Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D241/00—Heterocyclic compounds containing 1,4-diazine or hydrogenated 1,4-diazine rings
  • C07D241/02—Heterocyclic compounds containing 1,4-diazine or hydrogenated 1,4-diazine rings not condensed with other rings
  • C07D241/10—Heterocyclic compounds containing 1,4-diazine or hydrogenated 1,4-diazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members
  • C07D241/14—Heterocyclic compounds containing 1,4-diazine or hydrogenated 1,4-diazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
  • C07D241/24—Carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals

Definitions

• the present invention is directed to a new process for the selective preparation of piperazine derivatives.
• the piperazine nucleus is a constituent of many pharmaceutically useful compounds. Most of these compounds contain different substituents on one or both of the two nitrogens. A problem in the synthesis of these compounds relates to the differentiation of the two nitrogens in the synthesis sequence, such that selective derivatives of each can be made.
• the present invention is directed to a new process for the selective preparation of piperazine derivatives that are monosubstituted in the 2-position or are disubstituted at carbons 2 and 5, and which additionally, have a single substituent at one of the nitrogens or have two different nitrogen substituents.
• One aspect of the invention relates to the selective formation of N-protected esters or amides of PZC, of the general formula I
• R is a straight, branched or cyclic C1-C20 alkyl group, or an arylalkyl wherein aryl is
• phenyl or substituted phenyl and alkyl is _-C(. alkyl;
• R is defined as for R , or is benzyl, hydroxyalkyl, or an aminoalkyl group wherein alkyl is
• Y is OH, a group OR , wherein R 1 is as defined above, or NR 3 R 4 ,wherein R 3 and R 4 independently are hydrogen, C1-C20 alkyl, or aralkyl, wherein aryl is phenyl or substituted
• phenyl and alkyl is C2-C6 alkyl.
• R and R are each and independently C1-C20 alkyl, and Y is OR wherein R is
• the process for the selective formation of the compounds I comprises the following steps:
• R 2 and Y are as defined above and which is readily available either commercially or by methods known to one skilled in the art (see e.g. Barlin, G.B. (ed.) The Pyrazines, 1982, Wiley-Intersci., N.Y.) is hydrogenated in the presence of a catalyst and at least one equivalent of a C1-C20 alkoxycarbonyl-donating reagent, which is compatible with hydrogenation conditions, e.g. di-tert-butyldicarbonate, in an inert solvent compatible with hydrogenation conditions, and at temperatures and pressures commonly employed in such processes , giving the hitherto unknown N-l protected tetrahydropyrazinederivatives of the formula HI
• R 1 , R 2 and Y are as defined above, in good yields
• the compound of the formula HI is isolated by conventional laboratory techniques known to one skilled in the art, purified by silica gel chromatography or other well-known techniques known to a person skilled in the art, e.g. recrystallization, and further converted or, after removal of the solvents and the excessive alkoxycarbonyl-donating reagent, e.g. by reacting with 2-aminoethanol and then filtering through a pad of silica gel, directly used as the reactant in step iii; and
• the catalyst for the hydrogenation in step i) can be selected from a wide variety of transition metals, preferably from the platinum metals.
• the catalyst can be used as such, or can be supported on carbon, silica, aluminia or other inert materials known to the man skilled in the art, or can be a transition metal which is solubilized by means of organic ligands, e.g. phosphine ligands such as triphenylphosphine.
• organic ligands e.g. phosphine ligands such as triphenylphosphine.
• the alkoxycarbonyl-donating reagent in step i) is preferably in the form of an anhydride of a monoester of carbonic acid, for example di-tert-butyl- dicarbonate or dimethyl dicarbonate.
• the inert solvent in step i) can be chosen among a great variety of inert solvents known to the man skilled in the art.
• inert solvents that can be used are ethyl acetate, tetrahydrofuran, dioxane, toluene, dimethylformamide, ethylmethylketone and diisopropylether.
• Reaction temperatures may vary from room temperature to just below the boiling point of the solvent, and the pressure may vary from atmospheric pressure to 200 bar, both parameters depending on the reactivities of the catalyst and the substrate.
• Particularly preferred conditions *or obtaining the compounds of the formula HI by hydrogenation of a pyrazine involve the use of a palladium catalyst, e.g. 5% Pd on charcoal, in amounts ranging from 0.5-30 mol in an inert solvent, preferably ethyl acetate, at room temperature and at a hydrogen pressure of 1-5 bar, in the presence of 1.1-1.5 equivalents of di-tert-butyl dicarbonate.
• a palladium catalyst e.g. 5% Pd on charcoal
• Preferred conditions for isolating a compound of the formula ELI in step ii) involve removal of the catalyst by filtration through an inert adsorbent , e.g. Celite or silica gel, concentrating the mixture in vacuo and initiating crystallization of a compound of the formula DI.
• the product may be purified by recrystallization.
• step iii) for the conversion of a compound of the formula DI into a compound of the formula I can be performed by a variety of possibilities regarding reagents and conditions.
• One preferred reaction is hydrogenation in the presence of a transition metal catalyst chosen among the platinum metals known to catalyze addition of hydrogen over a double bond, in a suitable solvent, for example glacial acetic acid, ethyl acetate, tetrahydrofuran, dioxan, 2-propanol, toluene, and at a pressure ranging from atmospheric to 200 bar, and at a temperature ranging from room temperature to just below the boiling point of the solvent
• Another equally preferred reaction is reduction using a hydride reagent that is known to add hydrogen to double bonds.
• One particularly preferred reagent in the latter category is sodium cyanoborohydride in a weakly acidic solvent, for example acetic acid, or, when the group R 1 is not affected by strong acids, in diethyl ether in the presence of hydrochloric acid.
• Still another equally preferred reagent is a metal which transfers an electron to the double bond creating a radical anion which then reacts further to give overall addition of hydrogen.
• Preferred conditions for such reactions are the use of magnesium in methanol or lithium in 2-propanol. Conditions can be chosen so that a cis- or trans-isomer is formed predominantly.
• Preferred conditions for obtaining the cis-isomer is catalytic hydrogenation.
• Particularly preferred conditions for hydrogenation of the double bond of a compound of the formula HI involve the use of a palladium catalyst in amounts ranging from 0.1-20 mol% in glacial acetic acid at room temperature and at a pressure of 3-5 bar.
• the process according to the present invention provides an economical and convenient synthetic route to a wide variety of N-monoprotected 1, 4, 5, 6-tetrahydropyrazine derivatives and thereby to the corresponding monoprotected piperazine derivatives which in tum can be converted to a whole range of other compounds.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Plural Heterocyclic Compounds (AREA)

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Publications (1)

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• 1995
  • 1995-08-18 SE SE9502876A patent/SE9502876D0/sv unknown
• 1996
  • 1996-07-29 EP EP96925241A patent/EP0846106A2/en not_active Withdrawn
  • 1996-07-29 AU AU65397/96A patent/AU6539796A/en not_active Abandoned
  • 1996-07-29 CA CA002228896A patent/CA2228896A1/en not_active Abandoned
  • 1996-07-29 WO PCT/SE1996/000977 patent/WO1997007106A1/en not_active Application Discontinuation
• 1998
  • 1998-02-12 NO NO980607A patent/NO980607D0/no unknown

Non-Patent Citations (1)

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