Issue in Honor of Prof. Atta-ur-Rahman ARKIVOC 2007 (vii) 280-290
3 21
21 3
3 21
II. III. 162214 20 15 19
20 16 14
16 14
20 17 15
15 22 17
19
22 19
18
18
17
type II skeleton 18 typeI skeleton type III skeleton
10
9
10 6 11 8
7
5
12
23 N4 1 a 21 13
N
14
15 20 19
H
18 22 17
16
vincosan (I a) RUB, LOG, APO >1000 alkaloids
18
3N
isoeburnan (II a)
eburnan (III a)
H 14
21
APO
APO
15
20
56 alkaloids N
8 alkaloids
211672 3 16372 20
21
19
19 N
N
18
H 14 H 18 15 15 H3CO OX 20
14 stemmadenine derivative (I) ß
ß
19
17 APO
N N 1718
4 alkaloids
- HX 22 isoplumeran (II ß)
22
plumeran (III ß) APO
APO 14 alkaloids
340 alkaloiids
H N
ß207
21
3
2 14
N 22 16
15 N N2122 16 14 2 20 19 18 ß7 3 211719 1816 203 1415NNH 22 17
17 15 H3CO O 1918 ibogan (II) secodine derivative izoibogan (III) APO APO LOG 84 alkaloids 7 alkaloids 5 alkaloids Figures indicate approximate number RUB = Rubiaceae Dictionary of Natural Products of isolated alkaloids LOG = Loganiaceae Version 15/1, 2006 APO = Apocynaceae (Chapman &Hall/CRC Press)
Scheme 2. Indole alkaloids derived from secologanin and having an intact tryptamine aubunit
For our special purpose, a new bioorganic-type system of the structures was constructed,9 and its simpified version is shown in Scheme 2. The great majority of the indole alkaloids can be classified into one of the three main carbon skeletons. Type I skeleton has the carbon framework of secologanin in intact, the other two in rearranged form. As shown in the all-oxo-aglucone 4 (in Scheme 1) and in Scheme 2, these latter skeletons can be derived by dissociation of the C15– C-16 bond, and followed by subsequent association of C-17 to C-14 in the type II, and to C20 in the type III skeleton. An experimental analog of this bond cleavage was presented earlier.14 The formation of the melodan alkaloids is the result of a long molecular evolution, as is briefly outlined in Scheme 2. In the coupling reaction of 1 and 2, strictosidine 3 is formed, which, after deglucosylation, affords the large subclass of the type Ia (vincosan) alkaloids, i. e. compounds
14 1 4 56 8 9 11 12 13 20 19 18 N N H 7 2 3 21 22 17 16 15 ßa2 3N N 21 22 16 17 14 15 7 20 19 18 (RUB), LOG, APO strychnan (Iß) 530 alkaloids a2 3 N N21 22 16 17 14 15 7 20 19 N N H 2 321 1516 22 17 14 20 19 18 ß7 aspidospermatan (I ß) 28 alkaloids APO ISSN 1424-6376 Page 283 ©ARKAT USA, Inc.
