Nicotine is an alkaloid found in the nightshade family of plants (Solanaceae) that acts as a nicotinic acetylcholine agonist and a monoamine oxidase inhibitor[citation needed]. The biosynthesis takes place in the roots and accumulation occurs in the leaves of the Solanaceae. It constitutes approximately 0.6–3.0% of the dry weight of tobacco and is present in the range of 2–7 µg/kg of various edible plants. It functions as an antiherbivore chemical; therefore, nicotine was widely used as an insecticide in the past and nicotine analogs such as imidacloprid are currently widely used.

Nicotine is a hygroscopic, oily liquid that is miscible with water in its base form. As a nitrogenous base, nicotine forms salts with acids that are usually solid and water soluble. Nicotine easily penetrates the skin. As shown by the physical data, free base nicotine will burn at a temperature below its boiling point, and its vapors will combust at 308 K (35 °C; 95 °F) in air despite a low vapor pressure. Because of this, most of the nicotine is burned when a cigarette is smoked; however, enough is inhaled to cause pharmacological effects.

Optical activity

Nicotine is optically active, having two enantiomeric forms. The naturally occurring form of nicotine is levorotatory with a specific rotation of [α]D = –166.4° ((−)-nicotine). The dextrorotatory form, (+)-nicotine is physiologically less active than (–)-nicotine. (−)-nicotine is more toxic than (+)-nicotine.[17] The salts of (+)-nicotine are usually dextrorotatory.

Biosynthesis

Pharmacokinetics

As nicotine enters the body, it is distributed quickly through the bloodstream and crosses the blood–brain barrier reaching the brain within 10–20 seconds after inhalation. The elimination half-life of nicotine in the body is around two hours.

The amount of nicotine absorbed by the body from smoking depends on many factors, including the types of tobacco, whether the smoke is inhaled, and whether a filter is used. For chewing tobacco, dipping tobacco, snus and snuff, which are held in the mouth between the lip and gum, or taken in the nose, the amount released into the body tends to be much greater than smoked tobacco.[clarification needed][citation needed] Nicotine is metabolized in the liver by cytochrome P450 enzymes (mostly CYP2A6, and also by CYP2B6). A major metabolite is cotinine.

Other primary metabolites include nicotine N'-oxide, nornicotine, nicotine isomethonium ion, 2-hydroxynicotine and nicotine glucuronide. Under some conditions, other substances may be formed such as myosmine.

Glucuronidation and oxidative metabolism of nicotine to cotinine are both inhibited by menthol, an additive to mentholated cigarettes, thus increasing the half-life of nicotine in vivo.

In the central nervous system

By binding to nicotinic acetylcholine receptors, nicotine increases the levels of several neurotransmitters – acting as a sort of "volume control". It is thought that increased levels of dopamine in the reward circuits of the brain are responsible for the apparent euphoria and relaxation, and addiction caused by nicotine consumption. Nicotine has a higher affinity for acetylcholine receptors in the brain than those in skeletal muscle, though at toxic doses it can induce contractions and respiratory paralysis.[30] Nicotine's selectivity is thought to be due to a particular amino acid difference on these receptor subtypes.

Tobacco smoke contains anabasine, anatabine, and nornicotine.[citation needed] It also contains the monoamine oxidase inhibitors harman and norharman.These beta-carboline compounds significantly decrease MAO activity in smokers.MAO enzymes break down monoaminergic neurotransmitters such as dopamine, norepinephrine, and serotonin. It is thought that the powerful interaction between the MAOI's and the nicotine is responsible for most of the addictive properties of tobacco smoking.The addition of five minor tobacco alkaloids increases nicotine-induced hyperactivity, sensitization and intravenous self-administration in rats.

Chronic nicotine exposure via tobacco smoking up-regulates alpha4beta2* nAChR in cerebellum and brainstem regions but not habenulopeduncular structures.Alpha4beta2 and alpha6beta2 receptors, present in the ventral tegmental area, play a crucial role in mediating the reinforcement effects of nicotine.

In the sympathetic nervous system

Nicotine also activates the sympathetic nervous system,[40] acting via splanchnic nerves to the adrenal medulla, stimulates the release of epinephrine. Acetylcholine released by preganglionic sympathetic fibers of these nerves acts on nicotinic acetylcholine receptors, causing the release of epinephrine (and norepinephrine) into the bloodstream. Nicotine also has an affinity for melanin-containing tissues due to its precursor function in melanin synthesis or due to the irreversible binding of melanin and nicotine. This has been suggested to underlie the increased nicotine dependence and lower smoking cessation rates in darker pigmented individuals. However, further research is warranted before a definite conclusive link can be inferred.

Effect of nicotine on chromaffin cells.

In adrenal medulla

By binding to ganglion type nicotinic receptors in the adrenal medulla nicotine increases flow of adrenaline (epinephrine), a stimulating hormone and neurotransmitter. By binding to the receptors, it causes cell depolarization and an influx of calcium through voltage-gated calcium channels. Calcium triggers the exocytosis of chromaffin granules and thus the release of epinephrine (and norepinephrine) into the bloodstream. The release of epinephrine (adrenaline) causes an increase in heart rate, blood pressure and respiration, as well as higher blood glucose levels.

Nicotine is the natural product of tobacco, having a half-life of 1 to 2 hours. Cotinine is an active metabolite of nicotine that remains in the blood for 18 to 20 hours, making it easier to analyze due to its longer half-life.

Sumber: en.wikipedia.org

The Metabolism of Nicotine 

1 - Absorption of nicotine

Absorption of nicotine through cellular membranes depends on the pH. If the pH is acidic, nicotine is ionized and does not easily pass through membranes. At physiologic pH (pH = 7.4), 31% of nicotine is not ionized and easily passes through membranes.

The tobacco smoke pH is acidic, and this acidity only allows a little absorption in the mouth. Inhalation is therefore necessary to allow nicotine to be absorbed by the huge area of alveolar epithelium. In the lungs, nicotine is quicklyt absorbed by the systemic circulation. This absorption is easy because the blood flow is high in the lung capillaries : a volume equal to the blood volume of the body passes each minute. So, the rate of nicotine qickly rises when a cigarette is smoked. Absorbed nicotine is rapidly distributed among all the organs, and it reaches the brain within only  ten seconds.  

2 - Action on nicotinic receptors

The active form of nicotine is a cation whose charge is located on the nitrogen of the pyrrole cycle. This active form is very close to acetylcholine. It has been demonstrated that nicotine interferes with acetylcholine, which is the major neurotransmitter of the brain. Acetylcholine can bind to two different kinds of receptors: nicotinic receptors, which are activated by nicotine, and muscarinic receptors, which are activated by muscarine. Nicotine and muscarine are thus specific agonists of one kind of cholinergic receptors (an agonist is a molecule that activates a receptor by reproducing the effect of the neurotransmitter.)

Nicotine competitively binds to nicotinic cholinergic receptors. The binding of the agonist to the nicotinic receptor triggers off a conformation change of the architecture of the receptor, which opens the ionic channel during a few milliseconds. This channel is selective for cations (especially sodium). Its opening thus leads to a brief depolarization. Then, the channel closes and the receptor transitionally becomes refractory to agonists. This is the state of  desensitization. Then, the receptor  usually goes back to a state of rest, which means that it is closed and sensitive to the agonists. In case of continuous exposure to agonists (even in small doses), this state of desensitization will last long (long-term inactivation).

Operating cycle of a nicotinic receptor:  

Physiological normal conditions: After the opening of the canal by binding to acethylcholine, the receptor becomes desensitized before it goes back to the state of rest or it is regenerated.

Continuous exposure to tobacco: Nicotine substitutes for acetylcholine and over stimulates the nicotinic receptor. Then, the receptor is long-term inactivated and its regeneration is prevented by nicotine.

3 - Tolerance and dependence on nicotine

Nicotine rises the stimulation of nicotinic receptors. The excessive and chronic activation of these receptors is balanced by a down-regulation in the number of active receptors. The reduction of the number of active receptors reduces the psychotropic effect of nicotine. Due to the phenomenon of tolerance, the smoker needs to smoke more and more cigarettes to keep a constant effect.

Nicotine activates dopamine systems within the brain. Dopamine is a neurotransmitter which is directly responsible for mediating the pleasure response. Nicotine triggers off the production of dopamine in the nucleus accumbens. A prolonged exposure of these receptors to nicotine reduces the efficiency of dopamine by cutting down the number of available receptors. Consequently, more and more nicotine is needed to give the same pleasurable effect.

After a brief period of abstinence (overnight for instance), the brain concentration of nicotine lowers and allows a part of the receptors to recover their sensibility. The return to an active state rises the neurotransmission to an abnormal rate. The smoker feels uncomfortable, which induces him to smoke again. The first cigarette of the day is the most pleasant because the sensibility of the dopamine receptors is maximal. Then, the receptors are soon desensitized and the pleasure wears off. This is the vicious circle of smoking.

  4 - Chemical transformations undergone by nicotine

Nicotine is mainly transformed in the liver, but also in the lungs and the kidneys. The primary metabolites of nicotine are cotinine and  nicotine N-oxide, which are some products of the hepatic oxidation of nicotine by  P-450 cytochrome.

How can nicotine be dangerous for the body?

Nicotine and its metabolites may be dangerous for the body. Actually, nicotine is a strong carcinogen. In fact, nicotine can undergo several kinds of transformation like a pyrrole cycle opening. The methyl group on this cycle can become a very powerful alkylating agent when removed from the cycle.

The amine function of nicotine may react with nitrogen monoxide or with nitrous acid in order to form a "nitrosonium" type molecule. This compound may then be transformed by the body, which means oxidized and opened. This opening leads to two isomers, two "nitrosamino" type molecules (R2N-N=O) where one of the two R group is a methyl. This reaction occurs as follows:

A = 4 (N-methyl-N-nitrosamino)-1-(3-pyridyl)-butan-1-one          B = 4 (N-methyl-N-nitrosamino)-4-(3-pyridyl)-butanal

In acidic medium, the oxygen of the "nitrosamino" group is protonated and the double bond moves to the central nitrogen, which becomes positively charged. This new molecule is a methyl source. The "nitrosamino" group can then react with another amine, which removes the positive charge from the nitrogen. If the amine that reacts is a part of the structure of the DNA, an irreversible alkylation of the DNA occurs:

This alkylation is really  noxious and may help in the development of cancer as it prevents the normal development of the cell.

Sumber : http://www.chm.bris.ac.uk

Mid Semesters Exam Answers Chemistry Of Natural Products

1. Express their own ideas on how to convert a mixture of natural ingredients that have the potential (inactive) can be transformed into higher compounds that have a high potential for biological activity.

        My idea is generally to obtain a compound of natural ingredients that do not have the potential (not active) that can be converted into an active compound that has a high potential for biological activity, can be done in stages as follows:

a. preparation phase of the plant material
b. Phase extraction
c. Phase fractionation and purification
d. Elucidation structure of the isolated compounds
e. Testing activity of the active compounds


Example

Xanthone compounds found in the bark mangosteen wildly

Uncultivated mangosteen (Garcinia sp) is a species of the family guttiferae, Garcinia species. This plant has a botanical classifications as follows:
   Division       : Spermatophyta
   Sub Division: Angiospermae
   Class            : Dicotyledonae
   Family          : guttiferae
  Genre            : Garcinia
  Species          : Garcinia sp
         

      

Figure 1 wild bark and sawdust wild mangosteen Mangosteen (Garcinia sp)
                 

             Santon is a compound made tricyclic aromatic ring substituted with groups other than phenolic, methoxy and isoprene (Walker, 2007). The compounds xanthones such as 9-hydroxycalabaxanthone, 3-isomangostin, gartanin, 8-desoxygartanin (Walker, 2007), α-mangostin, γ-mangostin, β-mangostin, and methoxy-β-mangostin (Akao et al., 2008). Santon are scattered in various organs of plants classified for subsituen linked nucleus (Bennett and Lee,1989).

            Xanthones present in the mangosteen fruit, among others, 9 - hidroksikalabaxanton, 3 isomangostin, gartanin, 8-deoksigartanin, α-mangostin and β-mangostin (Zarena, et al, 2009.). The majority of natural xanthones were found primarily in higher plants that can be isolated from the four tribes, namely guttiferae, Moraceae, and Polygalaceae Gentianaceae (Sluis, 1985). Family of four is rich in xanthones, as guttiferae: alpha and gamma mangostin mangosteen (Jung et al, 2006; Harrison, 2002; Suksamrarn et al, 2002 ..). Santon is reported to have pharmacological activity can stimulate the central nervous system and has an activity antituberculosis vitro on Mycobacterium tuberculosis (Bruneton, 1999; Sluis, 1985). Santon type gentisin Mangiferin and has an antitumor activity as an inhibitor of monoamine oxidase and (Robinson, 1995). Xanthones found in the rind of Garcinia mangostana and has the IUPAC name of (1,3,6-trihydroxy-7-methoxy-2 ,8-bis (3-methyl-2-butenyl)-9Hxanten-9-yl). (Chitra, MV2010) Structure of Xanton dapa you see in the image below:
 
 Chemical constituents of Garcinia xanthones which it is derived

 

              

           α-mangostin                             β-mangostin

       

    

      9- hydroxycalabaxantone                   3-isomangostin

                      

               Gartanin                                             8-desoxygartanin

           Santon derived structures (Walker, 2007)

            More than 60 compounds were isolated from xanthones mangosteen different sections, for example α-mangostin, 1-isomangostin, 3-isomangostin, 9-hidroksikalabaxanton, 8-deoksigartanin, dimetilkalbaxanton, garcinon B, gargarcinon D, E garcinon, gartanin, mangostanol, mangostanin and mangostinon (Ji et al, 2007;. Walker, 2007). Xanthone compounds can inhibit the growth of colon cancer cells DLD-1 with IC50 values ​​methoxy-β-mangostin <β-mangostin <α-mangostin <γ-mangostin (Akao et al., 2008). Search Matsumoto et al. (2003) stated that α-mangostin antiploriferatif have activity against leukemia HL60 by inducing apoptosis. In addition, α-mangostin has antibacterial activity against Mycobacterium tuberculosis and has antioxidant activity (Jung et al., 2006). The phenolic compounds of coumarin derivatives, xanthones, a prenylated benzophenone and biflavon. Of a series of compounds that have been found in species in these taxa, shows the properties of bioactivity are very interesting and varied, such as anti-HIV, antileukimia, anticancer, antitumor, anti-inflammatory, anti-hypertensive, hepatitis drugs and inflammatory bowel disease (Dharmaratne and Wanigasekera 1996, Huang, 2001; Peres and Nagem 1997) Ersam 2006.


There are some steps undertaken to obtain the active compounds are:

a. Preparation of plant materials
At this stage the plants are prepared sample that will be used. The samples were taken from the bark of the wild mangosteen (Garcinia sp).

b. Phase extraction
At this stage the dried sample, then diracang well after finely ground. Then maceration with alcohol and distilled water 1:3 solvent for 72 hours and repeat three times, filtered, evaporated results maceration.

c. Phase fractionation and purification
The result of the process of maceration executed fractionation with n-hexane. Formed by two layers, namely the n-hexane layer and lower layer. The top layer is translucent while the lower layer is added klorometana to the nodes of color. After all, the new transparent color coating rejected. The rest is added with ethyl acetate.

d. Phase chromatography
In this phase, chromatography, chromatography in each fraction of compounds to know compounds of natural ingredients contained in each fraction.
 

e.Elucidation structure of the isolated compounds

f. Check activity of compounds active against larvae of shrimp isolated

2. Explain how the idea of a compound of natural ingredients that have a high biological potency and prospective for the benefit of sentient beings can be synthesized in the laboratory

1. Supply of plant samples x containing compounds of natural ingredients that would be synthesized in the laboratory. samples may be leaves, stems, roots and flowers, and the sample can be dried in puree.

2. The extraction with an appropriate solvent with a compound of natural ingredients contained in the plant that will be synthesized.

3. Subsequently in the fractionation, with the aim of mermisahkan by nature - the nature of the compounds contained, for example, polar compounds and non-polar.

4. In doing chromatography separates the components of a mixture for the purpose perfectly.

5. Purification or purification, the method gets the compounds of the pure components natural ingredients free of chemical components which are not needed.

6. The pure compound was obtained by the structure can be determined by spectroscopy, such as IR, NMR, UV.

3. Explain the basic rules in choosing a solvent for the isolation and purification of a compound of natural ingredients. Set an example for 4 classes of compounds of natural products: terpenoids, alkaloids, flavonoids and steroids.

Some of the selection criteria for the isolation and purification of solvents:
1. Selectivity: choice of solvent can affect the purity of the extracts

2. Chemical and thermal stability: solvent chosen must be stable under the conditions of the extraction process and the downstream

3. Compatibility with the solute: solvent is selected that does not react with the solute

4. Viscosity: low diffusion coefficient of viscosity of the solvent which would increase the extraction rate is also increased

5. Solvent recovery: to improve the economic process, the solvent must direkoveri so that it can be reused. Solvent with low boiling point cheaper direkoveri and reused.

6. Non-combustible for safety reasons should be selected solvents are not flammable.

7. Non-toxic: no sailor toxic safer for the production and workers.

8. Cheap and easily available: the choice of solvent must be solvent cheap and easy to obtain.


example:
1. flavonoids with a semi-polar acetone solvent
2. alkaloid with a non-polar solvent ethanol
3. trepenoid with a solvent methanol semipolar
4. steroids with the solvent n-hexane polar

4. Explain the basic starting point for the determination of the structure of an organic compound. When the compounds of natural ingredients such as caffeine is tersebuat. Express their ideas matter - whatever the subject is necessary to determine the general structure.

To identify the structure of a compound of natural ingredients can use spektoskopis IR, ¹³C NMR, UV, ¹ H NMR.
For example, using ¹³C NMR

Carbon-13 NMR (¹³C NMR or sometimes simply referred to as carbon NMR) is the application of nuclear magnetic resonance (NMR) spectroscopy to carbon. It is analogous to proton NMR (1H NMR) and allows the identification of carbon atoms in an organic molecule just as proton NMR identifies hydrogen atoms. As such ¹³C NMR is an important tool in chemical structure elucidation in organic chemistry. ¹³C NMR detects only the 13C isotope of carbon, whose natural abundance is only 1.1%, because the main carbon isotope, 12C, is not detectable by NMR since it has zero net spin.

Implementation

¹³C NMR has a number of complications that are not encountered in proton NMR. ¹³C NMR is much less sensitive to carbon than ¹H NMR is to hydrogen since the major isotope of carbon, the ¹²C isotope, has a spin quantum number of zero and so is not magnetically active and therefore not detectable by NMR. Only the much less common ¹³C isotope, present naturally at 1.1% natural abundance, is magnetically active with a spin quantum number of 1/2 (like ¹H) and therefore detectable by NMR. Therefore, only the few ¹³C nuclei present resonate in the magnetic field, although this can be overcome by isotopic enrichment of e.g. protein samples. In addition, the gyromagnetic ratio (6.728284 10⁷ rad T⁻¹ s⁻¹) is only 1/4 that of ¹H, further reducing the sensitivity. The overall receptivity of ¹³C is about 4 orders of magnitude lower than ¹H.^[1]

Another potential complication results from the presence of large one bond J-coupling constants between carbon and hydrogen (typically from 100 to 250 Hz). In order to suppress these couplings, which would otherwise complicate the spectra and further reduce sensitivity, carbon NMR spectra are proton decoupled to remove the signal splitting. Couplings between carbons can be ignored due to the low natural abundance of ¹³C. Hence in contrast to typical proton NMR spectra which show multiplets for each proton position, carbon NMR spectra show a single peak for each chemically non-equivalent carbon atom.

In further contrast to ¹H NMR, the intensities of the signals are not normally proportional to the number of equivalent ¹³C atoms and are instead strongly dependent on the number of surrounding spins (typically ¹H). Spectra can be made more quantitative if necessary by allowing sufficient time for the nuclei to relax between repeat scans.

High field magnets with internal bores capable of accepting larger sample tubes (typically 10 mm in diameter for ¹³C NMR versus 5 mm for ¹H NMR), the use of relaxation reagents,^[2] for example Cr(acac)₃ (chromium (III) acetylacetonate, CAS number 21679-31-2), and appropriate pulse sequences have reduced the time needed to acquire quantitative spectra and have made quantitative carbon-13 NMR a commonly used technique in many industrial labs. Applications range from quantification of drug purity to determination of the composition of high molecular weight synthetic polymers.

¹³C chemical shifts follow the same principles as those of ¹H, although the typical range of chemical shifts is much larger than for ¹H (by a factor of about 20). The chemical shift reference standard for ¹³C is the carbons in tetramethylsilane (TMS), whose chemical shift is considered to be 0.0 ppm.

Typical chemical shifts in ¹³C-NMR

Here the example of the determination of the structure of nicotine by 13C NMR