The chiral precursor (IV) was obtained by two alternative procedures. Addition of cyclopentylmagnesium bromide (II) to ethyl phenylglyoxylate (I) afforded the racemic hydroxyester (III). Basic hydrolysis of the ethyl ester group of (III) gave the corresponding carboxylic acid, which was resolved using cinchonidine.

An alternative asymmetric procedure consisted in the LDA-promoted addition of cyclopentenone (VI) to the chiral dioxolanone (V), followed by catalytic hydrogenation to furnish (VII). The dioxolane group of (VII) was then cleaved by basic hydrolysis yielding the target (R)-hydroxyacid (IV).

The alkylation of 4-(tert-butoxycarbonylamino)piperidine (VIII) with (S)-4- methylhexyl methanesulfonate (IX) provided the tertiary amine (X). Cleavage of the Boc protecting group of (X) gave aminopiperidine (XI), which was finally coupled with the chiral hydroxyacid (IV) by means of carbonyl diimidazole.

The chiral precursor (IV) was obtained by two alternative procedures. Addition of cyclopentylmagnesium bromide (II) to ethyl phenylglyoxylate (I) afforded the racemic hydroxyester (III). Basic hydrolysis of the ethyl ester group of (III) gave the corresponding carboxylic acid, which was resolved using cinchonidine.

An alternative asymmetric procedure consisted in the LDA-promoted addition of cyclopentenone (VI) to the chiral dioxolanone (V), followed by catalytic hydrogenation to furnish (VII). The dioxolane group of (VII) was then cleaved by basic hydrolysis yielding the target (R)-hydroxyacid (IV).

The alkylation of 4-(tert-butoxycarbonylamino)piperidine (VIII) with 5-bromo-2-methyl-2-pentene (IX) provided the tertiary amine (X). Cleavage of the Boc protecting group of (X) gave aminopiperidine (XI), which was finally coupled with the chiral hydroxyacid (IV) by means of carbonyl diimidazole.

The chiral precursor (IV) was obtained by two alternative procedures. Addition of cyclopentylmagnesium bromide (II) to ethyl phenylglyoxylate (I) afforded the racemic hydroxyester (III). Basic hydrolysis of the ethyl ester group of (III) gave the corresponding carboxylic acid, which was resolved using cinchonidine.

In a related procedure, hydroxyacid (IV) was coupled with 1-Boc-4-aminopiperidine (XII) employing EDC and HOBt to give amide (XIII). Acid cleavage of the Boc group of (XIII) yielded amine (XIV), that was finally alkylated with mesylate (IX).

The chiral precursor (IV) was obtained by two alternative procedures. Addition of cyclopentylmagnesium bromide (II) to ethyl phenylglyoxylate (I) afforded the racemic hydroxyester (III). Basic hydrolysis of the ethyl ester group of (III) gave the corresponding carboxylic acid, which was resolved using cinchonidine.

In a related procedure, hydroxyacid (IV) was coupled with 1-Boc-4-aminopiperidine (XII) employing EDC and HOBt to give amide (XIII). Acid cleavage of the Boc group of (XIII) yielded amine (XIV), that was finally alkylated with bromide (IX).

The condensation of chiral dioxolane (I) with 2-cyclopentenone (II) by means of lithium diisopropylamide (LDA) in THF, followed by reaction with N-phenyl-trifluoromethanesulfonylimide gives the enol triflate (III), which is reduced with H2 over Pd/C in methanol yielding the chiral dioxolane (IV)(as major isomer (93:7)). The hydrolysis of (IV) with NaOH in methanol affords impure acid (V), which was purified through crystallization of its (-)-cinchonidine salt. Pure (V) is finally condensed with piperidine-4-amine (VI) by means of CDI and DIEA in DMF to afford the target amide.

The alkylation of 4-piperidone monohydrate hydrochloride (I) with 5-bromo-2-methyl-2-pentene (II) in the presence of KI and K2CO3 afforded the tertiary amine (III). Subsequent reductive amination using ammonium acetate and sodium cyanoborohydride provided aminopiperidine (IV).

Racemic 2-cyclopentyl-2-hydroxy-2-phenylacetic acid (V) was resolved by recrystallization of its cinchonidine salt from toluene to furnish the (-)-(R)-enantiomer (VI). Coupling with amine (IV) by means of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) and 1-hydroxybenzotriazole (HOBt) then gave the target amide.