AKA: Morpholino oligo

"Morpholino oligos are so named because they are assembled from four different Morpholino subunits, each of which contains one of the four genetic Bases (A denine, Cytosine, Guanine, and Thymine) linked to a 6-membered morpholine ring.  Eighteen to 25 subunits of these four subunit types are  joined in a specific order by non-ionic phosphorodiamidate intersubunit linkages to give a Morpholino oligo."
"These Morpholino oligos with their 6-membered morpholine backbone moieties joined by non-ionic linkages afford substantially better antisense properties than do RNA, DNA, and their analogs having 5-membered ribose or deoxyribose backbone moieties joined by ionic linkages."

From: http://www.morpholino.com - a great site about morpholinos