Heterocycles (McM chapt 28) ocyclic or fused rings t. one ore more ring atom ≠ C (normally O; N; S) matic , partly saturated or saturated ring(s) Membered rings (Heteroatom N, O, S) S Thiophene N H Pyrrole O Thiophene Otherexam ples N N H Imidazole N S Thiazole N H Indole N H R'' NH R R' R =H R'=C O 2 H R '''=H Tryptophane R =H R'=H R'''=O H Serotonin R=Ac R'=H R'''=O CH 3 M elatonin N N H N N NH 2 A denine (purine der.) N N H H 2 N R R =C O 2 H: H istidine R =H : Histam ine N S N N H 3 C HO H 2 N CH 3 Thiamin (VitB 1)
17
Embed
Heterocycles (McM chapt 28) Monocyclic or fused rings Cont. one ore more ring atom ≠ C (normally O; N; S) Aromatic, partly saturated or saturated ring(s)
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Heterocycles (McM chapt 28)•Monocyclic or fused rings•Cont. one ore more ring atom ≠ C (normally O; N; S)•Aromatic, partly saturated or saturated ring(s)
5-Membered rings (Heteroatom N, O, S)
S
Thiophene
NH
Pyrrole
O
Thiophene
Other examples
N
NH
Imidazole
N
S
Thiazole
NH
Indole
NH
R'' NHR
R'
R=HR'=CO2HR'''=H
Tryptophane
R=HR'=HR'''=OH
SerotoninR=AcR'=HR'''=OCH3
Melatonin
N
NH
N
N
NH2
Adenine(purine der.)
N
NH
H2N
R
R=CO2H: HistidineR=H: Histamine
N
S
N
NH3C
HO
H2N
CH3
Thiamin(Vit B1)
X X X X X XX: S, Se
e- in d-orb.
Cyclopentadienyl anion
Thiophene
S
Criteria for Aromaticity (Hückel)(Monocyclic) ringPlanarNo of -electrons in conjugation 4n+2 (n: 0, 1, 2,....)
S
5-membered rings - electron rich - reactive i E-fil. Ar subst.
X+ E
XE
H XE
H XE
H X E
X+ E
X
EH
X
EH
X E
React. in -position generally preferredSelectivity not always goodReact.: Pyrrole > thiophene > furan
6-Membered rings (Heteroatom N)N
Pyridine
Other examples
N
Quinoline
N
N
Pyrimidine
NN
Pyridazine
Rare in nature
N
N
Pyrazine
N
NH
NH2
O
Cytosine
N
Quinine
H3CO
HO
N
N
Ant pheremone
NN
HydralazineAntihypertensive drug
H2NHN
NH
H H
H H
Pyridine as a base
N NH
+ H
NH
H H
H H
NH
H H
H H
H
pKa: 5.2
NH
pKa 0.4
NH
pKa 11.3
N
NH
pKa 7.1(≈amidine)
N
S
pKa 2.5
sp2 N less basic than sp3
Electrophilic Reaction on Carbon: E-phil. Ar. Subs.
6-membered rings - electron deficient - reactivity
N
NE
N
H
EN
E
+ E
+ res. forms
•Both C and N may react
•3/5 pos. most reactive C
•Diazines less reactive
•Sulfonation, Nitration, halogenatil
•Not FC react.
N NH
NH
H NO2
N
NO2H / NO2 H / NO2
+ res. formsBenzo ring most reactiveMuch slower react. than naphthalene
N N N N N
6-membered rings - electron deficient - reactive in Nu-fil. Ar subst.
N Cl
OMe
NOMe
Cl
+ res. form
N OMe
2 / 4 Pos. reactive; electron def. C, neg. charge partly on N in intermed3 / 5-Pos. much less reactive (benzenoid pos.)
DNA helicases: UnwindingDNA binding proteins: Prevents winding backDNA primase: formation of DNA/RNA primer (from free nucleosides in cell)DNA polymerase: Catalyse elongation of new strand (5’ - 3’)