Highly Regioselective Nitration Reactions Provide a Versatile Method of Functionalizing Benzocycloheptapyridine Tricyclic Ring Systems: Application toward Preparation of Nanomolar Inhibitors of Farnesyl Protein Transferase

One-Pot Synthesis of Metalated Pyridines from Two Acetylenes, a Nitrile, and a Titanium(II) Alkoxide

Four-component coupling process involving two acetylenes, a nitrile, and a divalent titanium alkoxide reagent, Ti(O-i-Pr)(4)/2i-PrMgCl, directly yielded titanated pyridines in a highly selective manner. The reaction can be classified into four categories: (i) a combination of an internal acetylene, a terminal acetylene, sulfonylnitrile, and the titanium reagent to yield alpha-titanated pyridines, (ii) a combination of an internal acetylene, a (sulfonylamino)acetylene, a nitrile, and the titanium reagent to yield alternative alpha-titanated pyridines, (iii) a combination of an internal acetylene, a (sulfonylamino)acetylene, a nitrile, and the titanium reagent to yield titanated aminopyridines, and (iv) a combination of an acetylenic amide, a terminal acetylene, a nitrile, and the titanium reagent to yield pyridineamides with their side chain titanated. Some of these reactions enabled virtually completely regioselective coupling of two different, unsymmetrical acetylenes and a nitrile to form a single pyridine. Synthetic applications of these reactions have been illustrated in the preparation of optically active pyridines and medicinally useful compounds.

The Mechanism of Selective Purine C-Nitration Revealed: NMR Studies Demonstrate Formation and Radical Rearrangement of an N7-Nitramine Intermediate

Modified purine derivatives are of great importance in biomedical sciences, and substitution reactions on the purine skeleton are intensively studied. In our laboratory, an efficient and selective purine C2-nitration reaction was developed using a mixture of tetrabutylammonium nitrate and trifluoroacetic anhydride. The resulting 2-nitro moiety appeared to be a versatile handle to introduce a variety of pharmacophores onto the purine skeleton. Since the mechanism of this selective purine C2-nitration reaction has remained unclear, we now present an extensive NMR study leading to its elucidation, using N9-Boc-protected 6-chloropurine as a model compound. Direct electrophilic aromatic nitration of the highly electron-deficient C2 position was excluded, and we demonstrate that this reaction occurs in a three-step process. Electrophilic attack by trifluoroacetyl nitrate on the purine N7 position results in a nitrammonium species that is trapped by a trifluoroacetate anion furnishing N7-nitramine intermediate 11. This intermediate was characterized at -50 degrees C by (1)H, (13)C, (15)N, and (19)F NMR. At T > -40 degrees C, the N7-nitramine intermediate undergoes a nitramine rearrangement, which generates a C2-nitro species that immediately eliminates TFA to give 2-nitro-6-chloro-9-Boc purine 10. The involvement of radicals during the nitramine rearrangement was unequivocally established by (15)N-CIDNP. Moreover, the emission signal observed for the rearranged product, 2-nitropurine 10, showed that it is primarily formed in an intermolecular process. A quantitative radical trapping experiment finally disclosed that 65-70% of the nitramine rearrangement takes place intermolecularly.

Synthesis of 5,6-dihydro-11H-benzo[5,6]-cyclohepta[1,2-b]pyridin-11-ylidene)-1-piperidine-N-cyanoguanidine derivatives as inhibitors of ras farnesyl protein transferase

A series of novel N-cyanoguanidine tricyclic farnesyl protein transferase (FPT) inhibitors was prepared. Replacement of a piperidine amide-group with a N-cyanoguanidine functionality increased FPT activity. X-ray crystal structure determination of 42 complexed with FPT revealed differences in the interactions of the amide and N-cyanoguanidine groups with the protein.

Synthesis of C-11 methyl-substituted benzocycloheptapyridine inhibitors of farnesyl protein transferase

[formula: see text] Synthesis of C-11 methyl-substituted benzocycloheptylpyridine tricyclic compounds has been achieved via two different methods. Methylation of C-11 has been effected by treatment of amine 4 with BuLi followed by Mel quenching. In a similar procedure, introduction of a C-11 substituent with concomitant rearrangement of the exocyclic double bond has been carried out. Potent farnesyl protein transferase inhibitors have been synthesized using the above methodologies.

Analogues of 1-(3,10-dibromo-8-chloro-6,11-dihydro-5H-benzo-[5,6]-cyclohepta [1,2-b]pyridin-11-yl)piperidine as inhibitors of farnesyl protein transferase

The synthesis of several 4-pyridylacetyl N-oxide derivatives of 4-(3-bromo-6,11-dihydro-5H-benzo[5,6]-cyclohepta[1,2-b]-pyridin-11-yl)pi perazine/piperidine 3 is described. This study was aimed at identifying fomesyl protein transferase (FPT) inhibitors in these two series of tricycles containing different phenyl ring substituents. The in vitro activity profile of the initial group of compounds 7a-7g led to the synthesis of the 8-methyl-10-methoxy and 8-methyl-10-bromo analogues 7i, 13i, and 13j. The 11R(-) enantiomers of these compounds were found to exhibit potent in vitro FPT inhibition activity.

Analogs of 4-(3-bromo-8-methyl-10-methoxy-6,11-dihydro-5H-benzo[5,6]-cyclo hepta[1,2-b]pyridin-11-yl)-1-(4-pyridinylacetyl)piperidine N-oxide as inhibitors of farnesyl protein transferase

A series of 3-substituted analogs 3 of 4-(3-bromo-8-methyl-10-methoxy-6,11-dihydro-5H-benzo[5,6]-cyclohepta[1,2 b]pyridin-11-yl)-1-(4-pyridinylacetyl)piperidine N-oxide 2 was prepared and evaluated as FPT inhibitors. The objective of this study was to identify other substituents at C3 in this series of FPT inhibitors that would have the FPT potency enhancement similar to that found for a C3 bromo substituent. The 3-methyl analog 17b was found to be tenfold less active than 2, and other C3 substituents having more steric bulk were found to cause a further reduction in activity.

(+)-4-[2-[4-(8-Chloro-3,10-dibromo-6,11-dihydro-5H-benzo[5, 6]cyclohepta[1,2-b]- pyridin-11(R)-yl)-1-piperidinyl]-2-oxo-ethyl]-1-piperidinecarboxamid e (SCH-66336): a very potent farnesyl protein transferase inhibitor as a novel antitumor agent

We have previously shown that appropriate modification of the benzocycloheptapyridine tricyclic ring system can provide potent farnesyl protein transferase (FPT) inhibitors with good cellular activity. Our laboratories have also established that incorporation of either pyridinylacetyl N-oxide or 4-N-carboxamidopiperidinylacetyl moieties results in pharmacokinetically stable inhibitors that are orally efficacious in nude mice. We now demonstrate that further elaboration of the tricyclic ring system by introducing a bromine atom at the 7- or the 10-position of the 3-bromo-8-chlorotricyclic ring system provides compounds that have superior potency and selectivity in FPT inhibition. These compounds have good serum levels and half-lives when given orally to rodents and primates. In vitro and in vivo evaluation of a panel of these inhibitors has led to identification of 15 (SCH 66336) as a highly potent (IC50 = 1.9 nM) antitumor agent that is currently undergoing human clinical trials.

Inhibitors of farnesyl protein transferase. Synthesis and biological activity of amide and cyanoguanidine derivatives containing a 5,11-dihydro[1]benzthiepin, benzoxepin, and benzazepin [4,3-b]pyridine ring system

Bioisosteric replacement of the C-6 carbon atom in piperidine I and piperazine II with S, O, and N heteroatoms is described. Amide and cyanoguanidine derivatives of these compounds were evaluated in vitro and found to be good inhibitors of farnesyl-protein transferase. An improved method of preparing the 5,11-dihydro-[1]-benzthiepin nucleus 6 was accomplished in high yield and with excellent regioselectivity using an AlCl3 melt protocol.

Potent, selective, and orally bioavailable tricyclic pyridyl acetamide N-oxide inhibitors of farnesyl protein transferase with enhanced in vivo antitumor activity

We previously reported compound 1 as a potent farnesyl protein transferase (FPT) inhibitor that exhibited reasonable pharmacokinetic stability and showed moderate in vivo activity against a variety of tumor cell lines. The analogous C-11 single compound, pyridylacetamide 2, was found to be more potent than 1 in FPT inhibition. Further studies showed that modification of the ethano bridge of the tricyclic ring system by conversion into a double bond with concomitant introduction of a single bond at C-11 piperidine resulted in compound 3 that had superior FPT activity and pharmacokinetic stability. Compound 4, a 5-bromo-substituted analogue of 3, showed improved FPT activity, had good cellular activity, and demonstrated a remarkably improved pharmacokinetic profile with AUC of 84.9 and t1/2 of 82 min. Compound4 inhibited the growth of solid tumor in DLD-1 model by 70% at 50 mpk and 52% at 10 mpk.