Nitrogen-Containing Compounds - Natural Products Chemistry: Sources, Separations, and Structures - page 77

N

NH 2

H 2 N

FIGURE 7.15 Chemical structure of a polyamine alkaloid spermidine.

H

H

N

H

H

H H

HO

FIGURE 7.16 The steroidal alkaloid solanidine.

4. Peptide and cyclopeptide alkaloids (e.g., Figures 7.6 and 7.7).

5. Pseudoalkaloids, which do not originate from amino acids, for example,
terpene-like and steroid-like alkaloids. Solanidine (Figure 7.16) is an
example of a steroidal alkaloid. In fact, it is a quite toxic substance, respon-
sible for neuromuscular syndromes via cholinesterase inhibition. The com-
pound or its glycoside is found in plants of the Solanaceae family, such as
the potato.

6. Purine-like alkaloids, for example, caffeine (Chapter 2, Figure 2.7), theo-
bromine, and theophylline.

7.4 NUCLEIC ACIDS AND BASE PAIRINGS
Nucleic acids are large biological polymers and include deoxyribonucleic acid, bet-
ter known as DNA, and ribonucleic acid (RNA). They constitute the most important
biological macromolecules; each is found in abundance in all living things. Their
function is to encode, transmit, and express genetic information.
Beginning in the 1920s, nucleic acids were found to be major components of
chromosomes. These are small, gene-carrying bodies in the nuclei of complex
cells. In addition to the elements C, H, N, and O, elemental analysis of nucleic acids
revealed the presence of phosphorus. However, unlike some proteins, the nucleic
acids do not contain any sulfur. When the nucleic acid is completely hydrolyzed, four
different heterocyclic bases are obtained together with inorganic phosphate and the
sugar 2-deoxyribose. These individual building blocks are shown in Figure 7.17. The
2-deoxyribose is attached to one of the bases to form a nucleoside. Further, when
the phosphate is also attached to the sugar in the form of a 5′-phosphate and the sugar
is further connected with a base, this unit is now called a nucleotide. Although the
nucleotide consists of three components, the base can be either a purine or a pyrimi-
dine. There are four bases in the DNA molecule and they are known as thymine (T),
adenine (A), guanine (G), and cytosine (C). In RNA, the uracil (U) replaces thymine
and ribose replaces 2-deoxyribose.