Toward a Systematic Nomenclature for (Neo)Lignanamides

Abstract

Phenylalkenoic acid amides, often referred to as phenol amides or hydroxycinnamic acid amides, are bioactive phytochemicals, whose bioactivity can be enhanced by coupling to form dimers or oligomers. Phenylalkenoic acid amides consist of a (hydroxy)cinnamic acid derivative (i.e., the phenylalkenoic acid subunit) linked to an amine-containing compound (i.e., the amine subunit) via an amide bond. The phenylalkenoic acid moiety can undergo oxidative coupling, either catalyzed by oxidative enzymes or due to autoxidation, which leads to the formation of (neo)lignanamides. Dimers described in the literature are often named after the species in which the compound was first discovered; however, the naming of these compounds lacks a systematic approach. We propose a new nomenclature, inspired by the existing system used for hydroxycinnamic acid dimers and lignin. In the proposed systematic nomenclature for (neo)lignanamides, compound names will be composed of three-letter codes and prefixes denoting the subunits, and numbers that indicate the carbon atoms involved in the linkage between the monomeric precursors. The proposed nomenclature is consistent, future-proof, and systematic.

Figure 1

Two examples of phenylalkenoic acid amides, feruloylagmatine (A) and feruloyltyramine (B), and three dimers: two homodimers of feruloylagmatine (C and D) and a homodimer of feruloyltyramine (E). The trivial names currently used for the dimers shown are murinamide A (structure 54 in Figure S1), hordatine C (33), and grossamide A (26).

Figure 2

Examples of the numbering used for hydroxycinnamic acid dimers: ferulic acid and caffeic acid connected by 7–O-4′ and 8–5′ (A) and by 9–O-7′ and 8–8′ (B) linkages.

Figure 3

Overview of the different phenylalkenoic acid subunits and amine subunits reported in phenylalkenoic acid amides, the monolignols present in (neo)lignanamides, and the different linkage types occurring in (neo)lignanamides. The R¹ and R² groups might differ from the R^1′ and R^2′ groups depending on the precursors of the dimer. R^A indicates the remaining part of the amine group. ^aFor anthranilic acids (Ant) the “n” behind Ant will be replaced by the number of the corresponding anthranilic acid. Structural elements of the different linkage types are given between brackets.

Figure 4

Structural formulas of FerTrm-4-O-8′-FerTrm-4′-O-7″/3′-8″-DFerTrm (compound 17, see Table 2 and Figure S1), DFerAnt2-7-N-9′/8–8′/9-N-7′-DFerAnt2 (compound 1), CouPutFer-4-O-8′-FerPutCou (compound 49), and (N5)-Fer-(N10)-CouSpd-(N1)-Fer-4-O-8′-(N1′)-FerSpd-(N5′)-Fer-(N10′)-Cou.