The chemical reactions and pathways resulting in the formation of beta-L-Ara4N-lipid A which occurs as a result of modification of the lipid A moiety of lipopolysaccharide by the addition of the sugar 4-amino-4-deoxy-L-arabinose (L-Ara4N). This strategy is adopted by pathogenic Gram-negative bacteria to evade cationic antimicrobial peptides produced by the innate immune system.