Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1999-02-04
2001-06-26
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S511000
Reexamination Certificate
active
06252094
ABSTRACT:
TECHNICAL FIELD
The invention relates to taxol prodrugs. More particularly, the invention relates to a method employing derivatization with onium salts of 2-halogenated aza-arenes for chemically switching between low solubility active forms and high solubility inactive forms of taxol and taxol memetics.
BACKGROUND
Taxol, an antineoplastic agent originally isolated from Taxus brevifolia, is approved for usage in the treatment of ovarian cancer and is expected to see usage in breast, lung, and skin cancers as well. However, since Taxol possesses an extremely low water solubility, i.e., less than 1.5×10
−6
molar, it has been necessary to formulate Taxol in a mixture of Cremaphor™, a polyoxyethylated castor oil, and ethanol in order to achieve a therapeutic concentration. This formulation can induce a variety of significant side effects including hypersensitivity reactions.
While premedication and slow administration of the drug can circumvent these problems in the clinic, the entire protocol is quite cumbersome and requires extensive close monitoring of patients. Although taxol's dramatic efficacy has driven clinical usage forward despite these problems, a water soluble form of taxol could completely obviate the need for this troublesome protocol.
One approach to bypassing these formulation difficulties, previously attempted by several groups including our own, is the introduction of solubilizing functionality that normal metabolic pathways could remove in vivo. Compounds of this type, termed prodrugs, consist, in the case of taxol, primarily of ester derivatives at the 2′ and 7 positions. Currently none of these protaxols have given success in the clinic. In each case, the prodrug is rapidly cleared from circulation by the kidneys.
Taxol is only one of a class of taxo-diterpenoids having bioactivity. Another preferred taxo-diterpenoid having clinically significant activity is Taxotere™. Unfortunately, all known bioactive taxo-diterpenoids have a low aqueous solubility.
What is needed is a method for chemically switching taxol and other taxo-diterpenoids between a high solubility and low solubility form in a manner which regulates its rate of clearance from circulation so that the prodrug is retained for a clinically significant period after administration.
Taxol itself is known to serve as a chemical switch with respect to tubulin. Binding of taxol to tubulin prevents its polymerization and the formation of microtubules. While unpolymerized tubulin is soluble in aqueous media, polymerization of tubulin leads to the formation of insoluble microtubules. Accordingly, the addition or removal of taxol drives the depolymerization or polymerization of tubulin and, in this manner, serves as a chemical switch for regulating the solubility of tubulin.
SUMMARY
The invention is a cyclic method employing chemical switching for solubilizing and desolubilizing taxo-diterpenoids with respect to aqueous solvents. The invention employs 2-halogenated onium salts of aza-arenes to derivatize taxo-diterpenoids so as to alter their solubility in aqueous solvents. The onium salt of aza-arene includes a delocalized charge which imparts polarity and aqueous solubility to taxo-diterpenoid derivatives. Solubilization includes a one step derivatization with the onium salt of 2-halogenated aza-arenes. Contacting onium salts of taxo-diterpenoid-C
n
,2-O-aza-arenes with the serum protein, causes the displacement of 2-O-aza-arene and the formation of a soluble protein:taxo-diterpenoid intermediate. This protein:taxo-diterpenoid intermediate then dissociates over time to provide a bioactive taxo-diterpenoid. Preferred taxo-diterpenoids include taxol, C-2 substituted analogs of taxol, and Taxotere™. Taxo-diterpenoid-C
n
,2-O-aza-arene may be produced in a one step synthesis by reacting onium salts of 2-halogenated aza-arenes with reactive hydroxyls on the taxo-diterpenoid. Reactive hydroxyls on taxol and Taxotere™ are located at C
2
′ and C
7
. A preferred onium salt of 2-halogenated aza-arene is 2-fluoro-1-methylpyridinium tosylate. Other employable onium salts of 2-halogenated aza-arenes are disclosed by T. Mukaiyama,
Angewandte Chemie
1979,18(18), 707-808, incorporated herein by reference.
More particularly, a first embodiment of the invention is directed a cyclic method employing chemical switching for solubilizing and desolubilizing taxo-diterpenoids with respect to aqueous solvents. Underivatized forms of the taxo-diterpenoid have low aqueous solubility and include a reactive C
n
-hydroxyl, i.e., a reactive hydroxyl at the C
n
position. Preferred reactive C
n
hydroxyls for taxol and Taxotere™ are located at positions C
2′
and C
7
. The method includes two steps. In the first step, the underivatized form of the taxo-diterpenoid is converted from low solubility to high solubility by derivatizing the reactive C
n
-hydroxyl with the onium salt of the 2-halogenated aza-arene to form the onium salt of a taxo-diterpenoid-C
n
,2-O-aza-arene derivative having high solubility. In the second step, the onium salt of the taxo-diterpenoid-C
n
,2-O-aza-arene derivative is converted from high solubility to low solubility by contacting the taxo-diterpenoid-C
n
,2-O-aza-arene derivative with serum protein for displacing the 2-O-aza-arene and forming a protein:taxo-diterpenoid intermediate. The protein:taxo-diterpenoid intermediate has a high solubility but then dissociates over time to produce the underviatized form of the taxo-diterpenoid employed in the first step, i.e., the taxo-diterpenoid is released from the protein:taxo-diterpenoid intermediate. The precise nature of the bonding between serum protein and the taxo-diterpenoid within the protein:taxo-diterpenoid intermediate has not been characterized, but can be stable over a period ranging from minutes to hours. A first alternative embodiment of the invention are directed to the derivatization of taxo-diterpenoids with onium salts of 2-halogenated aza-arenes. A second alternative embodiment is directed to conversion of onium salts of taxo-diterpenoid-C
n
,2-O-aza-arene derivatives to protein:taxo-diterpenoid intermediates using serum protein. In this second alternative embodiment, the taxo-diterpenoid-C
n
,2-O-aza-arene derivative is contacted with serum protein for displacing the 2-O-aza-arene and forming the protein:taxo-diterpenoid intermediate.
In a preferred embodiment, the taxo-diterpenoid-2-O-aza-arenes are represented by the following formula:
wherein R
x
is Ph or tBuO; R
10
is OAc or OH; RY is a C-2 substituent defined below; and R
2′
and R
7
are each selected from the group consisting of OH and an onium salt of a 2-O-aza-arene, with the proviso that at least one of R
2′
and R
7
is the onium salt of the 2-O-aza-arene. The onium salt of the 2-O-aza-arene can be represented by either of the following formulas for onium salt I or onium salt II:
wherein Z
1
and Z
2
are each either C or N; Z
3
is S or O; R
1
is selected from the group consisting of C
1
-C
6
alkyl, allyl, arenxyl, propargyl, and fused aryl; R
2
and R
6
are each selected from the group consisting of H, C
1
-C
6
alkyl, allyl, arenxyl, propargyl, and fused aryl; if Z
1
is C, then R
3
is selected from the group consisting of H, C
1
-C
6
alkyl, allyl, arenxyl, propargyl, C
1
-C
6
O-alkyl, OH, halogen, and fused aryl; if Z
1
is N, then R
3
is absent; R
4
and R
8
are each selected from the group consisting of H, C
1
-C
6
alkyl, allyl, arenxyl, propargyl, C
1
-C
6
O-alkyl, OH, halogen, and fused aryl; and if Z
2
is C, then R
5
is selected from the group consisting of H, C
1
-C
6
alkyl, allyl, arenxyl, propargyl, C
1
-C
6
O-alkyl, OH, halogen, and fused aryl; if Z
2
is N, then R
5
is absent; and S- is a counter ion.
R
y
is a C-2 substituent. Preferred C-2 substituents are represented by the following structures:
REFERENCES:
patent: 4960790 (1990-10-01), Stella et al.
patent: 5274137 (1993-12-01), Nicolaou et al.
patent: 5422364 (1995-06-01), Nicolaou et al.
patent: 5440057 (1995-08-01), Nicolaou et al.
patent: 5461169
Guy Rodney K.
Nicolaou K. C.
Pitsinos Emmanuel
Wrasidlo Wolfgang
Lewis Donald G.
The Scripps Research Institute
Trinh Ba K.
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