This document summarizes information about several drugs that act on the central nervous system (CNS). It discusses inhalational anesthetics like halothane, which produce depression of nerve conduction, breathing, and cardiac contractility by binding to potassium channels. It also describes ultrashort-acting barbiturates like thiopental sodium and thiamylal that are used to induce unconsciousness for surgery. Additionally, it covers the dissociative anesthetic ketamine, which induces a trance-like state providing pain relief, sedation, and amnesia. Synthetic routes are provided for several drugs, including halothane and ketamine.

1. Presented by: Sushmita Hiremath
Assistant Professor
Department of Pharmaceutical Chemistry
KLE College of Pharmacy Hubballi
DRUGS ACTING ON CNS

2.  Drugs acting in the central nervous system (CNS)
include medications used to treat a wide range of
neurologic and psychiatric conditions as well as drugs
that relieve pain, suppress nausea, and reduce fever,
among other symptoms. In addition, many CNS-acting
drugs are used without prescription to increase the
sense of well-being.

3. From PV Publication

4. Inhalational Anaesthetics:
 An inhalational anaesthetic is a chemical compound
possessing general anaesthetic properties that can
be delivered via inhalation. They are administered
through a face mask, laryngeal mask airway or tracheal
tube connected to an anesthetic vaporiser and an
anesthetic delivery system.

6. Mechanism of Action
 Halothane produces actions on multiple ion channels
due to which, there is depression in the nerve
conduction, breathing and cardiac contractility.
 It binds with potassium channels and produces
immobilizing effects.
 They also bind with NMDA and calcium channels and
causes hyperpolarization.

7. Synthesis of Halothane
i. Hydrogen fluoride is added to trichloroethylene and on simultaneous substitution
of chloride atoms in presence of antimony(III) chloride at 130oC produces
2-chloro-1,1,1-trifluoroethane.
ii. The above formed compound undergoes bromination at 450oC to produce halothane.

8. Ultra Short acting barbiturates
 "Ultra short-acting" barbiturates include Methohexital
(Brevital), Thiamylal (Surital), and Thiopental
(Pentothal).
 Ultrashort-acting barbiturates, such as thiopental
sodium and thiamylal, are used intravenously to induce
unconsciousness smoothly and rapidly in patients
about to undergo surgery, after which gaseous
anesthetics are used to maintain the unconscious state.

9. Methohexital
It is classified as short-acting, and has a rapid onset of action.
It is similar in its effects to sodium thiopental, a drug with which it competed in the
market for anaesthetics.

10. Methohexital Sodium Synthesis

11. Dissociative Anaesthetic:
 Dissociatives (also referred to as 'dissociative
anaesthetics') are a class of psychedelic drug. This
class of drug is characterised by distorted sensory
perceptions and feelings of disconnection or
detachment from the environment and self. The word
dissociative means detached from reality.

12. Ketamine Hydrochloride
Ketamine is a medication primarily used for induction and maintenance of anesthesia.
It induces dissociative anesthesia, a trance-like state providing pain relief, sedation,
and amnesia

14. The synthesis starts with the reaction of cyclopentyl Grignard
and o-chlorobenzonitrile to give o-chlorophenyl-cyclopentyl
ketone, followed by alpha bromination of the ketone, and then
reaction with methylamine to form an alpha-hydroxy imine (1-
Hydroxycyclopentyl-(o-chlorophenyl)-ketone-N-methylimine).
Heating this imine results in Ketamine via a novel alpha-
hydroxyimine rearangement.

15. References:
 PV Publication