There are thousands more heterocycles out there

But we’re not going to discuss them and we hope you’re grateful. In fact, it’s about time to stop, and we shall leave you with a hint of the complexity that is possible. If pyrrole is com bined with benzaldehyde a good yield of a highly coloured crystalline compound is formed: a porphyrin. Now, what about this ring system—is it aromatic? It’s certainly highly delocalized and your answer to the question clearly depends on whether you include the nitrogen electrons or not. In fact, if you ignore the pyrrole-like nitrogen atoms but include the pyridine like nitrogens and weave round the periphery, you have nine double bonds and hence 18 electrons—a 4n + 2 number. Most people agree that these compounds are aromatic. Some heterocycles are simple, some very complex, but we cannot live without them. We shall end this chapter with a wonderful story of heterocyclic chemistry at work. Folic acid is much in the news today as a vitamin that is particularly important for pregnant women, but is involved in the metabolism of all living things. Folic acid is built up in nature from three pieces: a heterocyclic starting material (red), p-aminobenzoic acid (black), and the amino acid glutamic acid (green). Here you see the precursor, dihydrofolic acid.

Although folic acid is vital for human health, we don’t have the enzymes to make it: it’s a vitamin, which means we must take it in our diet or we die. Bacteria, on the other hand, do make folic acid. This is very useful because it means that if we inhibit the enzymes of folic acid synthesis, we can kill bacteria but we cannot possibly harm ourselves as we don’t have those enzymes. The sulfa drugs, such as sulfamethoxypyridazine or sulfamethoxazole, imitate p-aminobenzoic acid and inhibit the enzyme dihydropteroate synthase. Each has a new hetero cyclic system added to the sulfonamide part of the drug.

The next step in folic acid synthesis is the reduction of dihydrofolate to tetrahydrofolate. This can be done by both humans and bacteria, and although it looks like a rather trivial reaction (see black portion of molecules), it can only be done by the very important enzyme dihydrofolate reductase.

Although both bacteria and humans have this enzyme, the bacterial version is different enough for us to attack it with specifi c drugs. An example is trimethoprim—yet another hetero cyclic compound with a pyrimidine core (black on diagram). These two types of drugs that attack the folic acid metabolism of bacteria are often used together. We will see in the next chapter how to make these heterocyclic systems and, other examples of how important they are in living things.

اخر الاخبار

اخبار العتبة العباسية المقدسة

أهالي كربلاء يحيون اليوم السابع لذكرى شهادة الإمام الحسين (عليه السلام)

مشروع أمير القراء الوطني يشهد مشاركة أكثر من 100 طالبٍ في مرحلته الثالثة

قسم الشؤون الفكرية يصدر دليلًا يوثّق القصص الفائزة في مسابقة فتوى الدفاع المقدسة

قسم الشؤون الفكرية يعلن عن توفير عددٍ من المكتبات الإلكترونية المتخصّصة للمؤسّسات الدينية والمكتبات العامّة

المزيد

الآخبار الصحية

نصائح عملية للحد من التعرق المفرط في الصيف

أطباء يحذرون: مكمل غذائي شائع قد يدمر الجهاز العصبي

تحذير طبي من تأثير جانبي "غير متوقع" لحقن التخسيس

حمامات الثلج قد تكون خطيرة وأحيانا مميتة.. ما السبب؟

المزيد

الآخبار التكنلوجية

أكبر جدارية شمسية في العالم تدخل موسوعة غينيس.. مشروع ضخم

تسارع دوران الأرض يثير القلق.. وتحذيرات من "كوارث محتملة" ؟

"سوذبيز" تطرح أكبر قطعة من المريخ على الأرض في مزاد علني

أوبن أيه آي تعتزم إطلاق متصفح إنترنت يعمل بالذكاء الاصطناعي

المزيد

مواضيع ذات صلة

Fusing rings to pyridines: quinolines and isoquinolines

Putting more nitrogen atoms in a six-membered ring

Benzo-fused heterocycles-Indoles are benzo-fused pyrroles

Five-membered rings with two or more nitrogen atoms Imidazole

Nitrogen anions can be easily made from pyrrole

Five-membered heterocycles act as dienes in Diels–Alder reactions

Electrophilic addition may be preferred to substitution with furan

Furan and thiophene are oxygen and sulfur analogues of pyrrole

Five-membered aromatic heterocycles are good at electrophilic substitution

Pyridine as a catalyst and reagent

Pyridine N-oxides are reactive towards both electrophilic and nucleophilic substitution

Pyridones are good substrates for nucleophilic substitution