UJIAN AKHIR SEMESTER

MATA KULIAH       : KIMIA BAHAN ALAM

SKS                             : 2

DOSEN                      : Dr. Syamsurizal, M.Si

WAKTU                     : 22-29 Desember 2012

PETUNJUK : Ujian ini open book. Tapi tidak diizinkan mencontek, bilamana ditemukan, maka anda dinyatakan GAGAL. Jawaban anda diposting di bolg masing-masing.

1.Jelaskan dalam jalur biosintesis triterpenoid, identifikasilah faktor-faktor penting yang sangat menentukan dihasilkannya triterpenoid dalam kuantitas yang banyak.

2.       Jelaskan dalam penentuan struktur flavonoid, kekhasan signal dan intensitas serapan dengan menggunakan spektrum IR dan NMR. Berikan dengan contoh sekurang-kurangnya dua struktur yang berbeda.

3.      Dalam isolasi alkaloid, pada tahap awal dibutuhkan kondisi asam atau basa. Jelaskan dasar penggunaan reagen tersebut, dan berikan contohnya sekurang-kurangnya tiga macam alkaloid.

4.      Jelaskan keterkaitan diantara biosintesis, metode isolasi dan penentuan struktur senyawa bahan alam . Berikan contohnya.

ANSWER

1.      Squalen Biosynthesis reaction (Making Triterpenoid)

Path begins at biosentesis triterpenoid acetyl coenzyme A did kodensasi type aldol produce a branched carbon chains which are found in mevalinat acid and subsequent reaction such as phosphorylation reactions, elimination of phosphoric acid and decarboxylation yield piroposfat isopentenyl (IPP) which selanjutnyaa berisomerisasi a dimethyl allyl pyrophosphate (DMAPP) by enzyme isomerase.

IPP which are the units of active isopern DMAPP join between the head and tail of this is caused by the attack of electrons of the double bond carbon atoms of IPP to DMAPP a shortage of electrons followed by the removal of phosphate ions produced piro geranil. after it is formed aqualane triterpenoids which experience structuring as shown below:

a.      EC 2.5.1.21 squalene synthase: Reaction: 2 (2E,6E)-farnesyl diphosphate + NAD(P)H + H+ = squalene + 2 diphosphate + NAD(P)+ (overall reaction) (1a) 2 (2E,6E)-farnesyl diphosphate = diphosphate + presqualene diphosphate (1b) presqualene diphosphate + NAD(P)H + H+ = squalene + diphosphate + NAD(P)+

This microsomal enzyme catalyses the first committed step in the biosynthesis of sterols. The enzyme from yeast requires either Mg2+ or Mn2+ for activity. In the absence of NAD(P)H, presqualene diphosphate (PSPP) is accumulated. When NAD(P)H is present, presqualene diphosphate does not dissociate from the enzyme during the synthesis of squalene from farnesyl diphosphate (FPP) [8]. High concentrations of FPP inhibit the production of squalene but not of PSPP

b.      EC 2.5.1.32 : geranylgeranyl diphosphate = 15-cis-phytoene + 2 diphosphate (overall reaction)

(1a) 2 geranylgeranyl diphosphate = diphosphate + prephytoene diphosphate

(1b) prephytoene diphosphate = 15-cis-phytoene + diphosphate

Requires Mn2+ for activity. The enzyme produces 15-cis-phytoene. cf. EC 2.5.1.99, 15-trans-phytoene synthase.

Enzymatic cyclization reactions

Enzymatic cyclization with the Help of Enzymes. Initiation cyclization by oxygen Molekuler.Simbol E-O2 * is used to represent oxygen "activated" by forming a complex with the enzyme.

biosynthesis Lanosterol

Sumber http://dc314.4shared.com/doc/5KpoKJFS/preview.html

factors that influence the scope of the results of triterpenoids is a method of isolation of factor where many existing methods of isolation. to produce triterpenoids, which method of isolation is an important factor to generate the numbers or results of triterpenoids same. one of the many methods that produce triterpenoids are Soxhlet extraction method, which is a method of immersion and heating causes pressure differences lead to breakage of the wall and the cell membrane of heating causing evaporation and condensation occurs after passing the air conditioner so that the steam is attached to the pipe wall and serkulasi occurred, repeated movement that causes the result of extract much triterpenoid.

2.      Determination of flavonol Substituents at the core is done by measuring the spectrum at a wavelength of 200-600 nm. Flavonoids shows typical spectra in the region, consists of two peaks, which is in the range of 240-285 nm (bands II) and 300-550 nm (tape I).

IR spectrum of quercetrin demonstrate functional groups OH (3294 cm-1), CC aliphatic (2931 cm-1), C = O (1728 cm-1), C = C aromatic (1504 and 1604 cm-1) and COC ether (1064 cm-1). 13C NMR spectra showed 14 carbon aromatic, one carbonyl, and six aliphatic carbon. Then the identification of the 1 H NMR spectra showed the presence of five aromatic protons, hydroxyl proton, five aliphatic protons and 3 methyl protons. Based on these data showed a compound of flavonoids (quercetin), which binds to a sugar group is rhamnosil. Based on data from HMBC, rhamnosil bound to C-3 of quercetin. These compounds are known as quercetrin (quercetin-3-O-rhamnosida).

http://digilib.uns.ac.id/pengguna.php?mn=showview&id=13616

Isoflavon

Antosianin

3.      In the acid extraction, the plant material is processed by the solution of a weak acid (eg acetic acid in water, ethanol, methanol, or). Bases is then added to convert alkaloids to basic forms are extracted with an organic solvent (if the extraction is done by alcohol, will be removed first, and the remainder is dissolved in water). Solvents are used when extracting the compound mixture is acidified water molecules. This solvent will be able to dissolve the alkaloid salts. It also can basify alkaloid-containing plant material by adding sodium carbonate. Bases are formed can then extract with organic solvents such as chloroform or ether

As for the solution of the alkaloid in the acidic water then the solution must basified beforehand. Further alkaloids can be extracted using organic solvents.  Another way to get the alkaloids from the alkaline solution is the method using a reagent penjerapan Lloyd. Alkaloid that is obtained is then eluted and precipitated using reagents Meyer. After that, the precipitate formed is separated by ion exchange chromatography method.

Grinding done to break down the cell walls of secondary metabolites botanicals that, in this case aalah alkaloids, can come out. Chloroform is used to pull the alkaloid bases. Dragendorff reagent and Mayer's reagent is a common reagent used for the identification of alkaloids. Acid HCl (1:10) in water is used to turn into salt alkaloid base is drawn back into alkaloid HCl chloroform. Due to attract alkaloid bases used chloroform is semipolar, it can be concluded that the alkaloid compounds is semipolar.

Example:
a) Purification Nicotine compounds, to alkaloids that are not heat resistant, insulation can be done using the technique of concentration by basify the solution first. By using this technique the alkaloid will evaporate and then be purified by steam distillation method.
b) Purification of morphine, an alkaloid morphine binds organicmisal acid binds with acetic acid to form acetic acid. Because it's time to identify, ammonia is used to free the alkaloid from organic acids and alkaloids make alkaline soluble in chloroform.
c) sample extract caffeine drip in holes 1 plate was tested by adding 1-2 drops of reagent meyer and allowed to settle. After that, the observed precipitation and its color. Sample extract caffeine in the 2 hole plate drops tested by adding 1-2 drops of reagent dragendroff and allowed to settle. After that, the observed precipitation and its color.

4.      Relationship between the biosynthesis, isolation and structural determination of compounds of natural ingredients are: Isolation role in the process by which we can get the pure compound (natural materials) of plants. then identified the elements of the pure compounds obtained by spectroscopic methods, followed by testing the biological activity of either crude extract or pure compound. Once known molecular structure is usually followed by a modification of the structure through the process of biosynthesis to obtain compounds with the desired activity and stability.

Cholesterol

Cholesterol Is Made from Acetyl-CoA in Four Stages

Cholesterol, like long-chain fatty acids, is made from acetyl-CoA, but the assembly plan is quite different in the two cases. In early experiments animals were fed acetate labeled with 14C in either the methyl carbon or the carboxyl carbon. The pattern of labeling in the cholesterol isolated from the two groups of animals (Fig. 20-30) provided the blueprint for working out the enzymatic steps in cholesterol biosynthesis.

Figure 20-30

Figure 20-30 The origin of the carbon atoms of cholesterol, deduced from tracer experiments with acetate labeled in the methyl carbon (black) or the carboxyl carbon (red). The individual rings in the fused-ring system are designated A through D.

The process occurs in four stages (Fig. 20-31). In stage 1 the three acetate units condense to form a six-carbon intermediate, mevalonate. Stage 2 involves the conversion of mevalonate into activated isoprene units, and stage 3 the polymerization of six 5-carbon isoprene units ta form the 30-carbon linear structure of squalene. Finally (stage 4, the cyclization of squalene forms the four rings of the steroid nucleus, and a further series of changes (oxidations, removal or migration of methyl groups) leads to the final product, cholesterol.

Figure 20-31

Figure 20-31 A summary of cholesterol biosynthesis, showing the four stages discussed in the text. The isoprene units in squalene are set off by red dashed lines.

1. Synthesis of Mevalonate from Acetate

The first stage in cholesterol biosynthesis leads to the intermediate mevalonate (Fig. 20-32). Two molecules of acetyl-CoA condense, forming acetoacetyl-CoA, which condenses with a third molecule of acetyl-CoA to yield the six-carbon compound β-hydroxy-β-methylglutaryl-CoA (HMG-CoA). These first two reactions, catalyzed by thiolase and HMG-CoA synthase, respectively, are reversible and do not commit the cell to the synthesis of cholesterol or other isoprenoid compounds.

The third reaction is the committed step: the reduction of HMGCoA to mevalonate, for which two molecules of NADPH each donate two electrons. HMG-CoA reductase, an integral membrane protein of the smooth endoplasmic reticulum, is the major point of regulation on the pathway to cholesterol, as we shall see.

Figure 20-32

Figure 20-32 Formation of mevalonate from acetyl-CoA. The origin of C-1 and C-2 of mevalonate from acetyl-CoA is shown in red.

2. Conversion of Mevalonate to Two Activated Isoprenes In the next stage of cholesterol synthesis, three phosphate groups are transferred from three ATP molecules to mevalonate (Fig. 20-33). The phosphate attached to the C-3 hydroxyl group of mevalonate in the intermediate 3-phospho-5-pyrophosphomevalonate is a good leaving group; in the next step this phosphate and the nearby carboxyl group both leave, producing a double bond in the five-carbon product, Δ³-isopentenyl pyrophosphate. This is the first of the two activated isoprenes central to cholesterol formation. Isomerization of Δ³-isopentenyl pyrophosphate yields the second activated isoprene, dimethylallyl pyrophosphate (Fig. 20-33)

Figure 20-33

Figure 20-33 Conversion of mevalonate into activated isoprene units. Six of these units will combine to form squalene. The leaving groups of 3-phospho-5-pyrophosphomevalonate are shaded in red.

3. Condensation of Six ActiUated Isoprene Units to Form Squalene

Isopentenyl pyrophosphate and dimethylallyl pyrophosphate now undergo a "head-to-tail" condensation in which one pyrophosphate group is displaced and a 10-carbon chain, geranyl pyrophosphate, is formed (Fig. 20-34). (The "head" is the end to which pyrophosphate is joined.) Geranyl pyrophosphate undergoes another head-to-tail condensation with isopentenyl pyrophosphate, yielding the 15-carbon intermediate farnesyl pyrophosphate. Finally, two molecules of farnesyl pyrophosphate join head to head, with the elimination of both pyrophosphate groups, forming squalene (Fig. 20-34). The common names of these compounds derive from the sources from which they were first isolated. Geraniol, a component of rose oil, has the smell of geraniums, and farnesol is a scent found in the flowers of a tree, Farnese acacia. Many natural scents of plant origin are synthesized from isoprene units. Squalene, first isolated from the liver of sharks (genus Squalus), has 30 carbons, 24 in the main chain and 6 in the form of methyl group branches.

Figure 20-34

Figure 20-34 Formation of squalene (30 carbons) by successive condensations of activated isoprene (five-carbon) units.

4.Conversion of Squalene to the Four-Iling Steroid Nucleus

When the squalene molecule is represented as in Figure 20-35, the relationship of its linear structure to the cyclic structure of the sterols is apparent. All of the sterols have four fused rings (the steroid nucleus) and all are alcohols, with a hydroxyl group at C-3; thus the name "sterol." The action of squalene monooxygenase adds one oxygen atom from O₂ to the end of the squalene chain, forming an epoxide. This enzyme is another mixed-function oxidase (Box 20-1); NADPH reduces the other oxygen atom of O₂ to H₂O. The double bonds of the product, squalene2,3-epoxide, are positioned so that a remarkable concerted reaction can convert the linear squalene epoxide into a cyclic structure. In animal cells, this cyclization results in the formation of lanosterol, which contains the four rings characteristic of the steroid nucleus. Lanosterol is finally converted into cholesterol in a series of about 20 reactions, including the migration of some methyl groups and the removal of others. Elucidation of this extraordinary biosynthetic pathway, one of the most complex known, was accomplished by Konrad Bloch, Feodor Lynen, John Cornforth, and George Popjak in the late 1950s.

Cholesterol is the sterol characteristic of animal cells, but plants, fungi, and protists make other, closely related sterols instead of cholesterol, using the same synthetic pathway as far as squalene-2,3-epoxide. At this point the synthetic pathways diverge slightly, yielding other sterols: stigmasterol in many plants and ergosterol in fungi, for example (Fig. 20-35).

Figure 20-35

Figure 20-35 Ring closure converts linear squalene into the condensed steroid nucleus. The first step in this sequence is catalyzed by a mixed-function oxidase (a monooxygenase), for which the cosubstrate is NADPH. The product is an epoxide, which in the next step is cyclized to the steroid nucleus. The final product of these reactions in animal cells is cholesterol, but in other organisms, slightly different sterols are produced