ABSTRACT
The structures and the IUPAC-approved numbering system of some naturally occurring compounds in the vitamin A group are depicted in Figure 1. A group of synthetic retinoids is shown in Figure 2. Approximately 2500 retinoids have thus far been synthesized and characterized (1, 2). Although some of the more recently synthesized retinoids, such as 2.i and 2.j, bear little chemical resemblance to retinol (1.a), they all possess a highly conjugated double-bond system, roughly similar physical dimensions, and similar types of biological activities. Inasmuch as some naturally occurring compounds, such as 1.c and 1.d, are also used as therapeutic agents, the distinction between naturally occurring and synthetic retinoids is no longer helpful relative to their usage in society. Thus, the general term “retinoids” embraces a large number of sometimes distantly related chemical compounds.
