New green synthesis and formulations of acyclovir prodrugs

Article abstract of DOI:10.1248/cpb.59.1089

Different green synthesis of alkyl esters of acyclovir (acyclovir prodrugs) is described. Hexanoic, decanoic, dodecanoic and tetradecanoic acyclovir esters were synthesized reacting acyclovir and the respective acid anhydride in dimethyl sulfoxide (DMSO), in solvents from renewable sources and without solvent (T=30 °C). Yields in prodrugs after 10 min of reaction were >95% using DMSO as solvent. The purification methodology was very simple, shorter and greener than previously described. The biosolvent, N,N-dimethylamide of decanoic acid, let us to obtain >95% yield at 24 h. This oily biosolvent is not dermotoxic and the reaction crude can directly be used in topic formulations. Syntheses without solvent proceeded successfully for acyclovir esters. Indeed, dodecanoate and tetradecanoate yielding >98% conversion of reactants in 30 min. In spite of requiring mild temperature (65 °C), substrate molar ratios were lowered to 1 : 1, thus conducing to a more efficient use of raw materials. The synthetic procedures were scaled up to a 300 g batch (yield 98-99% isolated ester). These esters can be used as acyclovir prodrugs in topic formulations. The esters release from an oil/water micro-emulsion and a hydrogel formulation were tested with good results.

Full text of DOI:10.1248/cpb.59.1089

September 2011
Regular Article
Chem. Pharm. Bull. 59(9) 1089—1093 (2011)
1089
New Green Synthesis and Formulations of Acyclovir Prodrugs
a
a
b
Rubén de REGIL-HERNÁNDEZ, Fernando MARTÍNEZ-LAGOS, Amalia RODRÍGUEZ-BAYÓN, and
José-Vicente SINISTERRA*
,
a
a
Servicio de Biotransformaciones Industriales; Parque Científico de Madrid, Santiago Grisolía 2, Parque Tecnológico de
b
Madrid, Tres Cantos, 28760, Madrid, Spain: and Department of Pharmaceutical Technology, Faculty of Pharmacy,
Universidad Complutense de Madrid; Plaza Ramón y Caja s/n, Ciudad Universitaria, 28040, Madrid, Spain.
Received January 5, 2011; accepted June 22, 2011; published online June 29, 2011
Different green synthesis of alkyl esters of acyclovir (acyclovir prodrugs) is described. Hexanoic, decanoic,
dodecanoic and tetradecanoic acyclovir esters were synthesized reacting acyclovir and the respective acid anhy-
dride in dimethyl sulfoxide (DMSO), in solvents from renewable sources and without solvent (Tꢀ30 °C). Yields in
prodrugs after 10 min of reaction were ꢀ95% using DMSO as solvent. The purification methodology was very
simple, shorter and greener than previously described. The biosolvent, N,N-dimethylamide of decanoic acid, let
us to obtain ꢀ95% yield at 24 h. This oily biosolvent is not dermotoxic and the reaction crude can directly be
used in topic formulations. Syntheses without solvent proceeded successfully for acyclovir esters. Indeed, dode-
canoate and tetradecanoate yielding ꢀ98% conversion of reactants in 30 min. In spite of requiring mild tempera-
ture (65 °C), substrate molar ratios were lowered to 1 : 1, thus conducing to a more efficient use of raw materials.
The synthetic procedures were scaled up to a 300 g batch (yield 98—99% isolated ester). These esters can be used
as acyclovir prodrugs in topic formulations. The esters release from an oil/water micro-emulsion and a hydrogel
formulation were tested with good results.
Key words acyclovir prodrug; green chemistry; transdermal formulation
Acyclovir is a potent inhibitor of Herpes Simplex which electroporation etc., which require more complex manufac-
also shows relatively fair inhibition to Varizella Zoster virus turing and administering procedures.
1)
and to a less extent to Epstein Barr virus Its wide and con-
The most suitable kind of prodrugs for passive transdermal
tinued clinical use as antiherpetic agent during the last 25 administration path is the linear alkyl esters due to their com-
2)
years has proved its safety Current antiherpetic treatments patibility with the skin lipidic matrix. In addition the high ac-
with acyclovir include tablets (200 mg, 400 mg, 800 mg or tivity of esterases in human skin favors the liberation of the
1
g), topical cream (5%), intravenous injection (25 mg/ml) drug by simple hydrolysis of acyclovir and the non-toxic
and ophthalmic ointment (3%). Nevertheless, acyclovir fatty acid.
shows some limitations due to its low bioavailability (15— Early attempts to synthesize acyclovir prodrugs date from
thus high doses early 80s with the work on 2,6-diamine-9-(2-hydroxy-
1,3,4)
20%) and low serum half-life (2—3 h),
10)
11)
and frequent administrations are required. Therefore, differ- etoximethyl)purine and 6-deoxyacyclovir. In 1990, ace-
ent prodrugs and topical formulations have been described in tate and hexanoate of acyclovir were synthesized in 2—3 h
order to overcome these inconveniences.
12)
by Hardnen et al. using acid anhydrides as acyl donors in
Transdermal administration of prodrugs is an interesting N,N-dimethylformamide (DMF) (toxic for the skin) and 4-
path to convey active principles systemically. This methodol- N,N-dimethylaminopyridine (DMAP) as catalyst, obtaining
ogy directly competes with oral administration. Indeed, ꢀ40% yield in monoester and diacyl derivatives as second-
13)
around 40% of drugs in clinical trials are intended to be used ary products. In 1994, Shao et al. followed this methodol-
5)
transdermally. This is due to the advantages that transder- ogy to synthesize some short chain esters of acyclovir but ex-
mal administration offers to achieve efficient and safe heal- tended the reaction time up to 2—3 d without reporting
1
4)
ing such as: avoiding first pass hepato-metabolic degrada- yields. A similar approach was described by Bando et al.
6)
7)
tion, giving stable drug levels in plasma, this procedure is in 1996 using acid chlorides instead of acid anhydrides as
invasiveness and it can be applied for longer periods of acyl donors but reduced the acyl chloride : acyclovir molar
time. The simplest transdermal technique is a passive diffu- ratio to 3 : 1. This group obtained high purity compounds
sion which has the additional advantage of being more pa- after 2 d and further precipitation in a NaOH solution. In a
tient compliant than its counterparts such as iontophoretic, similar effort Kim et al. in 1998 synthesized short chain
8)
9)
15)
Chart 1
∗
To whom correspondence should be addressed. e-mail: jose.sinisterra@fpcm.es
© 2011 Pharmaceutical Society of Japan

1
090
Vol. 59, No. 9
esters of 2-amino-6-fluoro-9-(2-hydroxymethoxy-methyl)purine, Table 1. Yields Obtained in the Esterification of Acyclovir (1) Using
1
6)
DMSO as Solvent Compared with the Best Described Yields
as potential prodrugs of acyclovir. These workers described a
three-step procedure with yields above 90%, but 5 d were
necessary to isolate the ester. In this procedure, the esterifica-
tion step was achieved in 20 min using 3 eq of acid anhy-
16)
Fatty acid
anhydride
Yield in isolated Reaction Yield
Reaction
Compound
16)
ester (%)
time (min) (%) time (d)
16)
drides and DMF as solvent. In 1999, Gao et al. conducted
Acetic
Butyric
Hexanoic
Decanoic
Dodecanoic
Tetradecanoic
3a
3b
3c
3d
3e
3f
95
96
97
98
97
98
10
10
10
10
10
10
84
—
37
—
37
—
1.5
—
1.5
—
1.5
—
the synthesis of several short ester prodrugs of acyclovir
13)
using a modified Shao’s procedure, reducing acid anhy-
dride amount from 20 to 3 acyclovir equivalents and the re-
action time to 1.5 d. In such work they reported yields around
8
0%, but they still observed 5—12% of double acylations.
To the best of our knowledge, the syntheses of long chain es-
ters of acyclovir (laurate and palmitate) have been referenced Table 2. Yields Obtained after 24 h in the Synthesis of Acyclovir Alkyl
1
7)
Esters Using N,N-Dimethylamides of Fatty Acids as Green Solvents
only in the Gao et al. review in which yields of 37% are re-
18,19)
ported. Recently, Stankova et al.
described the synthesis
Yield (%)
of acyclovir esters with peptidomimetics or with cinnamic
acid using coupling reagents and evaluated in vitro for their
antiviral activity against the replication of Herpes simplex
virus type 1 (HSV-1) and type 2 (HSV-2).
Solvents are necessary substances in all the chemical or-
ganic synthesis, so attention should be paid to choose the
best suited and less harmful to the environment. Therefore,
organic processes which make less use or substitute toxic
solvents are desired. In this way, the enzyme-catalyzed acyla-
tion of nucleosides in 2-methyltetrahydrofuarne (obtained
Compound
Solvent
DMAC10
Solvent
DMAA
Solvent
DMALA
ACVC6
3c
3d
3e
3f
97
97
98
99
30
NI
NI
NI
10
12
11
NI
ACVC10
ACVC12
ACVC14
NI: No isolated.
from biomass) instead of tetrahydrofuran (THF) has been re- from Biomass An alternate approach was to use solvents
20)
ported.
obtained from renewable sources, as the reaction medium.
In this work we present a series of alternative procedures N,N-dimethylamides of fatty acids, obtained from renewable
to synthesize short and long acyclovir fatty acid esters (3a— sources (triglycerides) were used to carry out the synthesis of
f) in a more efficient and sustainable way to be incorporated acyclovir esters. Three different solvents were used: N,N-di-
in topical emulsions for transdermal administration use.
methylamide of decanoic acid (DMAC10), a mixture of N,N-
dimethylamides of octanoic and decanoic acids (DMAA) and
N,N-dimethylamide of lactic acid (DMALA).
Results and Discussion
Synthesis of Acyclovir Esters in DMSO With the aim
As we show in the Table 2, the three solvents provided a
to carry out greener synthesis, we substituted dermotoxic qualitatively positive outcome for the synthesis acyclovir
DMF, used in all the described procedures above, by DMSO alkyl esters but at slower reaction rates than in DMSO, prob-
with low dermotoxicity and widely accepted as percutaneous ably due to the solvent viscosity which might create diffusion
24)
penetrant and drug solvent and so, useful in creams for topi- problems to substrates. TLC monitoring and HPLC analy-
21—23)
cal use.
The synthesis of acyclovir esteres took place at sis indicated that only the monoester was synthesized. De-
room temperature using DMSO as the solvent, 4-N,N-di- spite this approach rendered slower reaction rates compared
methylamino pyridine (DMAP) in catalytic amounts and acid to DMSO, solvent DMAC10 offered a double function: as
anhydrides as the acylating agents, obtaining near quantita- solvent and as a drug permeation enhancer for topical appli-
tive yields by HPLC. Free fatty acids (with low reactivity) or cations as will be discussed.
acid chlorides (liberating HCl in the acylation whic decom-
Optimization of the Synthesis Conditions In the syn-
poses the prodrugs 3a—f) were not used as the acylating thesis of 3c (used as the model), we made slight further mod-
agents due to the low reactivity or to the dermotoxic HCl for- ifications in the reaction conditions in order to improve the
mation, respectively. The reaction time was finished in process. We reduced both, the substrate molar ratio acy-
10 min and no acylations on the amino group were observed clovir/anhydride from 1/3 to 1/2, and the amount of solvent
in any case as can be deduced from NMR spectra and ele- used (DMAC10). We increased the acyclovir concentration
mental analysis of the isolated compounds 3a—f. The de- from 250 to 875 mM. The reaction was complete at 24 h
scribed purification procedure was simple and straightfor- yielding almost 100% acyclovir monoester, with no signs of
ward by precipitation in water. The overall time to isolate any sort of diacylation, identified and quantified by TLC and
pure acyclovir ester prodrugs in a solid form was reduced HPLC.
from over 1.5—5 d as reported to one hour maximum im-
From downstream point of view, solvent and particularly
proving the described syntheses. HPLC-MS analysis showed catalyst, were removed pouring and agitating 30 reaction vol-
that only 0.02% of DMSO remains in the dry powder. The umes of a 1/1 acetonotrile/water mixture for 5 min into the
scope of the synthesis is general because the yields are sus- reaction medium, filtering and letting dry at room tempera-
tained regardless of the fatty acid chain size (Table 1). This ture. This procedure guarantees the removal of catalyst, leav-
methodology outperforms the best results described by Gao ing any further purification just as a means to adjust the
16,17)
and Mitra.
amount of solvent remaining in the final product. From an in-
Synthesis of Acyclovir Esters in Solvents Obtained dustrial standpoint, the use of a green solvent such as

September 2011
1091
DMAC10 which serves also as a permeation enhancer for
percutaneous applications, offers the advantage of avoiding
the complete removal of the solvent from the reaction mix-
ture, and use this mixture as a permeation-enhancer-included
product ready to use “as is,” in the following stages of trans-
dermic formulation. In an industrial setting, the recovery and
recycling of DMAC10 can be achieved much easier than the
recovery of DMSO from water, due to its water immiscibil-
ity.
Following this positive outcome, the synthesis of the fatty
acid acyclovir esters (3d—f) were carried out to explore the
scope. In these cases, the solvent amount used was 20 ml and
the temperature was raised to 40 °C to help maintain the re-
action medium fluid. Reaction was completed (24 h) with
yields ꢁ98% (isolated product) and only the three mo-
Fig. 1. Acyclovir Esters Release Assays with O/W Emulsion Using Poly-
sulfone Synthetic Membranes (Tuffryn )
®
Each ester was incorporated at 5% (w/w) into the O/W emulsion. The amount of
noesters were obtained. The purification steps followed were ester that crossed the membrane was measured at 24 h.
the same as in the synthesis of 3c stated above.
Synthesis without Solvent With the aim to develop a
greener process, we performed the synthesis of acyclovir es-
ters without solvent, using the anhydride as the reaction
medium and using an anhydride/acyclovir ratio of 1/1. This
substrate ratio was only achieved for long (C12 and C14)
acyclovir anhydrides, because of their higher specific volume
which, unlike shorter anhydrides, occupy a larger volume per
weight and thus, are able to provide a large enough medium
volume to carry out the reaction. Conversion of acyclovir
into the respective ester, which reached over 98% in all
cases, followed by TLC and HPLC, was achieved after
30 min of the addition of acyclovir into a melted anhydride
and catalyst mix (55 °C). The monoesters of acyclovir were
purified by the same methodology described above.
Scale-Up of the Synthesis Due to 3c was the most inter-
esting prodrug as we will show, the scale up to synthesize
Fig. 2. Acyclovir Esters Release Assays with Hydrogel Formulation Using
Polysulfone Synthetic Membranes (Tuffryn )
®
Each ester was incorporated at 5% (w/w) into the hydrogel and the amounts of acy-
3
00 g of 3c was carried out dissolving 210 g (933 mmol) of 1 clovir in ester form that crossed the membrane into the receptor phase were measured
at 24 h.
in 2.1 l of anhydrous DMSO with 11.3 g (93 mmol) of
DMAP. After an inert atmosphere was established, 645 ml
(
2.79 mol) of hexanoic anhydride was added to the reaction releasing the highest amount of acyclovir to the receptor
and set vigorous agitation. After 10 min, agitation was phase (268, 197 mg, respectively).
stopped and reaction medium was poured into a suitable bu- A hydrogel formulation developed by Rodríguez-Bayón
26)
rette. The reaction medium was let to fall drop wise into a 4 l and Trujillo-Casares was also tested as the prodrug vehi-
vessel with water in full vigorous agitation. The white pre- cle. The data obtained from the prodrug release assays using
cipitate supernatant was then filtered and let dry at room the hydrogel are shown in Fig. 2. ACVC6 was the only acy-
temperature. This precipitate purification step was repeated clovir ester able to significantly cross the membrane. In this
until consuming all reaction volume. The characterization of case, the hydrogel formulation is superior to the emulsion as
the reaction products was accomplished by NMR. The reac- it enables a more than two-fold of total acyclovir release
tion yield was ꢀ98% (isolated product).
Prodrug Release Assays The acyclovir esters were sep-
(612 mg) than W/O emulsion did.
The Green Biosolvent DMAC10 as Release Promoter
arately incorporated into two different topical formulations: As we mentioned earlier, DMAC10 is considered relatively
an oil/water (O/W) emulsion and a hydrogel. The release as- safe solvent, according to the Environmental Protection
27)
says were performed in a Microette Plus Hanson Research Agency, and thus, as an oily substance, and compatible
®
using polysulfone synthetic membranes (Tuffryn ). The with the intercellular lipidic matrix of the skin, it was tested
assay consists in measuring the amount of acyclovir ester that to assess its capabilities as a permeation enhancer. The O/W
goes through the membrane. The acyclovir ester is embedded already used was adapted to include ACVC6 (5% w/w) and
in a topical formulation placed in a donor chamber over the solvent DMAC10 (5% w/w). Our results, shown in Fig. 3, in-
membrane. A suitable solution fills the receptor chamber dicate that solvent DMAC10 does have activity as perme-
under the membrane, from which samples are withdrawn.
ation enhancer, although its enhancement factor is around 1.1
The O/W emulsion formulation was previously described (298 mg, Fig. 3 vs. 268 mg, Fig. 1). This amount of acyclovir
25)
by Rodríguez-Bayón and Trujillo. The percentage of each that went through the membrane is comparable to the magni-
14)
acyclovir ester was 5%. Each ester was assayed separately tudes obtained by Bando et al. using geranylaz-cyclohep-
and the release profile obtained is shown in Fig. 1. As this tane-2-one (GACH) as permeation enhancer in rat skin.
figure shows, ACVC6 and ACVC12 were the acyclovir esters

1
092
Vol. 59, No. 9
Experimental
Acyclovir (1) was acquired from Cinfa S.A. Acid anhydrides, N,N-di-
methyl formamide and dimethyl sulfoxide were purchased from Sigma-
Aldrich. 4-N,N-Dimethylamino pyridine purchased from VWR International
Eurolab S.L. Solvents from renewable sources, N,N-dimethylamide of de-
canoic acid (DMAC10) and the mixture of N,N-dimethylamides from oc-
tanoic, decanoic and dodecanoic acid (DMAA) were supplied from Cognis
Iberica S.L. Reaction progress was followed by TLC on Macherey Nagel
Alugram Sil G/UV254 sheets visualized under UV light, by with HPLC on a
Shimadzu CBM-20A using a Teknokroma C18 (30 cm, 4.6 mm, 5 mM) col-
umn. NMR spectra of samples on DMSO-d for all products synthesized in
6
DMSO were recorded in a Brucker Avance AC-250 (250 MHz) spectometer.
Elemental analyses were performed by the C.A.I. of Micro-analysis Elemen-
tal de la Universidad Complutense de Madrid on a Leco CHNS 932. After
verifying the identity of products synthesized in DMSO by NMR, HPLC
and Elemental analysis, the following identification for products synthesized
in renewable solvents and with no solvent, was only done by HPLC analysis.
Synthesis in DMSO of the Acyclovir Esters. Acyclovir Acetate (3a)
Fig. 3. Acyclovir Hexanoate Release Profile in O/W Emulsion with Sol-
vent DMAC10 as Promotion Enhancer, Using Polysulfone Synthetic Mem-
branes (Tuffryn )
®
2
-Amino-9-[(2-acetyloxy)ethyl-oxy-methyl]-1,9-dihydro-6H-purin-6-one:
Formulation includes DMAC10 (5% w/w) and acyclovir hexanoate (5% w/w) into
the O/W emulsion. The amount of acyclovir in ester form that crossed the membrane
into the receptor phase was measured at 24 h.
The synthesis was carried out in a small flask under argon atmosphere. 2-
Amino-1,9-dihydro-9-[(2-hydroxyyethoxy)methyl]-6H-purin-6-one, (1, acy-
clovir), (337 mg, 1.5 mmol) was dissolved in 6 ml of anhydrous DMSO and
4-N,N-dimethylamino-pyridine (DMAP) (18 mg, 0.15 mmol) was added.
Argon atmosphere was set and the solution was stirred until reactants were
dissolved. The acetic anhydride (0.42 ml, 4.5 mmol) was added keeping the
inert atmosphere. After 10 min, stirring is stopped and the reaction volume
is transferred to a 10 ml syringe. The reaction medium was added dropwise
Conclusion
The synthesis of acyclovir esters—useful as prodrugs—
have been performed by different methodologies more envi-
ronmental friendly than those described in the literature. The
to a vigorously agitated beaker with 600 ml of water (100 reaction volumes).
1
substitution of dermotoxic and reprotoxic DMF by DMSO, a The supernatant precipitate was then filtered and dried to r.t. H-NMR
(
250 MHz, DMSO-d ) d: 10.6—the numbers of carbons and nitrogen in H-
common permeation enhancer, as the reaction solvent let us
to complete the synthesis in 10 min. The isolation of the mo-
noesters as the unique product, was performed using water as
a precipitating agent. The scale up of the synthesis of acy-
6
NMR are in accordance with IUPAC acyclovir nomenclature—(1H, s broad,
N1-H); 7.85 (1H s broad, C8H); 6.54 (2H, s broad, NH ); 5.36 (2H, s,
2
3
3
C10H ); 4.07 (2H, t, Jꢂ7 Hz, C13H ); 3.66 (2H, t, Jꢂ7 Hz, C12H ); 1.96
2
2
2
3
(
3H, t, Jꢂ7 Hz, OOC-CH ). Elemental analysis Calcd for C H N O : C,
3 10 13 5 4
clovir hexanoate (3c) up to 300 g proves the feasabilty to im- 44.93; H, 4.90; N, 26.22. Found: C, 44.61, H: 5.01, N: 26.45.
Acyclovir Butyrate (3b) 2-Amino-9-[(2-butanoyloxy)ethyl-oxy-methyl]-
,9-dihydro-6H-purin-6-one: The synthesis was carried out under the same
conditions as in 3a. The butyric anhydride (0.716 ml, 4.5 mmol) was added
plement it in industrial settings. The syntheses of medium
and long chain esters of acyclovir (3c—f) carried out using
DMAC10 solvents from renewable sources, rendered almost
1
1
keeping the inert atmosphere. H-NMR (250 MHz, DMSO-d ) d: 10.7 (1H, s
6
total conversion yields, yet at slower reaction rates but the se- broad, N1-H); 7.94 (1H, s, C8H); 6.58 (2H, s broad, NH ); 5.36 (2H, s,
2
3
3
lectivity towards a single monoacylated product was retained. C10H
); 4.09 (2H, t, Jꢂ7 Hz, C13H
2H, t, Jꢂ7 Hz, OOC-CH ); 1.47 (2H, c, Jꢂ7 Hz, OOC-CH CH ); 0.83
3H, t, Jꢂ7 Hz, OOC-(CH ) -CH ). Elemental analysis Calcd for
); 3.67 (2H, t, Jꢂ7 Hz, C12H
); 2.20
2
2
2
3
3
(
(
All the acyclovir esters syntheses were also performed with-
out any solvent, using the melted acid anhydrides as solvent
medium. For acyclovir dodecanoate and tetradecanoate, a re-
2
2
2
3
2
2
3
C H N O : C, 48.79; H, 5.80; N, 23.73. Found: C, 48.4, H, 5.89; N, 23.56.
1
2
17
5
4
Acyclovir Hexanoate (3c) 2-Amino-9-[(2-hexanoyloxy)ethyl-oxy-methyl]-
duction in the substrates ratio up to 1/1 was succesfully 1,9-dihydro-6H-purin-6-one: The synthesis was carried out under the same
achieved.
According to our results in the prodrug release assays,
acyclovir hexanoate and dodecanoate achieved the highest
transfer amount of total acyclovir into the receptor phase
conditions as 3a. The hexanoic anhydride (1.03 ml, 4.5 mmol) was added
1
keeping the inert atmosphere. H-NMR (250 MHz, DMSO-d ) d: 10.7 (1H, s
6
broad, N1-H); 7.84 (1H, s, C8H); 6.54 (2H, s broad, NH ); 5.35 (2H, s,
2
3
3
C10H ); 4.09 (2H, t, Jꢂ7 Hz, C13H ); 3.66 (2H, t, Jꢂ7 Hz, C12H ); 2.22
2
2
2
3
3
(
2H, t, Jꢂ7 Hz, OOC-CH ); 1.47 (2H, q, Jꢂ7 Hz, OOC-CH CH ); 1.22
2
2
2
3
from our oil/water emulsion formulation. However, when an (4H, mult, 2CH ); 0.84 (3H, t, Jꢂ7 Hz, OOC-(CH ) CH ). Elemental analy-
2
2
4
3
sis Calcd for C H N O : C, 51.99; H 6.54; N, 21.67. Found: C, 51.76; H,
hydrogel formulation is used as a vehicle instead of the O/W
emulsion, the transfer amount of total acyclovir reaches more
than double in the case of ACVC6.
14 21
5
4
6
.68; N, 21.44.
Acyclovir Decanoate (3d) 2-Amino-9-[(2-decanoyloxy)ethyl-oxy-methyl]-
,9-dihydro-6H-purin-6-one: The reaction was carried out under the same
1
As solvent DMAC10 may be used as a permeation en-
conditions as 3a. The decanoic anhydride (1.65 ml, 4.5 mmol) was added
1
hancer in transdermic applications, no need for complete keeping the inert atmosphere. H-NMR (250 MHz, DMSO-d ) d: 10.7 (1H, s
6
broad, N1-H); 7.82 (1H, s, C8H); 6.60 (2H, s broad, NH ); 5.35 (2H, s,
C10H ); 4.09 (2H, t, Jꢂ7 Hz, C13H ); 3.66 (2H, t, Jꢂ7 Hz, C12H ); 2.22
solvent removal might be required from the reaction. This
allowed us to obtain acyclovir prodrugs with a promotion en-
hancer included, in a mixture ready to be used in the follow-
2
3
3
2
2
2
(
2H, mult, OOC-CH ); 1.35 (2H, mult, OOC-CH CH ); 1.35—1.24 (12H,
2
2
2
mult, 6CH ); 0.84 (3H, t, OOC(CH ) CH ). Elemental analysis Calcd for
2
2
8
3
ing pharmaceutic preformulation stages. The permeation en- C H N O : C, 59.96; H, 7.70; N, 18.47. Found: C, 59.69; H, 7.85; N,
1
8
29
5
4
hancement observed with the use of solvent DMAC10 (5% 18.29.
Acyclovir Dodecanoate (3e) 2-Amino-9-[(2-dodecanoyloxy)ethyl-oxy-
methyl]-1,9-dihydro-6H-purin-6-one: The synthesis was carried out under
the same conditions as 3a. The dodecanoic anhydride (1.72 g, 4.5 mmol) was
w/w) in the O/W emulsion formulation was around 10%
compared to a blank emulsion. All the improvements stated
in this work, which include the use of green solvents and re-
1
added keeping the inert atmosphere. H-NMR (250 MHz, DMSO-d ) d:
6
ductions in the use of raw materials, solvents and energy, 10.65 (1H, s broad, N1-H); 7.82 (1H, s, C8H); 6.53 (2H, s broad, NH ); 5.35
2
3
3
represent sensible advances for the synthesis of acyclovir (2H, s, C10H
); 4.08 (2H, t, Jꢂ7 Hz, C13H
C12H ); 2.22 (2H, mult, OOC-CH ); 1.35 (2H, comp, OOC-CH CH );
); 3.66 (2H, t, Jꢂ7 Hz,
2
2
prodrugs.
2
2
2
2
1
.45—1.24 (16H, mult, 8CH ); 0.83 (3H, t, OOC(CH ) CH ). Elemental
2 2 10 3
analysis Calcd for C H N O : C, 58.93; H, 8.16; N, 17.19. Found: C,
2
0
33
5
4
5
8.78; H, 8.28; N, 17.01.

September 2011
1093
Acyclovir Tetradecanate (3f) 2-Amino-9-[(2-tetradecanoyloxy)ethyl-
oxy-methyl]-1,9-dihydro-6H-purin-6-one: The synthesis was carried out
Prodrug Release Assays The assays were performed in a Microettee
Plus Hanson Research, (U.S.A.) at 32ꢃ1.5 °C using polysulfone synthetic
membranes (Tuffryn ). Donor phases, either O/W23 emulsion or Hydro-
gel24 contained acyclovir ester at 5% w/w. Donor chamber was filled with
300 mg of donor phase. Receptor phase was phosphate buffer 0.15 M pH 7.4.
Receptor phase samples were taken at 0.25, 0.5, 0.75, 1, 2, 4, 6, 8, 10, 12
®
under the same conditions as 3a. The dodecanoic anhydride (1.97 g,
1
4
.5 mmol) was added keeping the inert atmosphere. H-NMR (250 MHz,
DMSO-d ) d: 10.7 (1H, s broad, N1-H); 7.82 (1H, s, C8H); 6.56 (2H, s
6
3
broad, NH ); 5.35 (2H, s, C10H ); 4.09 (2H, t, Jꢂ7 Hz, C13H ); 3.66 (2H,
t, Jꢂ7 Hz, C12H ); 2.22 (2H, mult, OOC-CH ); 2.17 (2H, mult, OOC- and 24 h. For the prodrug release assay using solvent DMAC10, it was added
2
2
2
3
2
2
CH CH ; 1.35 (20H, mult, 10CH ); 0.84 (3H, t, OOC(CH ) CH ). Elemen- to the O/W emulsion at 5% at the time of preparation.
2
2
2
2
12
3
tal analysis Calcd for C H N O : C, 60.65; H, 8.56; N, 16.09. Found: C,
22
37
5
4
6
0.38; H, 8.67; N, 15.89.
Synthesis in Solvents from Biomass. Acyclovir Hexanoate (3c) Acy-
clovir, 1.97 g (8.75 mmol); hexanoic anhydride, 3.71 g (17.5 mmol); DMAP,
.108 g (0.88 mmol); DMAC10, DMAA or DMALA, 10 ml. Reaction tem-
References
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(2003).
0
perature was set to 40 °C. Reactants were agitated during 24 h. In the purifi-
cation process 30 volumes (300 ml) of a 50/50 acetonitrile/water mixture
was added to the reaction mixture mainly to remove the DMAP and kept in
agitation until a homogeneous suspension was observed. The suspension
was filtered and allowed to dry to room temperature. HPLC method: iso-
cratic water/acetonitrile 60/40, 0.8 ml/min on a C18 30 cm 4.6 mm 5 mm col-
umn. Retention time: 6.2 min.
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Acyclovir Decanoate (3d) Acyclovir, 1.97 g (8.75 mmol); decanoic an-
hydride, 5.71 g (17.5 mmol); DMAP, 0.108 g (0.88 mmol); DMAC10,
DMAA or DMALA, 20 ml and the reaction temperature was set to 40 °C.
Reactants were agitated during 24 h. In the purification process 30 volumes
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(300 ml) of a 50/50 acetonitrile/water mixture was added to the reaction
mixture mainly to remove the DMAP and kept in agitation until a homoge-
neous suspension was observed. The suspension was filtered and allowed to
10) Spector T., Jones T. E., Beacham L. M. 3rd, Biochem. Pharmacol., 32,
2505—2509 (1983).
dry to ambient temperature. HPLC method: isocratic water/acetonitrile 11) Krenitsky T. A., Hall W. W., de Miranda P., Beauchamp L. M., Schaef-
2
4
5/75, 1.0 ml/min on a C18 30 cm 4.6 mm 5 mm column. Retention time:
.6 min.
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3213 (1984).
Acyclovir Dodecanoate (3e) Acyclovir, 1.97 g (8.75 mmol); dodecanoic
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187—196 (1990).
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anhydride, 6.50 g (17.5 mmol); DMAP, 0.108 g (0.88 mmol); DMAC10,
DMAA or DMALA 20 ml. Reaction temperature was set to 40 °C. Reactants
were agitated during 24 h. In the purification process 30 volumes (300 ml) of
a 50/50 acetonitrile/water mixture was added to the reaction mixture mainly
to remove the DMAP and kept in agitation until a homogeneous suspension
was observed. The suspension was filtered and allowed to dry to ambient
temperature. HPLC method: isocratic water/acetonitrile 25/75, 1.0 ml/min
on a C18 30 cm 4.6 mm 5 mm column. Retention time: 7.1 min.
Acyclovir Tetradecanoate (3f) Acyclovir, 1.97 g (8.75 mmol); decanoic
anhydride, 7.67 g (17.5 mmol); DMAP, 0.108 g (0.88 mmol); DMAC10,
DMAA or DMALA 20 ml. Reaction temperature was set to 40 °C. Reactants
were agitated during 24 h. In the purification process 30 volumes (300 ml) of
a 50/50 acetonitrile/water mixture was added to the reaction mixture mainly
to remove the DMAP and kept in agitation until a homogeneous suspension
was observed. The suspension was filtered and allowed to dry to ambient
temperature. HPLC method: isocratic water/acetonitrile 10/90, 1.3 ml/min
on a C18 30 cm 4.6 mm 5 mm column. Retention time: 5.7 min.
Synthesis without Solvents. Acyclovir Dodecanoate (3e) Acyclovir,
.97 g (8.75 mmol); dodecanoic anhydride, 3.25 g (17.5 mmol); DMAP,
.108 g (0.88 mmol); reaction temperature was 30 °C. After 30 min the reac-
22) Steinberg A., Ann. N. Y. Acad. Sci., 141, 532—550 (1967).
23) Blumenthal L. S., Fuchs M., Ann. N. Y. Acad. Sci., 141, 572—585
(1967).
1
0
tion was finished resulting in a 98% yield analyzed by HPLC. The purifica-
tion process comprised the same steps as those used when DMSO was used
as solvent. HPLC method: isocratic water/acetonitrile 25/75, 1.0 ml/min on a
C18 30 cm 4.6 mm 5 mm column. Retention time: 7.1 min.
Acyclovir Tetradecanoate (3f) Acyclovir, 1.97 g (8.75 mmol); decanoic
anhydride, 3.83 g (8.75 mmol); DMAP, 0.108 g (0.88 mmol); reaction tem-
perature was 30 °C. After 30 min of agitating reactants, the reaction was fin-
ished resulting in a 98% yield analyzed by HPLC. The purification stage
comprised the same steps as those used when DMSO was used as solvent.
HPLC method: isocratic water/acetonitrile 10/90, 1.3 ml/min on a C18
24) De Regil R., Rodríguez-Bayón A., Sinisterra J. V., Process for the
Manufacture of Acyclovir Prodrugs, Eur. Patent EP: 08 019 325.3, Oc-
tober, 2008.
25) Rodríguez-Bayón A. M., Trujillo-Casares S. H., Personal communica-
tion.
26) Rodríguez-Bayón A. M., Trujillo-Casares S. H., Proceedings of the
33rd Annual Meeting of Controlled Release Society, Versailles, 2009.
27) EPA, U.S. Environmental and Protection Agency, “Octanoamide, N,N-
Dimethyl and Decanamide, N,N-Dimethyl, Exemptions from the Re-
quirement of a Tolerance,” 40 CFR Part 180, OPP-2005-0031, FRL-
7698-3, DOCID, frl26fe05-14, 2005.
30 cm 4.6 mm 5 mm column. Retention time: 5.7 min.