 3.60 (2H, m), 
6.02 (1H, m), 6.15 (1H, m), 7.22 (1H, s), 7.55 (1H, s); MS m/e (rel. 
intensity) 457 (11%), 456 (37, M.sup.+), 228 (39), 44 (100); high 
resolution mass spectrum, calcd for C.sub.28 H.sub.24 O.sub.6 (M.sup.+), 
456.1573, found, 456.1558. 
If the above reaction in 90% sulfuric acid was allowed to continue for more 
than 1.5 h, both products were no longer present. 
EXAMPLE VIII 
Derivative (1), where R.sub.1 '=--CH.sub.3, R.sub.2 '=--CH.sub.3 and 
X=--Cl, was treated with 80% H.sub.2 SO.sub.4 at about 0.degree.-5.degree. 
in a manner analogous to Example VII. Again, two products were isolated 
(that is, the desired 5'-methylpsoralen and a dimer thereof), but the 
relative amount of dimer was decreased. 
EXAMPLE IX 
Derivative (1), where R.sub.1 '=--CH.sub.3, R.sub.2 '=--CH.sub.3 and 
X=--Cl, [7.47 g, 24.4 mmol] was shaken on a mechanical shaker with 70% 
(v/v) sulfuric acid (171 ml conc. H.sub.2 SO.sub.4 plus 74 ml water) for 
1.0 h. The mixture was then added to water (1.72 L) with vigorous 
mechanical stirring at a rate which allowed maintenance of T.sub.i at 
10.degree.-20.degree.. The mixture was then extracted with chloroform 
(2.times.500 ml). The combined extracts were washed with saturated 
NaHCO.sub.3 (600 ml), cooled to 5.degree. and washed with cold 1 M NaOH 
(400 ml), and then washed with saturated NaHCO.sub.3 (400 ml), dried and 
evaporated to a residue which was recrystallized from CHCl.sub.3 /ethyl 
acetate to yield 4,5',8-trimethylpsoralen (4.48 g, 80%): mp 
231.degree.-232.degree. (lit. reports a mp 234.degree.- 235.degree.; mp of 
material purchased from the Paul B. Elder Company, 
230.degree.-231.degree.); identical by TLC, NMR and UV comparison with 
authentic material; NMR .delta. 2.52 (6H, m), 2.57 (3H, s), 6.20 (1H, m), 
6.40 (1H, m), 7.50 (1H, broad s). 
EXAMPLE X 
Derivative (2), where R.sub.1 =--CH.sub.3, R.sub.2 =--CH.sub.3, R.sub.3 
=--CH.sub.3 and R.sub.4 =--H, [245 mg, 1.0 mmol] was dissolved in 88% 
formic acid (30 ml), then 85% H.sub.3 PO.sub.4 (3.3 ml) was added and the 
solution was stirred at 60.degree. (T.sub.b) for 4 h. The cooled reaction 
solution was added to cold water (200 ml) with stirring and cooling, and 
this solution was extracted with CHCl.sub.3 (2.times.125 ml). The combined 
extracts were washed with saturated NaHCO.sub.3 (100 ml), with 1 M NaOH 
(100 ml), then again with saturated NaHCO.sub.3 (75 ml), dried and 
evaporated to a residue (188 mg, 82%) which was chromatographed on 
kieselgel (20 g) with CH.sub.2 Cl.sub.2 to separate 
4,5',8-trimethylpsoralen (94 mg, 41%). 
EXAMPLE XI 
Derivative (2), where R.sub.1, R.sub.2 and R.sub.3 =--CH.sub.3, and R.sub.4 
=--H, was treated as in Example X, above, but acetic acid was utilized 
rather than the formic acid. An overall yield of about 40%, 
4,5,8-trimethylpsoralen was obtained. 
EXAMPLE XII 
Derivative (2) was treated as in Example X, above, but formic acid alone 
(i.e. without phosphoric acid) was utilized which adequately converted the 
oxime species to trimethylpsoralen. 
In summary, the present invention provides a good, general method for 
synthesizing 5'-methylpsoralens in high yield.