The ring hydroxyl group is then acylated with the fluorinated benzoyl chlor-
ide ( 194 ) to yield ester 195. Reaction with the carbenoid species from the
Tebbe reagent leads to formal replacement of carbonyl oxygen by a methyl-
ene group to form the enol ether ( 196 ). Catalytic hydrogenation reduces the
enol to the corresponding ether at the same time deleting the benzyl protect-
ing group. The presence of two adjacent chiral centers result in formation of
product 197 as largely a single enantiomer. The remaining task involves for-
mation of the pendant pyrrazolone ring. Alkylation of the morpholine nitro-
gen with substituted semicarbazide 198 leads to 199. Compound 199
undergoes internal displacement of the methoxy group on nitrogen, which
results in formation of the triazolone ring and thus 200.^29
The virus that leads to AIDS is renowned for its ability to develop resist-
ance to antiviral drugs. Successful treatment depends in some measure on
finding agents that act on the virus by novel mechanisms. Current therapy
thus combines drugs that act on three different stages of the viral
HNO201C 6 H 5 CH 2 Cl
NO202C 6 H 5 CH (^2) N
NOH
203
C 6 H 5 CH 2
NH 2 OH Na
ROH N
NH 2
204
C 6 H 5 CH 2
ClCO
C 6 H 5 CH (^2) N
POCl O
3
HN
205
C 6 H 5 CH 2 N
N Cl
206
C 6 H 5 CH 2 N CH 3 CONHNH 2
N NH
207
O NH
C 6 H 5 CH 2 N
N N
N
208
H 2
HN
N N
N
209
CH=O
O NH
FF
N N
N
212
N
O NH
FF
CO 2 C 2 H 5
O NH
F F
210 211
NaB(OAc) 3 H
life cycle. A new class of agents depends on the fact that the virus needs to
bind with specific receptor sites on the immune system cells in order to gain
entry into these cells. The very recent antiviral agentmaraviroc( 212 ) binds
to the same sites as HIV and thus prevents the very first stage in the
- COMPOUNDS WITH TWO HETEROATOMS 107