Proteins and most naturally occurring peptides are composed of amino acids in the L-configuration. However, D-amino acids have been detected in a variety of peptides synthesized in animal cells. Examples include opiate and antimicrobial peptides from frog skin, neuropeptides from snails, hormones from crustaceans, and venom from spiders. These D amino acid peptides are considered to be the most promising alternative for anticancer, anti-inflammatory, antimicrobial, and delivery agents.

About D-Amino Acid Peptides

The design of all-D-peptides has been applied to increase bioactive peptides’ resistance to endogenous enzymes, as well as their bioavailability. Retro-inverso peptides are obtained by replacing the standard L-amino acid residues with the corresponding D-amino acids and reversing the direction of the peptide backbone. Therefore, the original spatial orientation and the chirality of the side chains is unchanged. This results in a non-complementary side chain topochemistry between the analog and the parental L-peptide. The significantly improved biostability of D-peptides usually leads to longer in vivo circulation half-time, making the D-peptide based drug delivery system more attractive and efficient than their L-peptide counterparts. Success has been achieved immunologically in using retro-inverso peptides toward antigenic mimicry of their parent l-peptides. It was found that the retro-all-d-peptide isomer of p53(15–29), like its parent l-peptide, adopted a right-handed helical conformation in the complex. However, in some cases, the retro-inverso isomers are significantly inferior to their parent l-peptides. The low cellular uptake of D-peptides remain an unmet challenge. So the best way is to insert some key D amino acids into the peptide sequence. For example, some pharmaceutical important peptide antibiotics such as gramicidins, actinomycins, or bacitracins incorporate D-amino acids into the drug design. The assemblies of D-peptides deserve further exploration and may lead to more surprises. See more details from here: http://lifetein.com/Peptide-Synthesis-D-Amino-Acid.html Reference: http://www.pnas.org/content/102/2/413.full.pdf+html Google+

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