Homorubin. A centrally homologated bilirubin

(m.n)-Homorubins: syntheses and structures

“…This approach worked successfully in the synthesis of the first homorubin, where m = 2, with propionic acid chains at the usual locations, C(8) and C(12) [13] – and recently for the (2.3)-homorubin with butyric acid chains [14]. …”

“…Reverting to the “1 + 2 + 1” approach to linear tetrapyrrole synthesis, we employed a route similar to that used for preparing (2.2)-homorubin [13, 14] and (2.3)-homorubin [14]. Here and in the (2.2)- and (2.3)-homorubin, the required center dipyrrole sections differed only by the length of the carboxylic acid chain: acetic vs. the propionic and butyric of earlier work [13, 14].…”

“…In order to learn whether intramolecular hydrogen bonding might persist in a centrally homologated mesobilirubin, yet remain stable, we linked the two dipyrrinones to two CH 2 connector groups. We communicated [13] our synthesis of (2.2)-homorubin (Fig. 1C, where m = n = 2) and compared its properties to those of mesobilirubin-XIIIα.…”

“…Prompted by our first communication on homorubin [13], we undertook the syntheses and analyses of a series of (m.n)-homorubins (Fig. 1C), where m varied between 1 and 4 and n varied between 1 and 3.…”

“…Unfortunately, we were unable to prepare the (3.1) and (3.3)-homorubins and thus report only the (3.2) of the m = 3 set. The (2.2) and (2.3)-homorubins are known [13, 14]; the (1.2) is mesobilirubin-XIIIα, also known [15]. …”