Alfentanil is a narcotic analgesic with a
more rapid onset and shorter duration of
action than its structural relative fentanyl. The primary utility of alfentanil is in
surgical analgesia/anesthesia, especially for cardiac compromised patients and in
procedures of short duration.
A mixture of 22 parts of 1-ethyl-1,4-dihydro-5H-tetrazol-5-one, 45 parts of 1-
bromo-2-chloroethane, 26 parts of sodium carbonate, 0.3 part of potassium
iodide and 240 parts of 4-methyl-2-pentanone is stirred and refluxed
overnight with water-separator. The reaction mixture is cooled, water is added
and the layers are separated. The aqueous phase is extracted three times with dichloromethane. The combined organic phases are dried, filtered and
evaporated. The residue is purified by column-chromatography over silica gel
using trichloromethane as eluent. The pure fractions are collected and the
eluent is evaporated, yielding 28.4 parts (80%) of 1-(2-chloroethyl)-4-ethyl-
1,4-dihydro-5H-tetrazol-5-one as a residue.
A mixture of 1.8 parts of 1-(2-chloroethyl)-4-ethyl-1,4-dihydro-5H-tetrazol-5-
one, 3.45 parts of N-[4-(methoxymethyl)-4-piperidinyl]-Nphenylpropanamide,
5 parts of sodium carbonate, 0.2 part of potassium iodide
and 240 parts of 4-methyl-2-pentanone is stirred and refluxed overnight with
water-separator. The reaction mixture is poured onto water and the layers are
separated. The organic phase is dried, filtered and evaporated. The residue is
purified by column-chromatography over silicagel using a mixture of
trichloromethane and methanol (97:3 by volume) as eluent. The pure
fractions are collected and the eluent is evaporated. The residue is converted
into the hydrochloride salt in 2-propanone. The salt is filtered off and
crystallized from 2-propanone, yielding 1.5 parts (33.3%) of N-[1-[2-(4-ethyl-
4,5-dihydro-5-oxo-1H-tetrazol-1-yl]-4-(methoxymethyl)-4-piperidinyl]-Nphenylpropanamide
monohydrochloride monohydrate; melting point 140.8°C.
