Strychnine in Chemistry Structure Properties and Toxicity

Strychnine is a highly poisonous, bitter, colourless crystalline alkaloid that is mainly extracted from the seeds of a plant known as the Nux vomica tree that belongs to the Strychnos family of trees. It was first discovered by two french chemists named Perrie Joseph Pellepiter and Joseph Caventour in 1818 in the Philippines. 

This poison is manufactured largely in India due to the high availability of Nux vomica trees here. This is a highly reactive poison and can cause muscular convulsions and ultimately death due to choking if inhaled or swallowed. 

Strychnine is synthesised either by biosynthesis which is a natural process or by chemical synthesis in the laboratory. It is derived from secologanin and tryptamine and is chemically identified as terpene indole alkaloid. It belongs to a chemical group named corynanthe alkaloids. 

Strychnine: Structure, Properties and Uses

Strychnine is a poisonous crystalline alkaloid with a molecular formula C21H22N2O2. Its IUPAC name is Strychnidin-10-one with a molar mass of 334.4 g/mol. The molecular structure represents a strychnidine atom bearing a keto substituent at the tenth position of the atom. It behaves as an avicide and also as a glycine receptor antagonist. From the structure, it is evident that it is also an organic heteroheptacyclic compound that has a conjugate base of strychnine (1+) and is derived from hydride and strychnine.

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Various studies have demonstrated that small doses of strychnine can be beneficial to treat many human ailments such as muscle relaxation. But today strychnine is used as pesticides to kill rodents and small vertebrates. It has also been proven that strychnine is a very good antagonist at neurotransmitter glycine receptors located at the spinal cord, brain stems and similar higher centres in the human body. Thus it is used to increase muscular activity by aggravating neuronal activities and excitability.  The characteristics of any element or compound can be determined by its physical and chemical properties. Thus, these properties are of higher value in the study of chemistry and to derive experimental data.

Computed Properties are as Follows:

Experimental properties of Strychnine have been divided into two categories, namely, Physical properties and Chemical properties. A few of such major properties are listed below:

Physical Properties of Strychnine

Chemical Properties of Strychnine

Biosynthesis of Strychnine

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The above reaction is the diagrammatic representation of the biosynthesis reaction of strychnine. Strychnine is basically a terpene indole alkaloid that is derived from tryptamine and secologanin. When these two units undergo a condensation reaction in presence of an enzyme named strictosidine that acts as a catalyst to initiate the condensation reaction to form strictosidine. This step is inferred by the isolation of intermediates from Strychnos nux-vomica. This reaction is known as Pictet-Spengler Reaction. 

After this, a hydrolysis reaction occurs resulting in the opening of the ring by elimination of glucose. This opening of the ring results in a reactive aldehyde which is then attacked by a secondary amine to form an intermediate compound called geissoschizine.  Now, the reverse Pictet-Spengler Reaction cleaves C2-C3 bond and simultaneously forms C3-C7 bond by 1,2-alkyl shift. This reaction is followed by oxidation from cytochrome P450 enzyme to a spiro-oxidonol. 

After this, a nucleophilic attack from the enol present at C16 and elimination of oxygen establish a C2-C16 bond to form dehydropreakuammicine. Decarboxylation and hydrolysis of methyl weather lead to the formation of norfluorocurarin. After this, an aldol reaction is carried out by acetyl-CoA to the aldehyde to achieve pre-strychnine. From this stage, amine with carboxylic acid or its activated CoA thioester is added, followed by a displacement reaction of activated alcohol resulting in ring closure. This step finally leads to the formation of strychnine. 

Strychnine Mechanism of Action

Strychnine is basically an antagonist to glycine and acetylcholine receptors and therefore, termed a neurotoxin. In the presence of strychnine, neurotransmitters are bound to the receptors. Therefore, an impulse is generated from one end of the nerve cells to another. As proven from the facts that it majorly affects the motor nerve fibres of the spinal cord that control contractions in muscles. 

As glycine acts as an antagonist to the glycine receptors which is known as ligand-gated chloride channel located in neurons that are present in brains and spinal cords. Therefore, in the presence of glycine (an inhibitory neurotransmitter), a larger number of neurotransmitters must bind themselves to the receptors before any potential action is generated. The chloride channels present in neurons allow the negatively charged ions to flow into the neurons, resulting in hyperpolarization. Thus it pushes the membrane potential above its normal threshold level. 

Now, due to the presence of strychnine, which is also an antagonist of glycine, a lower level of excitatory neurotransmission takes place. This happens because strychnine binds covalently with the receptor, preventing the inhibitory glycine to have effects on postsynaptic neurons. Thus the inhibitory signals are prevented to run through neurons, hence, motor neurons are easily activated causing muscle contractions and death due to asphyxia.

Strychnine Tree

Strychnine is naturally derived from the seed of a tree famously known as nux-vomica. It is also referred to as strychnine tree in common language. Strychnine plants are usually medium-sized trees with thick and strong trunks. Its woods are very dense and closed grains. Although the wood of strychnine plants is very hard, its branches are thin and irregular and are covered with ash-coloured barks. Strychnine trees are commonly known as poison nuts, quaker buttons and semen strychnos.