Pharmaceuticals

Application of Organic Chemistry

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SSRIs

Selective Serotonin Reuptake Inhibitors

These are a class of drugs that are used to treat depressive disorders, anxiety disorders, and other psychological conditions. They are also known as antidepressants.

Common SSRIs

Fluoxetine

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This SSRI is used in Prozac, a drug known to treat depression, obsessive-compulsive disorder (OCD), bulimia nervosa, and panic disorder.

Paroxetine

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This SSRI is used in Paxil, Pexeva, and Brisdelle. These drugs are used to treat depression, obsessive-compulsive disorder (OCD), panic disorder, generalized anxiety disorder (GAD), social anxiety disorder (also known as social phobia), premenstrual dysphoric disorder (PMDD), and posttraumatic stress disorder (PTSD).

Fluvoxamine

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This SSRI is used in Luvox. It is primarily used to treat obsessive compulsive disorder (OCD).

Citalopram

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This SSRI is used in Celexa. This drug is commonly used to treat anxiety and depression.

Escitalopram

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This SSRI is used in Lexapro. This drug is used to treat depression, social anxiety disorder, obsessive compulsive disorder, body dismorphic disorder, and kleptomania.

Setraline

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This SSRI is used in Zoloft, a drug commonly used to treat depression, anxiety, obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and premenstrual dysphoric disorder (PMDD).

Normal Serotonin Transmission

In normal serotonin transmission, serotonin (a neurotransmitter produced by neurons in the brain) is released into the gaps between neurons (also known as the synaptic cleft) to transmit signals. After it has transmtted its signal by binding to serotonin receptors on the postsynaptic neuron, it is typically reabsorbed into the presynaptic neuron by the serotonin transporter (SERT), which marks the end of signaling.

SSRI Inhibition of Serotonin Transporter

SSRIs bind to the serotonin transport protein (SERT) on the surface of the presynaptic neuron. This prevents serotonin from being reabsorbed into the neuron. This results in serotonin remaining in the synaptic cleft longer, increasing its ability to bind to serotonin receptors on the postsynaptic neuron.

Increased Serotonin Signaling

Because there is more serotonin in the synapse, its ability to activate serotonin receptors on the postsynaptic neuron is enhanced. This results in a prolonged or stronger signal.

Common Aspects of SSRIs

Benzene Rings

Most SSRIs utilize benzene rings in their structure. Because benzene rings are nonpolar, they contribute to the fat-solubility of the molecule. This helps SSRIs cross lipid-rich barriers, like blood-brain barriers. Additionally, benzene rings engage in π-π interactions with serotonin transporter protein (SERT), the target of SSRIs. Benzene also provides chemical stability. The resonance of their structure makes them less prone to unwanted reactions in the body, increasing the drugs longevity and effectiveness. Lastly, benzene allows for the attachment of various functional groups at different positions, which enables fine-tuning of the compounds.

Groups

The addition of groups like fluoro, chloro, and nitro improves SSRIs in many ways. These groups are electron-withdrawing and hydrophobic, which contributes to the fat-solubility of the molecule, as did benzene. These groups can also enhance the π-π interactions between the drug and SERT, improving the drugs affinity and selectivity. The addition of these groups help SSRIs selectively bind to SERT over other transporters. Lastly, the halogen atoms, like fluoro and chloro, are chemically stable and resistant to metabolic breakdown by liver enzymes.