Compounds useful for the synthesis of dolastatin analogs

Details Compounds useful for the synthesis of dolastatin analogs Compounds useful for the synthesis of dolastatin analogs

1998-12-15

2001-06-19

Carlson, Karen Cochrane (Department: 1653)

Chemistry: natural resins or derivatives; peptides or proteins;

Peptides of 3 to 100 amino acid residues

4 to 5 amino acid residues in defined sequence

C530S333000, C514S017400, C514S018700

Reexamination Certificate

active

06248865

ABSTRACT:

The present invention relates to novel tetrapeptides, their preparation and use.
BACKGROUND OF THE INVENTION
Dolastatin 15 is a substance which is described in U.S. Pat. No. 4,879,278 and has the following formula.
Dolastatin 15 is attracting great interest because of its great efficacy against various tumors. Its isolation from the lumpfish which is difficult to obtain is lengthy and time-consuming, and the process provides the active substance in moderate yield and poorly reproducible quality. In order to make the active substance available in gram quantities for animal experiments, Pettit et al. (J. Am. Chem. Soc. 113 [1991] 6692-6693) have developed a synthetic method. The central intermediate in this is the etrapeptide of the formula Ia
WO 93/23424 describes antineoplastic active substances whose effect exceeds that of dolastatin 15. Many active substances in WO 93/23424 can be prepared from tetrapeptides of the formula I
where R
1
-R
4
are C
1
-C
6
-alkyl groups.
In order to make the peptides of WO 93/23424 and dolastatin 15 available in sufficient quantity for clinical tests it was necessary to find a process for preparing the tetrapeptides I which can be implemented industrially.
The solid-phase synthesis described in WO 93/23424 is unsuitable for preparing large amounts of product. It provides impure product which requires laborious chromatographic purification.
Pettit et al. (J. Am. Chem. Soc. 113 [1991] 6692-6693) describe an elegant laboratory synthesis for Ia. This entails the tripeptide Val-13 MeVal-13 Pro-13 OMe being reacted with
(Short name: Me
2
Val-13 OPfp) to give the tetrapeptide Ia.
The synthesis of Me
2
Val-13 OPfp takes place according to Pettit et al. U.S. Pat. No. 4,978,744 as follows:
Initially valine is dimethylated on the nitrogen. The resulting dimethylvaline must be reacted with a condensing agent and pentafluorophenol (HO-13 Pfp).
This process is very troublesome owing to the large number of reaction steps required. An additional factor is that pentafluorophenol is a very costly reagent which is unavailable in sufficient quantity for industrial syntheses. In addition, its use leads to fluorine-containing wastes which can be disposed of only with difficulty and possibly with formation of dioxins.
The use of condensing agents in the synthesis also leads to problems. Thus, it is known that handling dicyclohexylcarbodiimide may lead to sensitization and extremely severe allergic reactions. Workup of the batches produces the corresponding urea which can be removed from the product only laboriously and often only incompletely. Carbodiimides which, like N-ethyl-N′-dimethylaminopropylcarbodiimide, react to form water-soluble ureas are extremely costly and are not available in industrial quantities.
Replacement of pentafluorophenol/carbodiimide by pentafluorophenyl trifluoroacetate or its carbonates, eg. pentafluorophenyl 1,2,2,2-tetrachloroethyl carbonate (J. Org. Chem. 52 [1987] 2364) also provides no advantages.
Racemization occurs in active ester formation and peptide coupling and represents a serious problem in this method (see J. Jones: The Chemical Synthesis of Peptides, Oxford 1991, page 57).
Another published method for linking dimethylvaline to other amino acids (T. Shioiri et al.: Tetrahedron 49 [1993] 1913-1924), which uses diethylphosphoryl cyanide (DEPC) as coupling reagent, likewise involves serious disadvantages: DEPC is very costly, not obtainable in large quantity, corrosive and very toxic. The cyanide-containing mother liquors and washings must be disposed of as special waste.
SUMMARY OF THE INVENTION
The present invention relates to a process for preparing the tetrapeptides I, which makes use of intermediates which are available in large quantities, and which can be carried out without racemization and without environmental hazard.
The invention relates to a process for preparing compounds of the formula
where R
1
, R
2
, R
3
and R
4
are identical or different and are each C
1-6
-alkyl, which comprises condensing a compound of the formula II
where R
2
, R
3
and R
4
have the abovementioned meaning, with an amino acid of the formula III
R
1
—CH(NHZ)—COOH  III,
where R
1
has the abovementioned meaning, and Z is a benzyloxycarbonyl protective group which may be substituted on the phenyl ring, and dimethylating the resulting compound on the NH
2
group.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the formula I, R
1
, R
2
and R
3
, which are identical or different, are preferably ethyl, n-propyl, isopropyl, t-butyl, sec-butyl, 2-methylbutyl or 3-methylbutyl. R
4
is preferably methyl or ethyl.
The amino acids in the tetrapeptide preferably have the L configuration.
The coupling reaction of II with III can be carried out, for example, by the mixed anhydride method (see Houben-Weyl, Volume XV/2, 1974; J. Am. Chem. Soc. 74 [1952] 676; Coll. Czechoslov. Chem. Comm. 27 [1962] 1273). The carbonyl chlorides (preferably pivaloyl chloride, 2-ethylbutyryl chloride, isovaleryl chloride) or chloroformic esters (the methyl, ethyl, isopropyl, isobutyl, phenyl, chloroethyl and trichloromethyl esters are preferably employed) used as coupling reagents can be obtained in industrial quantities and are also very suitable for syntheses on the industrial scale. It is particularly advantageous that the couplings according to the invention take place without racemization.
Suitable solvents are tetrahydrofuran, dioxane, acetonitrile, dimethyl sulfoxide, ethyl acetate, dimethylformamide, methylene chloride, toluene, N-methylpyrrolidone and mixtures thereof. Methylene chloride, toluene and mixtures thereof are preferred. Particularly suitable bases for the reaction are: triethylamine, tributylamine, N-ethylpiperidine, diisopropylethylamine and N-methylmorpholine; triethylamine and N-methylmorpholine are preferred.
The reaction is carried out at from −40° C. to +30° C., preferably from −15° C. to +15° C.
The invention also relates to the compounds of the formula I where, however, R
1
, R
2
and R
3
are not all isopropyl radicals when R
4
is a methyl group, and to the salts thereof with various acids.
Examples of acids which may be mentioned are: hydrochloric acid, citric acid, tartaric acid, lactic acid, phosphoric acid, methanesulfonic acid, acetic acid, formic acid, maleic acid, fumaric acid, malonic acid, succinic acid, malic acid, sulfuric acid, benzoic acid and oxalic acid.
The compounds of the formula I are very suitable for preparing dolastatin 15 and numerous compounds described in WO 93/23424 (cf. Examples 214-246 and others) and are distinguished by high antineoplastic efficacy.
The compounds of the formula I are likewise effective for solid tumors (tumors of the lungs, of the breast, of the intestine, of the bladder, of the rectum, of the uterus, of the prostate), for leukemia, lymphomas and other neoplastic disorders.
The conventional three-letter code is used to abbreviate the amino acids. Me
2
Val means N,N-dimethyl-L-valine, MeVal means N-methylvaline, Me means methyl, tert-Leu means tertiary Leucine (HOOC—CH(NH
2
)—C(CH
3
)
3
), Me
2
tert-Leu means N, N-dimethyltertiary-leucine and Me tert-Bu-Ala means N-methyl-tertiarybutylalanine (HOOC—CH(NHCH
3
)—CH
2
—C(CH
3
)
3
), Hyp means 4-hydroxyproline, Bu means n-butyl, tBu means tertiary butyl, Hx means n-hexyl and Et means ethyl.


REFERENCES:
patent: 5864012 (1999-01-01), Amberg et al.
Pettit, et al., “Antineoplastic Agents 220. Synthesis of Natural (−)-Dolastatin 15” J. Am. Chem. Soc. 1991, 113, 6692-93.

Affiliated with

Also associated with

Rating

Compounds useful for the synthesis of dolastatin analogs does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Compounds useful for the synthesis of dolastatin analogs, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compounds useful for the synthesis of dolastatin analogs will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2478037