The synthesis and pharmacological evaluation of (±)-2, 3- seco-fentanyl analogues

Abstract

An efficient, five-step synthetic approach to various acyclic 1,3-diamines has been developed and applied to the preparation of a novel class of open-chained fentanyl analogues. The acyclic derivatives 5.1–5.5 (all new compounds) were synthesized with the aim of estimating the significance of the piperidine ring for the opioid analgesic activity of anilido-piperidines. The starting β-keto-amide 1.1, prepared by the aminolysis of methyl acetoacetate with methylphenethylamine, (93 % yield), was successively reacted with NaH and BuLi, to form the highly reactive α,γ-dienolate anion 1.1a. Regio and chemoselective γ-alkylation of the dienolate with various primary and secondary alkyl halides furnished the β-keto-amides 1.2–1.5 (76–91 %). Reductive amination of the keto-amides 1.1–1.5 with aniline and Zn powder in acetic acid, via the enamine intermediates 2.1–2.5, afforded the β-anilino amides 3.1–3.5 (74–85 %). After reductive deoxygenation of the tertiary amide group, using in situ generated diborane, the corresponding 1,3-diamines 4.1–4.5 were obtained (87–97 %). The synthesis of (±)-2,3-seco-fentanyls 5.1–5.5 was completed by N-acylation of the diamines 4.1–4.5 with propionyl chloride, followed by precipitation of the monooxalate salts (86–95 %). The parent compound, 2,3-seco-fentanyl 5.1, was found to be a 40 times less potent narcotic analgesic than fentanyl but still 5–6 times more active than morphine in rats, while i-Pr derivative 5.3 was inactive. Apart from the pharmacological significance, the general procedure described herein may afford various functionalized, 1,3-diamines as potential complexing agents and building blocks for the synthesis of aza-crown ethers.

Razvijen je efikasan postupak za dobijanje različitih acikličnih 1,3-diamina u pet faza, i primenjen u sintezi nove klase analoga fentanila otvorenog niza. Derivati 5.1–5.5 (svi su nova jedinjenja) sintetisani su sa ciljem da se proceni uticaj piperidinskog prstena na opioidnoanalgetičku aktivnost anilido-piperidina. Polazni β-keto-amid 1.1, dobijen aminolizom metilacetoacetata metilfenetilaminom (prinos 93 %), bio je sukcesivno tretiran sa NaH i BuLi, pri čemu je postao veoma reaktivni α,γ-dienolatni anjon 1.1a. Regio- i hemoselektivnim γ-alkilovanjem ovog dienolata različitim primarnim i sekundarnim alkil-halogenidima, dobijeni su β-keto-amidi 1.2–1.5 (prinos 76–91 %). Reduktivnim aminovanjem keto-amida 1.1–1.5 pomoću Zn praha i sirćetne kiseline, preko enaminskih intermedijera 2.1–2.5, postali su -anilino-amidi 3.1–3.5 (prinos 74–85 %). Posle reduktivne deoksigenacije tercijene amidne funkcije, koristeći in situ generisani diboran, odgovarajući 1,3-diamini 4.1–4.5 izolovani su u prinosima 87–97 %. Sinteza (±)-2,3-seco-fentanila 5.1–5.5 završena je N-acilovanjem diamina 4.1–4.5 propionil-hloridom, a zatim taloženjem u obliku monooksalatnih soli (prinos 86–95 %). Nađeno je da je osnovno jedinjenje, 2,3-seco fentanil 5.1, 40 puta slabiji narkotički analgetik od fentanila, ali još uvek 5–6 puta aktivniji od morfina u pacova, dok je i-Pr derivat 5.3 bio neaktivan. Osim farmakološkog značaja, opštim postupkom prikazanim u ovom radu, mogu se sintetisati različiti 1,3-diamini, uključujući i one sa funkcionalnim grupama. Ova jedinjenja mogu biti potencijalno značajna kao kompleksirajući agensi i kao intermedijeri u sintezi aza-kraun-etara.