$4-$ Salicylamides are inhibitors for an enzyme called scytalone dehydratase. SAR shows that

there are three important hydrogen bonding interactions. Explain whether you think

quinazolines could act as a bioisostere for salicylamides.

$5-$ Structure IX $(x=NH)$ is an inhibitor of a metalloenzyme called thermolysin and forms

interactions as shown. Explain why the analogue $(x=O)$ has reduced binding affinity by a

factor of $1000$ and why the analogue $(x=SH)$ has roughly the same binding affinity.