145 336 Isoprenoid Natural Products: Chapter 4 in Mann, pp 31-52 Terpenes- C 10 natural products derived from geranyl pyrophosphate (2 isoprene units) Sesquiterpenes- C 15 natural products derived from farnesyl pyrophosphate (3 isoprene units) Diterpenes- C 20 natural products derived from geranylgeranyl pyrophosphate (4 isoprene units) C 10 , C 15 , C 20 , etc. natural products derived from “isoprene units” C 5 unit Ruzicka isoprene rule OPP OPP OPP 337 Sesterpenes- C 25 natural products derived from geranylfarnesyl pyrophosphate (5 isoprene units) Steroids & Triterpenes- C 30 natural products derived from squalene (2 franesyl units joined head-to-head) Carotenoids- C 40 natural products derived from phytocene (2 geranylgeranyl units joined head-to-head) OPP
27
Embed
Isoprenoid Natural Products: Chapter 4 in Mann, pp 31-52 · 2017. 12. 6. · (4 isoprene units) C 10, C 15, C 20, etc. natural products derived from “isoprene units” C 5 unit
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
145
336
Isoprenoid Natural Products: Chapter 4 in Mann, pp 31-52
Terpenes- C10 natural products derived from geranyl pyrophosphate
(2 isoprene units)
Sesquiterpenes- C15 natural products derived from farnesyl pyrophosphate
(3 isoprene units)
Diterpenes- C20 natural products derived from geranylgeranyl pyrophosphate
(4 isoprene units)
C10, C15, C20, etc. natural products derived from “isoprene units”C5 unit Ruzicka isoprene rule
OPP
OPP
OPP
337
Sesterpenes- C25 natural products derived from geranylfarnesyl pyrophosphate
(5 isoprene units)
Steroids & Triterpenes- C30 natural products derived from squalene (2 franesyl units joined head-to-head)
Carotenoids- C40 natural products derived from phytocene(2 geranylgeranyl units joined head-to-head)
Conversion of geranyl-PP to terpenes involves a cyclization ofan alkene onto a carbocation
OPP
OPP
OPP
Linallyl-PP
OPP
H2O
OH O
Camphour
Can notcyclize
Biosynthesis of camphour
345
OPP
Linallyl-PP
OPP
H2O
OH
!-terpineolcamphene
H
1,2-hydrideshift
H
H
1,2-hydrideshift
H H
O1) H2O2) oxidation
thujone
150
346
Double bonds position of α- and β-pinene
OPP
PPO
!-pinene
"-pinene
OPP
!-pinene
"-pinene
- H+
347
Squalene Biosynthesis: head-to-head coupling of two farnesyl-PPunits catalyzed by squalene synthase
OPP
OPP
S-enzyme
HH
B:
CH3
H
NADP-H
CH3
HOPP
PPO
- OPP+
S-Enzyme_
+
Squalene
151
348
O P O P O -
O
O -
O
O -
O
H A
HO
HO
Farnesyl pyrophosphate (C15)
Squalene Oxide (C30H50O)
2
Squalene synthetase
Squalene (C30H50)
+
Squalene epoxidase
+
Squalenecyclase
Protosterol (C30H50O)
HO
+
HO+ HO +
H
CH3
H3C
HO
CH3
CH3
CH3H
H
H
H
P450
Steroid Biosynthesis: Polyene cyclization
349
H A
HO HO
Cholesterol (C27H46O)Lanosterol (C30H50O)
Protosterol (C30H50O)
CH3
H3C
HO
CH3CH3
CH3H
H
H
H CH3
H3C
HO
CH3CH3
CH3H
H
H
H
+
CH3
H3C
HO
CH3
H
CH3
CH3
H
Lanosterol (C30H50O)
152
350
Biosynthesis of abietic acid
HO2C
head-to-head ?
OPP
H+
OPP - H+
OPP
- H+
CH3 - H+
CH3
H+CH3
1,2-methylshift
abieticacid
351
Stereochemistry of the ring juncture in isoprenoid biosynthesis(polyene cyclizations)
Stork-Eschenmoser Hypothesis: olefin geometry (usually trans) ispreserved in the polyene cyclization reaction. E-olefins lead to trans-fused ring junctions.
OPPOPP
E
E
H
trans-fusedring
O
Protosterol (C30H50O)
CH3
H3C
HO
CH3CH3
CH3H
H
H
H
squalene epoxide
E E
E
trans-fused ring
153
352
Stork-Eschenmoser Hypothesis: conformational analysis of the polyene cyclization reaction
Transition state leading to the cis-fused product is disfavored