The naturally occurring amino acid that contains only one basic functional group in its chemical structure is

The products formed in the above reaction are

L-isomer of tetrose $$\mathrm{X}\left(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{4}\right)$$ gives positive Schiff's test and has two chiral carbons. On acetylation, '$$\mathrm{X}$$' yields triacetate. '$$\mathrm{X}$$' also undergoes following reactions

'$$\mathrm{X}$$' is

The one that does not stabilize 2$$^\circ$$ and 3$$^\circ$$ structures of proteins is